I own a pair of Thiel CS1.2 speakers which have a sensitivity of 87dB. I would like to build 2 tube mono blocks to drive them, and am looking for advice on the following:
1) How much power is recommended to adequately run those speakers? From what I've read, I will need a minimum of 50W per channel. Does this sound right?
2) Which amp should I build? Are schematics and parts easily available? What do you recommend?
3) I have good soldering skills, a basic understanding of electronics, plenty of very good tools. Is this enough, or am I biting more than I can chew for a 1st build of this nature?
4) My budget is about $300/amp, is this reasonable, or am I way out of line thinking I can do that on this "limited" budget?
5) What am I missing here?
Thanks in advance.
1) How much power is recommended to adequately run those speakers? From what I've read, I will need a minimum of 50W per channel. Does this sound right?
2) Which amp should I build? Are schematics and parts easily available? What do you recommend?
3) I have good soldering skills, a basic understanding of electronics, plenty of very good tools. Is this enough, or am I biting more than I can chew for a 1st build of this nature?
4) My budget is about $300/amp, is this reasonable, or am I way out of line thinking I can do that on this "limited" budget?
5) What am I missing here?
Thanks in advance.
50 watts would certainly be push-pull, unless you want to parallel tubes in SE
two GU-50's in pentode mode single ended could handle it i suppose.
if you dont know about the GU-50, heres a datasheet for 99% identical german tube
http://www.mif.pg.gda.pl/homepages/frank/sheets/043/l/LS50.pdf
there inexpensive on ebay. your going to wait a while for them to arrive from russia tho, takes about a month for shipments from russia for me.
i got a real russian datasheet/curves floating around my hard drive somewhere if you want it.
plenty of projects here for push-pull and single ended KT88 and 6L6 you can use the designs for.
for your budget, your iron is going to be your most expensive item. see what you can afford/locate for power and output transformers. Otherwise, more information is needed on what you want. pentodes or triodes, SE or PP
two GU-50's in pentode mode single ended could handle it i suppose.
if you dont know about the GU-50, heres a datasheet for 99% identical german tube
http://www.mif.pg.gda.pl/homepages/frank/sheets/043/l/LS50.pdf
there inexpensive on ebay. your going to wait a while for them to arrive from russia tho, takes about a month for shipments from russia for me.
i got a real russian datasheet/curves floating around my hard drive somewhere if you want it.
plenty of projects here for push-pull and single ended KT88 and 6L6 you can use the designs for.
for your budget, your iron is going to be your most expensive item. see what you can afford/locate for power and output transformers. Otherwise, more information is needed on what you want. pentodes or triodes, SE or PP
Last edited:
300$ isn't that much for one mono block. You're going the best way with some standard EL34 PP circuit with common available 3,4K output transformer. Good thing is you need no choke. EL34, ECC's are cheap and always available.
Just do some calc:
Pair EL34 - 30$
Two ECC8X - 20$
2x9pin + 2x8pin sockets: 12$
soldier points, wire, components and you we reach easily 100$ !
And still no transformers and chassis !
I'm not familiar with american transformer prices. But lets say Power: 70$ ; and OPT: 80$
Means 50$ left for the chassis which is very optimistic.
Just my opinion.
Just do some calc:
Pair EL34 - 30$
Two ECC8X - 20$
2x9pin + 2x8pin sockets: 12$
soldier points, wire, components and you we reach easily 100$ !
And still no transformers and chassis !
I'm not familiar with american transformer prices. But lets say Power: 70$ ; and OPT: 80$
Means 50$ left for the chassis which is very optimistic.
Just my opinion.
Perhaps biting off a bit more, but maybe not. $300 per monoblock is a little optimistic, especially if you are considering KT88's, which is a good way to get 60w/channel out of a pair of tubes.
EL34's in UL PP are good for 30W or so; your power needs really depends on your listening preferences and room size. It can be surprising how little power you need.
It appears that your speakers are a relatively flat 6 ohms or so impedance....
