Hello Mr. dB and flg. The schematic of the input board for BA3 shows it to be a Transconductance Amplifier [TCA]. Its output has opposed drains and it is void of loop feedback. diyAudio is a fertile ground to share new ideas, and to experiment with the proposed devices. Conventional wisdom has its place. But nothing [unless unsafe] should be cast in stone. The thinking that this is how it was, is, and will always be done is unhealthy and a counter productive approach for this hobby. For example; who would have guessed that Mr. Pass will ever use an interstage transformer in a power amp like F6? He never used this approach before; knowing the ills attendant to a transformer..Yes, Certainly. I beleive the article actually does not connect the output to the output stage does it?
I continue to enrich my two topics in Headphone Systems to be commensurate with my philosophy above. Best regards.
I used it as a preamp for my F5, and it is sweet. The soundstage is very wide.
Personally i felt the magic isnt there when i put it in a F4.
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The jfets were taken out for F4. However i do put a B1 infront of BA3 for volume control. Imho, F5 need good pre-amp, a B1 is not good enough to enjoy the F5.
Yes, this would be true but, by saying that, you are indicating, like a current source, it has high output impeadance. It does not. The output is loaded heavily effectively changing it to a voltage source.
Hello buzzforb and neoinc. My philosophy for diyAudio is like yours. Experiment, experiment etc. Best regards.
In front of Ba3, IMO. 10k is good, as you have Ciss of input Jfets and Mr Miller to deal with.
The definition of a voltage source amp can be a grey area. The output Z of a TCA need not be a very high value like >100 Ohms. For example, the several F-type TCAs in www.firstwatt.com have an output impedance ranging from 15-80 Ohms. The definition of a voltage source amp in my book is straightforward. The output is taken out of transistors connected in the common drain configuration; meaning opposed emitters; with, and without an attendant loop feedback. This is a classical definition. Another example in ACA#1. Its output transistors are opposed drains of MOSFETs; meaning an operating common source configuration. It has an output impedance of 10 Ohms in the abscence of loop feedback, and thus is a pure TCA in my book. Loop feedback lowers this TCA's output impedance a bit further; but not enough where it is <0.1 Ohm like a true voltage source amp. In my book, ACA#1 is a hybrid TCA-VSA. It embodies the best of both worlds to express its magic.
Is it possible to let the two 1M resistors (one from each channel) share a common bias voltage (like in B1)?
My apology flg. I mispoke [miswrote] regarding the underlined above. The output stage MOSFETs in ACA#1 are not opposed drains.
What is it about the sound of this pre - that you prefer over the differential pair version ?
Does adding a current mirror, to the differential pair, help with the matching of the jFET's ?
I'm wondering about how much audible noise those carbon variable resistors add.
If the 10K volume control is at the front of the pre, the noise would get amplified by the pre and power.
So I'm wondering if the volume control should be placed between the pre and power amp.
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Uu buddy,
the only absolutely valid (for you) answers on your questions are just a couple of hours of work/fun away from you. Build it, test it, enjoy it - or discard it.
Anyway, that's the only way to know your truth - some of your question have subjectively influenced answers, some are tiringly debatable (I'd never put a pot between the preamp and the amp but I'd rather bite my leg off than to defend that stand for the 137th time).
So, in the end, it's up to you...
the only absolutely valid (for you) answers on your questions are just a couple of hours of work/fun away from you. Build it, test it, enjoy it - or discard it.
Anyway, that's the only way to know your truth - some of your question have subjectively influenced answers, some are tiringly debatable (I'd never put a pot between the preamp and the amp but I'd rather bite my leg off than to defend that stand for the 137th time).
So, in the end, it's up to you...
You said that you've spent a months experimenting and here is the circuit that sounds best to me
So I legitimately ask you what it is you like this version, over the differential pair version, and you just about soil yourself.
The questions about the current mirror and location of the volume pot were pretty reasonable too.
Don't f**king bother.
Uu, it was years ago and I've built more than a dozen of different preamps since then. You can't expect me to remember all of the details how it sounded to me in that time - what was true to me then still stays written.
P.S. No need for harsh language, I'm not your employee - what I had, I gave. What's your contribution here ?
P.S. No need for harsh language, I'm not your employee - what I had, I gave. What's your contribution here ?
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