tardishead
Well-known member
I just bought a Farfisa Ballata for 1Euro
It's fantastic and is very close to the sought after Compact Duo which is the early Pink Floyd sound amongst others.
I have a manual but some of the circuit boards are different and predate the manual.
The lower manual keyboard sounds are a lot quieter than the upper manual and bass pedals. In looking into the mixer/preamp circuit board I discovered that the V+ is very low. 5.5vdc
Most circuits in Farfisas of this era run on 8v. Never have I seen as low as 5v .In stead of taking the V+ from the 8v rail which feeds the signal generators and other circuits - the Ballata takes the preamp/mixer v+ from the 20vdc which feeds the reverb driver and speaker amplifier by adding a 820R resistor and a cap. After this resistor I measure 5v which implies 18ma current draw. If it was a 10v drop that would mean about 12ma.
The preamp mixer circuits consist of five oc76 germanium transistors. I checked all the resistors and they are pretty close to tolerance so it would seem to point that the transistors are drawing more current than intended.
My question is could increased leakage over time account for this larger current draw? What is the best thing to do?
Simply lower the dropper resistor for less voltage drop?
Or replace those transistors?
It seems to sound good BTW.
But obviously raising v+ would improve headroom and noise issues. Is raising v+ likely to kill those transistors?
It's fantastic and is very close to the sought after Compact Duo which is the early Pink Floyd sound amongst others.
I have a manual but some of the circuit boards are different and predate the manual.
The lower manual keyboard sounds are a lot quieter than the upper manual and bass pedals. In looking into the mixer/preamp circuit board I discovered that the V+ is very low. 5.5vdc
Most circuits in Farfisas of this era run on 8v. Never have I seen as low as 5v .In stead of taking the V+ from the 8v rail which feeds the signal generators and other circuits - the Ballata takes the preamp/mixer v+ from the 20vdc which feeds the reverb driver and speaker amplifier by adding a 820R resistor and a cap. After this resistor I measure 5v which implies 18ma current draw. If it was a 10v drop that would mean about 12ma.
The preamp mixer circuits consist of five oc76 germanium transistors. I checked all the resistors and they are pretty close to tolerance so it would seem to point that the transistors are drawing more current than intended.
My question is could increased leakage over time account for this larger current draw? What is the best thing to do?
Simply lower the dropper resistor for less voltage drop?
Or replace those transistors?
It seems to sound good BTW.
But obviously raising v+ would improve headroom and noise issues. Is raising v+ likely to kill those transistors?