Trainwreck Liverpool

[Leevi]

I'm finalizing a project of Trainwreck Liverpool clone and have to say that the amp is extreme loud.


http://el34world.com/charts/Schematics/files/train_wreck/trainwreck_liverpool.pdf


I even tried the preamp without the extra amplification stage (1/2 12AX7) and the amp is still too loud.


Would like to hear your experience what you have done in order to get the loudness under control.


/Leevi

[sluckey]

This amp is supposed to be loud. There's a special knob you can put on the volume control that will allow you to set the volume to whatever you want.   

Maybe a master volume mod is what you need. Maybe VVR is an option.

There is a lot of discussion about this amp over at The Amp Garage. In fact, there's a whole forum dedicated to Trainwreck amps. I don't follow that forum but if I ever build a Trainwreck I would definitely take a look.

[kagliostro]

Ciao Risto









Franco

[Leevi]

I'm prepared to add a master volume but have not decided yet which type.

Since there is so much gain another challenge is to keep the background noise low.
This time the hum is not a problem;)


Leevi

[Leevi]

Hi Franco,


It seems that the type 1 and 2 are PPI Master Volumes, type 3 is a cross line master volume.
IMO type 4 cannot be applied in Liverpool since there is a volume control after treble.


Leevi

[kagliostro]

May be you are interested on this

http://ampgarage.com/forum/viewtopic.php?f=1&t=30062&p=370679&hilit=master#p370679

Ciao

Franco

[pompeiisneaks]

I'm in the process of building a Liverpool as well, and the La Mar PPIMV seems to fit perfectly in this build, but I'm not planning on trying it yet at least.  I seem to recall reading somewhere in the ampgarage forums that a MV in the Trainwrecks seems to alter the tonality quite a bit, and it's best to use an attenuator.

~Phil

[zendragon63]

Levi, these circuits are loud presumably due to concentrating the power on the mids and higher. Unless you have a venue for that amount of sound pressure, there is a lot of liberty that can be taken with master volumes, VVRs, and attenuators.

FWIW, I did ECL82 version and implemented a VVR style on the PA and PI, added a master volume before the PI. And made it where I could switch the clipper stage in or out--because I wanted access to a cleaner tone--and it is still plenty loud. The addition of the VVR only on the PA and PI doesn't allow the voltage to sag much at all in the preamp tubes and arguable takes a bit of the 'Trainwreck proper' bloom and magic out but most of that great tone is still there and is manageable around the house.

Yep, Amp Garage is THE place for everything Trainwreck. Regards

dennis   

[Leevi]

Some notes so far:


1. Master


I ended up to a traditional master before the PI. I selected 500KA instead of 1MA.
I also tried PPIMV which is OK as well but I noticed that it doesn't work pretty well
before postion 12 o'clock. Maybe that is a common issue with NFB amp?


The cross line master didn't work well.


2. Presence control


IMO 5KB works much better than 25KB.
In order to avoid oscillation it's better to place the 100K resistor close to the output jack
and use a shielded wire.


3. R7


I decided to use 68K. I made the C8 using parallel a ceramic and poly cap (as in the original one)


4. Power amp cathode


I divided the cathode in two parts as stated in some schematics of the Liverpool.
That makes it possible to drive the amp with two power tubes. I use 150 Ohm resistors
which set the cathode current to 35mA.


Leevi

[kagliostro]

The cross line master didn't work well.

The same assertion is present on the link I posted, seems that the better result are with type 2 (sometime also used in junction with an attenuator)

I divided the cathode in two parts as stated in some schematics of the Liverpool.

Good Idea, why push with 4 tubes if you have enough with only a pair

On VOX AC30CC2 they olso have a resistor in parallel with the standard resistor (with a switch)  that increase the cathode resistance to tame a bit the output power

Franco

[HotBluePlates]

I'm finalizing a project of Trainwreck Liverpool clone and have to say that the amp is extreme loud.

I even tried the preamp without the extra amplification stage (1/2 12AX7) and the amp is still too loud.

I don't know anything about Trainwrecks.  However, watching the video below, I always had the impression that linear-taper volume pots were being used.  The stock amp has no master volume, but distorts by 9:00 on the volume, even with a Strat.  That tells me high signal level & output tube distortion was the point.

