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RE: Perhaps you are ready to step up your learning.

Posted by 91derlust (A) on January 17, 2017 at 22:19:56

In Reply to: RE: Perhaps you are ready to step up your learning. posted by banpuku on January 17, 2017 at 12:34:55:

Hi Pat,

Glad you took my post in the spirit intended - sometimes when rushed I can come off a little abrasive!

Considering your objectives, the 20B would not be my first choice. The 20B should be as clear as a bell, transparent, and direct... probably without etch. But it won't provide that intimate, smooth, tonally dense sound you are are seeking.

The 6C6 should be the ideal tube (gain aside). My system, which also runs a 6C6 driving a 2A3, has a lovely alive, flowing, and textured and natural presentation from the bass and midrange, although there is some high-frequency emphasis (but not etch, ringing or graininess): sibilants seem emphasised on some poorly produced music. But, it is pretty recent and coincides with some other system changes (several actually) - I don't think it is due to the 6C6.

Added later:

I'm curious, can you explain what changes moved you closer to warm and fuller and those that moved you away from it?

Currently, you have some pretty funky stuff going on with the design. I reckon it may have sounded initially appealing/impressive, but may become tiresome with extended listening. I often read of people trying LED and battery bias then returning to more traditional biasing because it sounds more natural. The lack of output tube cathode bypassing greatly increases plate resistance and suggests a much higher tube load is warranted; running a too low a load (like in your current design) can create a rather high distortion, strained, etched sound. The output tubes of both channels is supplied from a single 50uF DC Link capacitor - that seems a little low, even for LSES - I have not used a DC Link, but I'd guess that is not helping your cause either... and the PS might be ringing, which might fake clarity but may become fatiguing with extended listening. But I have not heard these things as a system or independently, so I can't be sure.

My guess is that the sound you are hearing is caused by a few significant issues and layered-on compensation. It is important to make changes progressively and listen to each critically, then relax and listen for an extended period non-critically. Then make a decision as to whether you like the change. Basically, apply reductionist thinking then system thinking.

Looking at the over-all design shown (with 6C6 as pentode) I'd suggest:

Output: trying the Hashimoto at 3.5k load (if it has multiple primary windings) and bypassing the output stage cathode with a balanced-sounding metalised poly cap (NOT Mundorf, except maybe the plain Supreme).

Input/driver: using a larger PIO on the screen bypass (at least 4uF), and trying a traditional cathode 5W R (Mills WW/Kiwame/KOA Speer - if the correct values are avail.) bypassed with a balanced-sounding metalised poly cap.

PS: without some modelling, I can't say. I'd be looking at it though.

I guess what I am suggesting is that you return the amp to "known good" state - one that should satisfy your preferences - then experiment carefully.

All that said, I do wonder about your system's gain structure. If your preamp is outputting circa 17v (that sounds like the max - whether you achieve this depends on the source output and the preamp's gain), then you could drive your 2A3 with a 45 or 2A3! Or just build a different amp specifically designed to meet your needs and wants...

Cheers,
91.

"Confusion of goals and perfection of means seems to characterise our age." Albert Einstein

Edits: 01/18/17 01/18/17 01/18/17 01/18/17

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