Anyone elses DC-5's hum when cranked? (non tube issue)

[dogboy131]

My DC-5 sounds great, however when I turn up the individual volume I do get quite a bad hum on each channel.

Is this a common problem with the amp? It even does it when I have a totally clean clean at just above bedroom levels.

I have done the tube tapdance. And the cable dance, and the speaker cable dance, and the guitar dance, and the FX dance etc etc.

It is not volume hiss, it is a pronounced HUMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMM> :-(

 

[dogboy131]

I have also tried it in different buildings etc (in case it was an electrical source thing..)

 

[edward]

Nope, dead silent. Does yours do this w/o anything plugged in?

Edward

 

[dogboy131]

Yarp.

Looks like I have to take it to a tech eh?

 

[tetsubin]

Did you change the output tubes? They wear differently over time and the bias will get off, which creates a hum.

 

[Ken j]

Mine is dead quiet.

 

[adam972]

I have a similar problem. My amp sounds pretty quiet at bedroom levels, but when i bring up the output volume, or the master of either channel, i get a pretty solid 60 cycle hum. I have replaced all the tubes, and upgraded the transformers, but i still get the hum. Tonight i am going to trace all of the grounds with my m,ulti meter. What makes me think it might be the filter caps is that when it sits in standyby for a long time, when i flick it to ON, there is a slight wave of static that rises and then falls (sort of like the HBO movie trailer). But if i switch from standby to power quickly this does not happen, so i am thinking that the problem mightt be the caps not charging properly...from what i have found it is going to cost me the same amount to just replace the caps as it would to investigate the cap problem. anyone also have a rush of static when they turn their amp from standby to on?

 

[Sixstringpsycho]

Mines quiet unless an external factory creates feedback or a hum.

 

[anothersomeone]

Are you using the effects loop? When I use my effects loop, the further up I turn the saturation level on that, the more my DC-5 Hums...

I've learned to just not use the loop because I haven't found any help regarding that issue.

 

[adam972]

No, my amp does this even when nothing is plugged in at all. The hum is something i need to hunt down. but the really weird thing is that when i am playing on the rhythem channel, if i crank the gain on the lead channel above 6, i seem to get this microphonic swell that sounds like putting a microphone to close to the speaker it is being run through. Does anyone else have this problem?

I have contacted the 5 MB repair shops around me and all the always seem to be "out to lunch" or dont open till noon. just cant seem to figure out the problem. Im thkning about doing a re cap just as investigating a cap issue would be more expensive then doing a recap

 

[texmexboogie]

Ok, you stated non tube issue, but it sounds like it might be a tube issue. I have bought a Studio 22+ just recently and it had brand new 12AX7 Groove tubes and JJ EL84's place in it and it had the same issue you decribed. I was trading slots on the preamp tubes with no luck in getting rid of that howl. So I just pulled all the tubes and started from scratch. I confirmed that the Groove tube 12ax7's were EI production. These tubes sound really great, but due to there long plates they have a reputation of going microphonic. To get by with 1 EI in a high gain amp would be asking alot but all the preamp tubes is a disaster.

This is an easy test.
Remove V2 and turn on the amp. No noise? Good chance it is the tube. Get a short plate tube, JJ ecc83 is a good choice to tame this issue, and place it in V2. Better but not quite there. Change V1 then V3. I would do this before changing caps and such. Hope this helps

 

[adam972]

so some updates:

1.) When i bypass the preamp and go direct in with my guitar to the power amp section via the fx return, no hum, so atleast i am hunting in the preamp section.

2.)I have tried swapping every preamp tube. so i am getting this hum on both the rythem and lead channels, most notably increased when the master volume of each is increased (gain has little effect, other than the the lead gain which causes the microphonics)

3.) in V1, i tried the stock Mesa 12ax7, GT 12ax7, EH 12ax7, a JAN 5751, and a EH y7. All of them showed the same problem on the rythem channel. this same swap in V2 seems to get the same from the lead channel

4.) pulling V4 and everyhting is quiet, but i presume that is just killing the whole preamp section.

