I'm referring strictly to SS. Amp has both offset and bias pots. I understand anything up to 50mv offset on each channel is acceptable, 0 being ideal. However, the best I can get is 16mv on the left, 26mv on the right. Bias set at 150ma on each channel. My question is, does the stilted offset skew the bias adjustment? I could just change up the left channel offset to match the right, but not all SS amps have offset pots. I have others with dc servo control and still others with discreet components for the offset but they are never identical on both channels either. So I guess what I want to know is should there be a bias compensation on either channel to accommodate the difference in offset? |
The pots are there for that very purpose. Channel balance depends on quiescent current being equal in both channels. But my question addresses exactly that issue. Must it be equal or adjusted relative to offset for each channel in order to achieve an equal end result at the speakers? |
The amps in question are a pair of LSR&D Superamp monos with no offset pots, AmpzillaII which is a dcservo amp., Son of Ampzilla with both offset and bias pots, and some Bedinis also with no offset pots, a pair of early Boothroyd Stuart Meridian 105 monos with no offset adjustment. I recently sold a Meridian 559 with auto bias because IMO, it had no high-end characteristics at all. The 105's were fabulous and thought it would be more of the same but it sounded very average with no real redeeming qualities; not particularly fast, no great extension or linearity, imaging, sound stage etc.. I wondered if it was because it is not a fixed bias amp? When offset and/or bias is off, these are exactly the characteristics an amp displays. I guess my question is how much tolerance is engineered into auto bias?
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Thank you. That explains why I was disappointed with the 559. 10% is huge. I can easily detect anything that's not identical. Maybe I should be "Golden ears". Pinpoint imaging and transient response and therefore detail absolutely depend on a perfect bias adjustment in relation to each channel being the same. |
Karakanetz, I appreciate your knowledge on this subject and I don't mean to pester you about this but does offset influence speaker sensitivity? |
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Okay, Kirkus, you've clearly discerned that my issue is about what ends up reaching your ears. So is this why I hear an audible imbalance when using my multimeter I achieve identical specs and afterward complete the procedure while listening to music when I adjust the bias? |
I have no schematics but the LSR&D amp was designed by Marshall Leach at Georgia Tech University and is the well known Leach Low TIM amp. Few were commercially produced and subsequently became a DIY project for which Dr. Leach provided parts and instructions via mail order. It's easy to find schematics for this amp just by googling. There was nothing wrong with the 559 as far as I could tell. It functioned as it should. It was just unimpressive. All of the other amps I've mentioned sound better, the Leach being the best of the lot. The Ampzillas are a close second, Bedinis third and finally the 105's but only because they begin rolling off right at 20hz. It's probably why they sound so good otherwise. |
I don't know, maybe but the 105's keep you on the edge of your seat waiting for it to happen and it never does, no sub-audible bottom end at all. I adjust bias on all my amps. I have no auto bias amps. Some don't have adjustable offset. The LSR&D Superamp monos I have definitely have bias pots. There are no other ones in the circuit. The Leach Low TIM DIY circuit has had numerous upgrades over the years so you may have found an up to date version but the factory amps were few in number produced back in the late 70's-early 80's. Unfortunately and sad to say, Dr. Leach passed away this past November. Always returned his e-mails and was available to deal personally with any question you may have. |
Kirkus, I'm not experiencing a problem, just searching for an explanation on why after setting bias identically, I have to then pinpoint the adjustment while listening to program material. I believe Marakanetz answered my question. All of my amps are gone over and have been recapped and upgraded throughout. However resisters are usually left alone unless they're blown so I'm assuming it stands to reason the adjustment is much more critical; or is it? You tell me. I thought a stilted offset might require a stilted bias but apparently that's not the case. The bottom line is, and whatever the reason, on every one of my amps, perfect channel balance results in a stilted condition. Very close, but stilted. The channel with more offset always has a higher bias also. |
But if my procedure addresses or "corrects" the situation, is that not a best case scenario? Are you speaking of inherent characteristics of a given topology not equipped to deal with certain potential drawbacks, or are you referring to an unseen but needed repair? What's the option to stirring the soup? |