Take a look at the soloist, UL KT88 PP based on the classic Mullard 5-20 design with a few modern improvements. (a long thread....)
http://www.diyaudio.com/forums/tubes-valves/156699-mullard-5-20-kt88-pp-blocks.html
For a 30W version of the classic mullard circuit, check out Claude Byrith's El34 UL PP:
http://www.lundahl.se/pdfs/claus_byrith/amplifier_30wpp.pdf
Edcor transformers are a good idea and a great value.
EL34's in UL PP are good for 30W or so; your power needs really depends on your listening preferences and room size. It can be surprising how little power you need.
It appears that your speakers are a relatively flat 6 ohms or so impedance....
Take a look at the soloist, UL KT88 PP based on the classic Mullard 5-20 design with a few modern improvements. (a long thread....)
http://www.diyaudio.com/forums/tubes-valves/156699-mullard-5-20-kt88-pp-blocks.html
For a 30W version of the classic mullard circuit, check out Claude Byrith's El34 UL PP:
http://www.lundahl.se/pdfs/claus_byrith/amplifier_30wpp.pdf
Edcor transformers are a good idea and a great value.
Last edited:
The impedance curve of the speakers! Thiel speakers have large dips in the impedance curve. The big models dip down to 1 Ω. That behavior makes Thiel speakers POOR candidates as mates for tubed power amplification. It's a matter of damping factor. A "McShaned" Harman/Kardon Citation 2 stereoblock will work with your "small" Thiels. However, that is a $2000+ project and your budget is $600.
Build a nice tubed line stage, say 12B4 based, and mate it with the best SS power amplification your bank balance will tolerate.
Eli: Is this too lumpy? It was posted by a (ahem...) popular magazine. Looks like 6ohms more or less. I don't see any 2 ohm dips....
Attachments
87dB/W-M is a bit low but not really bad. My 96dB/W-M speakers will play at reasonable level with 32mW average and 1W peak.
The difference between 87 and 96 is 9.
9/3=3, 2^3=8, so 256mW average and 8W peak for normal listening levels isn't all that bad.
Figuring that the meter was c weighted you will need a bit more so a 30W amp is probably sufficient.
The difference between 87 and 96 is 9.
9/3=3, 2^3=8, so 256mW average and 8W peak for normal listening levels isn't all that bad.
Figuring that the meter was c weighted you will need a bit more so a 30W amp is probably sufficient.
IF that curve is correct, the speakers are a "piece of cake" for a "Deuce", on the 4 Ω taps, and some other designs might be OK. However, I don't trust the "pile". I might believe graphs that were published by Feldman or Hirsch. Even then, conflicts of interest could be in operation.
"Little" Thiels are not as nasty as their bigger brethren. Big Thiels are b@st@rds, in the impedance curve dept., and can clobber mediocre SS amps, never mind tubed stuff.
IME/IMO, system synergy in a system using Thiel speakers lies with tubed small signal amplification and high quality, like those Mr. Pass designs, SS power amplification. Mass market guano, of any sort, is out.
Great responses and suggestions so far, thanks.
My power requirements are not great, as I don't listen to music at extremey loud levels. Jazz, vocals and classical mostly, so dynamic range and definition are the goal. I am currently running the Thiels on an old Denon AVR-1800 surround receiver (in 2 channel mode), and they sound very nice, so I can only immagine what they would sound like on valves.
The Denon is rated at 110W @ 6 ohms, 1 KHz with 0.7% THD, and I have no way of measuring how much peak power the Thiels are drawing. Until I looked up those specs, and read what some of the fellow AK'ers here have posted about the innefficiency of the Thiels, I had decided on the Claus Byrith 4-30 (2 x EL34s) Mullard based PP monobloc, with a 30W output, but am now completely undecided.
I don't like the idea of a valve based pre-stage and SS power section, because the goal is to build a purely valve based setup. As a matter of fact, I can currently buy a Vintage hybrid Luxman for around $300 and not worry about the build completely, but where is the fun in that?
