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
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
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.
An externally hosted image should be here but it was not working when we last tested it.
Hello Brian;
Aaaah, the magic formula
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!
Aaaah, the magic formula
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!
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....
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....
"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('
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angel
Venlig hilsen Jan
Sound very interesting, how low is your input impedance? Do you think it can drive my 17Kohm input Zappulse.....?javascript:smilie('
')angel
Venlig hilsen Jan
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!!!
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!!!
Attachments
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.
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.
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
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!
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!
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
Jan Jensen
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
Jan Jensen
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
Thanks,
Mark
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