Experience with Toroids
I built a 100W Ultralinear using 2 pairs of EL34. (also tried KT88 in it).
Changing from a Hammond 1650T (EI) to a VDV2100 (Toroid) made a HUGE difference. Extended Bass and Tops and just generaly more detailed and smoother through the entire frequency range.
At one stage I had a fault where on one side only one of the EL34s was working which meant I had 45mA out of balance in idle current. I picked that up due to a sudden increase in hum - sound did NOT change significantly so I would suggest that while balancing of idle currents is more important than with EI transformers it is not as critical as some of the claims made here.
One thing - part of the "traditional" tube amp sound is the artificial enhancement of bass as the impedance of the primary inductance gets close to the rp of the output tubes (increased 2nd harmonic distortion). I got that "sound" with the Hammond 1650T (57H primary inductance). I did NOT get that with the VDV2100 (>500H primary inductance). With the VDV2100 the bass was subjectively weaker but went much lower.
The 4 pairs of EL34 in Triode Mode design WILL present a problem with driving the output tubes. Miller capacitance is huge. A White Cathode Follower driver stage would be just about essential. You certainly are'nt going to drive the Miller Capacitance of 4 Triode Mode EL34s on each side with a diffamp - at least not to the bandwidth of the output transformer anyway. An alternative, especially if using bias servos, is to individually buffer each triode with a direct coupled MOSFET Source Follower and apply the bias to the MOSFET gates.
Cheers,
Ian
I built a 100W Ultralinear using 2 pairs of EL34. (also tried KT88 in it).
Changing from a Hammond 1650T (EI) to a VDV2100 (Toroid) made a HUGE difference. Extended Bass and Tops and just generaly more detailed and smoother through the entire frequency range.
At one stage I had a fault where on one side only one of the EL34s was working which meant I had 45mA out of balance in idle current. I picked that up due to a sudden increase in hum - sound did NOT change significantly so I would suggest that while balancing of idle currents is more important than with EI transformers it is not as critical as some of the claims made here.
One thing - part of the "traditional" tube amp sound is the artificial enhancement of bass as the impedance of the primary inductance gets close to the rp of the output tubes (increased 2nd harmonic distortion). I got that "sound" with the Hammond 1650T (57H primary inductance). I did NOT get that with the VDV2100 (>500H primary inductance). With the VDV2100 the bass was subjectively weaker but went much lower.
The 4 pairs of EL34 in Triode Mode design WILL present a problem with driving the output tubes. Miller capacitance is huge. A White Cathode Follower driver stage would be just about essential. You certainly are'nt going to drive the Miller Capacitance of 4 Triode Mode EL34s on each side with a diffamp - at least not to the bandwidth of the output transformer anyway. An alternative, especially if using bias servos, is to individually buffer each triode with a direct coupled MOSFET Source Follower and apply the bias to the MOSFET gates.
Cheers,
Ian
jarthel said:
Menp holds the title of Head of R&D (or something like that) for Plitron -- at least in 1999 when i meet him.
I was lucky enuff to be a fly-on-the-wall when Meeno & Bill Perkins (another world-class transformer designer and C-core afficiando) whe they discussed the merit of toroid vrs C-Core. They were going so fast & most of it was over my head but i did come away thinking that very good OPTs could be made using either tech.
dave
So can you suggest a cheap and workable toroid from North America that would suffice for the average Joe? OT for SE el34 or a really small amp such as a cathode biased single ended el84 - those power transformers for example which did you use?
Shoog!
Can you tell me a bit more how do you chose your power toroids for OPT?
Somewhere I read that 20% of the nominal power rating is good for toroid OPT. For example: 100VA power toroid is good for 20W OPT.
A power toroid with 2x110Vac primary and 6Vac secondary would be good for a ca. 8K-6R PP-OPT.
Greets:
Tyimo
Can you tell me a bit more how do you chose your power toroids for OPT?
Somewhere I read that 20% of the nominal power rating is good for toroid OPT. For example: 100VA power toroid is good for 20W OPT.
A power toroid with 2x110Vac primary and 6Vac secondary would be good for a ca. 8K-6R PP-OPT.
Greets:
Tyimo
Tymio,
Both of your statements are about spot on in my experience. Unfortunately 6V 100VA toroidals are hard to source in my experience, though I think Piltron do standard powers at this spec - though they are more expensive than most other brands.
I have found that the results I have achieved have been fairly consistent between brands. I recently built a PP headphone amp using the budget toroidals from the Farnell catalogue, they worked very well.
Shoog
Both of your statements are about spot on in my experience. Unfortunately 6V 100VA toroidals are hard to source in my experience, though I think Piltron do standard powers at this spec - though they are more expensive than most other brands.
I have found that the results I have achieved have been fairly consistent between brands. I recently built a PP headphone amp using the budget toroidals from the Farnell catalogue, they worked very well.
Shoog
Cool,
Would this do for the OT of a single ended el34? They don't have a 100VA.
http://www.hammondmfg.com/182.htm
182Q6 80VA 12V C.T.@6.67A 6@13.34A Dual
What about the gap and all that? Really interesting stuff.
Eire as in Ireland? I'm Irish too.
Would this do for the OT of a single ended el34? They don't have a 100VA.
http://www.hammondmfg.com/182.htm
182Q6 80VA 12V C.T.@6.67A 6@13.34A Dual
What about the gap and all that? Really interesting stuff.
