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PostPosted: Sun May 17, 2020 11:54 am 
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When using the Triwatt for practice, at home, I usually have it at "bedroom volume", i.e. master volume under the 9:00 position. The problem is, when working at these volume levels, the master pot is too sensitive: I move it just a bit and it's too loud or too quiet. (This isn't unique to the Triwatt, in my experience, every tube guitar amp over two watts or so has this problem.)

So I'm thinking, would it be possible to put a resistor on a switch in front of the master volume pot? So with the that resistor switched in, the amp goes into "bedroom mode", so even with the master pot turned all the way up, it's the equivalent of having the master around 9:00 without the resistor. The intent is to have a mode with an artificially (but deliberately) low volume ceiling. And of course, with the switch off, the resistor is removed (or shorted out), so that volume control is restored to the default state.

Seems like this would be fairly simple. And I assume I could use a push-pull pot+switch, same as used by the overdrive control?

Thoughts?


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PostPosted: Sun May 17, 2020 2:00 pm 
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viewtopic.php?f=14&t=3264 Might give you a starting point and maybe PM Coco if no one else replies.

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PostPosted: Sun May 17, 2020 3:14 pm 
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Hankules wrote:
https://www.trinityamps.com/phpbb/viewtopic.php?f=14&t=3264 Might give you a starting point and maybe PM Coco if no one else replies.


That's talking about variable-voltage regulation (VVR), which is significantly more complicated than what I'm suggesting. My understanding of VVR is that it allows you to run the power tubes at a lower voltage, reducing volume but also getting power tube breakup/distortion at manageable volumes.

My suggestion is much simpler: it's just adding a resistor in series with the master volume, so that even when the master is at 100%, the signal is still limited by the resistor. The intent is to basically cap the available volume at "apartment friendly" volumes, while also allowing the master volume to have a lot more sweep range in this "polite" mode.


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PostPosted: Sun May 17, 2020 9:35 pm 
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zaphod wrote:
+! to kurtlives' comments.

Basically, the VRM/power scaling concept doesn't really work well with Hiwatt type amps. These aren't Marshalls. When developing the Triwatt, which is based very closely on classic Hiwatt designs, it became very clear that there was a specific voltage sweet spot for the right classic Hiwatt tone. If you went much above that, it started to sound shrill. If you went below, it got mushy and lost definition. Just use the built-in MV. If you wanted to add anything to that, you could also install a post-PI MV, which a few folks have tried with regular Hiwatts and appeared to work well.

Sorry, thought Zaphod's comment about a volume pot after the phase inverter might work for you. :oops:

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PostPosted: Sun May 17, 2020 10:27 pm 
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Hankules wrote:
Basically, the VRM/power scaling concept doesn't really work well with Hiwatt type amps. These aren't Marshalls. When developing the Triwatt, which is based very closely on classic Hiwatt designs, it became very clear that there was a specific voltage sweet spot for the right classic Hiwatt tone. If you went much above that, it started to sound shrill. If you went below, it got mushy and lost definition. Just use the built-in MV. If you wanted to add anything to that, you could also install a post-PI MV, which a few folks have tried with regular Hiwatts and appeared to work well.

Sorry, thought Zaphod's comment about a volume pot after the phase inverter might work for you. :oops:


No worries! I agree, PPIMV would probably be the best approach. Easier/less invasive than VRM, for sure, and almost certainly better than what I'm proposing. The main selling point of my idea is that---assuming it's actually viable---it's basically trivial.

That said, if I could get a little hand-holding on what a PPIMV circuit would look like in the Triwatt, I might consider it.


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PostPosted: Mon May 18, 2020 11:26 am 
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matt_garman, as for PPIMV controls, if you're not familiar with them, google, the different types of PPIMV controls. There's an amp guy that wrote some "pages" and in them is contained different types. (Not sure if I'm allowed to say who wrote them of the name of them, I'm not familiar on copy-write.) Specifically do some research on Type 3 master volumes. There are a few different types and they all have pros and cons. I've modified a "presence" control in an amp that I had, which was basically a cut control from old voxes. Turned it into a type-3 master volume. It's very similar to (and may actually also be called) a crossline master volume. Check out the schematic for the TC15, I think it uses this type of master as well.


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PostPosted: Mon May 18, 2020 2:06 pm 
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Matt: Yes, there are various ways to do PPIMV. Most of them use a dual gang pot to vary the two signals coming out of the phase inverter before they get to the output tubes.

The resistor mod you proposed sounds feasible. It would be easy to test the mod out to see if it does what you want. Just remove the wire going to the master volume control and clip in a resistor. If that doesn't work you can experiment with PPIMV.


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