500 Watt Amp hum -- Xover In vs Out

[andyadler]

Hello all. I'ver just resurrected a dormant TN1220 and 500-watt amp, running it off of Denon AVR-1910 receiver using the receiver's crossovers. When I connect the Hsu amp with the amp's internal crossover switch set to bypass, I get substantial hum from the 1220. If I switch in the amp's crossover, the hum is substantially reduced.

My question: since I'm connecting the amp to the receiver via a Y-connector to the inputs -- not using the filtered output jacks at all -- does it make a difference if the amp's internal crossover (51Hz) is active or not?

Hope this isn't too confusing -- and thanks in advance for any observations and/or suggestions.

Best...A.

[Pete_Hsu]

Hi Andy,

How high is the volume knob set on your 500w amp? Does the hum increase progressively at higher volumes on the 500w amp, or is there a constant hum at all volume levels? Finally, when you start to hear the hum from the 500w amp, if you disconnect the y-splitter from the 500w amp, does the hum go away?

A couple comments I would like to make: one is that, when running from the subwoofer rca pre-out on the receiver to the low level rca inputs on the subwoofer amp, one needs to only feed either left or right low level input, not both. By using the y-splitter, that would bump up the gain by an extra 6db, which would make it more likely to hear hum. Try just feeding one rca input on the 500w amp (either left or right input), and if need be, increase the subwoofer channel level on the receiver to your tastes. Secondly, it is just fine to make use of the internal crossover on the 500w amp. The internal crossover on the sub amp helps to filter out higher frequencies going to the sub, so that is why the hum is reduced. If one engages the internal crossover on the sub, then one will make use of both the outboard crossover set on the receiver, and the internal crossover set on the subwoofer.

Sincerely,

[andyadler]

Thanks for the quick reply, Pete. In answer to your questions -- yes, hum increases as the volume knob advances; and yes, hum disappears when interconnects are removed. I appreciate your observation re the extra 6db of gain with both channels driven, so I'll try the single-channel approach.

The calibration instructions for the receiver recommend defeating any internal crossovers in the sub, or if not, setting those crossovers to the highest frequency possible. Again, to clarify, does your 500-watt amp's crossover setting affecting what gets sent out of the speaker terminals, or just the output RCA jacks? And what would happen if I pulled the 51Hz module and left it empty? Would the amp still function correctly?

Best again...A.

[Pete_Hsu]

Hi Andy,

If the hum goes away when the interconnect is unplugged, then there is certainly a chance that the interconnect itself has gone bad. Try using a different cable to see if that makes any difference.

The internal crossover on the subwoofer amp--when engaged--will work via high level or low level inputs. So whether one runs speaker wire to the sub amp, or rca cables, the internal crossover will be active when crossover is set to 'In'.

I'll have to ask Dr. Hsu about the exact repurcussions of removing the crossover module completely. I would suspect that only the crossover functionality would be affected, without any negative effects elsewhere, but will get back to you on that one.

Thanks

Sincerely,

[Pete_Hsu]

Andy, according to Dr. Hsu, with crossover 'In', the amp will not work at all with crossover module removed (as expected). The amp will technically work with crossover 'Out', but not recommended for use with crossover module removed, as it can lead to output of the crossover to go to +15V or -15V.

Sincerely,

[andyadler]

Well, I moved the sub and amp to another location/system, and all is now well. Must have been some odd interaction. Thanks so much for your help!

Onward and upward in Louisville, KY...A.

[Pete_Hsu]

Good deal Andy, thanks for the update!