| Yet another 12B4 line stage, or is the 12B4 better than the Grounded Grid..... - Click HERE for Original Thread |
| Mark A. Gulbrandsen |
At the urging of a couple of other DIY members that claimed the 12B4 would stomp the Rosenblit Grounded Grid I decided to persur building one.... I left a trail of metal shavings fomr Cody to Rock Springs Wyoming as I partially assembled this on my last service trip. This IS alot more fon that watching cable TV on the motel rooms!
My grounded grid follows this basic diagram. I can't remember where I found this one but it was within a thread on this site that I found the link to it. Mine is pretty much a stock 12B4 as was my Grounded Grid. The only change I made to the grid when I built it was to use a different feedback resistor(less feedback) and a variable regulator IC in place of the fixed 12 volt IC. This allowed me to use the designed 12.6 volts on the filaments of the 12AU7's instead of Bruces 12 volts.
How do they compare.....? Listening tests were done with my Dynaudios driven by my DIY overbiased/overbuilt Aleph 2s. Source was from my Pioneer DV-45 CD player, a long time favorite of mine and one which has the proper DACs for the proper type of disks! All three types of CD's were used in listening tests.
The Grounded Grid is very detailed and open and extremely neutral and very dynamic. Overall its a very pleasing line stage to listen to once a good tube type is found. Yes, its somewhat tube fussy as I finally ended up settling on NOS Tung- Sols in mine. This seemed to be the best choice forthis line stage. JAN tubes while less microphonic were much more strident sounding on the high end. Did I say microphonic....... Yes. The grid suffers from this plague to some extent although I never found it to be a real problem. My stereo rack pretty is well isolated and on spikes.
Overall the grid has been very good and I've lived with it now for well over a year.
Then commeth the 12B4!
What can I say when something is so dramatically better. To try to sum it up I'll say that this simple circuit is the real meaning of more for less. By that I mean more music for less parts used. Somewhat the same basis for the Aleph series of power amps too.
This line stage has detail and top end that have to be heard to be believed and seemingly unlimited dynamic range. Its also drop dead neutral. As a comparison to the GG the 12B4 has alot more leading edge comming through than the Grid does and thats the single most obvious difference between the two. The bottom end and midrange performance are very simmilar to the grid but again with the 12B4 revealing even more detail and nuances deep in the music. This is very evedent on plucked bass and vibes and is pretty amazing. Background noises in recordings start to get annoying with the 12B4! Overall this is a much more musical line stage than the grid. Its hard to believe that high end tube equipment manufactirers have not hit on this tube, their engineers must be :dead: .
Are there any drawbacks? YES! This line stage has just about zero Power Supply Rejection and requires the very cleanest power you can give to it. Does it need to have a CSS or LED's to sound good. NO! This stock circuit is simply amazing running off my regulated bench supplys. The CCS mod might raise the PSR a good bit but good regulated supplies as Dr. Gizmo used to do and as I am doing also works very well. Its either going to take alot of iron or some well designed regulated power supply to get this unit hum free.
So have I retired my GG? No, it'll serve in another system in another room. Its also a very good piece but the 12B4 does indeed blow right past it.
Simply put the Grounded Grid runs at Warp 5 and the 12B4 runs at warp 9.
Build your self one!
Mark |
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| Mark A. Gulbrandsen |
A small tribute to Dr Gizmo... Nothing beats good regulated supplies!
A rebuilt Daven attenuator to 50K controls input level. The girlfriend hasn't said anything bout the supplies yet......
Mark |
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| Mark A. Gulbrandsen |
This is the basic 12B4 that I found. Hopefully I'm not stepping on anyones toes posting this here..... note that I used 220 UF for the cathode bypass caps. That is the only deviation from this drawing that I did.
Mark |
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| choky |
lookin' at short data for 12B4 (seems that Ri is in 1K range) you can try smaller Ra -maybe in range of 3K9 to 4K7.......your ears will decide
another one- I always place 1M resistor from grid to gnd- I don't trust any pot after several burned 12AX7s in guitar amps I repaired.....
and- bigger output cap can be good,depending of course of next stage input impedance
just a few thoughts.... |
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| grimberg |
Mark,
The 12B4 is not currently in production, or is it?
Which brands should I look for?
Who carries 12B4s?
Could you please post the schematic for the power supply you used?
Thank you! |
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| Steve Eddy |
| quote: | Originally posted by choky
another one- I always place 1M resistor from grid to gnd- I don't trust any pot after several burned 12AX7s in guitar amps I repaired..... |
Or better still, MagneQuest makes some very nice grid chokes.
se |
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| Mark A. Gulbrandsen |
Hi Grimberg,
12B4's are readily available, no ones buying them. I got mine locally from Salt Lake Instrument.... G.E. made NOS JAN 12B4's for 10 bucks each, they have a 4/71 code date on them. No low frequency noise, microphionics or other garbage that others have mentioned having problems with in other 12B4 threads. I suspect that the quality of the tube used has alot to do with those problems and its hard to beat a JAN tube.
I find it odd that a tube designed for verticle amp service would work this well in an audio circuit but what the heck. Its got about the lowest plate impedance of any tube out there sans the 2A3 and 6AS7.
The b+(260 volt) supply is an Eico bench regulated H-V supply. I have a pcb for the Chineese Lite Audio tube regulated supply and I now have a reason to build that one up. The filament supply is a 3 amp regulator IC fed from the already regulated Tektronix supply down below the line stage, I used an NTE1929 I.C. in mine cause thats what I could get locally. I plan on adding a simple but well bypassed zener shunt regulator into the line stage B+ later this week if time permits to see how that might work out. You definately will need ultra clean DC on this design!!! While the actual line stage is inexpensive to build expect to plow alot of dough into the supply end of things. Thats where the 12B4 gets to become alot more expensive than the Grounded Grid does!
Mark |
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| Mark A. Gulbrandsen |
| quote: | | Or better still, MagneQuest makes some very nice grid chokes. |
Steve,
No offense, but I'm definately not a big fan of iron in the signal path. Its nice for once to listen to a really great piece of gear should I say unobstructed...... I can't see why you guys would want to add unnecessary stuff to it. Or please elaborate as to why.....
| quote: | | another one- I always place 1M resistor from grid to gnd- I don't trust any pot after several burned 12AX7s in guitar amps I repaired..... |
I agree with this but I don't expect to wear out my Daven attenuator..... at least not in my lifetime. If I had placed an Alps or the like pot in there I would definately add something to be there "in its place in case".
Mark |
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| tubelab.com |
I have used the 12B4 before, usually as a driver, before I discovered PowerDrive. If you like 12B4's you should check out the 7233. It has a plate resistance of 230 ohms, about one fourth that of the 12B4.
These were used as series regulators. They were also used in HP sweep generators as the sweep source. May be overkill for a line stage. |
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| Steve Eddy |
| quote: | Originally posted by Mark A. Gulbrandsen
No offense, but I'm definately not a big fan of iron in the signal path. |
Yeah? Then why on earth are you using tubes? :D
| quote: | | Its nice for once to listen to a really great piece of gear should I say unobstructed...... |
Well, a grid choke's not what I'd call obstructed. We're talking something on the order of 1,000 Henry so at AC it's rather an open circuit.
| quote: | | I can't see why you guys would want to add unnecessary stuff to it. Or please elaborate as to why..... |
Well, I'm no tube expert but I believe that having a reliable DC path to ground at the grid helps keep the tubes from blowing. A choke is preferable as it offers a relatively low resistance at DC but has such a high AC impedance it rather takes itself out of the picture.