So what do you think, will the 4-30 do it?
My power requirements are not great, as I don't listen to music at extremey loud levels. Jazz, vocals and classical mostly, so dynamic range and definition are the goal. I am currently running the Thiels on an old Denon AVR-1800 surround receiver (in 2 channel mode), and they sound very nice, so I can only immagine what they would sound like on valves.
The Denon is rated at 110W @ 6 ohms, 1 KHz with 0.7% THD, and I have no way of measuring how much peak power the Thiels are drawing. Until I looked up those specs, and read what some of the fellow AK'ers here have posted about the innefficiency of the Thiels, I had decided on the Claus Byrith 4-30 (2 x EL34s) Mullard based PP monobloc, with a 30W output, but am now completely undecided.
I don't like the idea of a valve based pre-stage and SS power section, because the goal is to build a purely valve based setup. As a matter of fact, I can currently buy a Vintage hybrid Luxman for around $300 and not worry about the build completely, but where is the fun in that?
So what do you think, will the 4-30 do it?
I think your goals are optimistic given the restrictions of your budget. The situation is exacerbated by the concept of the monoblocks which implies almost twice the cost in cases, and an additional 1/3/ to 1/2 on power supply duplication.
unless you luck into some items (most especially the iron) you are ******* against the wind on hitting your budget with any use of reasonable quality componentry.
As the old saying goes, you can have it good, fast, and cheap - pick any two.
unless you luck into some items (most especially the iron) you are ******* against the wind on hitting your budget with any use of reasonable quality componentry.
As the old saying goes, you can have it good, fast, and cheap - pick any two.
OK, listening habits indicate that 40 or so W. should be sufficient. Above average (for tubed circuitry) damping factor remains in order, given an "unfriendly" load. While I am a BIG fan of Mullard style topology, I dislike the original EF86/12AX7 small signal selection. A substantial amount of GNFB is present and that brings slew limiting worries to the fore. Mullard's small signal pair are low gm types, which are anything but resistant to slew limiting. The H/K Cit. 5 employs Mullard topology, but the 12BY7/6CG7 small signal pairing is high gm and slew limiting resistant. 
Another reason for using the Cit. 5 as a starting point is the 6L6 family O/P tubes. The Russian 6П3С-E (6p3s-e) is reasonably priced and good sounding, which is exactly what a low budget project needs.
Edcor's model CXPP60-MS-6.6K looks OK for the O/P trafos. Magnetic headroom is essential, when the O/P trafo is inside a NFB loop.
Talk to Jim McShane about tubes, parts, and general Cit. 5 info.
Check AnTek out for power trafos.
Finally, any modern Mullard circuit build should employ a constant current sink (CCS) in the LTP phase splitter's tail, instead of a resistor.
Another reason for using the Cit. 5 as a starting point is the 6L6 family O/P tubes. The Russian 6П3С-E (6p3s-e) is reasonably priced and good sounding, which is exactly what a low budget project needs.Edcor's model CXPP60-MS-6.6K looks OK for the O/P trafos. Magnetic headroom is essential, when the O/P trafo is inside a NFB loop.
Talk to Jim McShane about tubes, parts, and general Cit. 5 info.
Check AnTek out for power trafos.
Finally, any modern Mullard circuit build should employ a constant current sink (CCS) in the LTP phase splitter's tail, instead of a resistor.
Attachments
Good point, ditch the monoblocks and you can meet your budget, especially with EL34's, 6L6's, russian equivalents, etc. No problem with a stereo chassis, it'll just be a little bigger & heavier than monos.
After building one chassis, you may thank yourself for not doing mono's.......
