Fisher E44 Turntable + Console Phono Thud/Rumble Help

[dplatner]

Hi all, I bought a Fisher E44 console with built in turntable at a vintage store. My issue is a low frequency thud/rumble coming from the sub woofers, maybe 5-10Hz bass rumble.

I have tried the following to troubleshoot this issue:
- My setup consists of a built-in turntable, a preamp/tuner unit, and an amplifier unit, all housed within the E44 console
- The rumble only occurs in the Phono channel, the AM FM and Aux channels work just fine
- If I completely unplug the turntable from the Phono channel and unplug the power to the turntable motor, the rumble still occurs, so I don't suspect the turntable is at fault
- When I switch from FM channel (works fine, no rumble) to Phono channel, it takes a second or two for the rumble to ramp up, which makes me think something is heating up and causing the rumble in a high temp state, maybe the tubes in the phono channel
- I have verified with a Digital Multi Meter (DMM) that there is a solid ground path from the chassis of the turntable to the preamp, the preamp to the amp, and the amp to the turntable
- I was tapping on the V8 and V9 tubes (these are the phono tubes), and some static changes occurred and possibly some changes in the rumble, but not conclusive. I didn't hear any different rattling or any difference in tapping V8 V9 tubes and other tubes
- I verified ground connection is good between the tube sockets on V8 and V9 and the preamp chassis
- I swapped V8/V9 tubes with V10/V11 (these are for the monitor) tubes, the rumble still occurs
- If I remove V8/V9 tube(s), of course the rumble goes away but that's interrupting the circuit completely
- Rumble is proportional to volume control, it is similar in both Left and Right balances
- The turntable can be used, but the rumble overpowers the volume from the record, so I need to resolve the rumble in order to use the turntable
- The rumble occurred at both the vintage store and my apartment, so I don't suspect interference caused by some high power electrical source nearby

Given that the sound occurs with no turntable even plugged into the phono inputs, I suspect the issue is in the preamp itself and something in the phono circuit. Tube swapping didn't resolve the problem, so I either have all bad tubes or the tubes themselves are not the issue. I will think about cleaning the tubes and sockets with de-oxit, maybe the connection is bad? I will try to test the tubes at an audio store or proactively buy new tubes to make sure 100% that the tubes are not the issue.

My question is, is there anything else I should be checking? What, within the preamp, could cause a low frequency rumble in only the phono channel? Tubes? Capacitors? Ground issue I haven't tested? Anyone else have experience troubleshooting this issue or have a recommendation for something i can try? No audio repair shop in the city will take this equipment at the moment because it's so big, so any help would be appreciated

Product Manual, including tube schematic: http://www.fisherconsoles.com/custom electra IV service manual page.html

 

[century tek]

Welcome!

It's not called rumble. Rumble usually occurs when the the turntable is too close to the speakers and feeds back through the cartridge when played too loud or lots of bass.

If its making sounds when nothing is plugged in to it then it has to be an ailing resistor or tube in the phono position. Both channels with noise would indicate the power feed to the phono channel.

 

[gadget73]

agreed, sounds like a bum component in the phono preamp. If swapping the tubes does nothing, it has to be something else. Is it about equal in both channels or is this single channel? Single channel is probably one bad resistor or something, both channels could be a power supply issue since there shouldn't be much that is common to both channels and the chances that two different parts would fail in the same way is pretty low.

If this has original power supply parts, bad caps could be the problem. Poor decoupling between the amp stages produces something called motorboating, which can sound like a lot of different things but its usually a regular puttering low frequency noise.


If you're not up for a DIY repair, see if the shop will accept just the chassis if you remove it. Should only be a few screws to pull it. The rest of the box will eat too much space for most people to want to deal with. Too blasted heavy too.