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Old 6th February 2012, 03:01 AM   #1481
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Zero feedback amp sound so lively but come with huge thd.
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Old 6th February 2012, 08:02 PM   #1482
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Default Zeus Line Level THD

Hi Jorge,

Quote:
Originally Posted by jorge1980 View Post
Zero feedback amp sound so lively but come with huge thd.
Yes, of course.

See my Zeus MOSFET SE Preamp & PP Power Amp System Test, i.e. full line level end to end, not just the pre or the power amp, and which is a bird's nest everything hanging out on the bench test too.

Zeus SE MOSFET Preamp PP MOSFET Power Amp Tests

1.1 watts = 2.89 volts into 8 ohms - 0.0054% THD
2.1 watts = 4.09 volts into 8 ohms - 0.0079% THD
4.2 watts = 5.78 volts into 8 ohms - 0.0110% THD

Note that the even 2nd harmonic is c. 4dB higher than the odd third harmonic in these measurements.

Huge, is it not?

Best wishes,
Susan.

Last edited by Susan_Parker; 6th February 2012 at 08:04 PM. Reason: Grammer
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Old 6th February 2012, 08:20 PM   #1483
mikelm is offline mikelm  England
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Quote:
Originally Posted by imfree707 View Post
Decades ago, I have used power transformer cores for audio, not super hi-fi, in PA amps, car stereo power amps, and other general purpose audio power amps, with fairly good results. I'd be interested in some discussion regarding performance limitations expected by use of power transformer iron in audio use. Thanks.
Well, I guess frequency response is the main limitation and toroidal cores will perform best in this regard.

I also suspect that low level details will be lost and I cannot suggest anything to remedy this.
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Old 6th February 2012, 09:37 PM   #1484
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Default Toroid Transformers

Hi Mike,

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Originally Posted by mikelm View Post
Well, I guess frequency response is the main limitation and toroidal cores will perform best in this regard.

I also suspect that low level details will be lost and I cannot suggest anything to remedy this.
For my multi-filar output transformers the use of a toroid will benefit LF extension. However the HF extension is not so good with drop off beyond 20 kHz when run into a constant impedance load (e.g. 8 ohms).

Menno Van der Veen (who is a really nice guy) has devised special winding techniques to overcome this with the tube/valve output transformers (available from Plitron) but note that these have a considerable impedance ratio between input and output.

In my own tests I wound both quad-filar and interlayered P:S:P bi-filar windings on a pair of test transformers (using 500VA cores) and they both gave the same sort of HF drop-off. I believe that this is to do with the non uniform winding one gets going round on a circular path. As with everything, more testing can be done here, time permitting.

If the speaker load has a rising impedance, then this issue may well not be a problem. Particularly if one custom designs the speaker and crossovers to compensate.

Personally I am moving towards bi-amping my main speakers with separate output amps (PP for the LF and a SE driver for the HF) with the crossover done at the 600 ohms line driver stage.

As to loss of detail...

Are you referring to Menno's 2011 AES paper "Signal Level and Frequency Dependant Losses Inside Audio Signal Transformers and How to Prevent Those" (which you can find here: Menno van der Veen's audio website )?

... listening tests of my system don't seem to show this as a problem. One has to use good grade of core of course, minimum M6 silicon steel laminations.

People (not just myself) can hear detail off vinyl (analogue mastered using magnetic tape) that simply isn't there on CD. So I don't think this is the limiting factor.

Best wishes,
Susan.
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Old 7th February 2012, 07:50 AM   #1485
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Hi Susan,

I was commenting on using using regular power transformer cores for audio signals ( as per imfree707's question ) and was assuming that they aren't really very good grade.

Based on my experiences with sabre buffalo DAC it won't be long before it's possible for digital to challenge analogue system low level detail. As long as implemented well, they can be both finely detailed and very pleasant to listen to.

I'm still curious how the very best audio transformers sound and will follow your latest projects with interest.

mike
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Old 7th February 2012, 11:56 AM   #1486
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Quote:
Originally Posted by Susan-Parker View Post
Hi Jorge,



Yes, of course.

See my Zeus MOSFET SE Preamp & PP Power Amp System Test, i.e. full line level end to end, not just the pre or the power amp, and which is a bird's nest everything hanging out on the bench test too.

Zeus SE MOSFET Preamp PP MOSFET Power Amp Tests

1.1 watts = 2.89 volts into 8 ohms - 0.0054% THD
2.1 watts = 4.09 volts into 8 ohms - 0.0079% THD
4.2 watts = 5.78 volts into 8 ohms - 0.0110% THD

Note that the even 2nd harmonic is c. 4dB higher than the odd third harmonic in these measurements.

Huge, is it not?

