Fisher 400 - volume channels uneven at low volume

TravAndAlex

Active Member
Hey guys... wondering if there is a fix for this. The right channel is much quieter than the left at very low volumes (unfortunately where morning radio listening levels are at). I've Deoxited it, and it is static free and working, but the channels don't even out until above 2 on the dial.
 
You have several options
1) Live with it and use the balance control
2) Replace the volume control (good luck finding one)
3) Have the current one rebuilt (Search for Mark Oppat)
4) Use less efficient speakers and your problem will disappear.
 
Agree with Dad.

If you're up to it, I've had some success in doing a complete teardown of the pot and wiping the traces clean. Much better effect than simply shooting Deox. You can also retension and re-track the tines while you're in there. There's a sticky on breaking one down.
 
The curse of the Fisher volume pot! Well said Dadbar, I found #4 to best solution for me. Find some AR-3s, or Dynaco A-25s. No Klipsch
 
The curse of the Fisher volume pot! Well said Dadbar, I found #4 to best solution for me. Find some AR-3s, or Dynaco A-25s. No Klipsch

Damn it. How did you know it was hooked to my KG-5.2's? :p Still noticeable on my JBL L96's. Haven't tried the 112's, but I imagine they are the same as the 96's. I'm not buying any more speakers! You can't make me. Ha!

Option 1 is looking very realistic.
 
hi….quick questions….i just bought a fisher 400 and had it serviced…..i love it….i think…..when i select phono, when the volume is turned up past 5 or 6…there is a slight hum that comes out of the speakers and gets louder when the volume gets turned up the closer to max i get….….is this normal….also the volume on the turntable is much lower than that of the tuner,and i just put in a new cartridge,is this normal……and one more question…..do the tubes on the receiver need to heat up before the sound quality gets really good ?….i know….i have a lot of questions….i am new to this vintage tube receiver thing and would love your responses….thanks so much….much anticipate your response…..b
 
I'm a new 400 owner as well, so I'm not going to be the authority on 'normal'. So take this all with a grain of salt.

Phono input is definitely quieter than Tuner or Aux on mine... although that is likely a function of turntable and cartridge as well. Are you using Phono Low or Phono High input? I believe Low is appropriate for most MM cartridges? Are you using a grounding wire between the receiver and your turntable - without one, this could explain the hum.

IMO if you are consistently running your receiver above mid volume, it may not be a good fit for you. If that much volume is needed, you should look into much more efficient speakers or a receiver with a lot more power to suit your tastes - this thing is only a somewhat optimistic 25 wpc.

It will sound fine once the tubes get to temperature (a few minutes). Theoretically, they will sound a bit better after being on for a while at operating temperature.

When they serviced it, did they replace most capacitors and the power supply (as per kits like Metalbone's)? If not, there may be more that should be done to get back in proper working order.
 
The loudness of the phono input depends a lot on your cartridge output. Not sure what the Fisher spec is for cartridge output, but if yours is lower than what the 400 expects, it will be quieter. Not much to do for it other than changing cartridges to one with hotter output.

The hum could be bad cables from the turntable or a bad ground connection from the turntable if its in good electrical shape. Also, there are likely supposed to be shields over the phono tubes. Missing ones can make it noisy.
 
With the Fisher 400, stick to cartridges that output 5mV or more. I use the Shure M91E with mine and don't notice a huge difference. When I used the Shure VXmR which outputs at 3mV, it was a pain to have to keep turning up the volume. The more you twiddle, the more opportunities to wear out that volume control even more.

This goes without saying, but make sure you are using a good set of 12AX7 tubes in the phono section. Don't get cute with something lower gain like the 5751.

To reduce hum, make sure your phono cables are not near the power cord or power transformer.
 
With the Fisher 400, stick to cartridges that output 5mV or more. I use the Shure M91E with mine and don't notice a huge difference. When I used the Shure VXmR which outputs at 3mV, it was a pain to have to keep turning up the volume. The more you twiddle, the more opportunities to wear out that volume control even more.

Interesting! I use an Ortofon Blue which (I just looked it up) is a 5.5 mV output... so yeah, if that one is slightly quieter than the other inputs, I imagine a 3 mV cartridge would be very quiet.
 
barry. You answered your questions pretty well for someone who doesn't know much about tubes.. The phono section has to boost the input level of millivolts to just about 1/3 of a volt (.33volt) at the preamp. Then the preamp has to boost that .33v signal to about 1 to 1.5v (sometimes 2+volts for some modern CD or DVD players). Hum at accelerated volume levels (above 5in volume) in phono is normal in most(99.99999999999994/10ths) cases with no signal.
Tubes heat up within a minute or 2 so they can conduct. Additional time the tube gets to steady down may or may not allow a better sound quality it depends on the actual tube type, and where in circuits they are.

The Diagram is from a SX-737 PIONEER but the idea behind the gain stages is the same. The phono stage has to really boost the signal and with that boost you'll get more opportunity for some hum.

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