trinityamps.com

I am soooo glad it wasn't the attenuator coloring the sound. Although if it was... then I just created a magic "brown" box. I could have been rich.

The very first clip I posted (see my first post viewtopic.php?f=7&t=2464) was the stock Trinity Plexi circuit except 220K grid reference and 5.6K grid stoppers on the EL84s and 33K slope resistor on the tone stack. Bright channel only dimed except bass on 0. I had not wired any of the switches other than the boost. You can see the gut shots in that thread as well.
It sounds so good right now I am not sure I want to change it. I might try the grid stoppers back at 8.2K. When I turn the NFB off will the 43K tail still be ok there?

-Les

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Les

http://www.soundclick.com/unimind

Here are my current plate voltages:

Mains: 122.1(AC)
B+: 337.8
V1: 136.2/142
V2: 255.1/156.5
V3:185.4/190.3
V4:315.6
V5:315.7

I am using Tung-sol preamp tubes and JJ EL84 and JJ EZ81.

-Les

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Les

http://www.soundclick.com/unimind

Updated per comments. I think that's it. Normal Channel is stock.

[see next version] below

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

That looks correct. Now which lurker is going to be our guinie pig and try that schematic?

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Les

http://www.soundclick.com/unimind

That looks OK for the simplified (non-NFB cathode-bias only) version.

That 47pF cap is meant to be across the PI V3's anodes, and it needs to be 100pF in this amp, like Unimind has done done it.

And I think we should also reduce the 220uF on the Normal channel to 3.3uF as per Unimind's recommendation in his other thread, quoted here. Also the coupling cap to 0.0047uF....

Update:
Made some changes to the normal channel to tighten up the bass.
Changed coupling cap to .0047uF
Changed cathode bypass cap to 3.3uF
Sounds much tighter now. Really has that 80s feel.


Yes, because it's path to ground is still via the 5k pot.

You missed one mistake. Edit: OK, the PI cap has been fixed now. There has been a change in the matrix.


If you needed to run the bass control at 0, then that tells me you would probably have done better with a 0.01uF for the tone stack Mid cap C4. The regular Marshall tone stack's bass control sweep is more in the bass guitar range, due to the fact it comes from the Fender Bassman. This simple mod pulls the bass control more into the regular guitar frequency range.

Edit: And one more thing!
We have got to include the cascade switch. That's where a lot of the fun of this amp lies.

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Great tones come in small glass jars!

Ok, the votes are in and I've updated the schematic for the normal channel (it was the Plexi Lead 50).

Also changed the bass cap, C4, to .01uf

Schematic


Layout


Are you cascading the Normal into the TMB or TMB into the normal?

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

It's lookin real good now! And it looks like it would work with the regular 18W Plexi turret boards.

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Great tones come in small glass jars!

I am running the normal into the TMB but remember that I took out the normal channel tone knob. I think you should start without the cascade and have someone try that and see what it sounds like. That is more inline with the standard 18 watt design just with the "brown" mods. I know I have cascading working and working well and that is the only reason I lowered the bypass cap on the normal channel. The 1959 circuit has the 820/330uf on the normal channel which I thought was ok by itself just it got a little muddy when cascaded.

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Les

http://www.soundclick.com/unimind

Les, there is already plenty of experience with cascaded 18W amps at Trinity. So I personally don't see a reason not to put the cascade straight in from the start - and it's on a switch anyway. So it's easy enough to try both ways. BTW Richard Johnson's 18W Plexi design on 18watt.com also has the cascade switch, so it's pretty familiar territory to us by now.

I also noticed from the other thread that your cool clips used a 7-string guitar. So I would assume we're talking about some pretty hot pickups. I suspect that someone with a less hot guitar may not achieve the same tones you were getting without the cascade mode engaged.

I knew the reason for the smaller cathode cap in the Normal channel. That kind of mod sometimes gets done on the big Plexis for the same reason.

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Great tones come in small glass jars!

Fair enough.
All of my previous clips were with my six string with the Duncan distortion pup. The seven string has the stock pup in it. I think it is a DiMarzio but it is not that hot that is why I use the super overdrive with it but with the drive all the way down. Just gives it a little umpf.

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Les

http://www.soundclick.com/unimind

Which is why I think the cascade mode is important to have on this amp, for those folks who's pickups aren't that hot and they prefer not to have to use pedals.

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Great tones come in small glass jars!

Schematic with Normal channel cascaded into TMB. The DPDT can be on the Normal Ch. 500K Volume control. This has worked nicely and tested too.



However, I am thinking, it might be more natural to go from TMB into Normal if that channel is most popular. Then, logically the pull/push switch would go on the 500K Gain control, making even more sense.

Remembering that when cascaded, the other input is out of circuit.

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

I tried it both ways and as I find I use the TMB more then the normal channel that I have the cascade from TMB to normal. However I think that how you voice your channels is going to deceide it for you.

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Fantasy Noise is what my shop of dreams is called and was the only way to beat my addiction, like many here I suffer from G.A.S.


Tele's make the best noise

Right and in my case I do not have the normal channel tone knob and I have the channel inputs internally jumpered from normal to TMB. When using the cascade I use the normal gain as the pre gain and the TMB gain as the 'main' gain if you will and then I still have the TMB master volume (pre PI) to control the overall volume.

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Les

http://www.soundclick.com/unimind

The issue is this. When you are overdriving a stage, you need to limit the bass coming in to the stage, so as not to get mush. So it's not a great idea to insert another gain stage after the tone stack, which can increase the relative level of bass. At the same time it's usually more convenient for most folks to be able to plug into the higher gain TMB channel and be using that when not in cascaded mode. The ideal solution would be therefore to insert the Normal channel in between the first and second preamp stages for cascaded operation. This is the way it happens with a real 1959 or 1987 Plexi.

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Great tones come in small glass jars!

This is VERY quick-n-dirty-n-simplified, but would something along these lines work?

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- This Space For Rent -

Of course that makes sense. Shows what kind of NOOB I am. Just disregard my last post please. It's a good thing I have you here to set me straight when my mind goes out the window. How 'bout another clip
http://www.unimind.us/Outa_Love.mp3
Edit: Bright channel only (no cascade) dimed, cathode bias, NFB OFF, boost ON

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Les

http://www.soundclick.com/unimind

Nice!! OK, I can hear reverb added in the mix. Were you using the boost pedal with this clip as well, or not?

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Great tones come in small glass jars!

Nope. Just guitar straight in.

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Les

http://www.soundclick.com/unimind

Nearly, but not quite, as you then end up with the "B" inout of the PI floating in the air, when it actually needs to be grounded.

Allso, after some more thought, I've come to the conclusion that the amp will work fine in cascaded mode, with the TMB section being placed in front of the Normal channel section. This is due to the reduced cap values Unimind has used in his modded Norma; channel, wich help keep the bass in check.

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Great tones come in small glass jars!