Bypassing the power amp

[tmac]

Hi!

I was considering buying a digital guitar amp modeller for silent practice/direct recording (e.g. pod) until I thought of the idea of using only the preamp section of my Express 5:25.

So I would like to try to record the signal from FX send on my Express 5:25, without generating any sound at all from the power section/connected speaker.

Since the FX loop is serial (?) it should be OK to use it as a Line-level output, and thereby bypass the power section? I could still have the cabinet connected to the amp's speaker output as a load to protect the output transformer/power tubes, but there would be no sound, since I have no signal going into FX return, right?

And on a side note: If I _can_ use the FX out and bypass the power amp as explained above, is it even neccesary to have output tubes installed, and the speaker connected?

I just wanted to run this by all of you on this forum so that you could warn me if any of this could be damaging to the amp. Thanks for any suggestions about this.

Torquil Sørensen
Norway

 

[tmac]

I decided to try it, connecting FX send to a line input on my Fostex HD recorder. To break the amp's internal signal chain I had to connect an unused jack to FX return. Unfortunately, it turned out that there was still a significant signal going through to the power amp on channel two. Around speech levels out of the speaker, when the FX send signal was around line level.

But the sound quality of the signal going into the Fostex was quite bad... E.g., there was way too much treble in the overdriven tones. Maybe there is an impedance mismatch problem. In addition, the reverb had no effect on the signal.

I'm now thinking that I would probably be better off with some small digital amp modeller for my silent practicing and silent recording. At least those bean shaped Pods don't take up a lot of space, and they will probably give me something better than this when connecting directly into the recorder.

Best regards
Torquil Sørensen

 

[MusicManJP6]

I decided to try it, connecting FX send to a line input on my Fostex HD recorder. To break the amp's internal signal chain I had to connect an unused jack to FX return. Unfortunately, it turned out that there was still a significant signal going through to the power amp on channel two. Around speech levels out of the speaker, when the FX send signal was around line level.

But the sound quality of the signal going into the Fostex was quite bad... E.g., there was way too much treble in the overdriven tones. Maybe there is an impedance mismatch problem. In addition, the reverb had no effect on the signal.

I'm now thinking that I would probably be better off with some small digital amp modeller for my silent practicing and silent recording. At least those bean shaped Pods don't take up a lot of space, and they will probably give me something better than this when connecting directly into the recorder.

Best regards
Torquil Sørensen

You had the right idea. You'll have to use your FX send to separate the preamp from the power amp signal. But, straight to a mixer is going to sound terrible. It is the raw preamp and needs a speaker and cab to round off the highs and make it sound like you are used to hearing. You can either use a cabinet impulse or a speaker emulator to make it sound better. Reverb is post fx loop (and maybe post poweramp) so you won't get that from the fx loop send. A modeler might be your best bet... and cheapest!