trinityamps.com

My MV on my tc dosen't have good range at the lower registers.
Is there anything I can do about that.

Andy

No one has worked on solving that one. But it's not the first time.

Must be time to review it.

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

Ah...no need for a new topic Coco...this is my quibble as well (the range in the lower registers as noted above). I don't use the MV at all because of this.

The other part is that I find the pot used for the TC-15 MV (push/pull) to have a very cheap feel. I find once you pull out on the knob to engage the MV the knob has a very flimsy feel. There's no resistance on the knob and it almost feels broke. Likely doesn't affect the sound, but it just feels flimsy...to me at least

Keith

Alpha PC mount?

Yes IIRC. It's actually a real nice, good quality precision pot. It just has a very low friction action, so that if you're used to pots with more friction, you start to think it's loose. But it's not.

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Great tones come in small glass jars!

Doesn't feel 'good' to me, even though it may very well be good functionally. I would like to get it out, if I could, and replace with a non push/pull knb where the MV is always in the circuit until you dime it.

Also, in the interest of ensuring it wasn't just me, my brother-in-law is visiting from Montreal so he had a spell on the TC-15 last night. I engaged the MV down low. After a couple minutes his impresions were the same as mine as he liked the MV off as it made the amp muddy and lose definition down low. Is there a way to fix this and am I the only person to have this complaint?

Keith

Ken Fisher refers to our TC15 MV in his Trainwreck pages as Master Volume Type 3 which is theoretically 'out' of the circuit when on max BTW.

You can try to sub a dual ganged pot and maybe some resistors for the standard cross-line MV. Here's a post-PI MV for an 18W



However, Ken Fisher believes this type of circuit can affect the tone of the amp when the MV is dimed more so than the cross line one we already use. But I've never tried it. Zaphod says it works well.

Fisher has a similar dual gang MV Master Volume Type 2 using 100K linear pots and a different wiring configuration which he used exclusively. My assumption is he felt it sounded best.

Both are worth a try if you want to experiment with the MV.

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

fwiw my master volume (which I rarely use if ever ) pot is as stiff as the others, its not "loose" feeling as is the OD on my triwatt.

it feels like there is grease or something in the pot which makes it feel draggy or stiff...

AJC

I didn't notice the tone isue with the MV on Fortis's TC when I built it, but I didn't spend a whole lot of time playing with it either. It sounded fine to me & quite useable. In fact, I remember really liking it with the MV low while pushing the EF86 channel.

I do have the same complaint about that pot though - about it feeling "cheap". I talked to Stephen about that a while ago. I've tried to find a pot with a better feel but have had no luck. I do have an imported push-pull pot with a nice feel and it even has solder lugs, but it's a SPDT. I haven't found a DPDT like it anywhere.

One could have CTS (or possibly other manufacturers) design a custom pot but it's an expensive proposition.

Another option is to use a standard Alpha pot & a mini-toggle to do the switching. I considered this when I built my Triwatt in fact.

I don't know how to fix the "range" issue on the lower end of the MV. You could use a VRM instead of the MV to get "bedroom" levels I suppose.

I think Bourns makes a pot but it's very hard to get what we want in small quantities. but I'll look into it.

There's nothing wrong with the pot, just the feel of it.

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

The TC-15 only needs an SPST (2 lugs) to disable the master volume according to the schematic. CTS makes a pot like this along with a few other manufacturers.

The Marshall style post-PI MV, as shown in the 18W example posted by Stephen, is effectively the same as no MV when dimed, provided you chose the correct values for the pots and the grid reference resistors. And at all settings it gives zero bleed between the two PI outputs.

That doesn't make sense to me, as clearly the 250k pot is strapped across the PI outputs all the time and will therefore always cause some bleed between the two sides. Obviously Trinity's pot-mounted switch conveniently overcomes that issue.

The trick is to double the value of the grid reference (aka "grid leak") resistors and to use a dual-gang pot also of double the value of the original grid reference resistors. So in an 18W the 470k resistors have been substituted by 1M resistors with 1M pots. 1M in parallel with 1M gives 500k, which is near as dammit close enough to the original 470k, and when dimed the MV is in effect no longer there. For a TC-15 or other typical Vox/Matchless amp you could use a 500k dual-ganged pot with 470k resistors on the tube grids, effectively giving 242k, which isn't significantly higher than the original 220k.

I haven't read that article, but that statement is incorrect, as I've just explained. The other nice thing about it is that the PI outputs each see a constant load, rather than the varying load you get with the Matchless cross-line MV. With the latter kind you get the two PI outputs fighting each other, in effect, as you turn the MV down.

Yes, that's correct, if you stick with the stock Matchless-style MV. So you could get a stiffer pot, but without resolving the low volume tone issue.

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Great tones come in small glass jars!

Ah yes - still had the Triwatt in my head. In that case, I think I did see some options out there, but none for the Triwatt scenario I guess.

This would be worth a try I think.

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

FYI a Triwatt with the footswitch relay option also only needs an SPST switch, since the actual switching is taken care of by the relay.

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Great tones come in small glass jars!

Yes indeed. If/when I get around to doing that mod I just might use that push-pull pot I have kicking around.

This doesn't change the "low level tone" but is an easy solution for the "feel" issue.

I took apart a standard Alpha 1M pot and cut the resistive material on the wafer so that the pot is out of the circuit when turned all the way up. That way it feels the same as all the others and I don't have to worry about volume jumps when the MV is dis-engaged.

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Deric®

I've seen that done too. Ken Fisher mentions this trick as well & it's cool.
I thought the Alpha pot was a little hard to work on to do that. You didnt take any pics did you? Did you have any problems doing it.

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

Edit:

OK - so, i was bored. Just did this to the MV pot in my 1.8Watt.

First: Carefully bend back the 4 tabs that hold the back of the pot...



Remove the back cover and set it aside...



Next: Identify which lug of the pot you want to disconnect.



I used an Exacto knife to scratch away the resistive material.



Put the cover back on the pot and bend the tabs back the way they were. Double check to make sure the back is secure and the pot rotates freely.



Back in the amp....



Total time: about 20 minutes including pulling the chassis, taking pictures and re-installing the chassis.

I suck at typing. Don't ask how long this post took....

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Deric®

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Deric®