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Hi All

Considering swapping out some carbon comp resistors on the sIII I was contemplating changing some on the gain pot (quieter) and the 100K on V2

1/2 watt should work, I was wondering the resistor across V2 is that would quieten the channel a touch?


My normal channel sounds BEAUTIFUL however TMB as you turn up the volume pot can be 'scratchy" I changed the volume pot (ALPHA A500K from jentronics) and was a huge difference but there is still something there from time to time. I set the GAIN to 8 or so and use the VOLUME as a MV.


Thanks

Dan

Hi!

I usually run my sIII V6 with the master all the way up since I think it sounds just a bit better that way. However the hiss is rather high at this point even with the gain at zero. So yesterday I swapped the 56k cathode carbon comp resistor on V2 out with a 1W metal film resistor. I first thought something was wrong because the amp was so quiet. I couldn't believe the difference when I struck a chord and noticed all was fine but no hiss! Prior to this I had changed all the 100k resistors earlier in the signal chain to metal film but it was still noisy, I didn't think the 56k could be the problem until yesterday.

It's strange I'm so used to how it sounded before that I wonder if there is also some difference in tone, or perhaps I just miss the hiss. I need to evaluate this for a while.

Edit: I read your post again and perhaps there is something else wrong, you said scratchy not hissy. Mine never was scratchy just hissy. Sure you don't have DC on the pot? It should be connected to the capacitor to block DC from the PI.

Does your amp have a VRM? If so, check out this thread:
http://www.trinityamps.com/phpbb/viewtopic.php?f=12&t=1176

A little past 1/2-way down there's a schematic marked "SCRATCHY POT LAYOUT - VRM INPUT MOD" that may apply.

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In my scratch-builds, for anything not in the power supply and anything not rated at 1W or higher I use 1/2-watt metal film. Hiss has never been an issue.

That said, my TC15 kit doesn't have any hissing issues either even with all of it's carbon-based resistors. It's a very quiet amp. Maybe you have a bad resistor somewhere?

Good tip on the 56K. Wouldnt have expected that.
dan_tramble, check to see of there is DC on you volume pot. when its scratchy.

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Stephen
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