Need Help repairing Nelson Pass BOSOZ preamp!

rogerfederer

determined amateur
Subscriber
my friend, AKer FMJunkie got this in a trade. then sold to my friend bob, who sold to me. it is a Nelson Pass "bride of son of zen" or BOSOZ or balanced zen line stage. 1 balanced input and 3 unbalanced. also, has built in crossover so there are >100hz outputs and <100hz outputs; if they work they could be very handy.

here are pics: http://albums.phanfare.com/isolated/8OWrL0el/1/14382797

it says "R2R volume control" ?? i found a bunch of threads like this: http://vicol-audio.ro/volume-controller.php anyone know what that is? like LDR?

and any one recognize the builder? signature looks like "Ben Provent.... III" when i google that i get nada.

btw, it sounds wonderful!
 
bumping this thread as the BOSOZ had a terrible accident. another device upstream (monarchy dip) went belly up and sent all kinds of loud noise and god knows what else to this lovely preamp. now it does not work. powers up and the volume knob clicks as before when you turn it, but it does not attenuate volume and the switch does not switch between different inputs.

so far i've had no luck w identifying the builder. any suggestions about someone who would be knowledgeable about such an unusual beast? need someone to fix it!
 
I once had a power surge take out one channel of a Goldmund power amp. It was late, so I shut everything down. The next day I turned everything on and the amp worked beautifully. That was a bit over 20 years ago and I still use the amp daily.
 
OK, caught it in the act! have been running it all day and its really warmed up. there is a lot of cross talk between the inputs. i have it switched to input 2 (tuner) and when i switch to input 1 (hooked up to DAC) i hear the tuner: loud and volume control doesn't work as well. i recall a couple of days ago i had the DAC playing and switched to input 2 and listened to tuner; the sound from input 1 bled into the sound from input 2.

does that ring a bell for anyone?

will take slimecity's advice and post over on diyaudio.com; thanks!
 
Your going to need a map to fix it. I would start by making a sketch of each board and identify inputs, outputs, Power and ground.

The rectangular white items that say Seimens are relays. You will need to measure coil voltage to see if they are being powered properly.

Most common preamp problem are power supply's. Also tap on the relays they go bad often.

Good luck, Looks like a nice unit.
 
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