Patchwork Reloaded: Circuit Optimization and Board Layout.

[AndrewT]

Originally posted by MJL21193
....... I don't have a millivolt meter,........

most/many DMM have a 200mVac scale.
The last digit represents 0.1mVac+-0.05mVac.
If the last digit is off then the signal is <0.05mVac.

I suspect your amp reads at least 1 on the last digit (equivalent to 0.1mVac).
and more likely 0.3mVac

This is not a good way to measure noise because most DMMs have a very poor upper audio frequency response. You are effectively measuring the 50Hz to 1kHz band. Even this restricted (but undefined) bandwidth gives a reasonable measure of hum and buzz.

[MJL21193]

Originally posted by AndrewT
most/many DMM have a 200mVac scale.
The last digit represents 0.1mVac+-0.05mVac.
If the last digit is off then the signal is <0.05mVac.

My DMM auto ranges but I can set it for mVAC. Doing so, I measured the output at the binding posts with the input shorted. It read 1.8mVAC BUT this is not correct. With the leads of the DMM flying, It shows a fluctuating voltage, not zero and with the leads shorted, It reads 1.7mVAC.
TBH, I don't trust any reading from this at these low voltages.

Did you download and listen to the clip I posted above? That tells much of what you want to know.

[AndrewT]

Originally posted by MJL21193
and with the leads shorted, It reads 1.7mVAC.
TBH, I don't trust any reading from this at these low voltages.

does it misbehave like this when on Vac autoranging.

If so you cannot use it for AC voltage measurement.

My non-autoranging DMMs all (3off) show 0.0mVac and 0.0mVdc when the leads are shorted together.

[MJL21193]

Originally posted by AndrewT
does it misbehave like this when on Vac autoranging.

If so you cannot use it for AC voltage measurement.

My non-autoranging DMMs all (3off) show 0.0mVac and 0.0mVdc when the leads are shorted together.

I found the "relative" button on the DMM and this zeroes the scale with the leads shorted. With this, it reads 0.1 - 0.2mVAC.
I tried it with my other, cheaper DMM (bought that for it's hfe tester) and the same result after it was zeroed.

How's that?

[AndrewT]

Originally posted by MJL21193
it reads 0.1 - 0.2mVAC.
How's that?

for a two/multi channel amp in it's casing, that is pretty good.

[MJL21193]

Thanks Andrew,
The case is not complete - the top is still open. It will get finished eventually, but I'm planning a change to the original 3 amp modules - I want to replace these with modules made from the new layout. At present, 3 of the modules are the new layout (left channel amps) and for consistency, I'd like to make the change.

Yeah, I'm a sucker for punishment...

[MJL21193]

[ostripper]

Beautiful, does not look like "patchwork". More like a
production run..


OS

[jaycee]

Hm I wouldn't be comfortable with the copper component markings, but other than that, they look the sex

[MJL21193]

Originally posted by ostripper
Beautiful

Thanks,
These are to replace the ones in my 6 channel amp.

Originally posted by jaycee
Hm I wouldn't be comfortable with the copper component markings, but other than that, they look the sex

No worries jaycee,
The copper silkscreen was closely inspected for shorts and I spent extra time sizing everything to make sure there wouldn't be a problem.

6 done, tested, ready to install.