question about amps (probably for mike)

william · Post by **william** » Fri Feb 27, 2009 1:44 pm

of course anybody's welcome to chime in, ive just talked to mike a bit about this stuff.

so, is it possible to add a master volume to just any amp? is it just a pot that limits the overall volume to the speaker, or what?

ive been talking about portable living room friendly tube amps for a while, and the problem always seems to be that even a 5w tube amp is going to be kind of loud, if i want it to break up, so the answer is to get an amp with a master volume. but the ones im liking dont have em, sooo...

lets say i get a champion 600, can i just add a master volume and use the old volume as the gain? in theory i mean. i guess the physiology of the actual amp may come into play, for all i know there is a PCB right behind the control panel that everything is mounted to that would keep me from adding anything.

theres plenty of space on the outside, id probably drill the hole right over the branding section between the knob and the light.

im interested in one of these cheap new amps both for practical reasons (stated above,) but also i would like to get more knowledgeable about amps in general, and this would be a lower risk way to fuck up an amp. i want to learn to modify the electronics, maybe replace the tubes, change the speaker, and retolex the cab, and itd be cheap parts wise on this amp and i wouldnt be fucking up some vintage piece.

thanks! if anybody knows of any gutshots of these amps please let me know!

Reece · Post by **Reece** » Fri Feb 27, 2009 1:50 pm

i don't know the answer but if it was just a simple pot why would people need attenuators?
i'm sure it's more complicated.

i'll get some gutshots of the champ 600 if you like though, i haven't screwed it all back together since it broke.

william · Post by **william** » Fri Feb 27, 2009 2:12 pm

Zaphod wrote:i don't know the answer but if it was just a simple pot why would people need attenuators?
i'm sure it's more complicated.

i'll get some gutshots of the champ 600 if you like though, i haven't screwed it all back together since it broke.

i was kinda thinking the same thing. a master volume and an attenuator arent the same thing though, right? but that doesnt really dissolve your argument...

i would love some gutshots! thanks.

...it broke? what happened?

Fibus · Post by **Fibus** » Fri Feb 27, 2009 2:18 pm

You can change out the speaker or even the tubes fairly easily to make it break up early. Here is a speaker on ebay ( LOINK ) that breaks up early apparently. There are other versions that break up later or around the middle as well.

Also you can get kits which can be used to change how soon the amp breaks up as well ( LERNK ).

I haven't tried either of these myself but from the videos they look ok. I might do one of them to my champ i just got as well.

Sloan · Post by **Sloan** » Fri Feb 27, 2009 2:18 pm

As far as I know Master Volume usually controls how much of the preamp signal reaches the power amp, hence why you can't get power tube distortion with a low master volume.

Guitar > Preamp/Tone controls > MASTER VOLUME > Power amp (big tubes y'all!) > Speakers

An attenuator acts as a speaker load (which your amp needs to survive) and is kinda like a Master Volume AFTER the power section.

Power amp > ATTENUATOR > Speakers

Some amps actually have the power section running full-bore all the time, like the non master volume Marshalls and the Peavey 5150.

Reece · Post by **Reece** » Fri Feb 27, 2009 2:20 pm

some resistors burned out. probably a sign of a larger problem. i think at some point im gonna post it back to rob (progrockabuse, who i bought it from) and he's gonna try and get it replaced from where he bought it to save having to pay for repairs somewhere.

anyway, gutshots, just of where the PCB and stuff is:

Sloan · Post by **Sloan** » Fri Feb 27, 2009 2:25 pm

Here's a good link on installing a Master Volume:
http://people.cornell.edu/pages/mt24/Amp/mm/mvols.html

Power-tube distortion

Power-tube distortion is required for amp sounds in some genres. In a standard master-volume guitar amp, as the amp's final or master volume is increased, more power tube distortion is produced. This is slow-onset distortion. As such a tube (or valve) power amp rated at 50 watts produces 50 clean watts or, when pushed harder, twice as many distorted watts. To make the amount of power-tube distortion independent from the volume heard at the guitar speaker, several approaches are used:

The "power soak" approach places the attenuation between the power tubes and the guitar speaker. This pushes the power tubes to full power and then drains away the unwanted excess power by sending it to a mostly resistive dummy load and allowing only a portion through to the guitar speaker. Some power soak products include the Rockman Power Soak, the THD Hot Plate, the Weber MASS, and the Marshall Power Brake. The power-supply approach places the attenuation in the power supply and power amp; it runs the power tubes at a lower plate voltage and lets the full resulting power through to the guitar speaker. This prevents wearing-out the tubes or blowing the output transformer, and obviates purchasing and transporting a separate, bulky power attenuator. Some power supply attenuation circuits include London Power's Power Scaling and Mojave's Power Dampening circuit.