Your budget looks wildly optimistic. Yeah, I did a 40W monoblock project for under $300, but my junk box is pretty well-stocked with both hollow state and solid state components. I had both a suitable OPT (at least so far as impedance matching was concerned, it was a NIB Stancor, but rated for 30W, and underpowered for my finals. I was concerned it might have been a PA OPT, but this turned out not to be the case, and it tested to 20Hz -- 50KHz (-3.0db) had two tertiary windings that I have no idea as to what they're there for (Google turned up nothing on this OPT) so I taped 'em off.) and a NIB Stancor PTX that was a perfect match. I didn't have a ripple choke, so I had to get that. I thought I had a pair of usable 6BQ6GTBs, but these proved to be gassy and the bias wouldn't stabilize, so I needed replacements. I needed two 6BQ7s and a 0A3; the other hollow state (5U4GB, 6FQ7, 6AQ5, 6KE8) I already had. Had all the solid state, circuit board blanks, sockets, and the 3KV, 0u01 surge suppression capacitor. Most of that $300 went for hardware, parts to make the cabinet (opted for red oak, as opposed to the cheaper poplar or pine) a plate current meter (NIB -- possible aviation war surplus meter, ca 1945+, as it looks like the meters you see in B-17s and Flying Fortresses) and other passive components I didn't have. Not having to purchase the expensive iron was a big saving.
When it comes to hollow state, you can build cheap or you can build good. You can't do both unless you're good at scrounging, know retired radio/TV repairmen or hams who were active back in the "good ol' days" so you can have a well-stocked junk box. You can keep an eye out for estate auctions, but the last one I attended was positively lousy with hollow state DiY-ers, so not many deals there. Fraud-Bay is also a possibility, but there it's strictly caveat emptor.
@ Eli Duttman. Are you then suggesting that I should go for a Citation 5 build, based on the circuit you attached? If so:
1) are there PCBs for this amp that are readily available? I came across a set of PCBs for sale for the Citation 2 online at www.yaegeraudio.com, but none for the Citation 5 that I could find anywhere
2) the schematics you attached are per channel, where can I get "complete" schematics for the stereo amp, including a BOM?
3) other than budget considerations, and given the fact that Citation 2 PCBs are available, why not build a 2 instead of a 5? Are better skills required? Is this too much for a newbie like me, as a 1st time build?
Thanks
1) are there PCBs for this amp that are readily available? I came across a set of PCBs for sale for the Citation 2 online at www.yaegeraudio.com, but none for the Citation 5 that I could find anywhere
2) the schematics you attached are per channel, where can I get "complete" schematics for the stereo amp, including a BOM?
3) other than budget considerations, and given the fact that Citation 2 PCBs are available, why not build a 2 instead of a 5? Are better skills required? Is this too much for a newbie like me, as a 1st time build?
Thanks
The Cit. 2 circuit requires EXPENSIVE O/P trafos to execute correctly.
The PCBs you mentioned are not original. Both the Cit. 2 and the Cit. 5 are point to point wired, with the assistance of turret boards.
The Cit. 5 schematic is the starting point, for the effort. Your Thiel speakers require 1st rate circuitry in the driving amp. Your budget is low. Trying to meet both the technical and monetary requirements is going to be DIFFICULT, indeed. As other posters have indicated, only a stereoblock build provides even a tiny chance of meeting the expenditure limit.
As a "noob", you probably are in way over your head. What sort of test instruments do you own?
Before you spend any money, EMail Jim McShane. Explain what you are considering and provide him with a link to this thread.
At the end of the day, the glitch is the Thiel speakers. Thiel makes GOOD sounding speakers. However, their impedance behavior and mediocre efficiency makes mating to tubed power amplification highly problematic, especially on a limited budget. The best advice I can give is that you build up a substantial monetary "war chest". Then, construct a top notch tubed line stage and acquire (build or buy) 1st rate SS power amplification. Give Denon full marks for making a home theater product that survives connection to Thiel speakers. A lot of cheaply made mass market units would have gone up in smoke.
The PCBs you mentioned are not original. Both the Cit. 2 and the Cit. 5 are point to point wired, with the assistance of turret boards.