Perhaps someone else can explain this better than I.
se |
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| mach1 |
Mark,
Great to see you took up the challenge ! |
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| planet10 |
Mark,
Are those standoffs from a tek scope?
dave |
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| Mark A. Gulbrandsen |
| quote: | | Are those standoffs from a tek scope? |
Yes they are. Let us give a moment of silence in honor of that unknown TEK scope that allowed me to use its organs for a transplant.......BTW: Not scrapped out by me... jist so everyone here is clear on that issue:bigeyes: . Thats something I just couldn't bear to do.....
Mark |
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| planet10 |
| quote: | Originally posted by Mark A. Gulbrandsen
honor of that unknown TEK scope |
Mine was declared dead by Allen Wright before i made it parts... lovely beasts those.
dave |
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| astouffer |
| I felt the same way about my tek scope until I tried doing any serious measurements and couldn't stop the drift. Then I thought about the calibration sticker on the front thats 40 years past due. Thats right it was due back in 1965. If you parted out a tek scope on ebay the price of the ceramic terminal strips alone could buy you a much newer model. Plus a 10Mhz scope is no good when an opamp oscillates at 40Mhz or so... |
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| blaaberg |
Hey,
I need a pre to my Zappulse class D poweramp. Could this one drive the 17kohm input, or maybee lower?
I too, woyld be glad to get a schematic of the Powersupply.
I`m absolutely a newbee, but would anyway try building a tube pre, and this one looked absolutely interesting.
Thanks to Mark for the great work :-)
Venlig hilsen Jan |
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| choky |
| quote: | Originally posted by Mark A. Gulbrandsen
Steve,
No offense, but I'm definately not a big fan of iron in the signal path. Its nice for once to listen to a really great piece of gear should I say unobstructed...... I can't see why you guys would want to add unnecessary stuff to it. Or please elaborate as to why.....
Mark |
"signal energy preservation"
no RC stage can compete with inductive loaded stage in that field.
one need to hear good choke or OPT stage to catch what I mean ,but-like always -it's matter of taste ,not universal truth.
same as - one way speaker against multi way speaker -to each his own |
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| apassgear |
Bordin Sap on 12b4 - AV Review forum
"Now, I'm waiting for my tube pre-amp to finish from a hi-fi shop. Last month, by chance, I did A/B testing between my solid-state preamp with a DIY one, using 12B4 tubes. I was so stunning with the results. The 12B4 preamp produces the best sonics I've ever heard from a hi-fi system! Tons for details, musical separation, tonal balances, extreme high, authoritative bass, airy, and much more. Highs are a lot better than my solid-state preamp. I would say even better than my friend's Mark Levinson No. 383." |
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| J Epstein |
| quote: | | All three types of CD's were used in listening tests. |
Country, Western, and what's the third?
-j |
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| Mark A. Gulbrandsen |
| quote: | | no RC stage can compete with inductive loaded stage in that field. |
What I'm talking about is not a simple RC stage..... but an active circuit. I have tried chokes but not on this sort of project. Since a simple pass transistor can make a cap look at least 10 times bigger(the multiplication of the caps value is based on the hfe of the device being used) you'd need a whole lot of choke to do what a 100,000 mfd cap could do. Change that simple pass transistor to a mosfet and it looks 10 times larger than the simple pass transistor version. Run that through another pass transistors and all thats left is a few microvolts of noise! Less space, weight, and a whole lot less cost! Take something like the power supply from the ARC PH-3 phono preamp. That power supply elevated to 300 volts would be totally suited to this sort of line stage. Cost to build the active circuit would be less than 25.00. This is why all the expensive iron just doesn't make sense to me....... I can achieve cleaner DC with cheap active circuitry and it would cost hundreds in iron and the results still wouldn't be as good.
Mark |
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| LuckyLyndy |
| quote: | | All three types of CD's were used in listening tests. |
(Mark G.)| quote: | | Country, Western, and what's the third? |
(J.)
I like that J! I think Mark was referring to SACD, Redbook, and DvD-A, but I may be wrong as well.
Or could it be Country, Western, and Classical Country? I mean what else is there?;) |
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| Mark A. Gulbrandsen |
Actually all comparisons were done using my old Gene Autry and Cab Calloway 78's that have been transfered to CD.....:D . The Cabster sounds simply uncanny through the 12B4! The background noise from the 78's sounds extremely detailed and realistic..... Might as well can all this 12B4 stuff and just play the dang 78's!
Mark |
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| Brett |
| quote: | Originally posted by Mark A. Gulbrandsen
Then commeth the 12B4!
What can I say when something is so dramatically better. |
I can say, I told you so.
| quote: | | Are there any drawbacks? YES! This line stage has just about zero Power Supply Rejection and requires the very cleanest power you can give to it. Does it need to have a CSS or LED's to sound good. NO! This stock circuit is simply amazing running off my regulated bench supplys. The CCS mod might raise the PSR a good bit but good regulated supplies as Dr. Gizmo used to do and as I am doing also works very well. Its either going to take alot of iron or some well designed regulated power supply to get this unit hum free. |
Agreed, but it's not vastly different from most CC tube stages. With an excellent PS, they really begin to shine. |
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| Brian Beck |
| I'm late to this thread, but wanted to add that I have been using an almost identical 12B4 circuit as the output stage in a Pioneer DVD/CD player (voltage output DAC). I use 8.2K plate loads, but a CCS in the cathode (well bypassed) to hold current constant. Elaborate power supply filtering (LCRCRCLC). Sounds simply fabulous. No noise, even with headphones. I left the opamps in so I can switch back and forth to **** off solid-state guys. I'm about to do a similar treatment to my Sony SACD player. Screw the warranty! |
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| wrenchone |
| I've had my eye on the 7233 for line amp applications. I was thinking of trying an Akido-type setup, but using a FET-based current source load, as I have some Supertex HV TO-220 depletion-mode MOSFETs looking for something to do. Iwas also looking at using a triode strapped 6AQ5/6005, which would give me a bit more gain. I was looking at the 12B4 as well, but I only have 1-2 used units on hand of unkown condition right now, and I'd like to try out what I've got... |
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| Mark A. Gulbrandsen |
| quote: | | Agreed, but it's not vastly different from most CC tube stages. With an excellent PS, they really begin to shine. |
Well, In another thread about the GG preamp there was a comment from a mamber that the 12B4 is alot less expensive to build. I would completely disagree with that. It's at least as expensive when one takes into aco**** the power supply required for the 12B4.
Brian,
Would you share your CCS ideas with us?
Thanks!
Mark |
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| Brett |
| quote: | Originally posted by Mark A. Gulbrandsen
Well, In another thread about the GG preamp there was a comment from a mamber that the 12B4 is alot less expensive to build. I would completely disagree with that. It's at least as expensive when one takes into aco**** the power supply required for the 12B4. |
That definitely wasn't me, as I've never posted on the GG preamp, and most common cathode stages have inherently poor PSRR when resistively loaded. A good quiet PS can be expensive of $ (unless you've been collecting iron for years as I have) and space, even if all it does is serve a "simple" circuit like the 12B4A one you posted. If you look at my previous posts on the 12B4 preamp I've been posting on here for at least 3 years, you'll see the lengths I go to to get the PS right, even in the predominantly balanced/differential circuits I prefer. |
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| Brian Beck |
| quote: |
Brian,
Would you share your CCS ideas with us? |
Oh, nothing special at all. I frequently use a CCS in cathode circuits. I just use a good old LM317 and a current setting resistor, well bypassed with a big electrolytic and a small “boutique” film cap. The reason I bother with a CCS in the cathode is to hold the tube’s operating point constant over life and the same between channels. This centers the operating point of the plate voltage and keeps the plate resistance (output resistance) and transconductance close to the same for reasonably well-matched tubes. An LM317 costs maybe $0.49, and I have a bucket of them, so why not use it in many cases? No one should say that they can be heard in such a cathode circuit; the bypass caps completely hide any deleterious effects of a solid-state CCS. All the CCS has to do is to be a good current source at low frequencies, and any high frequency irregularities are hidden by the bypass caps which “short out” the CCS at all audio frequencies. I often use two separate such current sources in push-pull output stages to force primary current balance and ensure DC magnetization cancellation. No adjustments over tube life.
