Epiphone Valve Standard - HUM

[noodler]

Just picked up an Epi Valve Standard for $199... couldn't pass up 15W and a 12" speaker for that price! However... maybe I should have! With the Master Volume at 12:00 it begins to HUM... very annoying at practice levels (don't gig yet... hence the name Noodler).

Any ideas to fix this problem would be much appreciated!

[mshaun]

I have a valve special and one of the first things I had to do was get rid of the hum. The fix for me was a 150uf 450v electrolytic cap in parallel with the existing filter caps. I was going to use two 100uf but the supplier substituted 150's. I connected it to the legs of the bleeder resistor R14. And installed it on an empty area of the board. This was so effective I'm not going to pursue it any futher, and it was bad.

[zaphod_phil]

Any ideas to fix this problem would be much appreciated!

First check where the hum is getting in. Remove the first preamp tube. Does the hum go away? If not, pull out the 2nd preamp tube. Now does that kill the hum? If not, then remove the PI tube. Has the hum gone? When the hum disappears you know it's coming into the amp somewhere around the tube you just pulled. Then you can start working from there.

[noodler]

Wow... that was quick! Would you mind taking a look at the schematic for the Standard since that's what I'll be working from? I don't know how different the two models are. Also, do you have any recommendations on how to "clean up" the tone somewhat? I find that there's not too much range in the controls and the overall sound is somewhat "muddy".

Thanks

[mshaun]

The other poster here, zaphod_phil has the answers. Most of my mods came from his suggestions. I will add that the change in output transformer made the biggest difference to the overall sound with a large boost in bass and dynamics. The large cap killed the hum on my special and the power suppy on the standard appears essentially the same. I made a dozen or so changes to mine that I'm very pleased with. I cut out the effect processor, connected preamp directly to power amp and changed a few caps and resistors according to information I found here. You are in the right place for advice. Good luck.

[bigjoe]

For Valve Standards mods check the post "Epiphone Valve Special Mods?" I basically highjacked it on page 7. Sorry about that.

page 7 link below:
http://www.18watt.com/modules.php?name= ... c&start=90

zaphod_phil most definately has the answers. I'll be getting an OT soon, but the mods he has suggested so far have improved the tonal response of mine even without the OT.

Also the PCB on mine has the ground trace cut in 2 places (for hum from what I understand) the board is grounded to the chassis in 2 places with wires. This was a mod on the special, I think was eventually incorpoarted into the production models. My standard was defintely done by the factory.

The tone stack stuff definately helped and changing C12 to 1000uf tightened up the sloppy bass.

The other thing that REALLY effected the voicing in a great way was adding the 5 zeners before the PS filter caps. I don't recall it helping the hum, but I expect a little as I play a Strat.

[noodler]

Is there a Dr. in the house? I pulled the tubes one by one and as soon as V3 (pre-amp) tube was out it the hum was gone. I have to plead ignorance now... I can handle a soldering iron but I just don't know enough about this stuff to know where to begin. Is there any way you can provide me with a laundry list of recommended changes that I can follow step by step? The only request is that I keep the DSP circuit in the loop (that everyone seems to hate) since I'd like to keep the reverb. I'm not looking for the Holy Grail of amps here... just something that doesn't hum and has better tone. Once again any help would be appreciated! By the way... I tried to follow the Valve Special Thread but got lost halfway thru.

[zaphod_phil]

OK, so that means the hum is getting in somewhere around the phase invertor, which is roughly somewhere in the middle of the amp. IMHO changing component values and such isn't going to improve anything. You need to start checking for loose wires, cracked connectors, poor solder jointes, etc. I'm assuming the stock amp doeesn't suffer from this hum, which bigjoe should be able to confirm.

Once the hum problems fixed, then you can look at mods. But if you want reverb just get yourself an EH Holy Grail pedal. That DSP stuff is right in the middle of the signal path and messes with the signal levels, even when you're not using any of the FX.

[noodler]

I should have clarified on my first post... this is a stock amp. No mods as of yet. I actually have two of these and they both sound the same. Kind of like a loud flourescent bulb.