The player always has their guitar volume control to dial back the volume.  Shrinking the output stage to 2x EL84's would also seem to make sense for a lower-volume Trainwreck.

I don't think these amps were ever intended to be used anywhere other than stage & studio.  If you change it too much, when does it cease being a Trainwreck?

Liverpool Demo

[kagliostro]

If you are still on the try path, you can give a try to PPIMV using separated pots instead of a double pot with single shaft

and feed a pair of tubes with one pot and the other with te other pot

or, as suggested a long time ago from Geezer, a DPDT switch to mute a pair of tubes

I don't remember well, but seems to remember that muting a pair of tube instead to disconnect it using a cathode switch

didn't alter the reflected impedance request from the power tubes




However the best way to have low power and preserve the tone, seems to be a VVR (PI + Power Tubes, no preamp, in junction with a PPIMV)

Franco

[Leevi]

If you are still on the try path, you can give a try to PPIMV using separated pots instead of a double pot with single shaft
and feed a pair of tubes with one pot and the other with te other pot

I think I will still try the PPIMV with dual pot since the preconditions have changed after my last try.

I don't remember well, but seems to remember that muting a pair of tube instead to disconnect it using a cathode switch
didn't alter the reflected impedance request from the power tubes

My idea with those double cathode resistors was that when I remove 2 tubes I have to compensate the impedance for instance
by changing the 16 Ohm load to 8 Ohm output.

When using the traditional master there must be an extra cap before the pot to eliminate DC from the plate.

If you change it too much, when does it cease being a Trainwreck?

My idea is to keep it close to Trainwreck as much as possible, actually the master vol is the biggest change I thought to do.

/Leevi

[Leevi]

I installed the PPIMV back and have to say that it works better.


With the previous traditional master everything was under control but you lost something
which is characteristics for this amp.


This amp is for players that must be able to use volume controls of the amp and guitar.


/Leevi

[kagliostro]

Which was your winner choice ?

Type 1 or type 2 ?

Franco

[Leevi]

Which was your winner choice ?

Type 2, I use this with cathode biased amps.


Type 1 is a must with fixed biased amps but works also with cathode biased amps,
but I was not interested to add extra caps there.


/Leevi

[kagliostro]

Thanks Risto

Franco

[Leevi]

It seems that the master volume type 2 is probably not the best choice.


When setting full preamp volume and low master the signal starts to block (blocking distortion?).


I changed the master to type 1 and situation improved a lot. One way might be to increase the grid stoppers on power tubes?


/Leevi

[kagliostro]

I don't know if this can solve your problem

however this arrangement solves bandwidth problems



The function of the 33k to 100K resistors (value to be determined for each different circuit) is to avoid frequency problems

(not a very difficult mod to be tried)

Franco

[Leevi]

Thanks for your fast response Franco.


I tried that but unfortunately it didn't help.
I'm not any more sure if it's question about blocking distortion.
The disturbed tone (like a fart) comes with a delay (<1 sec) after you have picked and let the note sound.
Might also be some oscillation issue?


/Leevi

[Leevi]

Here is a sample where you can hear the distortion:


http://www13.zippyshare.com/v/8BmzBh8E/file.html


/Leevi

[Leevi]

The problem has nothing to with the master volume type.
It's a pure oscillation issue and depending on how the signal wires are wired around the master vol pot.


/Leevi

[kagliostro]

Can you try a shielded cable to connect the MV pots ?

Franco

[Leevi]

Actually the root cause was that the PI input cap was too close to the wires going to the dual PPIMV pot.
I have learned that the PPIMV wires must be well twisted or shielded. Since there is huge gain
in the preamp the signal absorbed to PPIMV wires on higher preamp volume.


/Leevi

[kagliostro]

Actually the root cause was that the PI input cap was ..........

May be this ??


http://el34world.com/Forum/index.php?topic=11427.0


Franco

[Leevi]

Might be, interesting topic. Anyway I already changed the layout there which solved the problem.
/Leevi

[kagliostro]

Good 


Franco