Modifying Consumer EQ to reduce hum.

[NeglectedFred]

I've been racking my head today..

When I was 18 I bought a comsumer level component stereo EQ. It's made by a company called audiosource, the model is EQ eight.

When placed in the effects loop of bass or guitar gigs it does amazing things unlike any other EQ. It's certainly not transparent, colorless, clean, accurate, or any of the things that you would ever want in an EQ, but amazing nonetheless.

The problem is that it's noisey on ridiculous levels, and I believe the majority of it is 60Hz Hum.

I've tried to achieve similar results with other consumer levels EQ's (pioneer, yamaha), as well as my studio EQ's, inluding a furman rack EQ (blows), an Orban 674, and various processors with EQ's - nothing acts like the audiosource eq eight.

I tried the simple stuff, grounding the chasis, changing placement, changing cables, the noise is here to stay - but I've added a rocktron hush system after the EQ which has helped dramatically - still not enough.

The power transformer that I can see is a Hawk H48?

I see many opamps, appear to be NEC C324C.

Some other IC's by Toshiba TC4017bp..

The connectors are RCA connectors.

I always use the right channel since it's the furthest from the power transformer, but it doesn't really seem to matter.

I'm running in effects loop, so I don't believe impedance is an issue.

Please help. This problems has been haunting me fo 13 years. Anyone have any ideas? Would adding iso transformers anywhere help? Swapping out IC's or the Hawk transformer? I don't know what I'm doing, but I can't think of anything and getting rid of that cheap EQ is not an option.

Oh, also I should mention that this is the 2nd AudioSource EQ eight I've had, the first one blew up several years ago, I bought a replacement on Ebay for 15 bucks.. Both units are identical, even though the amount of noise really seems unacceptable by any standards.

[Dakota]

Would adding iso transformers anywhere help?

That's the first thing I'd try. I often have to put audio iso transformers w/ ground lift in line when getting back and forth between balanced +4 style gear and random consumer unbalanced -10 and other oddball gear.

[NeglectedFred]

OK, any ideas on what kind? I'm not real knowledgable of compononets and values and such.

Any preferred brands and models I should order? Affordability is somewhat of a factor - though I'd be willing to pay dearly when it comes down to it. Even just cutting the noise in half would put at a much more tolerable level.

I'm assuming I'd just connect straight to the input connector? Which wires to which pins?

I just checked the specs, the input is 100 Ohms on the EQ, I'm not sure, but I think my effects out is 600 Ohms. Should I get this?

http://www.edcorusa.com/products/transf ... 0-150.html

[Jim Williams]

No 7815/7915 regulators? That's yer problem. Modify the power supply, add a larger torriod power transformer, 30 va ought to do it at dual 15 to 18 volt secondaries. Then build in the regulators, mount them with thermal pads right to the chassis for heatsinking. With large caps you should be able to push 60/120 hz noise down to -120 db.

[NeglectedFred]

If you're being a smart ass then f*c% you, you should just go to hell.

If you're seriouse then f*c% me, I should just go to hell.

[Jim Williams]

That's not that hard of a mod to do. If you keep the old transformer, it's a couple dollars of parts. Just cut the feeds after the mains caps, run to the regs input pins, run the regulated output back and ground the reference pin (pin 2 on the 7815, pin 1 on the 7915). Use those plastic thermal pads and use the chassis as a heatsink. A couple of 4-400 screws and a couple of holes will do it.

[Dakota]

Neglected Fred:

It's unknown what your problem actually is. *If* it's a bad ground interaction or ground loop, then patching through an audio iso transformer may do the trick. I don't recommend putting a lot of time and $ into that approach if you're not sure that's actually the problem. An iso transformer may also make not a bit of difference.

Something like an ebtech hum eliminator would test this. Or a direct box with a ground lift.

*If* it's a crappy or badly aging power supply, then Jim Williams is right. He's not yakking your chain, he's a very very good tech.

[NeglectedFred]

Well, I think that's a pretty sensible place to start. Thanks guys.. I'm gonna look into this. I actually have a hum eliminator - I bought it for something else, ended up not needing it and loaned it to a friend. Maybe I can get it back this week and check it out.

I'll keep you posted, I might have some questions about doing the mod if I end up dsoing it, but I'll try the hum eliminator before hand - and I'll search for resources before I bother you guys anymore.

Would moving the power transformer to an external housing help at all?

[Dakota]

Would moving the power transformer to an external housing help at all?

*If* the problem is radiated electromagnetic noise from the transformer, then it would. If not, then no.

[nclayton]

I don't think you will get anything out of rebuilding the power supply. You haven't mentioned whether it hums in any other setup, but it probably doesn't, right?

Does the EQ have a 3 prong or 2 prong end on its AC cord?

If it's in an effects loop there's alway a chance for ground loop hum. The shield in the send patch cord goes from amp to eq, then the ground goes through the eq to the return cord, then back to the amp, and then back to the send, making a circle.

If the send and return patch cords are long, it can make a BIG ground loop, which will hum more. If they are spread apart from each other, that also makes the loop bigger and it can hum more. Use the shortest possible cables, and cable tie them together and see if it helps.

To break the ground loop you don't necessarily need an isolation transformer or hum eliminator (although that would probably work). You may be able to solve the problem by cutting the shield on 1 end of 1 of the cables. Most likely the eq only needs to make ground reference to the amp at either the send or return jack, but not both. Probably doesn't matter which, but if you cut the shield on 1 end of 1 of the cables, you might want to try different placements for that cable and see if any are better than others (try it on both send and return and also try it with the "cut" end on both the amp side and the eq side).

