Express with Variable Voltage Regulator

[UR12]

There has been experiments with adding Power Scaling to the Express in the past. I think Der Stever and Fischerman have both tried it with varied results. Glen and a few others have 'expressed' opinions on the matter. It seems the common belief is that it takes something from the amp. The one thing I haven't seen is anyone try and scale the whole amp instead of just the power section. Please correct me if I am wrong and I would love to hear anyone's comments on the matter. I tend to think that while that approach may not give you additional tonal control possibilities, scaling the whole amp keeps everything intact as far as the way the stages interact with each other, gain structure and balance. I'm not saying it's perfect, just different. Another draw back is that additional components have to be added to prevent DC leaking onto controls during periods of very low voltages. I don't like adding things to the signal path, but in tests with other amps including a 15w version of a Liverpool I could hear no degredation in sound with my ears. This will be my first attempt at an Express so any input would be welcomed.

I have the build under way and have came up with a layout that keeps everything component wise as close to stock as possible. I did replace the Stack o caps with a couple of JJ cap cans. I will also be using my board instead of KOCs kit so I guess I can't call it power scaling.

Here is a few pics of how I layed out the amp to make room for the VVR board.

[skyboltone]

Express looks good Dana. Are you close to releasing the scaleing product yet?

Dan Hall

[harryk]

I bought a VVR fixed bias kit from Dana to my Express but have not had time to install it yet. I am very interested in to see Dana`s solution for Express. I made one VVR with cathode bias configuration to one single ended small tube amp and scaled whole amp. It worked fine but I had to add one capacitor (some 22nF?) to input because of scratch sounds when turning guitar volume pot. Regards Harry

[jaysg]

Dana,

Correct me if I'm wrong...the biggest gripe coming from whole amp scaling is that the preamp supplies drop so low that a normal guitar level signal will overload the first triode? I've seen schematics where people use a diode instead of a resistor for the cathode RC pair. It makes some sense to me, but I've never experimented with it to see if I could even tell the difference.

Could a fixed biasing some of the triodes help? It seems like you'd probably want to use Schottky diodes. Dunno. Could also be altered from a panel switch.

[Ron Worley]

Man Dana, that looks really nice, you are one smart fella...

I will be very interested to see how this works out... I finally got my Express running today and biased. I agree you either need an AirBrake or something like this to make the Wreck usable in a non large club environment....

This puppy is LOUD.....

Ron

[UR12]

Express looks good Dana. Are you close to releasing the scaleing product yet?

Dan Hall

Hi Dan

I have been selling it to anyone who wants to contact me by PM or email. I haven't really done any advertising yet and don't know at this point if I did advertise if I could keep up with orders, so I may just continue to let word of mouth do it's thing for a while

I bought a VVR fixed bias kit from Dana to my Express but have not had time to install it yet. I am very interested in to see Dana`s solution for Express. I made one VVR with cathode bias configuration to one single ended small tube amp and scaled whole amp. It worked fine but I had to add one capacitor (some 22nF?) to input because of scratch sounds when turning guitar volume pot. Regards Harry

Harry
I was hoping you would have yours done first so you could help me get mine going

Dana,

Correct me if I'm wrong...the biggest gripe coming from whole amp scaling is that the preamp supplies drop so low that a normal guitar level signal will overload the first triode? I've seen schematics where people use a diode instead of a resistor for the cathode RC pair. It makes some sense to me, but I've never experimented with it to see if I could even tell the difference.

Could a fixed biasing some of the triodes help? It seems like you'd probably want to use Schottky diodes. Dunno. Could also be altered from a panel switch.

You are right about the guitar vol over driving the preamp tube. Usually you can just roll back a little on the guitar and compensate. I also have a limit set on my board so that you can’t go below 10% plate voltage. So if you were running 400VB+ then when you have the power level all the way down you still have about 40v left on the plates. The amp will still get whisper quiet but you won’t drop so much that you overdrive the front end of the amp. I am sure if you had some really hot pickups you might have to adjust it to 15 or 20% but that is something that can be tweeked. Diodes IMHO aren’t suited well for this kind of application because as soon as the voltage drops low enough for the cathode voltage to drop below .6v then the diode will not conduct any more. You would also want probably 2 or 3 diodes in series to give you 1.2 – 1.8 v bias when running normal voltages. .I have found that .6v also seems to be the point where the grids start to leak DC onto the controls.

