Power Scaling is Flawed?

[mooreamps]

My circuit is not too complex. It does not require FET's.
I figured it would only be a matter of time until someone else fiqured out how I do it, until I read all the feedback from the "gurus" on 18 watt.com. I guess I'm just not ready to release it into the public domain. It would be a very good project for you if you really understood how power tubes work.

-g

[Steve Conner]

That's neat if you figured out how to do it without MOSFETs or transistors or whatever. The complexity of the FET type circuits might give me a nerdy kick, but I think it turns a lot of homebrewers off.

The only power scaling idea I could ever think of was just to use a power MOSFET as a variable voltage dropper. Just the same as a classical linear voltage regulator, except you don't want it to regulate, just drop a fixed voltage, because sag is good.

Matamp once made an amp with a separate filament transformer and a mini Variac built into the cabinet.

I think someone (KOC?) once experimented with using a solid-state regulator on the AC input to the power transformer, which seems a bit weird. Maybe they used a triac in a lamp dimmer type circuit, but surely that would cause loud buzz.

Finally, maybe if you only scale the bias, along with the voltage to the power tube screens, you can simplify the circuit and get by with smaller MOSFETs if you're using them. The screens more or less control the power output of the tubes, and I believe the sag characteristic of the screen supply accounts for a lot of the dynamic feel of an amp.

[mooreamps]

Well, let's say for sake of arguement, I'm just a home brewer whaking and hacking on a VJ chassis. Here's a clip of how my circuit works. When the power tubes are dialed down, it's certainly very easy for my pre-amp to over-drive the power tubes.

http://www.youtube.com/watch?v=gq-pn-LlQM4

-g

[Amp Kat]

Hey that's pretty cool Gary and sorry for the rant but I think we just didn't know you but if you have a good design there I would try to keep it a secret too because as I said below it's pretty competitive right now.

[mooreamps]

Hey that's pretty cool Gary and sorry for the rant but I think we just didn't know you but if you have a good design there I would try to keep it a secret too because as I said below it's pretty competitive right now.

Thank you for the vote of confidence. I think it's a clever implemetation given the circuit can be done with a handful of common parts that just about anyone can do, including the big boys....

This weekend we take the model-18 and my Raptor 2x12 to the state fair for a live gig. We'll see if the crowd likes it or not.

-g

[tbryanh]

Hey that's pretty cool Gary and sorry for the rant but I think we just didn't know you but if you have a good design there I would try to keep it a secret too because as I said below it's pretty competitive right now.

Mooreamps said:
"Well, as long as I don't see my P/S circuit displayed, then I have no problem with it."

If he wants to keep a trade secret, that is one thing, but he was threatening everybody. Thats what caused the rant.

[Tom Phillips]

Mooreamps said:
"Well, as long as I don't see my P/S circuit displayed, then I have no problem with it."

If he wants to keep a trade secret, that is one thing, but he was threatening everybody. Thats what caused the rant.

Wow. I think that's reading too much into the statement. It didn't sound like a "threat" to me.
Now if he would have said "..., then I won't be responsible to what might happen to you some dark night when you're loading your car behind the bar after a gig." THEN I'd take it as a threat.

[tbryanh]

Wow. I think that's reading too much into the statement. It didn't sound like a "threat" to me.
Now if he would have said "..., then I won't be responsible to what might happen to you some dark night when you're loading your car behind the bar after a gig." THEN I'd take it as a threat.

Threatening in the way of suing in court for patent infringement. If he wants to be the next Randall Smith, that's his business. I would just appreciate it if got his start some other place.

[Tom Phillips]

Threatening in the way of suing in court for patent infringement. If he wants to be the next Randall Smith, that's his business. I would just appreciate it if got his start some other place.

Sorry. I missed the message where he threatened to sue anyone for patent infringement.

[tbryanh]

My apologies to everyone, especially to Gary Moore of Mooreamps. As far as I know, everyone is welcome here, and new members are very important.

[mooreamps]

My thoughts were, I would have been dissapointed if I uploaded my prints on to a public forum, and then see my circuits mass produced on an amp featured in a store like "musicians friend" or on EBay. I have no problem sharing my ideas with others provided they give me "honest" feedback. The concepts are simple enough they would be a good fit into the very cost and dollar driven designs of my competitors.

-g

[Steve Conner]

Oh, well if you want to discuss it off the forum, that's cool. I'd be very interested to see your design. How do you know I don't work for Peavey or Crate though?

[mooreamps]

Well, I guess that's a chance I'll just have to take. After I retire, I may end up in your neck of the wood's anyway. My family comes from the southern part of Ireland. If your willing, I'd consider sending you a parts kit for eval. Hit my e-mail if you want to talk off-line.

-g

[Tiago]

I think that the goal of power scaling is not really give "that" tone (whatever that means) at low volumes. It is to turn a high power amp into a low powered one. There are things that just cannot be simulated, like the "feel" on my back of a 100W amp pushing and pulliing air, the relationship of the response of our ears to different frequencies in different SPL's, etc. So unless you process a lot the sound after it comes out of an amp, it will be nearly impossible, IMHO.
Before I could afford TUT5 I did my own power scaling circuit, I would be very greatfull to release it to the community if there is some interest.

So, here goes the description of the circuit:
The B+ reducer circuit is based on a power mosfet. Simply the voltage on its gate is buffered (drops the usual G-S voltage) by the mosfet. That reference voltage is different from KOC one. In place of a high power HardToFindExpensive potentiomer, I used a small one just making a variation bettween 0.7 and 50V (something like that) and after that it is amplified by other circuitry to match the required voltage ranges.
Yes, it is very complicated, but I just can't sleep knowing that somewere in the world is a pot with 500VDC in it.
That circuitry would fit virtually any amp without modification. It could change B+ between almost full B+ to some 60V.

Now the bias voltage automatic adjustment is done simply with a tracking bias supply. With a voltage divider from B+ to V- gets then amplified in the desired proportion (adjustable by a trimmer) and then buffered by a darlington. Something that I learnded is that the amplifier stage shlouldn't be linear as when the B+ is reduced, the V- should be increased exponentialy, so some nonlinearity is needed, but thats easy.

I've also done my version of the power sag, but it didnt work well, so it's just not worth do it.

[mooreamps]

We did the gig in San Mateo with the model-18 amp driving a 2x12 Raptor cab. We'll post the video clips on YouTube shortly. Since the cag was mic'ed for the PA, these are the settings Mke used on the amp :

Pre-amp gain = 25%
Bass = 75%
Treble = 10%
Master Vol 6L6 = 40%
Master Vol EL34 = 0 %
Power Brake = 25%


-g