To complete the output filtering for the CD player, I used a passive LRC low-pass between the DAC and 12B4 grid to set a -3dB point at 58KHz, with only -0.026 dB impact at 20KHz.
A CCS as a plate load is a different beast and harder to get right, since you CAN hear the solid-state edge unless great care is taken (a la Gary Pimm’s designs). But great potential exists here, too. |
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| planet10 |
| quote: | Originally posted by Brian Beck
Oh, nothing special at all. I frequently use a CCS in cathode circuits. I just use a good old LM317 and a current setting resistor |
The 317 is limited to a minimum of 7mA as a CCS isn't it?
dave |
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| Brian Beck |
No, just divide 1.25 volts by the desired current to define the current-setting resistor value. I see no reason why the current couldn't go as high as 1.5 amps, although this resistor gets quite small in ohmic value. I've used them happily up to 50mA in tube cathodes.
Edit: Oops - Just re-read you post and you did say "minimum" current, not "maximum". Yes, you are correct; there is a minimum current, that is often stated as 10mA, but in fact can be less if you carefully study the LM317 data sheets for the temperatures and voltages likely to be encountered. So it wouldn't be used to bias a 12AX7, but I tend to pull a lot of current through tubes like a 6DJ8 or 12B4 to get the transconductance up, so this limitation is not a problem for me generally. For my CD output stage application with a 12B4, I run almost 30mA through each tube to achieve the "text book" 1K plate resistance. |
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| choky |
| quote: | Originally posted by Mark A. Gulbrandsen
What I'm talking about is not a simple RC stage..... but an active circuit. I have tried chokes but not on this sort of project. Since a simple pass transistor can make a cap look at least 10 times bigger(the multiplication of the caps value is based on the hfe of the device being used) you'd need a whole lot of choke to do what a 100,000 mfd cap could do. Change that simple pass transistor to a mosfet and it looks 10 times larger than the simple pass transistor version. Run that through another pass transistors and all thats left is a few microvolts of noise! Less space, weight, and a whole lot less cost! Take something like the power supply from the ARC PH-3 phono preamp. That power supply elevated to 300 volts would be totally suited to this sort of line stage. Cost to build the active circuit would be less than 25.00. This is why all the expensive iron just doesn't make sense to me....... I can achieve cleaner DC with cheap active circuitry and it would cost hundreds in iron and the results still wouldn't be as good.
Mark |
I'm glad that you find your preffered line stage ;)
I'm completely (spell spelll spellll??) aware of arguments and metodology argumented in yours (above) lines,and I also tried all that stuff in my tube beginings ( senturies ago ;) )
what is my preffered type of supply and type of line stage you can see if you click at www button on bottom of my post....
each approach have own arguments ,but only builder's taste is finally responsible for finall decision
hehe-to each his own
cheers! |
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| leadbelly |
| Would anybody be so kind as to spoonfeed me the gain of the line stage in question? TIA |
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| Brett |
| quote: | Originally posted by leadbelly
Would anybody be so kind as to spoonfeed me the gain of the line stage in question? TIA |
About 5.5, with no cathode bypass, about 4. |
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| HiFiNutNut |
Hi,
I was encouraged by our forum members especially Brett (Thanks Brett) and built a 12B4A line stage. It sounded wonderful. I initially used some lower quality parts. How it sounded almost completely depended on how good the filter caps I used. This was what I initially had:
380-0-380V Tx => Sovtek 5AR4 => 10H => 470uF (H.Q.) => (split into 2 channels) R => 330uF (L.Q. cap). I built a LM317 regulated heater supply. I didn't buy any caps and just used what I had on hands.
The sound was initially messy and hummed quit a bit. I found out that the 330uF caps were not good at all and replaced them with the Panasonic ED 100uF. The sound became pretty good but the hum was still there. Replaced the 100uF with ICW Clarity Cap (Polypropylene) 2 x 20uF = 40uF on each channel the HF sound was very satisfying but the bass was severely lacking. It hummed quite loudly and I couldn't enjoy the music. I then paralleled the 100uF with one ICW MKP 20uF for each channel and started enjoying the music since. It still had a bit of hum. The latest change was to use the 330uF low quality cap as the first cap, like this: 10H => 300uF (L.Q.) => R => 470uF (H.Q.) (split to 2 channels) => R => 100uF (H.Q.) + 20uF (MKP). What was the sound? still a touch of messiness, still a bit of hum, but overall - Excellent. I most certainly believe that sound wise it beats the Audio Research xxxx preamp my friend has that I liked so much which triggered me to look into building a tube preamp.
Then one of the tubes (Industrial grade Westinghouse) started making more and more noise (like firewood burning sort of cracking sound). Is that microphonic? leakage? I am pretty sure it was the tube because I swapped the tubes and the noise only came in the channel with the bad tube. It got so bad so I decided to shut it down and rebuild it.
I have ordered 4 x GE JAN Mil Spec 12B4A and 2 x Sylvania Mil Spec 12B4A and they will arrive at any time from now. I will compare their sound. I have bought 2 x 200uF Solen MKP for the last cap of the power supply. I am getting a new custom made Toroidal Tx to replace the old E.I. transformer as it hummed and gots VERY HOT! I am also replacing the 5AR4 because I don't like the preamp to run so hot with 5V x 2A = 10W wasted in rectification! I decided to make it mono stereo and have ordered 8 x UF4007 and the 8 x 0.01uF 1000V ceramic caps and will make 2 snubbers for the secondary wirings. 2 x 10H hammond chokes will arrive tomorrow. All filter capacitors are Panasonic TSHA and TSHB except the last caps being Solen MKP. It will be like this (mono): Tx 350V => Snubber => UF4007 => 10H => 100uF => 270R => 220uF => 270R => 470uF => 270R => 200uF (Solen). It will give me 300VDC running on 25mA + 2mA (breeder) with the AC ripples reduced to 0.02mA.
I have some questions about the layout of the preamp. I have one 2mm thick steel sheet to shield the Tx and chokes from the circuit in the steel chassis. How effective is such a shield? Can it eliminate (or reduce to an acceptable level of) RFI? If it can shield the RFI from the Tx and chokes, the energy must go somewhere. I guess it would be turned into currents in the chassis. How to do deal with it? I think a star ground should help.
Another question is whether I should make another 2 steel sheets and install them between the Tx and the 1st choke, and between the 1st choke and the 2nd choke. I may not have sufficient space to orient the chokes 90deg from each other. What is the best way to do it?
This is the new layout:
Thanks and regards,
Bill |
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| Klimon |
My two cents about the 12b4 linestage:
I built one following the schematic on diyparadise.com; using 12k anode resistor and 260V B+. Power supply is dual mono, capacitor input double pi filter with European Rgn1064 mesh anode rectifiers (electrically comparable to 5y3 but the mesh version is a big step upwards from anything else) - Sound is excellent; quite close to what Yeo describes: Prominent high tones; amazing neutrality + gain in soundstage; especially the increased depth struck me. Power supply capacitors are all motor-run caps (pio) which are in every amp a big improvement on electrolytics. Power supply is unregulated and I plan to keep it that way in the definitive version as there aren't too many arguments (soundwise) for a regulated ps. The 0,33µF coupling caps on the schematic are big-time overkill; I work with 0,056 Russian military teflon-in-oil capacitors (still around 7hz cut-off so you won't miss anything unless your speakers are huge tml's or big subwoofers + you gain everything by using smaller, faster and better caps). I'm planning to play with the loadlines soon; altering B+ and anode resistor & maybe cathode resistor. Will keep you posted if I find any audible improvements on the current version.
