Tales from the bench: Vintech 1073

Pro audio gear like preamps, compressors, etc are always fun because they give us a chance to break out of our usual PCB swap routines and do some old fashioned tech-ing. We received a Vintech 1073 clone from The Creamery recording studio in Brooklyn. Seems one of the channels of their Vintech 1073 just had a certain “character” to it that wasn’t sitting well.

As you can see from the fourth photo, a 1kHz test signal showed some definite “character” indeed. At first, we suspected that one of the transistors was going south, and expected to do a swap. I’ll admit right here the spoiler which is: we were not correct at first. At a shop like ours, speed is key, so the move is usually to suspect the thing most likely to go bad: switches, pots, power supplies, then the active components, then everything else. Reason: the part that breaks is usually the one that can get broken by the human. Like a switch, or an input amplifier (from feeding it a too-hot signal). So after checking the gain switch and jacks, our next suspect was the first stage transistor.

Luckily, with such a classic and well-known design, we didn’t need much in terms of a schematic…right? We hooked up the scope, and saw an obvious issue. Kind of an unusual trace for a failing transistor, but anything can happen, right? After swapping the unit with a new one, we still saw the same scope trace. That’s when the good ol’ DMM came out and revealed the real problem: the collector current on the first stage transistor was way too hot. Looking into some old Neve schematics and comparing with what was on the PCB, we found a resistor with the correct value, but wrong multiplier. Clearly someone grabbed from the wrong bin or maybe…colorblind? Any case 440 ohms is a whole lot different than 44k. So the poor NPN was slamming its little head on the ceiling. Once we replaced the resistor with the correct one, all was well.

While we do sometimes see issues caused at the factory, they are rarely so obvious as this one. Pretty unusual for such an established company, but I guess everybody gets a mulligan.

Work completed: 1 resistor swapped. Full bench test.

-Jon