5.) I have tried every combo possible with no avail...whats killing me is that at a good small room level(main output at 3 and master rythem at 2), there is no hum, it really only appears when i crank the master rythem or lead.

have you had any experience with the EH preamp tubes? I really like the way they sound in my Fender blues jr.

and to make things a little more odd. a few things i ahve noticed.

1.) the hum seems to decrease a little bit when i take the FX return knob all the way to full wet, even when nothing is turned on.

...I know my way around amps a bit, but with such open ended problems, i am hesitant to take it to a tech and start poking at $60 an hour.

 

[adam972]

to sort of sum up what i missed...when i got the amp it had a mix or mesa and gt preamp tubes, and then hum was there on both channels( as was the lead gain microphonics). Swapped out all the tubes for new EH preamp, (tube DR)power, and still getting the same exact level of hum.

 

[MJ Slaughter]

I just went through this with my DC-10 and had it resolved yesterday. Swapped out all the tubes with ones I already had without success. They were used but good as far as I knew. Yesterday I took it to my tech who put a new JJ 12AX7 in V1 and replaced a microphonic tube in V3. Now it's all good. I feel a little stupid for not starting out with new tubes but the labor was only $20 so I'll get over that. He told me that the JJ's are a much quieter tube and I guess in the V1 position it can make a difference.

 

[adam972]

I did a bit more hunting. The V1 isnt causing the problem, the V2 seems to be the one getting crazy. I looked at the schematics and it looks like the lead channel gain sits in between both sides of V2...i dont really use the gain channel, and i can get plenty of gain if i want to with that channel without approaching the microphonics...
...still though, i guess ill head to the tech to hunt down the general loud volume hum i am getting.
The problem you solved with the JJ, was that microphonic swell on the lead channel at high gain...or just a general leve of hum?

 

[adam972]

well im sick of this...so i am sure anyone reading this must be sick of it by now. Tonight, i found the only way i could clear the hum from both channels was to remove V3 ( FX return and 4th lead). I also noticed that with this tube installed, with nothing connected to the FX loop, turning the knob from 0 to totall wet had an effect on the hum. totally wet and the hum went away slightly...turn to 0 and the hum became more present.

So pairing this down...having the amp totally stock with tubes, if i insert my guitar in the FX return, that gives me a clean chain through the graphic eq, presence control and output level....going this route everything seems good. but what gets me stuck is pulling the V3 tube prevents this signal path...

i have tried varrious tubes in the V3 position, maybe i will just order one of those JJs tommrow to see if that helps. I feel like i am close...but perhaps i am very far away.

 

[adam972]

and to beat a dead horse....

When V3 is pulled, no hum, but you can barley hear the preamp signals from lead and rythem, and the master pots are unactive.

I did a little bit of reading online and then something hit me...what i have yet to figure out is why on the rhythem channel, i crank the lead channel gain...i will get the same microphonics...everyhting i have read and learned should tell me that when the rhythem channel is active, the LDR's should shunt the lead channel and it should be innactive.....!maybe!

,,,,so, i am going to whatever tech i can find tomm who is authorized boogie with:

channel microphonic bleed ( possible LDR issue).

Pulling V3 makes the hum go away on both channels.

 

[adam972]

so i have a date with an authorized tech tomorrow...man i cant wait to see what he has to say...it has taken me 3 weeks to get MD area tech on the phone.

 

[adam972]

Turned out to be faulty LDR's. They were shunting completly and my amp was having both channels somwhat active and that was pusing the voltage and thus the hum...being fixed as we speak

 

[adam972]

so i just got my amp back from the mesa boogie tech. he said the LDR's for channel switching were the culprit, so he went a head and replaced all three, one of which is on the EQ. That sounded like great news until i took it home, and the exact same problem wass there. I called him and he started saying it was prob my house power...which is funny because replacing the LDR's has no change in my problem. I took the amp to my inlaws (new construction), and to my office, and the same thing was happening....now i gotta get this tech back on the phone, get him to not be a dick because what he did didnt fix my amp, then make the 2 hour round trip to his shop to drop it off. maybe i should have just replaced the filter caps to begin with....