Best wishes,
Susan.
Thanks for the best information. But I think 4.2 watts can hardly drive normal speaker in standard listening room. If I want to listen full opera concert music I need around 105 db dynamic range, that mean I need 95db sensitivities speakers up. The problem that I need to know are bass respond and deep bass control of the amp? I was built class a amp and I feel deep bass control very awful,but upper bass to high frequency are excellent. Deep bass control seem to be better when I add little negative feedback (bjt project).
P.S. Do I need to find match pair for 2 x STW34NB20 mosfet because I hardly find perfect mosfet match pair (or less than 15% different)
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Old 7th February 2012, 02:09 PM   #1487
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Hi Jorge,

Quote:
Originally Posted by jorge1980 View Post
Thanks for the best information. But I think 4.2 watts can hardly drive normal speaker in standard listening room. If I want to listen full opera concert music I need around 105 db dynamic range, that mean I need 95db sensitivities speakers up. The problem that I need to know are bass respond and deep bass control of the amp? I was built class a amp and I feel deep bass control very awful,but upper bass to high frequency are excellent. Deep bass control seem to be better when I add little negative feedback (bjt project).
4.2 Watts in not max power. Just the typical operating range where the volumes are such that one would be hearing background detail.

I run speakers with a pair of Jordan Jx92s in SERIES connection.

Bass response is much better than most, as output impedance is low.

But I am NOT running full range with extended LF Bass. For that one should be using a dedicated Sub.

Quote:
P.S. Do I need to find match pair for 2 x STW34NB20 mosfet because I hardly find perfect mosfet match pair (or less than 15% different)
Some mosfet types are real close straight out of the tube, others are widely different. I normally buy at least a full tube of 30 parts to select from.

One reason I haven't tried the SIC fets yet (e.g. SJEP120R100A), they are too expensive.

Best,
Susan.
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Old 7th February 2012, 02:12 PM   #1488
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Hi Mike,

Quote:
Originally Posted by mikelm View Post
Hi Susan,

I was commenting on using using regular power transformer cores for audio signals ( as per imfree707's question ) and was assuming that they aren't really very good grade.

Based on my experiences with sabre buffalo DAC it won't be long before it's possible for digital to challenge analogue system low level detail. As long as implemented well, they can be both finely detailed and very pleasant to listen to.

I'm still curious how the very best audio transformers sound and will follow your latest projects with interest.

mike
Understood. Thanks.

In summary, the quality of iron is important. A couple of old cast iron window shash weights will NOT be okay

Best,
Susan.
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Old 7th February 2012, 09:11 PM   #1489
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Hi Mike,

Quote:
Originally Posted by mikelm View Post
Hi Susan,
I was commenting on using using regular power transformer cores for audio signals ( as per imfree707's question ) and was assuming that they aren't really very good grade.
Sorry if I came across a bit terse.

I have been trying to progress getting "better" cores and with everything that's happening in the global economy plus the ever stratosphying cost of copper (don't even bother to worry about silver) even "pragmatic" producers like Sowter have noticeably increased their prices.

I have just bought four 1kg reels of 1.0 mm magnet wire, and it was a bit of a shock.

Quote:
Based on my experiences with sabre buffalo DAC it won't be long before it's possible for digital to challenge analogue system low level detail. As long as implemented well, they can be both finely detailed and very pleasant to listen to.
My personal hobby horse is that at least part of the issue is in the brick wall filters. I want to be able to sample at 24 bits at something like 2MHz (that's data, not master clock)!

I don't see that happening any time soon though, even though Analog Devices does the AD7760 ADC that meets these numbers.

AD7760 | 2.5 MSPS, 24-Bit, 100 dB Sigma-Delta ADC with On-Chip Buffer | All A/D Converters | Analog to Digital Converters | Analog Devices

And yes, I do happen to have some. Just as usual not enough time.

Quote:
I'm still curious how the very best audio transformers sound and will follow your latest projects with interest.
mike
In my bi-amping with separate LF and HF outputs I am going to experiment with optimising the transformers specificity for the bandwidths concerned.

One of these is the possibility of using larger than normal gaps, in particular for the HF amp as it only needs to work at full power from 1KHz. Obviously there are phase issues to keep in mind but being able to design for the exact driver (JXr6HD) and crossover frequency (1.5kHz) gives more possibilities for refinement.

I don't use super tweeters, however if I did I would try using a straight air core. That way there are no iron losses.

The main thing though I should reiterate is that all these extra steps are chipping away at the really last small percentages. The "base" EI120 M6 pre & power version is still top Hi-End as far as sound is concerned.

I too however await with interest to see if I can a: measure, b: hear differences between the different types.

Best wishes,
Susan.
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Old 7th February 2012, 10:20 PM   #1490
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Quote:
Originally Posted by Susan-Parker View Post
Hi Jorge,



4.2 Watts in not max power. Just the typical operating range where the volumes are such that one would be hearing background detail.

I run speakers with a pair of Jordan Jx92s in SERIES connection.

Bass response is much better than most, as output impedance is low.

But I am NOT running full range with extended LF Bass. For that one should be using a dedicated Sub.



Some mosfet types are real close straight out of the tube, others are widely different. I normally buy at least a full tube of 30 parts to select from.

One reason I haven't tried the SIC fets yet (e.g. SJEP120R100A), they are too expensive.

Best,
Susan.
Thank you for your good answer.
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