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Originally Posted by Pete240885
You can get oscilloscopes seccond hand for around £100, you probably don't need dual channel for audio testing purposes, 20MHz is the standard, though you could get away with a 10MHz if all you doing is audio work without much difficulty, If you want to do anything more than the odd test dual channel is probably a worthwhile investment.
Don't be tempted to use your soundcarrd as a scope. fine for very low voltage work, no good for power rails - scopes are excelent on power rails, and will tell you more than your multimeter will.
I don't have a capacitance meter...i have alot of spare caps arround for swapping purposes though
I Spent a total £200 on my scope and a signal generator (seccond hand) and i've never looked back, but i'm doing more than one repair and it was useful in my student days  |
Well I could just about get a new amp for £300, so I don’t know if I’d want to buy a new oscilloscope, but £100 isn’t too bad, I’ll see how the live testing goes and take it from there, ta for the info anyway.
Quote:
Originally Posted by Pete240885
Now back on subject...
How do the various controls affect the noise? how does it differ from channel to channel if at all?
how have the affore mentioned tests gone?
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You can sort of roll off some of the nasty sounding distortion with the Treble and presence controls, but obviously then you’ve got no treble, and it seems to affect both channels, but it’s more noticeable on the Lead channel.
The link you gave me to the DSL mods page was very informative, and also slightly worrying, especially the bit where someone called the JCM2000 ‘
One of the most diabolical amps ever to see the light of day’ 
…I’m still working my way through that article and trying to figure out if it’s even worth the trouble of trying to fix this amp and I still haven’t got round to doing any live testing yet (I’ll probably start tomorrow) but after reading the first paragraph on that page:
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In a DSL100 I didn't find that specific problem but in all JCM2000's so far (TSL's, DSL's) I've found 220k grid block resistors on the power tubes instead of the customary 5k6 as indicated in all schematics - converting them to stock values definitely makes an audible change !
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…I checked the colours on the resistors he mentioned (R66 and R70) and providing I've interpreted the lettering on the PCB correctly, the resistors he mentioned are in fact the correct value (5K6 Ohms) there are two 220K resistors right next to them (R67 and R69) but those are also the correct value too according to the schematic, so I guess I'm OK with that one.