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Old 10th August 2012, 12:13 PM   #51
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Quote:
Originally Posted by liching1952 View Post
its up to you. Seeing the level here I will not proceed to defent this statement.
You wouldnt be able to no matter if you were a prof or a street sweeper.
Fact is fact and myths only really have a place in childrens books and witchcraft.
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Old 10th August 2012, 12:22 PM   #52
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Originally Posted by a.wayne View Post
OK... Now define how much is low, how much is enuff vs a lot ...


Yeah ...
That depends on the design, to quote values is not productive but if youre thinking lets just degenerate some more or kill loopgain with loading and increase bandwith youre just fooling yourself.
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Old 13th August 2012, 11:15 AM   #53
dadod is offline dadod  Croatia
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Here is the schematic of the low power TT amp with cascoded VAS.
It will be very nice if some of PCB experts(alex mm?) try to make the PCB for this amp. I think it is very simple amp with excellent data, and I am not so good in the PCB design. More powerful version could be a challenge to make the PCB.
Important is to have the drivers and Vbe multiplier on the same small separate heat sink(cca 5W dissipation for low power and 8W for high power).
dado
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File Type: pdf DADO-TT-100w.pdf (76.0 KB, 83 views)
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Old 13th August 2012, 11:37 AM   #54
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Dado care to post the spice file ?? Id like to have a closer look with my models. The figures you obtain are very good and Im a little surprised that this design and using TMC can have such figures. The concept is not new, Pioneer used it in the late 80 and Sony has been using the concept for the past 15 years and still do in their latest models but just more refined, neither used TMC though. Figures obtained by Sony with bipolars usually around .003 20hz to 20 Khz.
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Old 13th August 2012, 12:25 PM   #55
dadod is offline dadod  Croatia
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Originally Posted by homemodder View Post
Dado care to post the spice file ?? Id like to have a closer look with my models. The figures you obtain are very good and Im a little surprised that this design and using TMC can have such figures. The concept is not new, Pioneer used it in the late 80 and Sony has been using the concept for the past 15 years and still do in their latest models but just more refined, neither used TMC though. Figures obtained by Sony with bipolars usually around .003 20hz to 20 Khz.
Here it is.
dado
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Old 13th August 2012, 12:45 PM   #56
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Originally Posted by dadod View Post
Here it is.
dado
Ty.
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Old 14th August 2012, 07:40 AM   #57
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To summarize what are fortes of those two amps. Nothing new just proven circuit put together to get stable good sounding amp. Quite easy obtainable components. Very high Negative Feedback is used.

High power version:
Transconductance stage - Cascoded LTP with floating bias and Current Mirror
The tail current was set to 11.5 mA to get good Slew Rate and very low noise LTP transistors used

Transimpedance stage - Enhanced Cascode with TMC

Voltage amp(OPS) - Triple EF for high input impedance


Low power version:
Transconductance stage - Simple LTP with Current Mirror
The tail current was set to 11.5 mA to get good Slew Rate

Transimpedance stage - Enhanced Cascode with TMC

Voltage amp(OPS) - Triple EF for high input impedance

Power Supply is as important as the amp it self. Separate Capacitance multipliers for the Input Stage and Output Stage should be situated very close to the amp circuitry on the same Printed Circuit Board. In both amp Backer Clamp was used to prevent OPS saturation.
Any comments or suggestion is very welcome.
dado
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Old 14th August 2012, 08:19 AM   #58
Bonsai is offline Bonsai  Taiwan
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Some interesting comments earlier on about feedback.

Bruno Putzeys 'The F-word' (Jan didden kindly posted up a link to this article over in the Blowtorch thread) , should be required reading. Unfortunately, the low feedback, wide bandwidth as a route to sonic Nirvana is not based on engineering fact - and the earlier OP was correct in stating that we've known about this through JLH et al for at least 30 years or more, yet it still persists.

That said, my e-Amp does offer the opportunity through the use of jumpers to select TMC or MC and also to 'wide-band' the loop gain to >40 kHz by resistively loading the VAS. Loop gain is reduced by about 6-8 dB as a result. Currently its set for high loop gain and TMC.

I make no claims on the sonics either way, and my interest in using this approach purely so that I can change the loop gain characteristic and, if there is a clear difference, hear it.

I modified my original Ovation 250W power amp about a year ago for TMC and no VAS loading - so the loop gain is moderately high and the -3 dB Fo at a few kHz. The two amplifers sound very different, and yet currently are using the same comp scheme. So, there is a difference in the sound of amplifiers, and even when they use similar feedback schemes.
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Old 14th August 2012, 08:57 AM   #59
dadod is offline dadod  Croatia
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Quote:
Originally Posted by Bonsai View Post
Some interesting comments earlier on about feedback.

Bruno Putzeys 'The F-word' (Jan didden kindly posted up a link to this article over in the Blowtorch thread) , should be required reading. Unfortunately, the low feedback, wide bandwidth as a route to sonic Nirvana is not based on engineering fact - and the earlier OP was correct in stating that we've known about this through JLH et al for at least 30 years or more, yet it still persists.

That said, my e-Amp does offer the opportunity through the use of jumpers to select TMC or MC and also to 'wide-band' the loop gain to >40 kHz by resistively loading the VAS. Loop gain is reduced by about 6-8 dB as a result. Currently its set for high loop gain and TMC.

I make no claims on the sonics either way, and my interest in using this approach purely so that I can change the loop gain characteristic and, if there is a clear difference, hear it.

I modified my original Ovation 250W power amp about a year ago for TMC and no VAS loading - so the loop gain is moderately high and the -3 dB Fo at a few kHz. The two amplifers sound very different, and yet currently are using the same comp scheme. So, there is a difference in the sound of amplifiers, and even when they use similar feedback schemes.
Why to use resistive load of the VAS if you can use local VAS feedback, you are throwing useful gain down the sewer. If I remember correctly Bruno Putzeys say that he likes wide Open loop bandwidth if distortion is substantial and in this case to have uniform distortion over whole audio band. With very low distortion that is not important.
How do you describe the difference between loaded VAS and not loaded?
dado
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Old 14th August 2012, 12:21 PM   #60
Bonsai is offline Bonsai  Taiwan
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Quote:
Originally Posted by dadod View Post
Why to use resistive load of the VAS if you can use local VAS feedback, you are throwing useful gain down the sewer. If I remember correctly Bruno Putzeys say that he likes wide Open loop bandwidth if distortion is substantial and in this case to have uniform distortion over whole audio band. With very low distortion that is not important.
How do you describe the difference between loaded VAS and not loaded?
dado
Precisely because it allows me to experiment between lower loop gain, lower VAS stage local gain and the high loop gain options. High loop gain is not a prerequisite for success - I think the sound of both my amps attest to that.

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