Using a head as a poweramp

[James C]

Hello,

I've been looking at some rackmount preamps and have been wondering how to run them using a valve head as a poweramp. would i just need to run it through the effects return input of my amp?

would this then bypass the preamp of the amp (i.e. would it be just channel volumes that affect the sound, not gain and bass,mid,treb etc?)

would there be anything else i'd need to be aware of?

cheers

James

[Dmoney]

depends on the amp,

you need the amp schematic and to look where the loop is in relation to other controls. usually its after any EQ i think, but can also bypass master volume controls. presence controls are usually not bypassed but thats probably because they work using negative feeback from the powerstage, although im not sure they actually work if you us an outboard preamp

some amps have the master volume before the FX loop, so youd bypass that. you'd also bypass channel volumes.

some amps have fx return level controls, but i think you'd be controlling volume using the output level of the preamp.

i think some amps have FX loops built for certain levels. mic and line level effects. that might cause an issue?
i guess someone who knows a lot more than me will pipe up soon.

ive slaved heads together before, but not done what you're suggesting.

[jpfamps]

This should work fine.

Most fx "loops" are actually inserts after the preamp and before the power amp.

You may need to be careful of your gain structure, however this should be common sense.

The master volume of the "power" amps may or may not work depending on where it is in the circuit. A conventional presence control will still work though.

[James C]

cool, thankyou for the info guys

[Antag]

Yep, I've done this on both my Mesa Rectifier & my Engl Savage - for both those amps the Master Vol still worked...

[hunter]

I've had great results doing this with the Shiva and the XTC. In both cases, Master and Presence were still working.

I always found this to be punchier and fatter than the VHT2502 I have. I guess heads have bigger transformers and therefore bigger tone than it could be possible in a 2U rackmount.

[pagan7]

I use less celubrious kit than most here seem to but my rig consists of a Digitech GNX3000 guitar workstation, stereo out into the stereo effect returns of my Marshall AVT275 which has stereo power amps.
Master volume and presence still work and I have the 20db effects return gain switch set off and control the gain into the power amps with the output volume control on the GNX. Works great - for me  8)