Question about trainwreck performance....

[redshark]

I've been carefully reading threads in this forum and had a chance at the nashville show to play Orphan Annie and Christine.
I had become a big fan of the TW concept of simplicity and also the great "magic" that this amps deliver in their performance.
The question here is to all the experienced builders.

What is it in the circuit that creates that thing of mean to clean with not a lot of dB's lost?

I had built 2 clones, jtm45 and 5F4 and both of them being single channel amps clean with the volume knob of the guitar but the lost of dB's from dirty to clean is dramatic compared to TW amps.

What is it? transformer? bias of the stages? (preamp/power) more than 3 things interacting together?

Thanks for your answers!!

[funkmeblue]

It's in everything....short signal path......voltages.......that "extra" gain stage......power supply....the simplicity

[paulster]

I think it is a combination of two things.

One is that the gain stages are voiced such that clipping occurs in the PI, power stage and preamp over a comparatively small range of input volume, which means that you don't have to successively wind up each stage in order to get into a high gain lead voicing, it just comes on very quickly.

The second factor is the compression in the power supply, which reduces the volume of the amp by some degree once the power stage starts sucking some current.

As Glen has mentioned long ago and I mentioned a week or two ago, one of the things you can do with an Express (or Liverpool) to hear this effect is to get the gain up around noon, listen to the ambient hiss level and then hit an A or an E power chord and then quickly mute the strings. The hiss level will be well down on what it was, and will then ramp back up quickly.

This is because the power supply is sagging under load, presumably from the screens node downwards (since I haven't measured the voltages on all of the nodes under load), and the 1K screens supply resistor is the likely culprit since it presents a load significantly higher than you'd get if you had a choke filter in there instead.

The Express and Liverpool are designed each as a complete 'system', and Ken did a remarkable job at it.

[geetarpicker]

I agree with the posts above 100%! However I'll add one more detail. When you played my setup at the amp show I was also using old Celestion pulsonic cone G12M 25 watt speakers, and the AC30 ext. cab had original alnico blues. These speakers are also part of the "clean to mean" equation IMHO.

The old G12Ms in particular have a bit of compression when pushed, perhaps a bit more than other speakers I've owned and/or played. My Express on say an EV or Celestion Vintage 30 speaker is more dynamic, but then the dirty tones jump out more in ratio to the cleans. Somehow the old G12Ms smooth out the transition a bit, though I'll admit it's mostly the amp.

Live I use Scumback M75s with two clones I builit, and they also seem to help dail in this effect.

GK

[redshark]

Thanks for the answers guys!!
Keep them coming, I would like to understand this thing as much as posible.
Hey Glen!!
Well that is interesting that you think speakers contribute also. I've heard before that TW amps like low watt uneficient speakers. the only cab I own is an old jcm800 2x12 with 2 G12/65's in parallel.
Have you ever tried or heard a TW with G12/65's? they seem to be a more powerful greenback design.
If anyone tried this speakers with clones also i would like to know your comments about them.

[2tone]

Supposedly Dave Funk verified that the overdrive/distortion occurs first in the output, then the PI, and lastly in the pre amp. Ken had mentioned this too. The connection in distortion between PI and output is the feel factor. The pre amp is more stiff I think.

[jaysg]

This is because the power supply is sagging under load, presumably from the screens node downwards (since I haven't measured the voltages on all of the nodes under load), and the 1K screens supply resistor is the likely culprit since it presents a load significantly higher than you'd get if you had a choke filter in there instead.

Has anyone really looked at this? I'm wondering because, I wouldn't expect B+ to go anywhere...screens maybe. There's all that extra current capacity from the PT when compared to a more typical amp...at 35W, a PT might be rated for 175mA...not 300mA.

[dartanion]

Did we really answer the OP's original question?

"What is it in the circuit that creates that thing of mean to clean with not a lot of dB's lost?"

This I would say it has a lot to do with very little attenuation in the preamp. The absence of voltage dividers that dump gain between stages helps the Wrecks to have a strong enough signal when the guitar is turned down for this effect to work.

[/quote]

[geetarpicker]

This is because the power supply is sagging under load, presumably from the screens node downwards (since I haven't measured the voltages on all of the nodes under load), and the 1K screens supply resistor is the likely culprit since it presents a load significantly higher than you'd get if you had a choke filter in there instead.

Has anyone really looked at this? I'm wondering because, I wouldn't expect B+ to go anywhere...screens maybe. There's all that extra current capacity from the PT when compared to a more typical amp...at 35W, a PT might be rated for 175mA...not 300mA.

Put a meter on it and play the amp. The B+ does sag quite a bit in these things, though % wise not much more than say an old Marshall.

[ontariomaximus]

The screen node can easily drop 40VDC with an hard chord and the volume control at noon.

[redshark]

Glen!!

Have you measured how many dB's of volume you lose with your guitar volume on 10 and then on 3? (express)

also is this dB lost same on the liverpool?

[jjman]

Supposedly Dave Funk verified that the overdrive/distortion occurs first in the output, then the PI, and lastly in the pre amp. Ken had mentioned this too. ..............

I've verified this on my build and it's the key to the original question IMHO. Once the OP is clipping, hitting it harder isn't going to increase the volume much. Just more clipping and sustain. Same for the PI, then for the 3rd stage. On mine:

Control setting ~3 clean and near max volume.
Control setting ~4 dirty OP and basically max volume.
Control setting ~5 dirty OP and PI w/max volume.
Control setting ~7+ dirty OP and PI and #3 w/max volume.

Turning down the guitar volume does just about the same thing as turning down the amp since both volume controls are before any distorting stages.

[redshark]

another question guys, when you build the clones....what is the best electrolytic? I saw on Francesca Mallory but is there a way to get those? If that is not an option now...what do you use? atom sprague or F&T?
also on the tone and coupling caps are those orange drops series 715 or 716? and if not what is in there? anybody tried sozo's?

thanks for your answers!!!

[fishy]

Everyone has there own idea on what is best. As much as I want to do a TW style build justice, ultimately its for me and you do what you want to get it right and within your budget.

If you want to get as close as you can to the original, lay out the money for the Mallory caps but they have become extremely expensive. You can pay in excess of $100 for the cap stack!

I have used Mallory and a bunch of others s and I am hard pressed to tell the difference. Spragues are too big, other than that, I say use what you like.
Some have used cap cans with great success also.

The coupling caps you talk of are PVC Mallory and they are detailed in the bom. These are tricky to find but you can get them. I'm sure people have tried others. Again, use what you like or experiment unless you are trying to make an amp as close as possible to an original.

[Robbie]

I was wondering if anyone has looked at the output with an oscilloscope to see what was going on, eg. sag or waveform collapsing at max output?