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Hey Stephen and gang,

I notice the bass pot in the sIII schematic was changed from 1meg to 500k.

What effect did this have on the channel, with respect to how the bass pot works?

I must've worked off of an order copy, as mine is 1meg...

-Frank

Yeah, I changed it to give more control of the Bass. It seems to be just a bit better. For $2 you can try it out too.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

I tried both and prefer the 500K myself
Nigel

I might just be able to chuck a 1m resistor on the pot (instead of ordering a 500K).

Normally when I knock a 1meg down to 500k, I straddle the first and third lug with the resistor...however, in this case, The 3rd lug isnt used...

I wonder how I could make it work this way....

That should still work as it will lower the overall resistance of the pot.

Try adding 500K across the wiper to ground. That might change the range just enough.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Frank, you are just going to have to double the quantities of everything you buy so you have plenty in the parts bin, you keep kidding yourself that this is your last amp

LOL! Very true!!!!

So guys, just out of curiosity (because I would love to just fatten my TMB channel *oh* so slightly), what effect would this pot change have?

Other than that, I'm going to consider changing the coupler from v1 to a .022uf...

-F

It would give you a bit more control of the bass, maybe fatten up a bit. If you want to fatten it up, then I'll give you some tips...right out of the manual.

To Fatten Tone on TMB Channel
1. Change C1 to 0.022uF
2. Change C2 to 2.2uF -OR- change R5 to 2.7K -OR- both
3. Change R11 to 33K
4. Change VR5 to 500K-A or 250K-A to give the bass control more useful range

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

For starters I was going to try #1 on your list...since I've got experience with mucking with the preamp coupling caps...so I know what to expect...

-F

Report back on your findings please. Maybe you'll want to have a F-A-T-T & skinny switch

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

You know, that's a cool idea...although i suspect the .022uf coupling cap would also add some volume, wouldn't you think? resulting in a volume difference between the two settings?

-F

OK,

I've made two tweaks:

1) Dropped value of 1mg bass pot to 500k by straddling a 1mg resistor across lugs 1 and 3 of bass pot. Resulting in 500k pot...Very subtle but welcome change to the way the bass knob reacts!

2) Changed coupling cap from .0047uf to .022uf between v1 and v2 of TMB channel. This effectively destroyed the beauty of the TMB channel on the sIII....there was a slight increase in bass....but it also added a raspy, fuzzy distortion that I remembered from my 18watt lite days....I immediately reverted back to the .0047uf cap and the amp is literally perfect now.

This should teach me to make one change at a time! I made both changes at the same time and I thankfully backed out the coupling cap first...which returned me to just the sIII with the 500k bass pot.. Perfect!


This coupling cap experience actually raised an important issue that I've been constantly fighting with my lightning deluxe. As most of you know, I've fought a raspy buzzy tone in that amp for months...and I made a whole slew of changes to the preamp to get rid of it...and in some cases, reduced distortion that I otherwise would have wanted from the preamp. After hearing the coupling cap results from the sIII, the resulting sound is *very* similar to what my lightning had done...so I am tempted to revert the lightning's preamp to the amount of gain I want...and see if playing with the coupling caps will fix the problem. (granted the current coupling cap in there is on 500pf, so I can't imagine going any lower! )

I'll report more on that in the lightning forum if the changes render something worthwhile!

-Frank

Good feedback. Looks like changing that coupling cap from .0047uf to .022uf between v1 and v2 of TMB channel is not the greatest idea.
Fat & Raspy -

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Yeah, it turns the amp from a high school cheerleader into Rosie Odonnell!!!

Does that mean it sounds good after nine Coronas?
Nigel