Hum Issue

[tkam]

Ok let me explain how my speaker rig is currently setup.

I have the APL 3910 and the Modwright 9100ES going into the two of the inputs on the Modwright SWL 9.0SE. The modwright pre's outputs are connected to the D-Sonic power amp.

Now on to where the problem(s) come into play. I also have my denon 4308ci recievers front channel pre-outs connected to the HT Bypass input on the Modwright pre. The ht bypass input essentially ignores the volume control on the modwright allowing the volume to be controlled by only the reciever.

When I have the reciever on (and the ht bypass input on the modwright pre selected) I have a pretty nasty ground loop hum. The hum is not there if the reciever is off or I'm using one of the other sources hooked up to the modwright pre. So it has to be related to the reciever in someway. Initially I thought it was caused by my cable tv not being grounded correctly but I have addressed that issue and can rule it out as being the cause.

The denon reciever doesn't use a grounded plug so theres no oppourtunity to try a cheater plug.

At this point I'm running out of ideas. I'm tempted to try sticking one of these in-line between the pre-outs in the reciever and the ht bypass input on the pre-amp.

[Dusty Chalk]

Does it know the words? Okay, sorry, I had to get that out of the way.

What happens if you leave your receiver off and turn the ht bypass on? And I assumed you tried disconnecting the receiver from the pre, and verified that the hum went away (since you're blaming the receiver). If not, do so. Also try cranking up the volume on silence.

Also, how are things plugged in electrically (all on the same strip, etc.)?

[JBLoudG20]

Ok let me explain how my speaker rig is currently setup.

I have the APL 3910 and the Modwright 9100ES going into the two of the inputs on the Modwright SWL 9.0SE. The modwright pre's outputs are connected to the D-Sonic power amp.

Now on to where the problem(s) come into play. I also have my denon 4308ci recievers front channel pre-outs connected to the HT Bypass input on the Modwright pre. The ht bypass input essentially ignores the volume control on the modwright allowing the volume to be controlled by only the reciever.

When I have the reciever on (and the ht bypass input on the modwright pre selected) I have a pretty nasty ground loop hum. The hum is not there if the reciever is off or I'm using one of the other sources hooked up to the modwright pre. So it has to be related to the reciever in someway. Initially I thought it was caused by my cable tv not being grounded correctly but I have addressed that issue and can rule it out as being the cause.

The denon reciever doesn't use a grounded plug so theres no oppourtunity to try a cheater plug.

At this point I'm running out of ideas. I'm tempted to try sticking one of these in-line between the pre-outs in the reciever and the ht bypass input on the pre-amp.

Do you have the pre connected to a different wall socket?

[tkam]

What happens if you leave your receiver off and turn the ht bypass on? And I assumed you tried disconnecting the receiver from the pre, and verified that the hum went away (since you're blaming the receiver).

Also, how are things plugged in electrically (all on the same strip, etc.)?

If I leave the reciever off and switch the pre-amp into ht bypass there is no hum. Disconnecting the reciever from the pre also results in no hum. I've tried having them both plugged into the same strip and different strip resulting in no change.

Do you have the pre connected to a different wall socket?

I acually have sockets on two seperate circuits right by the speaker rig I've tried them both on the same circuit and on seperate ones doesn't help.

[Torpedo]

I'm afraid that despite all your efforts, the receiver will keep humming. Most of those devices using TV reception circuits hum like mad, and IMHO they should stay away from a serious audio system.

[JBLoudG20]

I'm afraid that despite all your efforts, the receiver will keep humming. Most of those devices using TV reception circuits hum like mad, and IMHO they should stay away from a serious audio system.

I highly doubt that Denon, producing his $2000+ unit would allow this. Its not a hum caused by TV frequency interference.

[Torpedo]

The hum doesn't come from the "TV frequency" just from the dialing circuits. I ignore the reason, but this is a common problem when plugging receivers, no matter how expensive, into serious audio systems.

Sometimes removing the TV antenna connection the hum gets better or disappears, but looks like tkam tried that already.

[Pars]

Back before they had the wider neutral prong, present now even on two-wire plugs, common practice was to reverse the plug and leave it where it resulted in lowest noise. If you can try that on the receiver, it might help.

As far as I know, transformers such as the one inside the Denon do not designate one of the primary leads as neutral and the other as hot, so it is somewhat arbitrary in how they are hooked up. At least in the transformer wiring diagrams I have seen, one side isn't designated as Hot, etc. (Of course, if this is wrong, someone please correct me ).

[luvdunhill]

At least in the transformer wiring diagrams I have seen, one side isn't designated as Hot, etc. (Of course, if this is wrong, someone please correct me ).

well, depends on the transformer, but you should observe phasing dots if the transformer manufacturer denotes this. The "dot" corresponds to neutral.