Simon |
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| Brian Beck |
| That's 7Hz if you never connect the line stage to anything and the cap only sees the 470K grounding resistor that is part of the line stage. If you drive a power amp with a 100K input resistance (pretty high these days), you'll see a -3dB point of about 35Hz. Not good. If you load it with 20K (which the 12B4 could drive), you'd see a roll-off at about 140Hz. I think 0.056uF is just too low to advise for general use in the output of a line stage, as good sounding as it might be. I think 0.33uF is marginal too. |
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| Mark A. Gulbrandsen |
I agree with Brian on that. I am at 2mfd right now and I intend to go to 5 mfd when the caps arrive... Multicap PPMFX
Mark |
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| Klimon |
| I'll have to do a little listening-test to check it out. Is it so very different for a preamp? At first I used a 0,47 cap; then switching to the 0,056 cap I didn't notice a more rolled-off low-end. My high-eff. speakers only reach around 60hz but I did a short test on my transmissionlines (around 25hz low-end) and it sounded okay - didn't do an a/b test though. Could you tell me how to calculate / measure the input impedance of a power amp? And how to insert it into the formula for calculating the -3db point of the preamp? I'll also give it a try with a pair of 5µF caps on the transmissionlines; if you guys are right the audible difference should be HUGE... |
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| Brian Beck |
Klimon,
Even if your speakers don't go low enough for you to notice a huge difference in level with an undersized coupling cap, a too-small cap will introduce a phase shift well up into the mid-bass that might smear the "presence" and "air" that truly deep bass response can provide. Granted, the high frequency response of a small cap might/should be better. Perhaps you could experiment with bypassing a larger film cap with your nice 0.056uF Teflon caps.
Input R (call it “Rin”) is probably easier to calculate than it is to measure unless you are very skilled and equipped to make these test measurements. If you will post a schematic of the front end of your power amp (or whatever the 12B4 will directly drive), we can help you to calculate it.
Once we know your power amp’s Rin we can calculate the -3dB roll-off frequency as follows:
f-3db = 1/(2*pi*C*Rtotal), where Rtotal = [(Rin*470K)/(Rin+470K)] + 1000.
The last resistance value (1000 ohms) accounts for the approximate output resistance of the 12B4 stage and is so low compared to the other resistances that you can usually safely ignore it. |
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| Mark A. Gulbrandsen |
Hi Brian,
Thanks for the formulas!! Now all I need is a scientific calculator to do them.... Math is not my forte by any means. Would you also be willing to share the general layout of the LM317 as a CSS with the 12B4 for us? I would love to incorporate that feature into my line stage. I think I can figure out the correct resistor for the current sense.....
Thanks,
Mark |
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| Brian Beck |
Here is a schematic showing a 12B4 with a cathode current source which I used in the output stage of a cheap, but decent, Pioneer DVD/CD player from a couple of years ago. The LCR low-pass filter is only needed for the CD application and should be deleted for line stage use. I found I didn't need a grid stopper and I won’t use them where they’re not needed. Your mileage might vary with a different grid circuit (like a volume pot, etc.) I ran this triode fairly hot (at around 3.6 watts of plate dissipation) because I wanted 30mA of plate current which is needed to give the 12B4 a low plate resistance and high transconductance. The circuit has worked flawlessly for two years and sounds superb. I plan to implement something similar in my Sony SACD player.
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| Mark A. Gulbrandsen |
WOW!
Thanks a ton Brian. I will work on that when I get back from my next buisness trip....
Best,
Mark |
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| Klimon |
Hello Brian;
Aaaah, the magic formula :D
I've changed to 1µF a few days ago and it sounds much better; to my surprise not only more bass but the whole (mids?) sounds much more relaxed now - your description as 'presence and air' describes it nicely. The power amp I'm currently on has 220k input r. ; I'll do my homework later to see what I had been missing (and should install as definitive cap) -
Do you know if for a power amp Rtotal equals the grounding resistor or are there here also other variables that constitute Rtotal?
Cheers! |
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| Mark A. Gulbrandsen |
I had a one day reprive from leaving on this service trip so I installed Brian's CSS mod. Result is that the sound is now alot cleaner than it was... I also did install 5 uf coupling caps (nothing fancy yet just Electrocubes), am driving a pair of Aleph 2's and they have a pretty low input impedance. The combination is quite breathtaking. Now for a change I am listening to whats IN the music..... you can'y miss annything running with this linestage...... Absolutely fantastic!
I have to laugh... over the past 25 years I built and owned alot of line stages, only to end up with something so simple.... I hope that everyone that builds line stages will someday end up here...
Mark
Live.... From the armpit of Wyoming.... |
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| choky |
| quote: | Originally posted by Mark A. Gulbrandsen
I had a one day reprive from leaving on this service trip so I installed Brian's CSS mod. Result is that the sound is now alot cleaner than it was... I also did install 5 uf coupling caps (nothing fancy yet just Electrocubes), am driving a pair of Aleph 2's and they have a pretty low input impedance. The combination is quite breathtaking. Now for a change I am listening to whats IN the music..... you can'y miss annything running with this linestage...... Absolutely fantastic!
I have to laugh... over the past 25 years I built and owned alot of line stages, only to end up with something so simple.... I hope that everyone that builds line stages will someday end up here...
Mark
Live.... From the armpit of Wyoming.... |
simplicity is hard to achieve.........
I know that-after all this years
:clown:
ps. I'm still for (at least-trying) lower value of anode resistor |
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| blaaberg |
"I had a one day reprive from leaving on this service trip so I installed Brian's CSS mod. Result is that the sound is now alot cleaner than it was... I also did install 5 uf coupling caps (nothing fancy yet just Electrocubes), am driving a pair of Aleph 2's and they have a pretty low input impedance."
Sound very interesting, how low is your input impedance? Do you think it can drive my 17Kohm input Zappulse.....?javascript:smilie(':angel:')
angel
Venlig hilsen Jan |
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| Mark A. Gulbrandsen |
| quote: | | Sound very interesting, how low is your input impedance? Do you think it can drive my 17Kohm input Zappulse.....? |
Shouldn't be a problem, just be sure the output capacitor is large enough.... use Brian's formula above to calculate that. The input impedance of my Aleph 2's is only 10K annd it drives them quite nicely.
Mark
Just don't let your amp Zap the signal;)...... |
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| pinkmouse |
| Hey Mark, tried it with the Krells yet? |
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| Sherman |
| quote: | Originally posted by choky
simplicity is hard to achieve.........
I know that-after all this years ... |
As Einstein said- "Everything should be as simple as possible, but no simpler." |
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| Mark A. Gulbrandsen |
| quote: | | Hey Mark, tried it with the Krells yet? |
Have not yet as mine is in the same boat as yours... we did Lyndon's chassis first. Am going to do mine when I get back to town. It should drive it without any difficulty since the input impedance is about twice the Alephh's...
Mark |
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| sklimek |
I drew this schematic up from the information that Brian Beck generously posted here. I was hoping someone could take a look and confirm some questions I have on it.
I took out the low pass filter for the DAC; there is no grid stopper so I believe it is a straight shot from the pot? Also, I put C8 & C9 in parallel to create the ~ 445uF
as noted.
