Liverpool: It's alive...HELP!!

Express, Liverpool, Rocket, Dirty Little Monster, etc.

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hans-jörg
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Re: Liverpool: It's alive...HELP!!

Post by hans-jörg »

Hi,
I built a Liverpool 2 holer these days too - also without Presence (because of the post PI MV (LarMar), but WITH NFB. This NFB is necessary with LP! It starts with Vol 3-4 to saturate. At noon I´m on max, over this point it´s almost useless. But its clean until 4 (with single coils) :)
And that's all correct with the LP.
It´s not very usefull to bring it down by decreasing the 150k to ground, or a ecc81 as V1 (except you want a Fender derivate 8) )
Just put there a NFB 100k -47k and you will be happy.
If this don't helps, than I guess you have a Pot grounding problem with Vol or tone stack too (as mentioned above).

Btw. it cleans up perfectly with guitar vol. decreasing.

It´s a hot but sweet amp when you find the sweet spot.

All the best

Hans-Jörg
Last edited by hans-jörg on Fri Oct 31, 2014 5:14 pm, edited 1 time in total.
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JoeCon
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Re: Liverpool: It's alive...HELP!!

Post by JoeCon »

Hans

OK so a 100K resistor from the OT 8 ohm tap with a 47k to ground. And this connects to the point where the tail and cap are going to ground now, yes??

OK I'll try that, but it sounds like the Liverpool is gonna be too much overdrive for me. I'm an old guy who likes some sustain and overdrive but not his much...wow!

Thanks...
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hans-jörg
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Re: Liverpool: It's alive...HELP!!

Post by hans-jörg »

[quote="JoeCon"]Hans

OK so a 100K resistor from the OT 8 ohm tap with a 47k to ground. And this connects to the point where the tail and cap are going to ground now, yes??

quote]

Sorry, but no. Only a 100k or a 47k between 8 ohm. and tail R. Simple a NFB without presence circuit.
Btw. I have a cut control instead of presence.

Hans-Jörg
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JoeCon
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Re: Liverpool: It's alive...HELP!!

Post by JoeCon »

Hans

Aiken says:
The series feedback resistor, in conjunction with the resistor to ground, determines the amount of voltage being fed back. If you want to feed back more voltage, you make the series resistor smaller, or the shunt resistor larger, or you use a higher impedance tap on the output transformer.

So you need two resistors.

Also
In one case, the result will be a non-inverting amplifier, where the feedback resistor is connected from the output of the amplifier to the "other" side of the phase inverter (not the side with signal applied to it). The gain set by the ratio of the feedback resistor and the resistor to ground from that input. The input impedance of this type of global negative feedback amplifier is very high, so it won't load down the circuit driving it.

So the input for negative feedback has to be the cap, C11 and tail R11 on the PI side not coming from the preamp, yes??

Anyone??
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RJ Guitars
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Taming the Liverpool

Post by RJ Guitars »

Joe, I strayed from the standard layout on a couple Liverpool variations and for an amp that was designed on the edge of stability, it can be tricky. I eventually found the tools to troubleshoot and find the problems but it was a journey down the river of pain before I got it sorted out. I worked on it, on and off over a couple years. http://ampgarage.com/forum/viewtopic.php?t=11528 Skip to the page three if you want to go straight to the "fix" that finally tamed the beast.

I found that on the O'scope you could see that the phase inverter was getting the fire knocked out of it long before I had the amp or guitar turned up much at all. The signal quickly went "Abby Normal" and the amp sounded perfect for expressing maniac rage in a punk metal band, lacking useful volume range for anything most folks would call guitar music. Most of my fix came in the changes I made to the PI section, but I decided to keep going and try a handful of other taming tweaks after that.