[Pars]

well, depends on the transformer, but you should observe phasing dots if the transformer manufacturer denotes this. The "dot" corresponds to neutral.

Ahh, thanks. I always put the dots the same way for instance if wiring a pair of 110V primaries in parallel. I wasn't aware of a meaning for the dot, so I'll keep that in mind.

[JBLoudG20]

well, depends on the transformer, but you should observe phasing dots if the transformer manufacturer denotes this. The "dot" corresponds to neutral.

Learned that the hard way, with a $100 transformer.

[Pars]

Learned that the hard way, with a $100 transformer.

Ouch!! The dot corresponding to neutral, or to keep the windings in phase?

[n_maher]

Ouch!! The dot corresponding to neutral, or to keep the windings in phase?

I'm guessing it had to be on the secondary side since there really shouldn't be a way to damage a trafo on the primary side by wiring either end to the hot or neutral for that matter. I know of at least one man'f who's told me as much and every Hammond trafo that I've used certainly hasn't had markings on the primary wires.

[luvdunhill]

I'm guessing it had to be on the secondary side since there really shouldn't be a way to damage a trafo on the primary side by wiring either end to the hot or neutral for that matter. I know of at least one man'f who's told me as much and every Hammond trafo that I've used certainly hasn't had markings on the primary wires.

I'm pretty sure it is possible to damage them this way.

Which Hammond trafo doesn't have markings, just out of curiosity?

[JBLoudG20]

I'm pretty sure it is possible to damage them this way.

Which Hammond trafo doesn't have markings, just out of curiosity?

Sure is! Nate, do me a favor, and swap the wiring on one primary on your BFT. Smoking enamel smells like shit.

When there are dual primaries, they need to in phase, or the transformer hums, then starts to sizzle, then bellows some horrible smelling smoke.

[n_maher]

When there are dual primaries, they need to in phase, or the transformer hums, then starts to sizzle, then bellows some horrible smelling smoke.

Well of course if there are dual primaries then you would have to wire them appropriately, but in those cases the instructions are pretty clear I think. But in the case of transformers with a single primary (like any of the Hammond 270 series from my experience, or single primary trafos from SumR) it doesn't matter which way you wire them.

Here's Hammond's wiring diagram for the 270 series.

And Here's the 370 series:

[JBLoudG20]

The problem comes from a label where no voltages were labeled, and the Dots did NOT correspond with the same position (one dot was on the top of primary 1, bottom of primary 2). I, for whatever stupidass reason, didn't pay attention to the dots, and wired the top to the top, bottom to the bottom. Didn't do that one again.

That was on the first VanTOTL I built. Oh well live and learn.

Speaking of learning, my teaching assistant ship was approved, so I now get to help with the learning process of our EE undergrads. They're fucked.

[luvdunhill]

I just tested this last night. Trafo was an R-core with single primaries with marked phase. A 3A fuse blew when they were installed in one orientation, but not the other. YMMV.

[Pars]

I just tested this last night. Trafo was an R-core with single primaries with marked phase. A 3A fuse blew when they were installed in one orientation, but not the other. YMMV.

Sounds like you need to do a Lucas fuse mod; specifically the 1482A slow blow one... You get that thing running in the 3A fuse blow mode, its gotta sound way moar better, right?

[guzziguy]

Yes, but you need to use a silver nail to get the best sound.

[DigiPete]

Todd,

I had hum and it was coming from unshielded ICs I got from Enigma. Switched to shielded IC and hum is gone (Denon 3808 to an Adcom amp)

A buddy of mine has hum and its because his Modwright hi-dollar preamp is too close to his fancy CJ amp. He still has not been able to move his pre to entirely eliminate the problem.

Hope some of this helps.

Pete

[tkam]

Thanks for the tips Pete, I've actually tried both shielded and unshielded cables so I don't think thats it. Also I've tried the Denon directly to the D-Sonic and the hum is still there so that rules out the modwright being part of the problem.

I've found a few posts over at avs complaining about the same thing with the 4308ci so I'm beginning to think it's a problem stricly with the pre-outs. Might end up having to send it in for repair and hope for the best.

This weekend I'm planning to run the speakers directly to the speaker outs on the denon that way I can see if it's just the pre-outs or a more serious issue.

[Torpedo]

I regret to be insistent, but I don't think the Denon is misfunctioning, those hums on AV receivers are quite common

Good luck fixing it mate

[grawk]

Common doesn't mean correct

[tkam]

I regret to be insistent, but I don't think the Denon is misfunctioning, those hums on AV receivers are quite common

Good luck fixing it mate

The fact that it didn't happen in the first 6-8 months of owning it leads to me disagree with your assumption.