Ned

[NeglectedFred]

Well, in 13 years, as you can probably imagine, I've used it in a million ways with a million different cables. It's always noisey, but guitar and bass amps are the worst for sure.

I'd like to wish it were that simple, but it's not. It's my sound, and the real bummer is that a substitute isn't possible. This eq almost sounds like a multiband exciter rather than an eq - although the reaction is instant, sometimes I feel like exciters react slowly on the bottom and lack tightness.

It's a 2 prong plug but I've grounded the chasis to my monster 3500 (I know, I know, I'm burning in hell for having monster gear).

I got my hum eliminator and used both channels (one right into the EQ, and one back to the effects loop) as well as one at a time.
I might dare say the hum was unaffected.

I'm sure the majority is 60Hz, because when I unplug my guitar or bass the same noise is so loud that it actually registers 3 led's on the spectrum anylizer right at 60Hz.

[The Scum]

So you need to follow the usual procedures for troubleshooting:
1> Identify the source of the problem.
2> Address that source.

Anything else is guesswork.

Using the isolation transformers, you've looked at one possible source of noise - the external interfacing. You could really exonerate the interfacing by testing the unit in isolation - short the input to ground, and see what's on the output using some test equipment.

Do you have an oscilloscope? Multimeter? How willing are you to go sleuthing for schematics?

Jim W's answer is good info - you told us some of the semiconductors, but didn't mention the power supply. If there are no voltage regulators, then it's another likely target. With an oscilloscope, you could verify that pretty easily. (And the dude recorded the freaking Mentors. There's nothing some forum troll can say that's going to ruffle his feathers.)

The power transformer could be the source of the hum - if it is magnetically induced, then moving the transformer away (and/or moving to a Toroid)could help. This can be easy to test for if the transformer has some slack in the wiring - loosen the bolts that hold it, and move it around a little - if the hum changes radically, it's probably magnetic.

If you can verify that the interfacing is good and the power supply is quiet, then you need to start looking into circuit upgrades. Schematics will be invaluable.

Don't forget that the thing could be such utter junk that in fixing the hum, it's ineffable character may be altered such that it loses is magic...the exciter characteristic could be amplitude modulation caused by a hummy unregulated power supply and chips with poor PSRR.

[NeglectedFred]

So you need to follow the usual procedures for troubleshooting:

Do you have an oscilloscope? Multimeter? How willing are you to go sleuthing for schematics?

Jim W's answer is good info - you told us some of the semiconductors, but didn't mention the power supply.

Sorry guys, I'm not entirely savvy. I'm certainly compitent enough to pull out a soldering iron and get dirty. I assembled a seventh circle A12, and I make my own cables, but that's it - no schematic reading or troubleshooting skills. I have a multi meter.

Actually I did tell you about the power supply. It's a Hawk H48, just a transformer, that's all I see for power section. But maybe there's more, I don't know what to look for. It appears everything else is on there twice (left and right channels) so I think that's it.

I appreciate everyone's input, I'm the first to admit that I'm a novice with this stuff. I'll see if I can figure out what I need to do to perform Jim W's advice - get parts and figure out what goes where.

I'm actually really excited to give this a shot.

Oh, btw, I should mention tht on bypass the hum is gone completely - does this fact eliminate the possibility of reducing the hum by distancing the transformer?

[Professor]

I'm a little confused at where the device is plugging into your signal path. Are you using the effects loop from an amplifier so that the "effects send out" connects into the EQ and then the EQ output returns to the "effects return input" (or however they might be labeled? Or is this something you're trying to plug in among a bunch of stomp boxes?
I'm asking because in either case I would be really suspicious of whether the effects loop sends and returns are meant to connect to line level inputs and outputs and not to instrument level inputs and outputs. That sort of difference doesn't usually induce that kind of sever hum, but I suppose it could be a part of the problem.
Normally my first guess would be a ground plane difference between the EQ and the amp, but the sure fire way to kill that dead is by isolating the signal into and out from the EQ with isolation transformers. And you said that doing that had no effect on the hum. But then somehow hitting the bypass stops the hum cold - and that suggests it's not a ground plane hum because you would still be connecting the grounds of the EQ chassis & amp chassis.
Just out of curiosity, have you tried plugging the EQ into a regular stereo system to see if the hum is present there? After all, it could just be that the EQ is broken.

-Jeremy

[NeglectedFred]

I'm a little confused at where the device is plugging into your signal path. Are you using the effects loop from an amplifier so that the "effects send out" connects into the EQ and then the EQ output returns to the "effects return input" (or however they might be labeled? Or is this something you're trying to plug in among a bunch of stomp boxes?
I'm asking because in either case I would be really suspicious of whether the effects loop sends and returns are meant to connect to line level inputs and outputs and not to instrument level inputs and outputs. That sort of difference doesn't usually induce that kind of sever hum, but I suppose it could be a part of the problem.
Normally my first guess would be a ground plane difference between the EQ and the amp, but the sure fire way to kill that dead is by isolating the signal into and out from the EQ with isolation transformers. And you said that doing that had no effect on the hum. But then somehow hitting the bypass stops the hum cold - and that suggests it's not a ground plane hum because you would still be connecting the grounds of the EQ chassis & amp chassis.
Just out of curiosity, have you tried plugging the EQ into a regular stereo system to see if the hum is present there? After all, it could just be that the EQ is broken.

-Jeremy

It's a home stereo componenttype of EQ. It's plugged into the effects loop of whichever amp I use it on. Send to In via 1/4" to RCA / Out to Return via RCA to 1/4, although now it's Send to Hum Eliminator in-A, Out A into EQ In, EQ Out to Hum Eliminator In-B, Out-B to effects return.. Just so we're clear I'm not completely novice at plugging things in..