Having said all of that I haven’t really tried fixed bias on the preamp tubes so maybe I’ll give it a go on this amp after I get it finished and see what happens.

Man Dana, that looks really nice, you are one smart fella...

I will be very interested to see how this works out... I finally got my Express running today and biased. I agree you either need an AirBrake or something like this to make the Wreck usable in a non large club environment....

This puppy is LOUD.....

Ron

Yep. These things are louder than crap which is one of the reasons I wanted to experiment with an Express. That is one of the biggest complaints I hear about the Express is that it is just too darn loud. I have used my board on a Liverpool inspired amp (15w combo) and also on my combined Rocket/Liverpool amp and it works great and retains a lot of the tonal characteristics of the amp at very low volumes. I did the whole amp on all of my builds and I really prefer this to the 2 control, only power tube, setup. If everything goes right, I should have the amp done by next weekend and we’ll see how it goes.

[nickt]

Looking forward to the finished product Been holding off finalising my layout until I receive the VVR board. Might just pinch yours since mine's giving me headaches

One question: you've used the two JJ's before in place of the "stack-o-caps (TM)" - what do you do about the inability to put the screen cap and the preamp caps to separate grounds (ie does it make a blind bit o'difference) ?

thanks
Nick

[UR12]

One question: you've used the two JJ's before in place of the "stack-o-caps (TM)" - what do you do about the inability to put the screen cap and the preamp caps to separate grounds (ie does it make a blind bit o'difference) ?

thanks
Nick

So far, it hasn't been a problem on the EL84 amps where I have used cap cans. I haven't noticed any difference in tone with my ears. All of the caps ground to the same point in front of the stack at the bleeder resistor lug. I will have a seperate wire for the OT plates and the rest of the amp. I have also had to go from 2x 40uf caps to 2x 50uf on the first cap. The other can is a 40/20/20/20. If you could find a dual 40uf cap can you might get a little closer to the real thing.

[Richie]

I have an amp here using the VVR2 and it is a somewhat Concorde modded amp,50 watts.. and i put a low profile heat sink on the side.
The VV2 works very good in this amp.

[Fischerman]

I used the old version of Power Scaling where you have a Fixed B+ and a Variable B+. I originally built it such that I only scaled the power tubes and had a post-PI MV...then later I tried also scaling the PI and used a simple 1M-A pot before the PI for a MV (like a Marshall JCM800 MV). I preferred only scaling the power tubes...you could get very similar tones but I thought ease of operation was better scaling only the power tubes. Also...some of the 'extra' tones you get with power scaling were much better when only scaling the power tubes.

FWIW, IMO the power scaling on my amp works beautifully. I can get the amp to sound very close to the cranked tone at much, much lower volumes. I can't really get the feedback but my amp doesn't feedback very well anyway...it's just a 'bad' Express (or was...it's now more like a 'bad' Concorde and is only marginally better than before...if that). The 'problem' is that I just don't care for the tone of my amp...but it doesn't matter whether I crank it or use the power scaling since it sounds essentially the same either way. On my amp the bias tracks beautifully and I even got lucky in that the Scale control and MV 'track' each other very well. That is, put both on 10 and you have the full volume...put both on 5 and you have the same amount of power tube distortion relative to PI/preamp distortion just quieter. Just set the MV to about the same setting as the Scale control and the gain structure is essentially 'stock'. I was so pleased with all of this...but the tone (at any volume) just doesn't do a thing for me. Very frustrating...I was kinda proud of it except for that and I've piddled with it quite a bit (to the point of having to build/install a completely new preamp board...still sucks).

As far as scaling the whole amp...I've never tried that. Just from my own intuition though...it seems that part of the beauty/charm of an Express is controlling the amp via your guitar volume control (something I'm not very good at). So if you have to 'only turn up to 7-1/2 and never more' to get your cranked tone...it just seems very demanding on the player but again this is something I'm not very good at. You'd think that you would want to just be able to reach down...quickly twist that volume knob full clockwise and let her rip...instead of concentrating on turning up to exactly 7-1/2 or what ever. So I would guess that if you're going to scale the whole amp you'd want some sort of buffer/attentuator/doohicky somewhere between guitar and input triode such that you can use your guitar volume like normal.

