Fisher 400 Loudness Switch Wiring

[streetwise]

Does anybody have pictures or a diagram of the loudness switch wiring. I rebuilt my receiver and I have an imbalance in volume, when I disconnect the left channel loudness wire from the volume control it returns to full volume.

 

[larryderouin]

With the unit UPSIDE DOWN, The Front of the Unit is to your Right. You have 2 wires from the balance control, and 2 coax wires from the Phase Inverter area. Black with a stripe (green), and WHITE with a stripe. Pins are 1-2-3 side wall to balance pot.

Front POT (closest to attachment nut.)
Pin 1 White wire from Balance pot.
Pin 2 Center lead of WHITE COAX.
Pin 3 Shield lead of WHITE COAX (Ground)

Rear POT
Pin 1 Blue wire from Balance pot.
Pin 2 Center lead of BLACK COAX
Pin 3 Shield lead of BLACK COAX.

Underneath is the leads for the loudness circuit
White is for the Front Pot
Violet for the Rear Pot.

The ends aren't too clear to see where they go as the heatshrink is all the same color, but you get the general idea.

And next time, TAKE PICTURES!

 

[streetwise]

hey larry do you have any of the loudness switch itself. my guess is the cap on the left channel isn't placed right as the wires were placed differently on the switch itself. and yes I should have taken very in depth pictures for my own benefit and for others

 

[larryderouin]

With Unit upside down the caps will be on the TOP and CENTER PINS of the switch. Make sure the 22K resistors are connected also at the top pin.

 

[dcgillespie]

Also be very careful that you don't cross the channels. The treble boost cap must connect to the top of the same control whose loudness tap the the loudness switch ultimately connects this cap to when the loudness switch is turned on.

Dave

 

[streetwise]

hmm interesting wiring all seems right. Thanks Larry for the pictures, for whatever reason the second I attach the purple wire to its tap on the volume control the volume cuts down to a whisper in the left channel. I would love to figure it out but as long as the wire is disconnected volume is regular and loudness works on the right channel. Still if you have any further ideas they would be interesting to hear thanks

 

[dcgillespie]

If you disconnect the wire from the loudness tap on the volume control in either channel, the channel with it disconnected SHOULD get very much louder. It is the fact that the loudness circuit provides such attenuation when the loudness switch is turned off, that it can provide the low boost that it does when turned on. When the loudness switch is turned on, it is simply not attenuating the low frequencies nearly as much as when turned off (hence, the bass boost effect), while also connecting a a simple treble boost circuit that is disabled when the switch is turned off. Therefore, when you turn the loudness switch on, both the bass frequencies and treble frequencies are effectively boosted at the same time.

Dave

 

[streetwise]

Ok so what are your thoughts here Dave its not like a small jump in loudness though If I have my balance control on the cusp of being full left just before 7 and 8 o'clock both left and right are balanced with the purple wire on the loudness tap. it sounds like the signal is getting lost somewhere to me not just a simple attenuation of bass and treble

 

[larryderouin]

Can you take a picture of your unit, the same as the two I posted, for comparison. Also a slightly larger one of the whole corner of the 400. This way we can actually see your wiring and possibly note any mis-wiring or missing wiring. Did you do anything to the Tape Monitor, speaker or low Filter switch wiring? De-Oxit the switches and exercise them briskly, then spray with Faderlube. Also do the Rotary Function switch.

Larry

 

[dcgillespie]

I'd first disconnect the two leads to the loudness taps on the volume control (one for each channel), and then measure the value of the two 22K resistors associated with the loudness switch. They need to be well matched for the volume control to track properly between the channels.

Dave

 

[streetwise]

left channel reads 22.01, right channel is 21.82. pictures are on the way Larry

 

[streetwise]

If you need anymore pictures let me know. best i can do with flash at this hour

 

[dcgillespie]

Use an external high level source of known balanced outputs HAVING ITS OWN LEVEL CONTROL, and connect it to the Aux inputs. On Your Fisher (with both loudness tap leads properly connected), center the balance control, turn Loudness Switch off, and turn volume to max. Control volume by level control on source. If sound is now balanced, then the problem lies with the volume control in the Fisher. If still unbalanced, then the problem lies with an active amplification stage in the Fisher.

Dave

 

[streetwise]

Ok Dave seems its fixed

 

[dcgillespie]

So......What was it?

 

[streetwise]

Lets see if this post goes through, had trouble yesterday posting more than three words. I tried maxing volume and channels did balance, after considering giving up on it, I tapped the white wire and noticed it felt loose on the loudness tap it seems it had snapped of the loudness tap so the issue was actually the other channel not having contact with the loudness tap. Thanks Larry & Dave for all of your help figuring out what was going on. Do you think replacing the 22k resistors will tighten the balance any more?

 

[dcgillespie]

Nope. They're already within 1% of each other. Glad you found it!!

Dave