Peavey transtube fex output not driving amp to full volume

[Richard Keller]

I have a Peavey Transtube Fex connected to a Peavey Dpc amp that will not drive the amp to full volume. I have an Emmons D10 going into a Hilton vp, then into the Transtubefex , then into the amp. With everything at full volume the amp is loud in a small room, but no where near full volume on the amp.
If I run the output of the Transtube Fex into a mixer and boost the signal then run into the amp, it will go to full volume.
Has anyone else experienced this with a transtube fex? Looking for suggestions on how to fix the problem. Or is this normal? Maybe the transtube fex just does not have a strong enough output to drive the amp to full volume.
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[Jim O. Underwood]

Hey Richard, you might check the input and output settings in the Global section. These could of changed. I typically set the output on the tubefex to about 80% when playing steel through it to avoid unwanted distortion. Hope this helps.....

[Ken Fox]

I agree with 80 percent or more to drive a power amp:

For a regular amp I posted this a whole back:



I have been playing with two today in the shop and made some changes in the "Global" volume/tone settings:

Pregain at 40-50 percent
Post gain at 20-30 percent

Greatly reduced background noise using a guitar amp (1959 Bassman clone). The gain structure seem a lot different than a Profex 2 and Bassfex, needs a whole different setting. A Profex/Bassfex can hardly stand to see the green light on or it can clip on low notes. The Tubefex/Transtubefex inputs does not seem to be so hot and can take more input signal. The resulting signal to noise ratio is much inproved. Just watch the input for clipping, as you may have a stronger pickup. I was using a Truetone and a old Goodrich pedal LSW) with their built in buffer circuit.

The global volumes are adjusted with any setting that does not have a tube in the preset (ie a Newman preset/setting). A preset with a tube (TB) will not allow global volume/tone changes, except in very early versions of Tubefex software. The menu is obtain by hitting the Global button until INP ** shows up. After setting just press "PLAY" twice to escape.

Give it a try, nothing ventured, nothing gained.


Also the Tubefex and Transtubefex are very prone to cause "ground loop hum", as a result of two different paths to ground when it connects to the amp with a typical shield guitar cable.


I recommend a "Hum-X" by Ebtech to resolve that.

[Richard Keller]

Thanks for your replies. I have a tube (TB) in my effects settings , so I adjust the pre and post gain with the knobs on the face, instead of the global settings. I have the post gain all the way up and the pregain about 60% .
It seems that the transtube fex just does not put out enough signal to drive the DPC amp fully. I have the volume controls on the DPC amp all the way up.
I guess I will have to boost the signal from the transtube fex thru a mixer or something.

[Ken Fox]

I know that was an issue with the Profex 2. There was a mod to increase it form 1 volt to 2 volts output. The Tubefex was the same output, from the manuual:

Total Harmonic Distortion
Less than 0.02% at 1 kHz (1 V RMS)

I would assume the Transtubefex was identical to both for output voltage.

The input sensitivity for the DPC750 is 1.0 Volts RMS for full rated output into a 4 ohm load.


So by all that it means the TTFEX will have to run wide open to get the DPC750 to full power, with the DPC turned wide open.

[Richard Keller]

Ken
I gave you the wrong information on my amp. It is a Peavey DECA 528. Does this amp have the same input specs as a DPC?

Thanks for taking the time to answer my question.

[Ken Fox]

Yes, 1 volt RMS for full rated out into 4 ohms.

[Richard Keller]

Ken I saw your comment about a modification for the output. I looked at some old posts and saw back in 2002 you were talking about this also. It looks like it is just putting a 10K resistor in parallel with the feedback resistor on the opamp. According to my tube fex schematic that would be R117 and R118. I think I will give this a try and see if that helps. Thanks a lot for your help Ken.

[Ken Fox]

Keep us posted on that. As those are SMT devices that could be tough to do. Perhaps just two new 5K SMT resistor replacing the two old 10K resistors?

[Richard Keller]

Thanks for the suggestion Ken. I have some SMT resistors ordered. I will post the results when I get them installed.

[Richard Keller]

OK, I made the output mod. I got a schematic from Ken Fox a couple weeks ago, thanks for sending it Ken. After looking closer at the schematic, I found that the two resistors (R117 & R118) that needed to be modified we regular resistors, not Surface mount. I happened to have a couple of those in the basement, so I made the mod.
It did improve the output and make it drive the amp a little more, then I went into the global settings and found the input and output were both set at 30%.
The original suggestion from Jim Underwood was to check these settings. I thought that if you were running a tube [TB] in the presets that this did not affect the volume. Well I was wrong. I boosted the output to 100% and wow, I had all the volume I could ever need.

So, thanks Ken and Jim for your suggestions. I did both the output mod and changed the global settings and have a nice loud amp setup now. My wife keeps telling me to turn it down.

[Tony Contreras]

I’ve been doing to searching and wanted to know if the same mod can be done with the Tubefex. As in same resistors and values. I would like to boost it to 3v to drive certain tube power amps. I’ve tried asking for help on Facebook and not only got nowhere but was basically trolled because it’s not the preamps intended purpose and it only belongs in a studio, not driving poweramps. Garbage, this tubefex is coming on stage with me and I need it to push these amps.

Additionally, would it be possible not only to have the 3v mod but also keep a separate 1v output section? If not that’s no big deal to me. Thanks in advance for any help you can provide!!


Tony