Experiences with Class A2 811 Shishido style amp and speaker matching [long]

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Hi All
I wanted to share my experiences with preamp and amp building and speaker matching. This is a long email, and I learnt a lot by just seaching and browsing thru this group.
I had build a 811A shishido style monoblocks 4 years ago. The configuration was
7788 [Triode Mode] -- 1:1 IT --> 6W6 [Triode Mode] -1:0.7 IT-> 811A
The IT's are all custom build from Electra Print. The grid of 811A was biased at +22V drawing a grid current of 28mA. The schematic of this amp is at the one-electron website: http://one-electron.com/Randall/ganti_2.html.
I had Vandersteen 1B's as the speaker. For those speakers, this configuration was match made in heaven.
Last year Nov. I bought a pair of Zu Cable Druid's, 100db efficient speaker. I plug those into my amp, Awful!!!! the sound was piercing, the highs were like arrows entering your brain, flat sound stage. I thought I made a big mistake, but the company offers 60 day trial period, and when I spoke to them, they said let the speakers break in, and they get better. I borrowed SS amp and ran music thru it 8 hours a day for 3 weeks. It started getting better from sound stage perspective, but those awful highs were still there.
As I was reading here, I gathered I had way too much capacitance, as indicated in the circuit at one-electron. I thought maybe that is contributing to the harshness. Then, I did some changes to power supply, by using GE and CD Oils caps for the first stages of filtering, and Cerafines for the final stages of filtering.
For 811A Supply, the filter was CLC
[15mF -> 10H -> 100mF]
For 6W6 and 7788, it was CLCRC
[15mF -> 4H -> 30mF -> R [adjusted for each tube] -> 47mF
The 15mF is GE Motor Oil, and the 30mF is CD Oil caps.
No luck!! So, I removed the 6W6 and connected 7788 to 811A making it a 2 stage, little better but still could not stand it. By now I suspected the 7788 is not jelling in this setup, and I read up at Electra Print Web site that the IT's are designed with a mean source impedance such as 5K ohms in mind. The triode connected 7788 has a Rp of 1.2K, so after reading up here about Rp and IT matching, I felt 7788 is the culprit. So, I switched to a new tube line up:
Parallel 6SN7 - Cap Coupled -> EL34 [Triode Mode] - 1:0.7 IT -> 811A
I was using a pair of Hovlands for caps.
Wow!! what a difference, much relaxed sound, bigger and deeper sound stage. Lived with it for sometime, but I was bothered with the capacitor, I see people here have their own different views, and mine was with the IT's somehow the sound is bigger, and relaxed, and all this is subjective :-) and my own feelings.. So, I removed the Cap and put back the IT, and Parallel 6SN7 had approx Rp of 4K, from what I read here - a bit high, but what the heck!!. I did not perceive much difference, and I still could get the remanants of those irritating peaks at high frequencies.
After further reading here, and looking thru the IT circuits at Direct Heating Sakuma web site, I decided to put a 390K resistor across the secondary of the first IT, between 6SN7 and EL-34. This was an amazing change, 'cause the system suddenly dialed in, and you know it by the first note of music that comes out, al those irritating highs were gone, and there was much more body.
I felt I was almost there but not quite. After talking to John Levrault [many of you probably know him], he suggested trying 6CK4 in place of EL-34. And I also felt the parallel 6SN7 was not right in this setup, then John Atwood from one-electron suggested 6BL7. I looked at the specs of 6BL7, and felt it fits the bill perfectly, with non-parallel single stage has approx Rp of 2.1 in configuration I was going to use. I made the change, to yet another new line up :-)
6BL7 - 1:1 IT -> 6CK4 - 1:0.7 IT -> 811A
Things were getting better and better, I was finally extremely happy with the speaker purchase, but... I read about 6CK4 and found people preferred 6AH4, ordered a couple from Antique, they came yesterday, and I replaced the 6CK4 with 6AH4, much much better, more mellower, and the system just feels right. The tonal quality has a good balance with the slight edge that is needed, but full bodied, the sound stage extends way beyond the speakers on the sides and the depth is amazing..
Now I feel, I am done with the amp/speaker matching, now to listen to music after 3.5 months of tweaking - bordering on sheer despair to exhilaration..
This long email is thank everybody here, whose contributions have helped me. I do most of testing with ear, as I don't have a scope and don't know how to use it, and my wife is the final judge, and she has this great ability to tell me how the sound changed with each of my tweaks, in essense she is my scope :-).
I will get the new circuit out to John and maybe he will post it on his web site when he has the time..
Sridhar

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Schiit Audio

Topic - Experiences with Class A2 811 Shishido style amp and speaker matching [long] - sganti 09:45:31 02/18/06 (3)

Re: Experiences with Class A2 811 Shishido style amp and speaker matching [long] - fred76 20:52:59 02/18/06 (0)

Nice write-up! - Jim Dowdy 11:55:37 02/18/06 (0)

Re: Experiences with Class A2 811 Shishido style amp and speaker matching [long] - Jimmy 11:40:26 02/18/06 (0)

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