The Maven Peal Sag Circuit is the only patented power-supply that applies nonlinear analysis to power-supply design instead of the tradition attenuation approach. As a result, the Sag Circuit offers power tube distortion and response control at reasonable volumes, along with other features such as a built-in power conditioner and zero power supply hum. Unlike other attenuation approaches, the Sag Circuit adds power amp distortion and response control to transistor amps as well as tube-based amps.

In the re-amped dummy load approach, the tube power amp drives a mostly resistive dummy load rather than a guitar speaker. The dummy load is typically the internal dummy load inside a power attenuator, with the load selector switched all the way to internal load rather than a mix of internal load and guitar speaker. A line-level signal is tapped from the dummy load, optional signal processing (such as equalization and reverb) is applied, and then the signal is sent through the final amplifier, typically solid-state run only in the linear region, which finally drives a guitar speaker. The guitar speaker contributes complex physical transducer dynamics at a quiet listening level controlled by the final amp, or even more complex dynamics if the speaker is pushed into distortion.

In the isolation box approach, the guitar amplifier is used with a guitar speaker in a separate cabinet. A soundproofed isolation cabinet, isolation box, isolation booth, or isolation room can be used. The guitar speaker and microphones are placed inside a soundproofed space separate from the control room or listening area, such as in a double-walled isolation room in a different floor of a house. A speaker cable runs from the tube guitar amplifier in the control room out to the miked guitar speaker cabinet out in the separate isolated area. The microphone cables then run back from the isolated area back into the control room. Professional recording studios often use this approach to obtain power-tube distortion independently of the listening volume.

~ http://en.wikipedia.org/wiki/Guitar_amplifier

william · Post by **william** » Fri Feb 27, 2009 2:42 pm

wow, good feedback!

zaphod, thanks for the pics. looks like id have no problem drilling right where i speculated.

sounds like an attenuator would be much more useful than a master volume. is the difference just where you put the pot? or is an attenuator actually more complex hardware?

i like the idea of cranking the volume on the amp and then using the guitars controls to adjust the sounds, but if that means uncomfortable volumes in a smaller room/ solo or practice environ then its not really practical. sounds like a master volume wont give me the cranked sounds i want because the power tubes wont break up.

is an attenuator literally just a pot that adjusts the signal going to the speaker itself, and therefore leaving the amp unchanged? because thats exactly what i want.

seems like they do more the same thing, but either before or after the power amp. itd be kinda cool to have a drive, master volume, and attenuator. supreme control!

Post by **Mike** » Fri Feb 27, 2009 2:56 pm

Everyone here has covered it pretty much. A Master Volume can give you gain in the form of preamp breakup, but it's not simple to install, particularly into a PCB amp, and working on them is very dangerous. I would consider myself competant to do it after a degree in electronics and a lot of pedal experience but I would still have a large amount of trepidation in doing it since I don't want to die. I am a clumsy person.

william · Post by **william** » Fri Feb 27, 2009 2:59 pm

Mike wrote:Everyone here has covered it pretty much. A Master Volume can give you gain in the form of preamp breakup, but it's not simple to install, particularly into a PCB amp, and working on them is very dangerous. I would consider myself competant to do it after a degree in electronics and a lot of pedal experience but I would still have a large amount of trepidation in doing it since I don't want to die. I am a clumsy person.

right. this is what i needed to hear.

ill stick to retolexing the thing, and get an OCD or something, i guess.

what about some kind of component that goes between the amp and speaker? is this an attenuator, or a good idea, or a stupid idea?

