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Old 18th July 2010, 06:50 PM   #1811
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"Légion Etrangère", rude guys...

I've pointed the pins for measuring voltage on the pic.
What value should I find there ?
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Old 18th July 2010, 06:56 PM   #1812
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Indeed. Roughly +/- 10-11V
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Old 20th July 2010, 12:43 AM   #1813
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Default Well that was easy...

... I wrote some time ago about the DCB1 sounding odd because it was rolling off as the frequencies got into the midrange and got progressively worse through the treble. I did three things to it and it straightened out. I changed out the gate stoppers for some carbon composition types (was using Koa Spear metal films) replaced the volume control and increased the current in the regulator to 100 ma. I suspect that the regulator current was just too low. I now have a little DC offset in the output of 1.2 mV and .6 mV where it was not measurable before.

Didn't listen to it very long as I will need to use the heat sinks on the MOSFET's now but the depth of stage is impressive. Now I can start trying a few things to see what the final values are going to be. I'm going to go to 150 ma on the regulators and see how that works out.

Now it's getting to be fun again.

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Old 20th July 2010, 07:35 AM   #1814
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Was it some wrong value in the current setting and was especially low? Maybe the gate stoppers could have been wrong in value too?
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Old 20th July 2010, 11:18 AM   #1815
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The gate stoppers were 220 Ohm. The initial current was set by a pair of 68 Ohm resistors in parallel per side. Each set of resistors had 2.14 Volts across them so I don't know what to think of it. ???
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Old 20th July 2010, 11:29 AM   #1816
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Probably it was oscillation. We are talking about the audio part gate stoppers?
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Old 20th July 2010, 01:27 PM   #1817
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Quote:
Originally Posted by Macronaut View Post
... I wrote some time ago about the DCB1 sounding odd because it was rolling off as the frequencies got into the midrange and got progressively worse through the treble. I did three things to it and it straightened out. I changed out the gate stoppers for some carbon composition types (was using Koa Spear metal films) replaced the volume control and increased the current in the regulator to 100 ma. I suspect that the regulator current was just too low. I now have a little DC offset in the output of 1.2 mV and .6 mV where it was not measurable before.

Didn't listen to it very long as I will need to use the heat sinks on the MOSFET's now but the depth of stage is impressive. Now I can start trying a few things to see what the final values are going to be. I'm going to go to 150 ma on the regulators and see how that works out.

Now it's getting to be fun again.
First at all, why did you knew that it was rolling off? Did you used measurement equipment to check it? Or did you use any software tester like rightmark and a soundcard?
Because I have, and mine outputs straight as a line. Please, do that before making assumptions based on subjective impressions. Post your picture from rightmark too so we can aim to diagnose your problem.

Going from metal films to carbon composition is not going to make any objective difference.
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Old 20th July 2010, 01:45 PM   #1818
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I understand your concern with the subjective side of this. However... it was so obvious that there was a problem and I don't really have anything at my disposal to use for measurement. The sound was not unlike that of turning the treble all the way down to the -10 db mark on an integrated amplifier. Sorry I cannot provide anything more than that for now.

I Googled Rightmark which looks interesting. I'll look into that as time permits. Life requires me to tend to too many other things for now.

Last edited by Macronaut; 20th July 2010 at 01:56 PM.
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Old 20th July 2010, 01:51 PM   #1819
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Probably it was oscillation. We are talking about the audio part gate stoppers?
Yes. I had ordered the wrong type of resistor for the input. I had intended to just use that to make the circuit work before I ordered any of the 'audio quality' resistors recommended in the BOM.
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Old 20th July 2010, 01:54 PM   #1820
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So now its subjectively flat? Because to such a degree of treble loss you describe it should have been a very serious problem. Most likely oscillation. Do you have long interconnects on input/output? What type of wire construction, shielding?
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