Also, would 400V for the coupling and 50V for the bypass caps be about right? Are all the resistors ½ watt, what about the wattage of the plate resistor?
And I was reading Brian’s post here about optimally using a 20K input resistance on your amplifier. The design that I am using specifies a 100K, may a 20K be substituted here w/ no problems? Ultimately I would like to see this 12B4 preamp drive my tube amp and a future Aleph 30. And last elementary question is what value attenuator would be best suited here for the 12B4???
Thanx!!! |
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| sklimek |
| Here is the front end of my tube amp in question showing the 100K input resistance. |
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| Brian Beck |
Sklimek,
You have a 100K input resistance to your power amp. This is what you’d plug into my earlier equation to figure the 12B4 coupling cap size.
For the 12B4 cathode bypass caps, I just used what I had on hand – a paralleled pair of 220uF caps, bypassed by a 4uF Wonder cap and a 0.01uF Wonder cap. Roughly 445uF. Don’t feel that you have to exactly duplicate it. This value gives a pretty low -3dB roll-off of 0.3 Hz. I’m a bandwidth freak – on both ends – don’t mind me. You can safely reduce the value to 200uF or even 100uF. But be sure the caps are decent and bypass them/it with a good film cap.
Your cap voltage ratings sound about right. Just make sure that your 320 volt supply doesn’t surge above 400 volts before the tube warms up. Power supply designs vary in this regard.
For the 6.25K, I used a 10 watt wire-wound, a rectangular sand-filled item, again what I had in the parts bin. (Actually it’s a standard 6.2K value, now that I peeked at the back of the CD player again, but no real difference). The resistor will dissipate about 5 watts, so keep it well away from any other components and maybe put it where it can ventilate. I put mine on the outside of the CD player, on the back next to the tubes which poke out horizontally. I built a guard to keep fingers from hot tubes, hot resistors, and high voltage on the resistor leads. Please be careful on this. And, no, I didn’t use a low-inductance resistor. It measures as expected.
Try it without a grid stopper. The need for a stopper will depend upon how well you wire your layout, keeping inductance low in the grid circuit. If you want you can try a 100 ohm stopper to see if it sounds different.
I tend to put a 1MEG metal film to ground at the grid after the pot just in case the wiper goes open or is momentarily intermittent with dust. This maintains the grid at a ground reference avoiding loud pops and scratches. Most people don’t bother, but it’s cheap and doesn’t appreciably load the pot. You can use any pot you want, but a decent one would be a 100K ALPS, blue or black style. A fancy stepped attenuator might be better, but a lot more money too. |
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| Mark A. Gulbrandsen |
| quote: | | For the 12B4 cathode bypass caps, I just used what I had on hand – a paralleled pair of 220uF caps, bypassed by a 4uF Wonder cap and a 0.01uF Wonder cap. Roughly 445uF. Don’t feel that you have to exactly duplicate it. |
Exactly! I did some listening tests and found that the need for the film bypass cap is an absolute must.... gives lower esr at high frequencies. In mine I used two Sprague 220 mf 63 volt caps paralleled by a .22uf 630 volt Wonder SETI cap.... luckily I have a bunch of these in the parts drawers. The difference with and without that film cap is amazing in itself... My output caps are Electrocube 5mf paralled with a .01 Wonder Cap. I might add another of the .22's across the output just to see what happens. The sound is now better balanced top to bottom.... even though the before was the best I'd heard out of my system... the .22's stay in mine!
LuckyLyndy stopped by for a short listening session this afternoon..... but I will let him report what he thought.
As far as I'm concerned the Grounded Grid is dead issue at this end.....
Mark |
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| amperex |
| I will build this 12B4 as well & compare to my simple (not the PS) 6P5GT linestage. Tnx all. |
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| LuckyLyndy |
My good friend in Rhode Island is not going to be happy about these results. He has a super modified Grounded Grid with all the bells and whistles. And with his Cary Slam monoblocks, and ProAc Futura speakers, it is a lush sound. As Paulie said, "I want liquid honey! I don't care for analytical analog at all!"
Well, that is what the 12B4 does offer. A very cystalline presentation of the music. Very good upper treble, midrange, and not monster, but real bass. Mark had his older system hooked up, the HUGE Aleph 2 monoblocks with his Dynaudio Audience 9's. His significant other saw me coming up the sidewalk, and retreated with a book to the bedroom
;)
Mark played some late 50's Verve jazz, and Anita O'Day's voice, which had in one passage been sibilant, along with the high hat, was now clear. Then we went to the folkie band, Be Good Tanyas, singing "The Littlest Birds Sings the Prettiest Songs" by Jolie Holland. The guitar and women harmonies were exquisite.
I will be building my 12B4 as a Christmas present to myself.
Lyndon
Salt Lake City
Where another foot of fresh powder for skiing will be present at Alta and Snowbird tomorrow!
:snowman: |
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| blaaberg |
A complete newbee just started :-)
And bought a couple of 12B4A
http://members.shaw.ca/t-linespeakers/12B4.pdf
My plan is using DC heaters at 6V
Can you advise a schematic of a suitable powersupply,
then I would bee very happy :clown:
Jan Jensen |
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| Mark A. Gulbrandsen |
Ok, this Glassware article on a H-V regulator is very interesting to say the least and it might be the cats meow for use with the 12B4. It features low output impedance over a very wide range and it could easily be setup to deliver the 320 volts thats required by Brian's 12B4 line stage. Any input on using this circuit would be appreciated.... I was thinking of an IRF740A as the pass device, but any other suggestions for a similar but higher voltage device would be appreciated as the 740 is rated right at 400 volts.
Thanks,
Mark |
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| Looneytunes |
Hi all,
I'm a total newbie. I’ve never built a thing that made sound. But, I'm fascinated by the whole idea of it, and I'm fascinated by tubes.
I found the Etude preamp on the internet and thought that it might be a good way to get started in tubes. Audio circuits can't get much simpler than this, right? I'm also thinking that this project might teach me a thing or two about power supplies. When I saw Mark's posts comparing the 12B4A with the GG preamp (with the 12B4 winning big time), that did it for me. I'm going to build one!
I have a lot to learn, both about tubes and electronics in general. I have already bought an electronics book (kind of basic), a Beginner’s Guide to Tube Audio Design, and I'm reading your posts. Things are slowly starting to make a little sense, but I still have a long way to go. Unfortunately, I don't know any of the tricks. I hope you all can help me out in that department.
I need to start buying some parts to play with... tubes for starters. I found both GE and RCA 12B4As on the internet for only $4.10 each (pretty cheap, I'd say). Can anyone tell me which is better? Also, how many should I buy for a project like this? I know that I only NEED two. But, should I buy a bunch extra so I can find match pairs, or to have some handy to replace the ones that meet an (ahem) untimely demise?
Any and all suggestions and/or tips on how to get started would be very much appreciated.
Hopefully, I won't electrocute the cat! :hot:
Thanks |
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| Mark A. Gulbrandsen |
You would probably have really good luck with JAN 12B4's more so than run of the mill 12B4's. JAN(Joint Army Navy) tubes were built to much higher standards than every day tubes were. I have only tried out JAN tubes so far because others have had problems with noisy/microphonic 12B4's. Jan tubes should only cost you a little more than the regular tubes. I paid 10.00 each for my NOS 12B4's.
Above all don't electrocute yourself or the cat. If you're not familiar with High Voltage safety then you really should become familiar with it way before you apply any voltage to any circuits.
Good luck!