Dana you build beautiful amps and I'm sure yours will come out much better than mine and I'm anxious to see your results...those are just my random thoughts and limited experience.

One last thing...I had no clue about how much heat the MOSFET would generate nor how much cooling was necessary...I did not install my MOSFET where you are just because since I was using the chassis as the heat sink I didn't want any heat from the power tubes to possibly interfere with heat dissipation. I installed mine on the sidewall near the power switch (using the insulator just like your pic but no added heat sink). I can feel the heat from it when running and it does get warm.

Oh yea...love the cap cans! Never liked that stack-o-caps.

[Fischerman]

oops double-post.

[UR12]

Hey Fischerman

Thanks so much for sharing your thoughts and experiences. I really appreciate the input form someone who has been there, done that. The TW amps are really something of a monster in that they are “On the verge” as most people say. I do like the tone of these amps and especially the Express. In the hands of the right players they sound awesome and can make chills run down your spine. If I can keep that kind of tone and quiet down the amp I will be a very happy guy. The experiences that you have shared with us have given me more hope and now I can’t wait to get this thing done to see what she sounds like.

The “Scaling the whole amp” thing doesn’t really affect the way your guitar vol works until you get down to the very lowest of vol settings. By limiting how low the amp can go (10% of full vol) it really isn’t an issue unless you have some really hot pickups. If you are running your power at 1/2 – 35 watts you still have all the control of your guitar vol knob that you would if you had the power control set to full. It is only an issue when you get way down into the ½ watt and below range. It’s not like you have to play at 7 ½ instead of 10 above ½ watt. Once you get down that low you are probably going to be adjusting more than the vol as you will probably have some highs roll off , speakers not moving enough air, etc, etc.

The heat thing is always an issue. I have a couple of thoughts as to how I am going to approach it. I have a heat sink that I am going to install and in addition, I was thinking of installing a shield between the power tubes and the heat sink, not unlike the one in a Hiwatt. You’re right on the bubble with a 35 watt amp. I don’t usually add a heat sink on my 30 watt builds but the 35 watt to 50 watt requires them. The heat sink that Richie posted pics of in the previous post does a good job on that 50+ watt amp. I took an old car stereo amp, that the cabinet was basically one big heat sink, and cut out a portion to fit on the side of the amp. I have also been collecting heat sinks from some old computers to see if I can adapt one of those. These are ones that are passive and do not have the fans on them. I’ll post some more pics as I go along.

[Fischerman]

The TW amps are
really something of a monster in that they are “On the verge” as most people say.

I remember Bruce Collins mentioned once that in discussions with Kenny, Kenny had mentioned that he had 'tried everything' in attempts to stabilize some of these amps. Maybe that's the problem with mine...either it's unstable (ultrasonically) or it's too stable. My amp is quiet regarding noise, no hum, gets very loud and doesn't overheat or anything, no 'bumps' in the volume control (like you get when an amp goes unstable sometimes) and I can run it full up with treble full up and it doesn't seem to mind. It's always 'behaved' quite well...until you listen to it.

[billyz]

Dana,
Thanks for the fast delivery of the VVR! It is a thing of beauty. The Circuit board and workmanship are superb.
I have not had to time implement it yet and will be watching to see what others think is the best approach. The whole amp or just the power amp side.

I am curious about the way you limited the voltage drop. Sounds like a good idea.

Oh, and great looking build , I like the way you are using the Can caps, really opens up some real estate. And , actually looks better than the gooped glued down caps, easier to service in the future too.

[drz400]

I have done scaling a few times
Not on a wreck but a beefy plexi style circuit.
Personally I didnt care for scaling the whole amp, it sounded too fuzzy too quick. After trying every possible combination, phase and power tubes, whole amp, just power tubes, tried PPI master of every type. The best tone to my ears was a Pre phase master and scaling the power tubes only. I almost figured it wasnt worth it until I tried that. This was with a London Power kit circuit. YMMV