Mods to my Ampeg SVP-PRO!

[jazzbass_5]

not regulated just rectified.

 

[beans-on-toast]

The schematic is confusing but the heater voltage is already rectified (full wave) to DC.

Thanks. A DC heater is one less concern. Regulation can work better in some cases than rectified and filtered.

I'd still want to see how it is performing with a scope. Since this pre has issues, adding a small cap (0.1uF 50V) at each tube across the heater can help by filtering any high frequency hash. heater noise has a way of getting into the audio pathway.

 

[jazzbass_5]

I don't understand. Meaning it's to bad there is so much variance in this model. My 1997 SVP Pro is very quiet my 2003 model had 60 hertz hum and excessive preamp hiss. I tried a few things to reduce the noise and even thought I had it once with a tube swap but in the end it was still there.

 

[beans-on-toast]

My thoughts are a ground loop between the output and the power amp (a 1:1 audio isolation transformer is the proper and safe way to deal with this), or possibly noise getting into the V5 stages (via a defective tube, noisy heater supply, noisy plate supply or possibly an internal ground loop or poor ground current steering.

Going down the ground loop path...

Ampeg SVP Pro humming - solved

Not sure what this product does, but I'd want the 1:1 isolation transformer.

 

[jazzbass_5]

Looks like a notch filter maybe for the output? I dunno...

 

[agedhorse]

Looks like a notch filter maybe for the output? I dunno...

Has nothing to do with a notch filter. It's a way to isolate the signal grounds.

 

[jazzbass_5]

Has nothing to do with a notch filter. It's a way to isolate the signal grounds.

Sorry, I'm in my work van, looks at a glance like something you'd connect inline with the output to the power amp, I did not have time to read the specs or anything. Just saw 1/4 inch in and outputs.
Notch filter came to mind.

 

[jazzbass_5]

Hence the question mark and the "I dunno"

 

[byacey]

This preamp has a transformer balanced line level output. Perhaps that could be used?

Edit: Forget what I suggested; it's mic level.

 

[beans-on-toast]

It turns out, the Behringer box contains two transformers, one for each channel.

趣味のオーディオ実験室＞オーディオ関連のケーブルなど＞§線－２１：ＨＤ４００ (BEHRINGER)

 

[byacey]

I wouldn't trust Behringer to be offering much of a quality transformer. Core distortion at bass frequencies is usually the first indication of a poor transformer.

 

[agedhorse]

Sorry, I'm in my work van, looks at a glance like something you'd connect inline with the output to the power amp, I did not have time to read the specs or anything. Just saw 1/4 inch in and outputs.
Notch filter came to mind.

Search google on audio isolation transformer, it's interesting stuff.

This preamp has a transformer balanced line level output. Perhaps that could be used?

Edit: Forget what I suggested; it's mic level.

That was my first thought, but the same conclusion... though it could be converted to line level. It would be "necessary" in this case for the power amp to have balanced inputs.

 

[beans-on-toast]

I've used the JT-11-FL. Good product.

Line Output Transformers | Jensen Transformers

 

[jazzbass_5]

Search google on audio isolation transformer, it's interesting stuff.



That was my first thought, but the same conclusion... though it could be converted to line level. It would be "necessary" in this case for the power amp to have balanced inputs.

I will, thanks.

 

[jazzbass_5]

This preamp has a transformer balanced line level output. Perhaps that could be used?

Edit: Forget what I suggested; it's mic level.

I have heard of some owners using that and it does seem to help with the noise. Been awhile since I read that thread. I believe it bypasses V5 when you do, but I'm not positive and would have to look.

 

[byacey]

V5 (both halves) are out of the picture when using the balanced output. It's also before the master volume control.

 

[jazzbass_5]

V5 (both halves) are out of the picture when using the balanced output. It's also before the master volume control.

That's what I thought

 

[jazzbass_5]

Update:
2 1/2 years later and my SVP-PRO mods are still running strong. It's been my main rig for a lot of shows.
I reconfigured a few of my rigs and racks and took some pictures while it was out. The unit has preformed flawlessly with the 12vdc rails and cooling fan. Although it may have created a few polar vortexes and strange weather patterens here in Western New York.

Back in the rack.

 

[jazzbass_5]

And last night's rig. Yes that's a quilter BB800 power section in there.