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PostPosted: Wed Oct 21, 2015 1:56 pm 
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Joined: Thu Apr 09, 2015 6:56 pm
Posts: 5
Hello All!

I'm a happy owner/builder of a Trinity Tweed Deluxe kit with VRM that I've been I've been running since July. It's my #1 amp right now and I absolutely love it. I probably use it 2-4 hours per day. I use the VRM all the time.

I recently started noticing that when turning the VRM down past, say, ten o'clock, that it seems to make little to no difference in volume past that point, and all the way (counter-clockwise) to shutting off the amp. I still have a fair amount of volume left at that point.

Maybe I'm expecting it to act like a volume pot throughout the entire range of control, but I never tested it below about 11-12 o'clock until a couple of weeks ago. I notice that the MOSFET does run quite warm, heating up the PT side of the chassis quite a bit. I haven't put a meter to it yet to see if it's actually affecting the B+ as the control is rotated down past ten o'clock.

Here's my question: Should there be a steady decrease in volume/voltage all the way to quiet before reaching shut-off?

Thanks in advance for any help!

--Steve


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PostPosted: Thu Oct 22, 2015 5:33 pm 
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Joined: Sun Feb 17, 2008 4:47 pm
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Location: Toronto, Canada.
Do check the B+ to see if it is scaling all the way through the pots rotation.


We use logarithmic (also know as audio) pots for volume controls typically. The relationship between perceived loudness and gain is not a linear relationship but closer to logarithmic so that is why we use an audio pot.

Since the VRM is not changing the gain (dumping signal to ground) like a traditional volume/gain control the taper of the pot is a bit trickier. Some people use audio (A) pots, some use linear (B) pots. Neither are ideal but both work well enough.

If you want to take the VRM to lower levels replace the stock 100K resistor going from ground to lug 1 of the VRM pot. This resistor sets the lower limit of the VRM. Higher values here will give get you "lower volume settings". Try 100K-330K.

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PostPosted: Fri Nov 13, 2015 10:58 am 
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We increased the stock low limit resistor to 220K so that shouldbe in your kit. Rest per what kurtlives said.

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