Farfisa Compact - No Sound

[glebert]

I picked up a 60's Farfisa compact a while ago that needed some mechanical repairs and now I'm getting to the electrical function. I'm getting no sound whatsoever on either the main or bass outputs. I was told by the guy I got it from that the oscillator cards were oscillating, but I have not verified. No power amp on this unit, only tube preamp. It looks like the power supply has already been recapped. The selenium bridge rectifier and diode are still there. I haven't started doing voltage measurements yet, finally got the thing in a stable position to be able to do some testing. Silly 1960's Italians...

Anyway, any suggestions would be welcome. If the voltages look at all off I'm thinking to replace the selenium parts with silicon straight away.

Farfisa_Combo_Compact_schematics.pdf

[glebert]

Not looking good. I don't seem to be getting any appeciable voltage (AC or DC) into or out of the HT diode. Resistance across HT secondary very high, over 30k but the reading is kind of flaky. I didn't mention the organ came to me with a 3A fuse installed instead of 0.5A, so someone might have pushed their luck a little too far on this one.

Getting voltage out on the 22VAC secondary and out of the bridge rectifier. Resistance on that secondary winding something like 3 ohms.

[Jazz P Bass]

I would install a small 110/220 step up transformer in it.

[mozz]

Not going to help any if the secondary resistance is 30k.

[glebert]

I would install a small 110/220 step up transformer in it.

Definitely considering that. I also have a Crate VC3112 chassis in my bone pile. That power transformer could probably supply all the voltages except the 9V coming off the filament windings but I'm not sure if that even goes anywhere.

I haven't measured current but when I put it on a light bulb limiter there is more current draw (light from 150 watt bulb) than I would expect, so I don't know if it is just a matter of an open secondary.

[glebert]

I disconnected the HT secondary from the selenium diode and found that secondary completely open. I found something on another forum of a Farfisa that had a broken solder joint inside the transformer where the windings meet the leads. Since this organ was one step from the trash (or maybe listing it local to anyone who wanted it for free), I figured it was worth a shot. Got the bell covers off enough to see that one of the HT wires was not connected. Soldered it back down and then was getting a couple hundred ohms across that secondary. Powered on LBL and variac and I'm getting 160VAC at the secondary, Considering the drop of the bulb I think that means it's OK. Going to replace the selenium diode with silicon and power up slow and see what happens.

[glebert]

Installed silicon diode and reconnected HT secondary. Still wasn't getting sound, then realized I hadn't plugged in the giant bundle of wires that connect the power supply to the rest of the organ. Again with the silly 60's organ designers, some wires are hardwired to the PS and then a bunch are on an assembly that is like a monster molex connector without the plastic.

Plugged those wires in and the organ came to life (mostly). Some things not working right, but getting sound from all the treble keys and the vibrato and tone boosts seem to be working. Getting little to no sound from the bass keys, I don't think the reverb is working, and some keys are not getting good contact with all of the stops (I think that this the terminology) so as you go up the keyboard a key will drop down in pitch. Maybe I just have a card that is out of tune, I haven't really dove into that yet. Transformer seems to be running a little hot, so that is the thing that I am worried about long term, but it feels good to finally make progress on this organ and get to play it. I really like the sounds, I would definitely choose this over the Wurlitzer 200 I have that is very much a one trick pony.

[glebert]

I found some interesting information on this model organ. Seems Farfisa did a piezo driver and pickup (maybe actual phono cartridges) for the reverb springs to get around Hammond's patent. They needed really high voltage to drive it, and probably really high impedance for the pickup, so they had to use tubes for that because the transistors at the time were not capable.

If this one ends up having more problems with the transformer, or if someone else is trying to fix one with a bad transformer, it seems the whole organ can be run off the 8VDC except the reverb and the light bulb for the optional volume pedal (that uses the 9VAC on the schematic). In that situation I think one could convert the reverb to hammond style, use a simple op amp circuit for drive and pickup, and get all the voltages necessary off a transformer with a single secondary with a fairly low voltage. It would need to provide moderate current, but the total power draw for this with tubes is supposed to be about 20 watts so a few amps at 8V should be plenty. Of course if the reverb isn't working it might make sense to just integrate a digital reverb pedal in there.