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PostPosted: Thu Jan 26, 2012 2:23 pm 
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I've ordered the VRM kit from Stephen and will initially install it to regulate the DC for the entire amp, an 18W TMB. However, in case I subsequently decide to go with the more complicated installation on just the power amp and PI, two questions:

  • Other than THIS SCHEMATIC, is there anything here on the forum (or another forum, perhaps) that gives installation details, a layout diagram, etc. for the PA/PI installation?
  • What additional parts are required for that version? The above linked schematic lists some different resistor values on the split power rail. Are those what is to be used? Anything else besides the two 1N4007 diodes?

TIA!


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PostPosted: Thu Jan 26, 2012 3:33 pm 
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1. Not that I know of. Try searching?

2. Not sure what the two diodes are doing besides dropping 0.7V to each power rail.
If you go this route your going to have a parallel power supply. The VRM circuit will have it's own power rail then the preamp power rail will be separate. The two are in parallel. Look at Matchless (or Trinity TC-15) design for parallel PSU.

When the PSU is in parallel you don't have the large current draw "downstream" like in a series power rail. Because of this you need larger resistors to drop more voltage so the preamp is getting the correct voltages.


I'm not sure how much of that made sense but basically your going to need to alter the dropping string resistors that supply the preamp.
I'd just scale the whole amp though.


If you scale the whole amp you gotta add blocking caps and re-wire the input. Not hard to do, a bit of a pain.
If you scale the output and PI you gotta mess around with the PSU. Not hard to do but more of a pain imo. Calculations, adding turrets, etc...

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PostPosted: Thu Jan 26, 2012 4:43 pm 
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Those two diodes isolate the scaled supply from the unscaled supply. ie. If the filter caps in the unscaled supply are charged to say 300vdc and then you turn down the scaler to say 100 vdc, you don't want the caps to influence the scaled side by feeding current back and holding the voltage at 300 for a brief period..
If you scale the output section and not the rest of the amp you need a way to reduce the drive to the output section when the B+ is dialed down because it will be easily driven into distortion. A PPIMV is called for here. Same idea for scaling the o/p and the PI... you'll need to reduce drive to the PI for the same reason.
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PostPosted: Thu Jan 26, 2012 4:52 pm 
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You sure about the diode? Cause the way I see it they are always going to be forward biased.

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PostPosted: Thu Jan 26, 2012 4:59 pm 
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kurtlives wrote:
You sure about the diode? Cause the way I see it they are always going to be forward biased.

If the scaled side of the diode is lower than the unscaled side the diode will be reverse biased and the unscaled side won't feed the scaled side.


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PostPosted: Thu Jan 26, 2012 4:59 pm 
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Just going by what I see in this schematic:

Image


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PostPosted: Thu Jan 26, 2012 5:25 pm 
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duhvoodooman wrote:
Just going by what I see in this schematic:
A few months back I built an 18 watt with VRM on PI & PWR tubes only. I set the VRM up based on that schematic & it works great. You do need to play with the preamp resistors since the power to that section now bypasses the resistors to the pwr section.....the preamp voltages will be very high otherwise.

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PostPosted: Thu Feb 16, 2012 11:44 pm 
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Installed the VRM module tonight (full B+, no splitting of the power rail) and it works great. I haven't noticed any scratchiness in the inputs thusfar, so haven't bothered to install the blocking caps at the V1 inputs yet. But I've only played through it for a few minutes, so that may become necessary if the scratchiness appears.

That open space between the PT and the turret board is a great place to install the module, and I just enlarged the pre-drilled hole in the back panel between the mains socket and the impedance switch and installed the VRM control pot there.

One question--when I turn the standby switch on, I get a very brief (~1/2 sec.) buzz that rapidly increases in frequency and disappears--not very loud and seems to be independent of the amp's volume setting. Is this just normal VRM start-up behavior?

Coupla photos:

Image

Image


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PostPosted: Fri Feb 17, 2012 1:29 pm 
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I havent noticed this, but recommend you twist the control wires, even though they are short.

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PostPosted: Fri Feb 17, 2012 1:44 pm 
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b0b0 wrote:
duhvoodooman wrote:
Just going by what I see in this schematic:
A few months back I built an 18 watt with VRM on PI & PWR tubes only. I set the VRM up based on that schematic & it works great. You do need to play with the preamp resistors since the power to that section now bypasses the resistors to the pwr section.....the preamp voltages will be very high otherwise.


How did you find the drive at low volumes; did you need to compensate as discussed before?

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PostPosted: Fri Feb 17, 2012 2:26 pm 
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coco wrote:
I havent noticed this, but recommend you twist the control wires, even though they are short.

Interesting. Because they are carrying DC, I figured that wasn't needed. Is it because the rectified DC hasn't had any of the ripple filtered out at that point? In any case, I'll try making that change next time I'm "under the hood". But I think I'm just gonna enjoy playing through the amp for at least the next week or two! Image


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PostPosted: Fri Feb 17, 2012 7:28 pm 
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coco wrote:
How did you find the drive at low volumes; did you need to compensate as discussed before?

I didn't make any allowances for overloading the PI since the last thing in either channel before the PI is a volume pot. I just use the VRM as a master volume & adjust the channel volumes & TMB gain to taste. I haven't really noticed it being an issue. Mine has a single input going to both channels so I can blend them with the channel volumes. It's also set up with a channel cascade switch, but I don't use that mode much.

I had my brother-in-law's dead Epi Valve Standard on the bone pile (swapped him for some guitar mods), so I gutted it & started over. It already had Merc trannys so I didn't really need much other than a turret board, cap cans, better tubes, & a VRM. It has a Celestion Vintage 30 in it at the moment, but it's a bit harsh. I have an extension cab with a G12K that sounds MUCH better.

Attachment:
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BTW- Perched on top is the much-evolved single-ended amp you & Z helped me with quite a while back

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PostPosted: Sat Feb 18, 2012 12:08 pm 
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Nice attenuator you have there. :)

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PostPosted: Thu Jan 03, 2013 2:29 pm 
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rather than start an all new thread...have i got the wiring right as shown in my diagram...

power comes into the pot to the middle lug of the body...while the outer lug then goes to the fuse and to the lamp?

from the stand-by switch into the VRM module and then out to the filter cap...


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PostPosted: Thu Jan 03, 2013 5:33 pm 
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If the long black wire going off the picture should be going to the fuse which is connected to mains coming in( if i remember correctly)

So in your pic the long black wire should be conected in the middle and the one on the outside should be going to the lamp and the transformer


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PostPosted: Thu Jan 03, 2013 7:32 pm 
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you're right....that long one heads back to the fuse...thanks...I'll modify my pic and repost tomorrow in case some one else has the same question


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PostPosted: Thu Jan 03, 2013 7:33 pm 
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you're right....that long one heads back to the fuse...thanks...I'll modify my pic and repost tomorrow in case some one else has the same question


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PostPosted: Mon Jun 03, 2013 8:42 pm 
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Did anyone ever post the updated VRM graphic for the TC-15?

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PostPosted: Sat May 20, 2017 5:59 am 
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agitprop wrote:
Did anyone ever post about Gynectrol for the TC-15?


I've looked but I can't find it. Did you find it?


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PostPosted: Sat Jun 27, 2020 3:22 pm 
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Hello. I am looking for layout to assist in installation of vrm kit in trinity 18 watt sIII.
I cant make the schematic links posted by duhvoodooman I see on this thread work. my main question is in regards to placement of dc blocking caps

**update****
just found vrm builders guide, looks like that has all the info I need.


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