The Cit. 5 schematic is the starting point, for the effort. Your Thiel speakers require 1st rate circuitry in the driving amp. Your budget is low. Trying to meet both the technical and monetary requirements is going to be DIFFICULT, indeed. As other posters have indicated, only a stereoblock build provides even a tiny chance of meeting the expenditure limit.
As a "noob", you probably are in way over your head. What sort of test instruments do you own?
Before you spend any money, EMail Jim McShane. Explain what you are considering and provide him with a link to this thread.
At the end of the day, the glitch is the Thiel speakers. Thiel makes GOOD sounding speakers. However, their impedance behavior and mediocre efficiency makes mating to tubed power amplification highly problematic, especially on a limited budget. The best advice I can give is that you build up a substantial monetary "war chest". Then, construct a top notch tubed line stage and acquire (build or buy) 1st rate SS power amplification. Give Denon full marks for making a home theater product that survives connection to Thiel speakers. A lot of cheaply made mass market units would have gone up in smoke.
I would listen to that
I guess Eli streches himself quite far to say this, repeatedly
a 2ohm stable 80watt is probably what you need
Broskie has a new cathode follower buffer tube pre (buffer means no signal amplification)
I think it also has low output impedance, which is good for SS
only two tubes means cheaper to keep going
I guess Eli streches himself quite far to say this, repeatedly
a 2ohm stable 80watt is probably what you need
Broskie has a new cathode follower buffer tube pre (buffer means no signal amplification)
I think it also has low output impedance, which is good for SS
only two tubes means cheaper to keep going
After much thought and some research I've decided to build 2 monoblocks based on Pete Millet's Uniamp II boards. Obviously my budget will have to go up as $600.00 won't cut it. I would like help on a couple of things please, but here is where I'm at now:
1) I purchased the boards on eBay from Pete Millett ($68.00)
2) I ordered all of the passive components from Mouser ($120.00)
3) I will be ordering all of the tubes in the next couple of weeks
- 4 x Gold Lion KT88 ($200.00)
- 4 x Tung Sol 6SN7 ($200.00)
- 2 x Raytheon 5U4G ($80.00)
4) I would like to use the Lundhal LL1690 for input ($130.00 a piece)
5) I would like to use James Transformers JS-6236HS for output (not sure on pricing but probably around $180.00 a piece!)
I'm already at $1,288.00 and nowhere close to being done! The iron and the tubes are obviously the most expensive components, and I'm not done with the iron. I still need a Power transformer and a choke, miscellaneous mechanical components, and chassis.
What can I "compromise" on at this point in order to control the budget, but still come out with decent sounding amps?
a) Can I substitute the James transformers with something else? What?
b) Which power transformer and choke do you recommend?
c) Is it okay to use Chinese or Russian tubes and still get decent sound? (I know that the Gold Lions are Russian reissues)
Please feel free to comment on any of this, as this is my 1st build and can use any advice.
Thanks - Samer
1) I purchased the boards on eBay from Pete Millett ($68.00)
2) I ordered all of the passive components from Mouser ($120.00)
3) I will be ordering all of the tubes in the next couple of weeks
- 4 x Gold Lion KT88 ($200.00)
- 4 x Tung Sol 6SN7 ($200.00)
- 2 x Raytheon 5U4G ($80.00)
4) I would like to use the Lundhal LL1690 for input ($130.00 a piece)
5) I would like to use James Transformers JS-6236HS for output (not sure on pricing but probably around $180.00 a piece!)
I'm already at $1,288.00 and nowhere close to being done! The iron and the tubes are obviously the most expensive components, and I'm not done with the iron. I still need a Power transformer and a choke, miscellaneous mechanical components, and chassis.
What can I "compromise" on at this point in order to control the budget, but still come out with decent sounding amps?
a) Can I substitute the James transformers with something else? What?
b) Which power transformer and choke do you recommend?
c) Is it okay to use Chinese or Russian tubes and still get decent sound? (I know that the Gold Lions are Russian reissues)
Please feel free to comment on any of this, as this is my 1st build and can use any advice.
Thanks - Samer
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.