Mark |
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| Bryan |
I can second the JAN 12B4A. I've tried a BUNCH of different makes (RCA, Sylvania, JAN, and a few others that escape my mind) and the JAN were the least microphonic. Tubes within the same manufacturer will vary as well, so at 4.10/tube, I would buy a bunch and find a few pairs that are good. When I purchased my 12B4A's, I was paying about 1.80-2.20/tube. This made searching out pairs relatively affordable.
In my pre, I use a LCLCLC - VR - CCS to feed the plate, and I have to say it is glorious. I run the 12B4A at about 20-25mA. It's a very resolving and detailed set-up! I wont go back!
BK |
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| GeWa |
| quote: | | In my pre, I use a LCLCLC - VR - CCS to feed the plate, and I have to say it is glorious. I run the 12B4A at about 20-25mA. It's a very resolving and detailed set-up! I wont go back! |
Do you mind sharing the schematic of this PS with us? ;)
Regards |
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| Bryan |
Sure, but I need to draw up the schematic as it currently stands. I will try to do so this evening...
Briefly, it is a hammond 175VCT Transformer, with each leg of the secondary feeding a 12AX4 damper diode. There are two schotcky rectifiers off the plates of the 12AX4, forming a tube hybrid rectifier. The B+ is filtered through LCLCLC where all chokes are 20H Hammonds. The first cap is a 50uF unylytic (only b/c I ran out of real estate), the second is a 50uF ASC motor run, and the final is a 60uF ASC motor run. From the third cap I use an appropriate dropping resistor to series connected OA2 and OB3 VR tubes to ground, each bypassed with very small ASC cap, which regulates B+ at 190V. This feeds a Pimm self biased CCS which in turn feeds the plates. The amp is complete dual mono.
Sorry if this is more confusing than helpful. I'll get the scheme up tonight... |
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| GeWa |
Thanks Brian.
I almost get the picture of the PS. What I also understand is that it will take up quite some space with all those chokes and cap's. If someone can come come up with a deicent SS power supply for this amp I would realy appreciate it. :D
Regards |
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| Bryan |
This is VERY true...
I have two chassis, one for PS and the other for audio. The PS chassis is COVERED with iron. 2 HV tranies, 4 damper diodes, 4 12.6 volt tranies, and 6 chokes... Fortunately, the last cap is housed in the audio chasis, close to the plates. It is NOT light, but I can say it was well worth the trouble... |
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| Mark A. Gulbrandsen |
| quote: | | If someone can come come up with a deicent SS power supply for this amp I would realy appreciate it. |
I left a link to what should be the perfect solid state supply for this line stage...., a bit complex but not expensive to build... back in post 60... Let me know what you think....
Mark |
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| Looneytunes |
Thanks Mark, Thanks Bryan.
I think I've hunted down some JAN 12B4A tubes. I'm planning to buy 8 of them. I hope I'll find one close pair in the group. If I'm being overly optimistic about my odds, someone please let me know and I'll buy more. Besides, who knows where this is going. I may get adventurous and use the extra tubes for to build a balanced circuit.
Brian, I look forward to seeing your power supply. I saw you working on it in another thread, but I don't think I saw the final schematic. I'll bet there is no noise or grain at all.
And Mark, I was kidding about the cat. I can actually be very careful. I learned a very long time ago (when wearing tennis shoes) that the shortest path between an electric fence and ground is through your dog's nose touching the back of your leg. Double-YEEEOW! :hot:&:hot: (The pup kept his distance for a long time after that.) Luckily there wasn't enough current to toast the both of us. I plan to study-up before I plug this in, and there won't be any pets or anything else around that might add to the element of unpredictability. I also plan to enlist the help of a buddy that works with high voltage electronics to help me get me started.
At last, there is a question in all this. Are there any breadboarding parts that I should buy before I start? I don't want hot wires flapping in the breeze. If there are, can anyone recommend a good source for them?
Thanks for the help. |
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| dhaen |
| quote: | | I learned a very long time ago (when wearing tennis shoes) that the shortest path between an electric fence and ground is through your dog's nose touching the back of your leg. Double-YEEEOW! & |
That's really funny:D (from a distance....) |
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| planet10 |
| quote: | Originally posted by Looneytunes
Are there any breadboarding parts that I should buy before I start? |
Clip-leads... you should see some of the creations made with clip-leads....
dave |
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| Sherman |
| quote: | Originally posted by Looneytunes
... I plan to study-up before I plug this in, and there won't be any pets or anything else around that might add to the element of unpredictability. I also plan to enlist the help of a buddy that works with high voltage electronics to help me get me started.
At last, there is a question in all this. Are there any breadboarding parts that I should buy before I start? I don't want hot wires flapping in the breeze. If there are, can anyone recommend a good source for them?
Thanks for the help. |
I'm with Dave on the clip leads, but if you buy cheap ones from a surplus outlet be sure to check them all out for solid connections and continuity! I wasted 15 minutes once trying to figure out a problem with a circuit when it was just a bad clip lead!
When I turn on a new project for the first time I usually plug it into a three-prong (earth grounded) extension cord which is plugged into a switched outlet. That way I can stand across the room and turn it on. The displays on my meters are large enough for me to see from that distance so I can monitor voltages and currents. |
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| Bryan |
Hey Guys,
Here is a rough drawing of the PS as it is in my amp. I need to double check the VAC output of the power tranny, and confirm the dropping resistor for the VR tubes is 2.7K.
Never the less, this should give a clear idea of what I have done.
Hope it helps....
Bryan |
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| Mark A. Gulbrandsen |
Any tubes the glow are to me worth trying out:D . I've always been a fan of gas regulators but have never messed around with them very much, always went the solid state route. Does your power supply have a fairly low output impedance and how is the impedance at different frequencies? Also, how "quiet" are gas regulators compared to the solid state circuit I posted alink to in post#60? Keep in mind that the op amp in post 60 operates at unity gain so it doesn't generate much noise of its own, if any.
Thanks,
Mark |
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| choky |
| quote: | Originally posted by Mark A. Gulbrandsen
Any tubes the glow are to me worth trying out:D . I've always been a fan of gas regulators but have never messed around with them very much, always went the solid state route. Does your power supply have a fairly low output impedance and how is the impedance at different frequencies? Also, how "quiet" are gas regulators compared to the solid state circuit I posted alink to in post#60? Keep in mind that the op amp in post 60 operates at unity gain so it doesn't generate much noise of its own, if any.
Thanks,
Mark |
gas shunt stabs (when properly implemented) are dead silent;
feeding both halves in some lalala RCA style RIAA stage without hiss is good enough ?
;) |
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| choky |
| quote: | Originally posted by Bryan
Hey Guys,
Here is a rough drawing of the PS as it is in my amp. I need to double check the VAC output of the power tranny, and confirm the dropping resistor for the VR tubes is 2.7K.
Never the less, this should give a clear idea of what I have done.
Hope it helps....
Bryan |
in my xperience - with shunt stabs -best way is when you burn AT LEAST same current in reg as your active stage ;
takin' in account that OA3 is capable of some 40mA max and calculating that 12B4 needs atleast 30 mA to sing,you are pretty close to margin
try to analyze few old books for paralell connecting of gas stab tubes or-even better - wire shunt resistor for 30mA in parallel to OA combo,and let them to burn just 20mA
(old trick :angel: ) |
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| tja |
| quote: | Originally posted by Mark A. Gulbrandsen
Ok, this Glassware article on a H-V regulator is very interesting to say the least and it might be the cats meow for use with the 12B4. It features low output impedance over a very wide range and it could easily be setup to deliver the 320 volts thats required by Brian's 12B4 line stage. Any input on using this circuit would be appreciated.... I was thinking of an IRF740A as the pass device, but any other suggestions for a similar but higher voltage device would be appreciated as the 740 is rated right at 400 volts.