Reece · Post by **Reece** » Fri Feb 27, 2009 3:02 pm

aye that's an attenuator.

how quiet do you want the thing to be? i played the champ 600 in halls with rooms on three sides and didn't get any complaints. the champ 600 isn't really a dirty amp either, i've never had it up to full without the little speaker distorting but i don't think you're gonna get much drive out of it.

Post by **Mike** » Fri Feb 27, 2009 3:03 pm

That's an attenuator, like the Weber Mass or the THD Hotplate. A lot of people swear by them but they're not cheap and the more you're attenuating the sound the more it is tonally affected by the attenuator, also part of the equation is always raw air being moved by the speaker. You can attenuate a roaring power amp stage down to a whisper but there will still be something missing. Personally I think a Master volume or a pedal is the way to go, I've never been that impressed with the attenuation route.

blacktaxi · Post by **blacktaxi** » Fri Feb 27, 2009 3:36 pm

how much do these champions go for new? here in Ukraine they're greatly overpriced, and for the money you can get a much more useful practice amp.

if you haven't bought one yet, i'd advice you to refrain from the all-tube-mojo and get something with EQ at least. unless you dial this 600 really loud, you won't really feel the "tubeness" of it, at least i didn't. and when it's real loud - without EQ it sounds shit, IMO. if i were getting a little portable practice amp, i'd get a solid state stuff. it's way cheaper (taking into account it at least has an EQ), and the single 6V6 breakage in champion 600 sounds like flabby shit to me.

william · Post by **william** » Fri Feb 27, 2009 4:57 pm

ill go play one and see what i think. its all useless until i know what im dealing with.

they arent expensive at all, i think.

SSSHHHHWOAOAOAOAOAOAO. price just went up. fuckers. 259, yeah, i can get a fucking silverface champ almost for that. i saw a vibro champ at guitarcenter the other month for 349.

they were much cheaper like last month, i think.

anyhow, thanks for the info everyone. its good to know more of the specifics on amp workings in general, they apply to more than just this amp, after all.

i will be going with mikes advice in another of my threads and go with a low watt silverface, and an OD pedal.

fuck fender right now, seriously.

http://guitars.musiciansfriend.com/prod ... D=44097308

Sloan · Post by **Sloan** » Fri Feb 27, 2009 5:18 pm

william wrote: sounds like an attenuator would be much more useful than a master volume. is the difference just where you put the pot? or is an attenuator actually more complex hardware?

An attenuator acts as a resistive load. A speaker is a dynamic resistive load - it's resistance actually changes depending on the signal. This is why some purely resistive attenuators don't sound or feel "good". You can actually make a 'dummy load' with just some large resistors wired together, but it won't be the same, since a speaker responds in a dynamic fashion.

Some of the expensive attenuators emulate a speakers dynamic resistance and also try to makeup for lost 'tone' at lower volumes, probably based on Fletcher Munson curves. I think this is what they call "Frequency-compensation".

vincel · Post by **vincel** » Fri Mar 06, 2009 9:28 am

As Mike said, working on this shit yourself can be pretty dangerous.

Some of you may have heard of this guy. Don't be discouraged by his tendency to go all CAPS ON!! I bought one of his little modded combos a couple of years ago, and I'm still really pleased with it.

vivadeluxxe · Post by **vivadeluxxe** » Fri Mar 06, 2009 11:13 am

blacktaxi wrote:how much do these champions go for new? here in Ukraine they're greatly overpriced, and for the money you can get a much more useful practice amp.

I got mine for Â£90 just after xmas, they've gone up loads since then tho because of the price hike...

I've seen quite a few champs on ebay with the master volume mod and better tubes, but watching a few youtube vids of them, it doesn't make enough difference to be worth the extra money....

paul_ · Post by **paul_** » Mon Mar 09, 2009 2:14 am

The Gretsch Electromatic branded version is still 2 bills yo

http://guitars.musiciansfriend.com/prod ... sku=481874

Same amp

Justin J · Post by **Justin J** » Mon Mar 09, 2009 3:47 am

you could probably just replace the stock 6v6 with a 6k6 (out of production, but you can them nos for pennies). that should considerably lower both the overall volume and the headroom. you probably wouldn't need to alter the circuit except maybe swap out the cathode bias resistor. or if these are adjustable bias, just rebias the amp.