12U7 LTP vs. 6922 cascode

mr2racer · 27th September 2011, 04:46 PM

Hey All,

I hve a pair of Dnaco Mark VI monoblocks that I converted to a LTP 12Au7 front end and 6922AU7 driver section with KT88 outputs. After a few months of listening I'm not happy with the amps. They just sound a bit harsh at volume. (Ithink this may be caused by too much voltage on the 12au7"s. I recently built a pair of Mark III clones using a cascODE 6922 front end. Would the cascode be preferable?

Kevin

DF96 · 27th September 2011, 05:14 PM

The LTP and cascode are such different circuits that it is a bit difficult to conceive that they might be alternatives for a given job. LTP is used when you need a balanced input and/or a balanced output, and are happy to lose a little gain and add a little noise but greatly reduce even-order distortion. Cascode is used when you need high gain and low input capacitance for low level signals so distortion is not a problem. Oh, and they have very different PSRR.

ppl · 27th September 2011, 08:14 PM

Why not Both an LTP built with (2) Identical cascodes

mr2racer · 27th September 2011, 08:59 PM

Sorry about the really poor typing. I was trying to to this while at work before the boss noticed what I was doing. I don't have balanced inputs or outputs and I don't need more gain. Getting a Mark VI apart is a bitch. And If I was going that far I thought I might use the cascode since I have four 6922's. But the original design used the LTP so I'll try to make that work.
But I still have these 6922's. Could you use a pair of cascode 6922's as a line amp?
Kevin

dgta · 27th September 2011, 11:13 PM

Quote:

Originally Posted by mr2racer

I hve a pair of Dnaco Mark VI

I don't have balanced inputs or outputs

But the original design used the LTP so I'll try to make that work.

Kevin

If the first statement is true, both the 2nd and 3d are false.

Mark Vi is pentode VA > Concertina splitter > PPP finals.

Free Dynaco tube schematics

gingertube · 28th September 2011, 12:04 AM

You may want to look here:
CURCIO AUDIO Dynaco Mark-4 Amplifier Upgrade
Curcio Audio Engineering (CAE) offer a 6922/6DJ8/6N1P Differential Cascode front end upgrade board for the MKIV. It has an integrated HV regulator on the board to address the fact that cascodes have low power supply rejection.
I've used these boards, they work well. Only problem I ever had was a "running water"/"surf" sort of sound from one card which turned out to be a microphonic tube and not a circuit fault at all.
Cheers,
Ian

dgta · 28th September 2011, 05:32 AM

Ian, that one sure doesn't look like a differential cascode to me. And no regulator:
http://www.dynaco-doctor.com/MK4-DVR-DOC.pdf

Do they make another board?

SemperFi · 28th September 2011, 06:06 AM

Quote:

Originally Posted by mr2racer

... I was trying to to this while at work before the boss noticed what I was doing...Kevin

LOL. Been there done that.

gingertube · 06:30 AM

OOPS - is my face red.
I was thinking of this one - the MK3 "Premium Mod", their PCB-1A board or ASM-1A Kit.
http://www.dynaco-doctor.com/mk3des_3.htm
That is the one I have used. I used it with 6SN7 cathode followers after it to drive parallel push pull KT88.
It was only a prototype amp using Hammond 1650T Output Tranny and I only ever built the one channel but I liked it.
It sticks in my mind because I also tried that prototype monoblock with PAT4006 Plitron Torroidal Output Tranny and decided I liked the half the price Hammond better. It was also 5 or 6 years ago before I went off on the Baby Huey track.
The one I linked is cascode into a triode diffamp and seems to be the same circuit as MK3 "standard" upgrade board.

Sorry about that.
Cheers,
Ian

revintage · 06:22 AM

dgata,
That´s not the one.

The diff cascode was first presented in GA. I have also tried them but built them from GA instead of buying cards. I had them in a pair of MkIV mnay years ago. The late Bo Hansson of Opus3 also produced a amp, Candela, with the same front end and 6L6, that was no hit for me. Ian and have different opionions as I didn´t like this driver at all.

mr2racer,

No success until I combined the front-end with E182CC CF. Then it was OK but not more. AS pointed out by Ian this was for a pair of EL34. Driving two pairs of 6550/KT88 isn´t the same thing.

If you have built something with 12AU7 I can understand it sounds unsatisfactory.