Thanks,
Mark |
IRFP450? (is rated at 500V, 180W).
Take |
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| Bryan |
As I designed the PS, the VR tubes tap 20mA, and the 12B4A between 20-25mA, so the load is equally shared. I have not done any serious measurements, but I can say that the supply is quiet.
If I was doing this again, I would decrease the B+ a little bit, as I am wasting a lot of volts dropping the B+ before the regs...
I do have a very slight amount of hum, but this is caused by the physical proximity of all the iron of the PS chassis (and maybe a little bit of messy wire which needs tidying up in the audio chasis). I cant hear noise from the reg tubes, and my hearing is pretty darn good ;)
Bryan |
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| 240z4u |
Well I am convinced.
I spoke to mark via email and thats the final straw. I was looking at audio research, conrad-johnson etc.. unfortunately at my budget (350 or so) I really could not afford anything too exciting.
Looks like I am going to give this a go. I have had some experience fixing solid state amplification so I am somewhat confident.
Any thoughts as to stuff I should read before doing this project besides the newbie pages? I have read most of them but have trouble putting a finger on things without getting dirty.
I am also very aware of the danger of high DC voltages, and understand that sipping on a cocktail whilst piddling in tube equipment probabally is NOT the best idea :whazzat:
I will continue to watch the progression. I am not sure whether to do solid state regulation or tube. I guess I will cross that bridge when I get there!
This site rules, and thanks alot for the great information!!!!
Evan |
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| mach1 |
I use the Tubecad PSU linked at post 60 on my phono preamp and it sounds great. If you build it use the 'design trick' discussed. It keeps frequencies above approx 250Hz (I can't remember the exact figure) out of the feedback loop so the sound 'breathes' a lot more. You still get a rock solid bottom end with lots of slam.
You can experiment with different value feedback resistors to vary the feedback cutoff frequency to get the sound you like. The higher the frequency the 'tighter' the sound.
If you want another great sounding cheap psu for the linestage try the following:
Obtain a transformer - rectifier combination putting out around 350V. Place a high quality 6-10 uF cap after the rectifiers (yes only 6uF ! pio are great in this application) followed by an IXCP10M45S wired as a CCS set at around 75mA (reasonably heavy heatsinking required). Feed this into a shunt reg consisting of 2 x 0D3 (or 0A2) regulators (assuming you want a plate voltage around 150 - 175v) bypassed with only 0.01uF, followed by a an IXCP10M45S CCS for each 12B4 (set to approx 25mA - small heatsink required). No iron, tiny amount of capacitance, three chips and two reg tubes. For an upgrade swap the 0D3s for a tubecad style shunt reg and use Gary Pimm style CCSs.
have fun |
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| apassgear |
| quote: | Originally posted by Mark A. Gulbrandsen
Ok, this Glassware article on a H-V regulator is very interesting to say the least and it might be the cats meow for use with the 12B4. It features low output impedance over a very wide range and it could easily be setup to deliver the 320 volts thats required by Brian's 12B4 line stage. Any input on using this circuit would be appreciated.... I was thinking of an IRF740A as the pass device, but any other suggestions for a similar but higher voltage device would be appreciated as the 740 is rated right at 400 volts.
Thanks,
Mark |
Mark.
I have used IRF840 for simillar aplication good to 500V with good results :) |
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| mach1 |
Voltage and current capacity aside, the key parameter for mosfet selection in this application is low output capacitance.
The IRF710 is champion in this area with a low 34pF. If you need >400V I recommend the 2SK1119. This can handle 1000V and has roughly half the output capacitance of the IRF840 (100pF v 190pF).
have fun |
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| Looneytunes |
Dave & Sherman, thanks for the tips. I'll add a load of clip leads to the list. And, a remote power switch too. I hadn't considered the possibility of blowing out the windows, but... ;)
I've also been following everyone's posts on the power supply. Being a NewB, I need to keep it simple. Can anyone recommend a simple power supply design to get me started? Considering where I'm at, an unregulated supply might be best for now. It doesn't have to be great; I can always improve it (or replace it) later.
Thanks everyone. And, I second Evan... this site is the best. |
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| bordins |
Hi apassgear, thanks for putting my comments about 12B4 at AV forum here. :)
Please forgive me for my poor EE knowledge. I'm still confused what you're talking about. I'm not sure you guys are trying different ways to supply power to 12B4, in order to make the "best" sonics out of it ?
What're sonic differences between different types of power supplies ? Diode, bridge, diode tube, regulated (LM), ... Mine just got diode tube PS which is in between full bridge and full tube. Another friend told me regulated PS is the best. I'm still not sure what best means ? :xeye:
One observation from my friends about a 12B4 preamp (I borrowed) is that it sounded so fantastic, but forwarded ! The sound stage is very wide, but imaging is forwarded. I think it is because of too high B+.
My current build sounds not forwarded, but a bit less airy than the other one.
Any suggestion would be greatly appreciated.
Cheers.
BTW, I ordered Oritek X-2 interconnect. Hopefully, it'll put my 12B4 preamp to the next level. |
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| Mark A. Gulbrandsen |
| quote: | | What're sonic differences between different types of power supplies ? Diode, bridge, diode tube, regulated (LM), ... Mine just got diode tube PS which is in between full bridge and full tube. Another friend told me regulated PS is the best. I'm still not sure what best means ? |
Well, I don't think there IS a best power supply per say. Some claim that alot of iron sounds best while others say regulated is best. Both have just about as many advantages and disadvantages as the other. I have tended to favor regulated over the years but I am getting itchy to try an iron based supply and listen to hear which is better at least on my 12B4 line stage. Since it is so revealing it should be easy to hear the effects of different supplies.
Supplies fdefinately do affect how a unit sounds to some degree but in the end its still a matter of taste. Since I'm powering my 12B4 from a regulated H-V bench supply for now I at least have something to compare it to.
Personally I feel there are some important advantages to regulated supplies over heavy iron type. It isn't necessarily cost... a properly designed regulated power supply is also not going to be inexpensive to build. Regulated supplies can also be noisy and their output impedance can vary over the frequency range we deal with. However a good supply such as in the link below that has fairly flat output impedance, low noise, and very tight regulation should sound very good. It also takes up a heck of alot LESS space. This allows for incorporating the regulators right into the line stage itself... keeping the regulator very close to the actual operating circuit and keeping noise levels on the dc line down. I would however definately keep the raw power source out of it and locate that elsewhere.
I believe I've located a good regulator here. Its claims are for use on MC preamps so it has to be a quiet one. Since the 12B4 has poor PSRR this sort of regulator ought to work really well. Am planning on building it next week if time permits so we'll see.
| quote: | | One observation from my friends about a 12B4 preamp (I borrowed) is that it sounded so fantastic, but forwarded ! The sound stage is very wide, but imaging is forwarded. I think it is because of too high B+. |
I don't experience that forwordness that you experienced with your borrowed 12B4. There can be a closeness unlike anything I've heard when the recording is mic'd that way but otherwise what I've experienced is massively more detail much better imaging and a wider deeper sound stage over my Grounded Grid line stage. Vocals that are close mic'd are as though they are right in the room with you. Those that have been over to hear it agree its pretty incredible.
If you build your own you might want to build it similar to Brian Becks diagram that uses the CSS to bias the tube, his diagram is posted a few pages back in this thread. His circuit is definately a large improvement over the original circuit and it only costs a few dollars more to implement. Just be sure to bypass those electrolytics with a really good quality film cap... Multicap, Wonder-
Cap, Auracap, Whatevercap or something equivelent. Then you can sit back and marvel at all the stuff you were missing in all your recordings.