In addition to the resistor swap that Richie mentions, the changes I made systematically tame the various sensitive and problematic sections of the amp... ultimately I think I took it too far because this is now an extremely good sounding well behaved amp... but it's not as wild and merciless as the other pools I've been around. I learned from this effort that there are a lot of subtle instability issues that you can tame if for no other reason so you can go after a bigger problem. Lemme know if you try any of this stuff... I found it in the archives here of TAG - much of it provided by many of our forefathers that don't post much any more
Last edited by RJ Guitars on Fri Oct 31, 2014 7:42 pm, edited 1 time in total.
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JoeCon
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Re: Liverpool: It's alive...HELP!!

Post by JoeCon »

rj

will check that out. But yes I have a thrash metal punk band amp now....
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Re: Liverpool: It's alive...HELP!!

Post by RJ Guitars »

JoeCon wrote:rj

will check that out. But yes I have a thrash metal punk band amp now....
Stuck my foot in that nicely I did...
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JoeCon
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Re: Liverpool: It's alive...HELP!!

Post by JoeCon »

Well who would have thunk it. A simple resistor can make such a difference!
I tacked in another 100K over R7 for a 50K total and the "Pool is playable!" Still wild but not untamable. Still very very bright but some cap changes can help with that.
Now when I crank the volume back it cleans up nicely and when wound out to 10 screams! Yes this is NOT a Rocket...wow.
Still work to do but this got it into the ballpark. Thanks to all and especially Richie for the help.
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Richie
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Re: Liverpool: It's alive...HELP!!

Post by Richie »

If its a little bright, you can replace the .002 with a .003, or .0039 or .0047.

or just tack another .001 or .002 across the cap you already have there.

this should take the brightness off the top, and thicken it up some. but still have treble if needed.
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gktamps
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Re: Liverpool: It's alive...HELP!!

Post by gktamps »

JoeCon,

Richie's tips are spot on, so keep them in mind if you want to keep tweaking your amp. I bought a Liverpool from him and asked him to dial down the wildness, and these are the steps he took to do the job. The amp is a joy to play, and still gets as hairy as I ever want it to be.

Cheers,

Greg
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Re: Liverpool: It's alive...HELP!!

Post by RJ Guitars »

gktamps wrote:JoeCon,

Richie's tips are spot on... Greg
I concur as well. The Liverpool is so aggressive that even with the mods it will tear your head off when you dime the guitar and dig in with your pick. I used those same resistor and coupling cap values on both my little 2 hole EL95 powered LP's with great results.
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JoeCon
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Re: Liverpool: It's alive...HELP!!

Post by JoeCon »

Gentlemen,

This is only my 3rd build from scratch and the first where I have really tweaked after the initial build. My Rocket and Rockster were right on first time.

This Liverpool is a real learning experience and I appreciate the great advice and problem solving you have provided me. That is what makes this site so good, you can learn so much here from excellent knowledgeable builders. And for me learning from you guys is what it's all about.

So Thank You and I'll let you know how this turns out!
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hans-jörg
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Re: Liverpool: It's alive...HELP!!

Post by hans-jörg »

JoeCon wrote:Hans

Aiken says:
The series feedback resistor, in conjunction with the resistor to ground, determines the amount of voltage being fed back. If you want to feed back more voltage, you make the series resistor smaller, or the shunt resistor larger, or you use a higher impedance tap on the output transformer.

So you need two resistors.

Anyone??
Hi, for sure you are right. I have there a 4k7 resistor to ground from this junction. I took a look at weekend.

sorry for confusion.

Best
Hans-Jörg
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JoeCon
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Re: Liverpool: It's alive...HELP!!

Post by JoeCon »

OK
So the plan this week is:
try a 47K in R7.
a .004uF in C8,
lower gain V1 tube like 5751,
disconnect bright switch,
check grounds on pots...
Get "the beast" under control.
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JoeCon
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Re: Liverpool: It's alive...HELP!!

Post by JoeCon »

So is C2 in the Liverpool 50pF or 500pF?? I see two layouts with different values there...
And both the Express and Rocket have a 500pF there. Hmmm.....
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