27th September 2011, 04:46 PM	#1
mr2racer diyAudio Member Join Date: Jul 2009	12U7 LTP vs. 6922 cascode Hey All, I hve a pair of Dnaco Mark VI monoblocks that I converted to a LTP 12Au7 front end and 6922AU7 driver section with KT88 outputs. After a few months of listening I'm not happy with the amps. They just sound a bit harsh at volume. (Ithink this may be caused by too much voltage on the 12au7"s. I recently built a pair of Mark III clones using a cascODE 6922 front end. Would the cascode be preferable? Kevin

28th September 2011, 06:19 AM	#9
gingertube diyAudio Member Join Date: Oct 2004 Location: Adelaide South Oz	OOPS - is my face red. I was thinking of this one - the MK3 "Premium Mod", their PCB-1A board or ASM-1A Kit. http://www.dynaco-doctor.com/mk3des_3.htm That is the one I have used. I used it with 6SN7 cathode followers after it to drive parallel push pull KT88. It was only a prototype amp using Hammond 1650T Output Tranny and I only ever built the one channel but I liked it. It sticks in my mind because I also tried that prototype monoblock with PAT4006 Plitron Torroidal Output Tranny and decided I liked the half the price Hammond better. It was also 5 or 6 years ago before I went off on the Baby Huey track. The one I linked is cascode into a triode diffamp and seems to be the same circuit as MK3 "standard" upgrade board. Sorry about that. Cheers, Ian Last edited by gingertube; 28th September 2011 at 06:30 AM.

28th September 2011, 06:19 AM	#10
revintage diyAudio Member Join Date: May 2007 Location: Eskilstuna, Sweden	dgata, That´s not the one. The diff cascode was first presented in GA. I have also tried them but built them from GA instead of buying cards. I had them in a pair of MkIV mnay years ago. The late Bo Hansson of Opus3 also produced a amp, Candela, with the same front end and 6L6, that was no hit for me. Ian and have different opionions as I didn´t like this driver at all. mr2racer, No success until I combined the front-end with E182CC CF. Then it was OK but not more. AS pointed out by Ian this was for a pair of EL34. Driving two pairs of 6550/KT88 isn´t the same thing. If you have built something with 12AU7 I can understand it sounds unsatisfactory. __________________ Brgds Lars Last edited by revintage; 28th September 2011 at 06:22 AM.

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27th September 2011, 05:14 PM	#2
DF96 diyAudio Member Join Date: May 2007	The LTP and cascode are such different circuits that it is a bit difficult to conceive that they might be alternatives for a given job. LTP is used when you need a balanced input and/or a balanced output, and are happy to lose a little gain and add a little noise but greatly reduce even-order distortion. Cascode is used when you need high gain and low input capacitance for low level signals so distortion is not a problem. Oh, and they have very different PSRR.

27th September 2011, 08:14 PM	#3
ppl diyAudio Member Join Date: Apr 2001 Location: Seattle, WA U.S.A.	Why not Both an LTP built with (2) Identical cascodes

27th September 2011, 08:59 PM	#4
mr2racer diyAudio Member Join Date: Jul 2009	Sorry about the really poor typing. I was trying to to this while at work before the boss noticed what I was doing. I don't have balanced inputs or outputs and I don't need more gain. Getting a Mark VI apart is a bitch. And If I was going that far I thought I might use the cascode since I have four 6922's. But the original design used the LTP so I'll try to make that work. But I still have these 6922's. Could you use a pair of cascode 6922's as a line amp? Kevin

28th September 2011, 12:04 AM	#6
gingertube diyAudio Member Join Date: Oct 2004 Location: Adelaide South Oz	You may want to look here: CURCIO AUDIO Dynaco Mark-4 Amplifier Upgrade Curcio Audio Engineering (CAE) offer a 6922/6DJ8/6N1P Differential Cascode front end upgrade board for the MKIV. It has an integrated HV regulator on the board to address the fact that cascodes have low power supply rejection. I've used these boards, they work well. Only problem I ever had was a "running water"/"surf" sort of sound from one card which turned out to be a microphonic tube and not a circuit fault at all. Cheers, Ian

28th September 2011, 05:32 AM	#7
dgta diyAudio Member Join Date: May 2011	Ian, that one sure doesn't look like a differential cascode to me. And no regulator: http://www.dynaco-doctor.com/MK4-DVR-DOC.pdf Do they make another board?

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