Eire as in Ireland? I'm Irish too.
You will have to go Parafeed.
Microwave Oven Transformers make reasonably good plate chokes - though there bulky and need to be hidden inside the case.
Shoog
Microwave Oven Transformers make reasonably good plate chokes - though there bulky and need to be hidden inside the case.
Shoog
Toroid with 813s
I have been slowly building an 813 pp amp with a home wound 350W mains toroid and while I am a long way from getting it finished i have found an easy way to balance the current in the toroid. It's called a compass, with a compass resting on the transformer it's possible to see a 1.5mA current imbalance which with about 100mA Ia I reckon is pretty good.
Good luck,
Mike.
I have been slowly building an 813 pp amp with a home wound 350W mains toroid and while I am a long way from getting it finished i have found an easy way to balance the current in the toroid. It's called a compass, with a compass resting on the transformer it's possible to see a 1.5mA current imbalance which with about 100mA Ia I reckon is pretty good.
Good luck,
Mike.
Im a fan of the C core design, if only because toroidal winding machines are so very expensive and complicated.
I was at a DIY meeting over the weekend and got to hear Shoog's latest proof-of-concept headphone amp using PS toroids as output transformers and I can attest to the stunning sound from this amp.
Everything about this amp sounded right, it reached down low with a grunt to the clean bass & the highs had a wonderful sparkle to them while also preserving exquisite sustain & decay of notes.
Being an old cynic, this was the first time I have been so impressed by a piece of audio kit. Normally, I would think a piece of kit was an incremental improvement over what I had heard in the past but this seemed to leap out from the crowd.
Now, I know I should be wary of this effect as it's said that the kit that grabs your attention is probably exagerating some aspect of the soundscape! But in this case I don't think it applies as it was among some other good headphone amps.
Oh, and BTW his power amp also using PS toroids as output trafos (but a different circuit & tubes to H/phone amp) also sounded excellent even better than the last time I had heard it!
Everything about this amp sounded right, it reached down low with a grunt to the clean bass & the highs had a wonderful sparkle to them while also preserving exquisite sustain & decay of notes.
Being an old cynic, this was the first time I have been so impressed by a piece of audio kit. Normally, I would think a piece of kit was an incremental improvement over what I had heard in the past but this seemed to leap out from the crowd.
Now, I know I should be wary of this effect as it's said that the kit that grabs your attention is probably exagerating some aspect of the soundscape! But in this case I don't think it applies as it was among some other good headphone amps.
Oh, and BTW his power amp also using PS toroids as output trafos (but a different circuit & tubes to H/phone amp) also sounded excellent even better than the last time I had heard it!
As for winding the toroid, I hand wound it using a long shuttlecock and about 4 days spread over 2 weeks to let my fingers recover.
Cheers
Mike.
Cheers
Mike.
Thanks John. Its good to know the effort is worth it.
I personally wouldn't build with anything other than Toroidal's now. The case is absolutely proven as far as I am concerned. Also the need for tight DC current balance has encouraged me to turn all my output stages differential with CCS bias blocks, and this has had significant benefits on the overall result.
Shoog
I personally wouldn't build with anything other than Toroidal's now. The case is absolutely proven as far as I am concerned. Also the need for tight DC current balance has encouraged me to turn all my output stages differential with CCS bias blocks, and this has had significant benefits on the overall result.
Shoog
Heres the thread discussing the headphone amp;
http://www.diyaudio.com/forums/showthread.php?s=&threadid=108745&highlight=
I will post the DC7 schematic when I get home (not presentable enough for a sexy picture).
Shoog
http://www.diyaudio.com/forums/showthread.php?s=&threadid=108745&highlight=
I will post the DC7 schematic when I get home (not presentable enough for a sexy picture).
Shoog
Lowrider said:
Quote from the site (my bold underline) :-
I would like to know how the core was slit to give a gap. Was it cut into sections and glued or slit every turn or two?
Obviously, it is viable. Anyone for unwinding a toroid and trying ?
Andy
Plitron 3035SE toroid OPT
I think I have a say here because I built the 300B monos with this OPT few years ago. Then, I built the 2A3 monos with Hammond 1627SE, 45 stereo with Hammond 1628SE and now replaced with Lundahl 1620 30mA OPT.
I would say the Plitron has good quality design and good sound. It sounds very dynamic and clear with extended high frequency. It sound different from EI and C-core OPT that it may not the cup of tea for some people. To me, my investment on Plitron is quite worthy.
Look, I use my 300B with Plitron as my symbol.
Johnny
I think I have a say here because I built the 300B monos with this OPT few years ago. Then, I built the 2A3 monos with Hammond 1627SE, 45 stereo with Hammond 1628SE and now replaced with Lundahl 1620 30mA OPT.
I would say the Plitron has good quality design and good sound. It sounds very dynamic and clear with extended high frequency. It sound different from EI and C-core OPT that it may not the cup of tea for some people. To me, my investment on Plitron is quite worthy.
Look, I use my 300B with Plitron as my symbol.
Johnny
Yes the transformers are in the case. I think their about 30VA.
Heres the DC7. Since this schematic the parafeed cap is now 4uf and the interstage has been converted to a center tap choke - this brought a significant improvement to the top end.
Shoog
Heres the DC7. Since this schematic the parafeed cap is now 4uf and the interstage has been converted to a center tap choke - this brought a significant improvement to the top end.
Shoog
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