The best amplifier I have built so far

[TonyTecson]

I re-iterate my post.

This is an easy to build excellent amp. Easily repeatable with readily available components.

I never said that this is the BEST amplifier in the WORLD.

The valves are commonly available and the Hammond 1650H transformers are available from DigiKey.

In my original build thread I described how I got around the B+ / Cathode / Heater transformer voltages. You could always get a custom transformer built but I used common 2020 components.

The hum problem could well be down to my using a balanced pre-amp in unbalanced mode originally. I've now converted the amp to balanced input and it is brilliant.

For once, the Chinese have got it right and it's easy to build with a ready populated PCB.

The original schematic shows 5K OPTs which may be better but mine is fine with the Hammond 1650H which is 6K. I'm pairing it with B&W CM8s2's which are slightly lower than 8Ohms which would make a difference.

congratulations, do mot mind us, we were merely discussing the topology...

 

[Chris Hornbeck]

every coupling cap is a zero, having low frequency roll offs

When I say this, EE folks jump all over me. I suppose it's not academically correct, but it does aid comprehension. Yes, it's a pole, and no, I'm not changing. Well, maybe.

All good fortune,
Chris

 

[TonyTecson]

Steve Bench defined poles as having clockwise response with frequency, zeroes counterclockwise....that made sense to me so i look at it the same way...

 

[wg_ski]

When I say this, EE folks jump all over me. I suppose it's not academically correct, but it does aid comprehension. Yes, it's a pole, and no, I'm not changing. Well, maybe.

Each coupling cap adds a pole AND a zero. The zero at DC. The zero causes the phase to lead and provides UP slope. The pole causes phase to lag and provides DOWN slope. Always. It is forgetting about the zero at DC that confuses things.

In a band pass system, mid band is not zero phase. No slope and often used as reference, but not zero.

And I get a “B” in controls. Pissed me off. Because after THAT course my success rate in making amps stable shot up from 50% to 99. There is always the 1% you can’t explain.

 

[TonyTecson]

well if you consider dc as zero hertz, then yes...

 

[rongon]

I thought DC is *defined* as zero hertz.
Single-pole, ideally with no frequency fluctuation.

How can DC be anything other than 0Hz?

 

[rongon]

I re-iterate my post.

This is an easy to build excellent amp. Easily repeatable with readily available components....

For once, the Chinese have got it right and it's easy to build with a ready populated PCB.

Good to know of a Chinese-made ebay PCB that works correctly. Did you post a link to the PCB you're using? Thanks.

 

[wg_ski]

Sort of worked correctly. Recall the problem with the bias pots. Way too easy for the user to accidentally damage something.

 

[Chris Hornbeck]

In a band pass system, mid band is not zero phase. No slope and often used as reference, but not zero.

This insight will be very useful to me in future. It's a brilliant perspective, and I thank you very much.
Chris