3-input LTP PI

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Tommy_D
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3-input LTP PI

Post by Tommy_D »

Hi all

Thinking about my next build, was wondering if a 2-channel Reverb Deluxe through a 3-input LTP is achievable? One channel would be the reverb side of Deluxe, other would be a 5f6-a preamp.

Aiken says you can have 2 inputs to LTP + negative feedback. However I'm not clear on practicalities of phase described here
https://www.aikenamps.com/index.php/the-long-tail-pair

Alternatively could mix channels with 220k resistors like in original Deluxe Reverb? Would that change the tone of 5f6-a side?

Pointers really appreciated! thanks
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crgfrench
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Re: 3-input LTP PI

Post by crgfrench »

I have a 2-input LTP with NFB in my current 36 watt build. The channels don't mix until they get to the PI. Sounds awesome with & without NFB engaged.
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geoff 1965
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Re: 3-input LTP PI

Post by geoff 1965 »

not sure about the deluxe/5f6 but my 6V6 project preamp is based on the trinity mk2 plexi 18W except the normal channel is lite2 based parallel and the TMB channel.i have both channels going into the same side of the standard 18W LTP with no problems.i've also cascaded the lite2 into the TMB channel so basically it's like 3 channels.
i find the aitken "phasing" a bit unclear as well!
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crgfrench
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Re: 3-input LTP PI

Post by crgfrench »

If you look at my schematic you'll see it is just like what Aiken calls "3 input PI". Its great.
download/file.php?id=12536&mode=view
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Tommy_D
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Re: 3-input LTP PI

Post by Tommy_D »

Oh wow, thanks Craig!

so that does work like a charm? No issues whatsoever??

Would that change drastically the tone of either channel vs. having 2 amps? That would be a VERY cool build!

Geoff, would you have a schematic for your build please? looks like the same as Craig's though
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geoff 1965
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Re: 3-input LTP PI

Post by geoff 1965 »

18WattPlexiMkIISchematic5 (1).pdf
here's the schematic Tommy,my power section is 6V6 and both triodes for normal channel " i have 4 ecc83 bases" and the 22n &10n channel couplers going into pin2 of PI with the effects loop in the downloads and a 100n going to ground from pin7.
i think Craig's look's more suitable for your purpose though
You do not have the required permissions to view the files attached to this post.
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crgfrench
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Re: 3-input LTP PI

Post by crgfrench »

Tommy_D wrote:
Tue 08/11/20 10:49 am
so that does work like a charm? No issues whatsoever??

Would that change drastically the tone of either channel vs. having 2 amps? That would be a VERY cool build!
Like a Lucky Charm! No issues at all. Quietest amp I've ever owned -- no hum, no hiss, no buzz, just dead quiet until you strike a note. And then: like honey dripping off a hot buttered biscuit.

Now -- that said I have tested both channels independently, but I have not yet jumpered the channels across the input jacks to blend them -- that might induce some noise, I don't know yet; hopefully I will try that tonight. Also, I'm just wiring in the FX loop today so that could introduce something. But, so far it's a phenomenal circuit in both channels, with NFB on or off, and also at full or half power. The NFB really cleans it up, I was surprised how much headroom it opens up.
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crgfrench
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Re: 3-input LTP PI

Post by crgfrench »

geoff 1965 wrote:
Tue 08/11/20 11:18 am
18WattPlexiMkIISchematic5 (1).pdf
here's the schematic Tommy,...
I love that Trinity Plexi design, I'd like to build that soon.
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geoff 1965
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Re: 3-input LTP PI

Post by geoff 1965 »

still at experimental stage Craig and the TMB channel is new to me but there is a mass of tone & overdrive with the cascade mod!
just in the middle of sorting a stupid error! i picked up a 290-0-290 220ma PT thinking if i decide in future to build a 36W or use a GZ34 rectifier i'll have a suitable PT and like an idiot i wired it into my little cage 18W which has EZ81 and noval tube sockets! so i'm putting the 220ma into the 6V6 with the octal sockets and if i end up not liking the 6V6's i've got the option of EL34's.
i'll post my progress on a seperate post when back on track
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Tommy_D
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Re: 3-input LTP PI

Post by Tommy_D »

Great stuff - thanks

Why don't I try this way, see how it sounds. I can always switch to 220k mixing resistors, easy change
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geoff 1965
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Re: 3-input LTP PI

Post by geoff 1965 »

download/file.php?id=10428
here's where i got the idea of both channels thru one side Tommy
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Tommy_D
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Re: 3-input LTP PI

Post by Tommy_D »

Thanks Geoff

Out of curiosity, how did you calculate the value of the caps before the 220k resistors?

That’s something I still need to figure out for my build
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geoff 1965
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Re: 3-input LTP PI

Post by geoff 1965 »

i don't have the 220K's,can you add a schematic showing what you are thinking of?
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Tommy_D
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Re: 3-input LTP PI

Post by Tommy_D »

This one for example
http://ampwares.com/schematics/twin_reverb_ab763.pdf
You can see 2x 220k resistors feeding one input of the LTP

Craig, on the 3 input LTP, was wondering if there is a difference in tone depending on which input you connect? (leaving the feedback loop where it is)
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Re: 3-input LTP PI

Post by crgfrench »

Tommy_D wrote:
Wed 08/12/20 3:38 am
Craig, on the 3 input LTP, was wondering if there is a difference in tone depending on which input you connect? (leaving the feedback loop where it is)
Within a channel, if you plug into the high gain jack it's a bit louder than plugging into the low gain jack but the tone is the same. Switching to the other channel input changes the tone considerably, since the channels are voiced differently.
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