Mark |
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| Ed Lafontaine |
Hey guys, my lurking took me into T3h Geek Zone, where I found this power supply. Just trying to increase the options without being redundant.
http://geek.scorpiorising.ca/circui...upplySCHEMA.png
"The pass BU806 should be mounted on an adequate heatsink - a 5W one is good for most preamp apps. The error-amplifier too, should be heatsinked, a 2W is good for all apps.
Circuit protection is the underrated 1/8W, 470 ohm resistor on the pass transistor's emitter - it's a "fusable" link ;-) " |
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| kooltubes |
| quote: | Originally posted by bordins
One observation from my friends about a 12B4 preamp (I borrowed) is that it sounded so fantastic, but forwarded ! The sound stage is very wide, but imaging is forwarded. I think it is because of too high B+.
My current build sounds not forwarded, but a bit less airy than the other one.
|
Hi Bordins,
I have experienced the same thing before and I came to the conclusion that the sound is affected by the operating point and the PSU!
There are those who prefer running the 12B4 at high current, while other will be happy running them at lower current. You can voice your preamp by altering the cathode resistor in order to find the sweet spot, but you may need to fine tune your psu each time you do so; it's a long but rewarding process :bawling:
My PSU is simple: 2x 6CJ3+10H+25mf (oil)+10H+25mf (oil) then for each channel: 20H+50mf (oil)
The 12B4 is resistor loaded (7K5) and 390R at the cathode //330mf
The soundstage is huge :bigeyes:
I am waiting for some 12A4 to experiment.
I am wondering if there would be any further benefit using a parallel feed output à la Magnaquest? |
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| Mark A. Gulbrandsen |
Thanks for that link Ed. I just happen to have a couple of BU806's in my junk box. So I will also build this one and see......
Mark |
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| choky |
| quote: | Originally posted by Ed Lafontaine
Hey guys, my lurking took me into T3h Geek Zone, where I found this power supply. Just trying to increase the options without being redundant.
http://geek.scorpiorising.ca/circui...upplySCHEMA.png
"The pass BU806 should be mounted on an adequate heatsink - a 5W one is good for most preamp apps. The error-amplifier too, should be heatsinked, a 2W is good for all apps.
Circuit protection is the underrated 1/8W, 470 ohm resistor on the pass transistor's emitter - it's a "fusable" link ;-) " |
| quote: | Originally posted by Mark A. Gulbrandsen
Thanks for that link Ed. I just happen to have a couple of BU806's in my junk box. So I will also build this one and see......
Mark |
that's my bunch of mates ;) |
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| planet10 |
| quote: | | Originally posted by Mark A. Gulbrandsen .. a properly designed regulated power supply is also not going to be inexpensive to build. Regulated supplies can also be noisy and their output impedance can vary over the frequency range we deal with. However a good supply such as in the link below that has fairly flat output impedance, low noise, and very tight regulation should sound very good. |
PSU is VERY important. The whole purpose of a linestage or a poweramp is to regulate how much of the power supply rail(s) gets sent out the output.
A passive supply has the advantage of not adding a whole lot of grunge to the rails & the ability to supply & sink current.
A regulated supply is another circuit and it needs to have a smooth & very low impedance with wide bandwidth. Most regulated supplies tend to be series regs (because they are easier to build and less wasteful of energy). They can't sink current very well thou. A good shunt reg. like a passive PS, can source & sink current, but are less efficient. The Broskie reg linked above is a shunt reg. A well worked out shunt reg with exceedingly good performance is Allen Wright's Super Reg (<0.005 ohms output impedance with low noise & very wide bandwidth). You can buy the book (Preamp Cookbook -- one of my top 3 recommended tube books) and diy it or you can be lazy & buy the kit. Even wit this subperb reg in the circuit he still recommends a choke load supply for its superior regulation.
A good shunt reg will have much wider bandwidth & much lower impedance than is possible from any passive supply, but getting a good one from scrtach is a real challenge (just a little off and they make a real good oscillator)
dave |
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| Mark A. Gulbrandsen |
Thanks for the link Planet 10!! I had read stuff on that site a couple of years back but had forgotten all about it. 125 euro for the kit???? Pretty pricy but could be done for less by DIY. I would be more tempted to buy the book and build it myself.... the book would be good to have anyway.
Thanks,
Mark |
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| kooltubes |
| You can buy a tube regulator pcb for $20 (no tubes though) it's a Lite audio you will need an EF86 and an El 84 or EL86; the board comes with a filament regulator. Check on ebay or www.liteaudio.com |
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| planet10 |
| quote: | Originally posted by Mark A. Gulbrandsen
.... the book would be good to have anyway.
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Yes... it is a hoot, gives some solid info & lays out AWs philosophy. Even having the book, i'd probably buy the reg kit myself...
dave |
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| Mark A. Gulbrandsen |
| quote: | | Even having the book, i'd probably buy the reg kit myself... |
Aw, thats no fun..... Kits are way too easy..... Unless there are some special spec'd out parts I can't see why not to build it DIY?
| quote: | | You can buy a tube regulator pcb for $20 (no tubes though) it's a Lite audio you will need an EF86 and an El 84 or EL86; the board comes with a filament regulator. |
I have one of those boards here. I don't think it can supply 60ma of current for both channels, so you would probably require one board per channel. The board by the way is extremely nice!!
Mark |
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| Looneytunes |
Thanks everyone for the great power supply discussion. I definitely have some research (and a lot of catching-up) to do.
From Dave: | quote: | | ...You can buy the book (Preamp Cookbook -- one of my top 3 recommended tube books)... |
Dave, I'll definitely get the Cookbook. What are your other two top books? Does anyone have any other "highly-recommendeds" to add to the list?
I'll probably start with Brian's or Kool's power supply. Lots of iron, but by the time I get the parts , I should have a basic understanding of what is going on. Can anyone suggest a good source (and manufacturer) of pio capacitors? Is quality critical considering where the parts are used?
From Bryan: | quote: | | I do have a very slight amount of hum, but this is caused by the physical proximity of all the iron of the PS chassis ... |
Bryan, how far would you recommend separating the tranny & chokes to get rid of this hum? Also (and please excuse the NewB question), but I remember reading that all of the iron needs to be rotated 90 degrees from each other to minimize coupling. If I remember correctly, your design places a tranny plus 2 chokes (per channel) on the power supply box. Can I "decouple" (I hope this is the right word) the three pieces by rotating them by 90 degrees over all three axes?
From Evan:| quote: | | Any thoughts as to stuff I should read before doing this project besides the newbie pages? |
Evan, I found the "Online Tube Audio Resource Guide" a virtual treasure trove of information. If you haven't found it already, you can find it at: http://www.tubeseller.com/docs/tube_links.pdf. You'll even find links to complete texts there.
Thanks to everyone for the help and great information.
Wynn |
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| GeWa |
O.K. guys, to make it even harder here's another compact regulated power supply.
Welborne-Labs PS10
Regards |
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| bordins |
| quote: | Originally posted by Mark
Some claim that alot of iron sounds best while others say regulated is best. Supplies definately do affect how a unit sounds to some degree but in the end its still a matter of taste.
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It always comes to a subjective conclusion in the audiophile world.
| quote: | Originally posted by Mark
I don't experience that forwordness that you experienced with your borrowed 12B4. .... what I've experienced is massively more detail much better imaging and a wider deeper sound stage over my Grounded Grid line stage.
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I had similar experiences at first when I auditioned a 12B4 preamp. But when I took it to my friend's place where 3-4 experienced audiophile arrived on different times, they all said the same thing, without knowing others' comment.
They commented that my "first sighted love" because my ears got attracted by so revealing sonics. :) But if I listen to it for a long period of time, it might introduce hearing stress.
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