Power soak for guitar amp... ideas?

[redrabbit]

I have just reacquired a fantastic valve amp after lending to a mate for a few years... Even better, he revalved it at some point so all in perfect order.

Only problem is that it's a 130w monster, and even on low power setting (22w, I think) it's way too loud to drive the valves to breakup.

I'm now aware that one can buy attentuators to further soak the power, but can only find ones rated to 100w. Might be a dumb question, but if I buy something like a Bugera to put between the post amp and speakers, and only use on the 22w setting, will that be safe?

Or, what about one of those pedals that seem to go between pre- and post amp in the effects loop like the JHS little black amp box?

Any advice / experience regarding either approach would be much appreciated. If I just need a bigger attentuator, recommendations also appreciated (my budget is up to 150 quid).

Amp is a 1980s Peavey Heritage.

[HiAsAKite]

I'd be very interested in the answer to this - I have a similar challenge with a Marshall VS65R I acquired recently - ok, "only" 65 watts, and it only has valve pre-amp stage - but wow does it sound good (compared to the SS amp I was before anyway). But !$!k me its loud! (and its "only" 65W")

So yes - being able to attenuate that to -- frankly anywhere between 1 and 5 watts would be useful. So same challenge as the OP

[franki68]

You can try a volume pedal in the effects loop .

[HiAsAKite]

Have tried that on my vs65r, but (admittedly the vol peddle is part of a multieffects until) cranking up the amp saturated the effects pedal input ... (the input if which i can attenutate on the effects box), but also seemed to lose the valve amp "breakup" sound on the clean channel..
.....ands it that sound as you overdrive the clean channel that sounds so great on it.

Will try again tonight with all effects stripped out (ie effects unit just acting as a vol pedal) to check im not imagining things...



I was thinking in terms of something on the output side to soak up the power, just provide 1/8th or 1/16th of the power to the speaker.

Will try the pedal in case I'm missing something/being dumb.

OP... is use of vol.pedal any use to you? Not sure if there is an fx loop on your amp?

[gazza285]

The Peavey runs its output stage in ultralinear, it is designed to provide clean power all the way up to maximum output, it is not going to give you any power valve breakup, certainly nothing musical anyway.

The Valvestate would benefit from a pot in a box type volume control in the effects loop to give the pot on the front a more useable control at lower volumes.

[HiAsAKite]

Thinking about the above more.. I probably need just a "pure" vol pedal, which i can put in the fx loop without changing the sound/worrying about input saturation etc...

[HiAsAKite]

gazza285 said:

The Peavey runs its output stage in ultralinear, it is designed to provide clean power all the way up to maximum output, it is not going to give you any power valve breakup, certainly nothing musical anyway.

The Valvestate would benefit from a pot in a box type volume control in the effects loop to give the pot on the front a more useable control at lower volumes.

Thanks Gazza.. Will give a go

[redrabbit]

gazza285 said:

The Peavey runs its output stage in ultralinear, it is designed to provide clean power all the way up to maximum output, it is not going to give you any power valve breakup, certainly nothing musical anyway.

The Valvestate would benefit from a pot in a box type volume control in the effects loop to give the pot on the front a more useable control at lower volumes.

@HiAsAKite, Gazza...

The Peavey seems to have solid state preamp and valves in power amp only. So although it does have an effects loop I assume that a volume pedal in there would be no use...would need something between power amp and speakers. But that might be totally wrong.

Gazza, would an attentuator between amp and speakers really gave no effect? Tried to research ultralinear amps, can't find anything intelligible.

[gazza285]

redrabbit said:

@HiAsAKite, Gazza...

The Peavey seems to have solid state preamp and valves in power amp only. So although it does have an effects loop I assume that a volume pedal in there would be no use...would need something between power amp and speakers. But that might be totally wrong.

Gazza, would an attentuator between amp and speakers really gave no effect? Tried to research ultralinear amps, can't find anything intelligible.

Ultralinear valve amps are designed to reduce second order harmonic distortion, so increasing the clean headroom. Your fundamental problem is that you are wanting to hear that distortion, but from an amp that has been designed to reduce it. You can use an attenuator to overload the power valves, but all you will get is harsh sounding third order harmonic distortion.

[gazza285]

HiAsAKite said:

Have tried that on my vs65r, but (admittedly the vol peddle is part of a multieffects until) cranking up the amp saturated the effects pedal input ... (the input if which i can attenutate on the effects box), but also seemed to lose the valve amp "breakup" sound on the clean channel..
.....ands it that sound as you overdrive the clean channel that sounds so great on it.

Will try again tonight with all effects stripped out (ie effects unit just acting as a vol pedal) to check im not imagining things...



