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Old 18th September 2007, 10:13 PM   #21
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Hi Cheff,

Sorry about that. I didn't notice that there were three pages.

Graeme
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Old 18th September 2007, 10:17 PM   #22
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No problemo
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Old 19th September 2007, 04:39 PM   #23
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Very nice indeed, both in terms of circuit details and construction. Seems you are already way ahead of my humble efforts.

I have a few comments if you are interested in experimenting further (which is another way of asking you to do some tests that I am not yet in a position to do!).

1. What is the open loop gain of your circuit? Just wondered how much feedback is being applied and hence what the damping factor might be with overal feedback.

2. Have you tried experimenting with reducing the source resistors in the diff pairs? I appreciate that adding these lowers the gain and improves linearity but I wonder whether it will not also reduce the SuSym effect? It is fairly easy to use a single resistor per diff pair to achieve the same DC conditions but without the local feedback. I'd be interested in the results.

3. How about adding some SE operation at low levels as per the X.5 amplifiers? All it takes is a resitor from -ve to output on each side of the amp. Word has it that this results in am improved sound for this kind of amp. it would be interesting to see whether you can confirm this.

4. How does the front-end vs overal feedback sound, i.e. what is the subjective difference?

Sorry for all the questions.

Ian.
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Old 19th September 2007, 08:13 PM   #24
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Hi Ian
Quote:
Originally posted by Ian Macmillan
Very nice indeed, both in terms of circuit details and construction. Seems you are already way ahead of my humble efforts.

I have a few comments if you are interested in experimenting further (which is another way of asking you to do some tests that I am not yet in a position to do!).

1. What is the open loop gain of your circuit? Just wondered how much feedback is being applied and hence what the damping factor might be with overal feedback.

2. Have you tried experimenting with reducing the source resistors in the diff pairs? I appreciate that adding these lowers the gain and improves linearity but I wonder whether it will not also reduce the SuSym effect? It is fairly easy to use a single resistor per diff pair to achieve the same DC conditions but without the local feedback. I'd be interested in the results.

3. How about adding some SE operation at low levels as per the X.5 amplifiers? All it takes is a resitor from -ve to output on each side of the amp. Word has it that this results in am improved sound for this kind of amp. it would be interesting to see whether you can confirm this.

4. How does the front-end vs overal feedback sound, i.e. what is the subjective difference?

Sorry for all the questions.

Ian.
Thanks for kind comments

And no, we're not hunting the same hare (sorry, litteral translation of a french expression) I just wanted to test something different, just to "see" how it goes Your efforts for improving and sequeling the Aleph-X are worth the work, and be sure I follow this with careful attention.

Now to your questions :

1) I have to check it carefully, and I may say something stupid without verification, but a quick calculation of the front end gain gives a rough 1400 (or 63dB) for the open loop differential gain. I'll check tomorrow and tell you.

2) No, I've not experimented this. In fact, I was so happy with this arrangement in the UGS preamp that I didn't look any further. The drawback here is that it won't be easy to implement on those boards, where space is - alas - tight, and the other offset adjustment has to be moved to the negative drains - or I miss something... Nevertheless, it's worth wondering if local source degeneration can be reduced with no adverse effects. Let me think a while about it...

3) That sounds quite interesting. I'll make the test asap and report back, it's an easy mod. But allow me some more time since :

4) I've still got to test it. I need time to settle down and make careful comparisons. Normally, it's planned for this week-end. I'll be back for report

So stay tuned...

Cheers,
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Old 19th September 2007, 09:15 PM   #25
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Quote:
Originally posted by CheffDeGaar
1) I have to check it carefully, and I may say something stupid without verification, but a quick calculation of the front end gain gives a rough 1400 (or 63dB) for the open loop differential gain. I'll check tomorrow and tell you.
I have built something like it, so I bet it's a bit less than 60 dB
at low frequencies with that 10K loading.

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Old 19th September 2007, 10:16 PM   #26
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Quote:
Originally posted by Nelson Pass


I have built something like it, so I bet it's a bit less than 60 dB
at low frequencies with that 10K loading.

Thanks Nelson

I must confess the language barrier and the Babylon Tower syndrom don't allow me to access all the subtleties of native english... Should I consider "a bit less" as an euphemism to say I'm wrong ? (I knew I should have hold my tongue before checking )

BTW, what haven't you built ? Do you have something like a "museum of horrors", where you keep (even on a photograph), all the designs you tried ? I do have (a modest) one, with partly desoldered pcbs and breadboards pieces... Sometimes a treasure chest for finding the missing part

Nostalgia ain't what it used to be...
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Old 19th September 2007, 10:46 PM   #27
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I'm just placing a friendly bet. The closest thing I did
was about 60 dB and it looks like you have a little less
gain than I did.

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Old 20th September 2007, 07:50 AM   #28
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Thanks Mr Pass, and sorry for my poor english understanding...

I checked both my simulations and equations, and they both say around 60dB and above : 63dB for equations, and 61dB for sims.
I'll try to make the real test on bench this week-end,and I think it will surely be decreased a bit by the reality principle

Cheers
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Old 20th September 2007, 08:09 AM   #29
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Cheff,

Thanks for being so considerate with regards to my questions. Also don't worry about your English - its fine.

Ian.
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Old 20th September 2007, 04:27 PM   #30
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Absolutely wonderful work, both on the circuit design and the physical implementation.

Cheers,
Terry
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