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Old 20th October 2009, 03:17 AM   #631
sandyK is offline sandyK  Australia
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Douglas Self uses low value resistances in both FB and input for the reason Hugh stated, then bootstraps the input to the feedback point to increase input impedance.

SandyK
ref. Audio Power Amplifiers-D.Self vol.3 P.86
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Old 20th October 2009, 03:51 AM   #632
gaetan8888 is offline gaetan8888  Canada
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Quote:
Originally Posted by sandyK View Post
Douglas Self uses low value resistances in both FB and input for the reason Hugh stated, then bootstraps the input to the feedback point to increase input impedance.

SandyK
ref. Audio Power Amplifiers-D.Self vol.3 P.86
Hello

You mean this one, have you try it in a amp ?

Can be interesting to try it in the Haksa amp.

Thank

Bye

Gaetan
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Last edited by gaetan8888; 20th October 2009 at 03:57 AM.
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Old 20th October 2009, 04:47 AM   #633
mlloyd1 is offline mlloyd1  United States
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anybody got any pics of known good original 2SC3423 transistors? i got some recently that i'm not sure about ...

thx,
mlloyd1
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Old 20th October 2009, 04:55 AM   #634
Sheldon is offline Sheldon  United States
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In this thread: RMI-FC100, a single stage audio power amplifier
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Old 20th October 2009, 05:21 AM   #635
AKSA is offline AKSA  Australia
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Michael,

This is a picture hastily taken a few minutes back in strong sunlight of an original, Toshiba, factory bought device.

Cheers,

Hugh
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Old 20th October 2009, 06:53 AM   #636
mlloyd1 is offline mlloyd1  United States
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hugh:

thanks! what i have looks exactly like what you showed. i can sleep in peace now. see you guys later ...

mlloyd1
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Old 20th October 2009, 09:36 AM   #637
AKSA is offline AKSA  Australia
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Michael,

My pleasure. The contrast/resolution is not wonderful, but you can discern the font used, which is usually the giveaway.

Gaetan,

Yes, indeed, I found that achieving the required flat response was almost impossible without incorporating an opamp, and furthermore when Paul B. showed me a way to non-phase invert, it revealed that the opamp was very effective at reducing phase shifts, which create issues with passive Baxandall circuits.

We could have simply increased the gain of the HP amp to accommodate the losses of the tone control, but the phase anomalies would still have been there, and the opamp solution seemed the best. I would like to use a single ended solution, but it should be possible to achieve that with an opamp anyway by stringing a resistor from one rail to the output.

Gareth,

The AKSA has a very high impedance network, 47K/2K2, and yet has that magic sound much reported here and elsewhere. I'm not too sure it's necessary, and I suspect that a high impedance fb network loads up at high amplitude and might subtly change the output impedance of the amp, since the AKSA has an output which rises with loading, to a certain point.

The next move is to publish the tone control, something I hope to do tomorrow after Paul and I have had a chat about it.

Cheers,

Hugh
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Old 20th October 2009, 09:52 AM   #638
gaetan8888 is offline gaetan8888  Canada
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Quote:
Originally Posted by AKSA View Post
Gaetan,

Yes, indeed, I found that achieving the required flat response was almost impossible without incorporating an opamp, and furthermore when Paul B. showed me a way to non-phase invert, it revealed that the opamp was very effective at reducing phase shifts, which create issues with passive Baxandall circuits.

We could have simply increased the gain of the HP amp to accommodate the losses of the tone control, but the phase anomalies would still have been there, and the opamp solution seemed the best. I would like to use a single ended solution, but it should be possible to achieve that with an opamp anyway by stringing a resistor from one rail to the output.

The next move is to publish the tone control, something I hope to do tomorrow after Paul and I have had a chat about it.

Cheers,

Hugh

Hello Hugh

I ad the same phase anomalies problems and impossibility to get flat response wen I was simulate a passive tone control for the LF55 and for the coming RC amp.

So you will bias the op-amp into class A.

Until now I think that the THS4031 are a very good choice for that job and this op-amp seem to be allready bias close to class A, have you chose a candidate op-amp for that tone control ?

Thank a lot for the times and works you give to all of us for that Haksa project.

Bye

Gaetan

Last edited by gaetan8888; 20th October 2009 at 10:05 AM.
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Old 20th October 2009, 05:49 PM   #639
Nico Ras is offline Nico Ras  South Africa
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Hi Guys,

I have been up to my neck and got back to the thread a few momnets ago. I am impressed by everyones progress and understanding of why amps sound differrent. All well designed amps are good, subtle changes is what makes them sound different.
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Old 20th October 2009, 05:55 PM   #640
Nico Ras is offline Nico Ras  South Africa
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The same argument applies. All well composed music is good - but only some become No1 hits. Ever thought about why this is so?
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