I was thinking in terms of something on the output side to soak up the power, just provide 1/8th or 1/16th of the power to the speaker.

Will try the pedal in case I'm missing something/being dumb.

OP... is use of vol.pedal any use to you? Not sure if there is an fx loop on your amp?

The effects loop is too hot for pedals designed to run at instrument level, it is designed for line level effect units, typically rack mounted.

If it is the clean channel preamp that is breaking up, then yes, a simple one pot volume control in the effects loop will act as a master volume to bring that channel down to a more manageable level. If it is a combination of the preamp overdriving the input stage of the power amp section, then you will lose the break up.

I cannot remember the schematic, and it must be twenty five years since I had a Valvestate amp in bits, but I am fairly sure that the clean channel does not use the valve, so any breakup you are getting is from solid state devices.

Edit. I have had a look at the schematic, the clean channel does use the valve, so hopefully using a one pot volume control in the effects loop will give you the desired result. You could also plug a shorted jack into the effects return, and then use the FX blend pot to control the volume.

Edited by gazza285 on Sunday 7th March 16:06

[redrabbit]

gazza285 said:

redrabbit said:

@HiAsAKite, Gazza...

The Peavey seems to have solid state preamp and valves in power amp only. So although it does have an effects loop I assume that a volume pedal in there would be no use...would need something between power amp and speakers. But that might be totally wrong.

Gazza, would an attentuator between amp and speakers really gave no effect? Tried to research ultralinear amps, can't find anything intelligible.

Ultralinear valve amps are designed to reduce second order harmonic distortion, so increasing the clean headroom. Your fundamental problem is that you are wanting to hear that distortion, but from an amp that has been designed to reduce it. You can use an attenuator to overload the power valves, but all you will get is harsh sounding third order harmonic distortion.

Thanks Gazza, that's good knowledge. I'm actually quite happy with it as it is, but had wanted to see what properly 'driven' valves sounded like. Good to have it back either way!

[HiAsAKite]

gazza285 said:

HiAsAKite said:

Have tried that on my vs65r, but (admittedly the vol peddle is part of a multieffects until) cranking up the amp saturated the effects pedal input ... (the input if which i can attenutate on the effects box), but also seemed to lose the valve amp "breakup" sound on the clean channel..
.....ands it that sound as you overdrive the clean channel that sounds so great on it.

Will try again tonight with all effects stripped out (ie effects unit just acting as a vol pedal) to check im not imagining things...



I was thinking in terms of something on the output side to soak up the power, just provide 1/8th or 1/16th of the power to the speaker.

Will try the pedal in case I'm missing something/being dumb.

OP... is use of vol.pedal any use to you? Not sure if there is an fx loop on your amp?

The effects loop is too hot for pedals designed to run at instrument level, it is designed for line level effect units, typically rack mounted.

If it is the clean channel preamp that is breaking up, then yes, a simple one pot volume control in the effects loop will act as a master volume to bring that channel down to a more manageable level. If it is a combination of the preamp overdriving the input stage of the power amp section, then you will lose the break up.

I cannot remember the schematic, and it must be twenty five years since I had a Valvestate amp in bits, but I am fairly sure that the clean channel does not use the valve, so any breakup you are getting is from solid state devices.

Edit. I have had a look at the schematic, the clean channel does use the valve, so hopefully using a one pot volume control in the effects loop will give you the desired result. You could also plug a shorted jack into the effects return, and then use the FX blend pot to control the volume.

Edited by gazza285 on Sunday 7th March 16:06

That makes a lot of sense.. thank you!

[HiAsAKite]

HiAsAKite said:

That makes a lot of sense.. thank you!

Ok- so finally managed to get round to try it. Good and bad news:

1) Putting a shorted cable across the FX return loop does mean that the FX Mix control allows me to run the clean channel volume high, and attenuate using the FX Mix.
- so that's good

2) However - the tone that comes out is crystal clear, clean, and without a hint of an overdriven tube in there... So great for clean tone (but it was great anyway), but not achieving what I wanted to achieve

So this suggests that:
a) the break-up I'm getting on the clean channel when racking the volume up on headphones must be taking place post FX loop (which in theory in theory in the solid state side of the circuit).Which suggests that short of putting an attenuation load on the speaker output, there is little I can do..

Which is not what I expected...

[gazza285]

Checked the schematic.

The headphone socket is fed with a voltage divider direct from the power amplifier output, so yes, you will hear the power amp driver distortion. It is unlikely to be the output transistors overdriving, because that would lead to fairly rapid loudspeaker death.

You could always use a low powered amplifier fed from the headphone jack, then into the combo speakers.

Or just buy a nice pedal.