JCN1218
Well-known member
Hi everybody,
I've been looking around the forum, especially the official build thread for this unit, and so far I haven't found a solution, though I am a little farther along than I was.
So right now, on channel 2 of my stereo build with rotary switches, I'm able to complete calibration steps 1&2, but I can't complete the final step because my unit seemingly has no gain reduction, and I can't figure out why. I've re-flowed solder into all of my solder joints, and the voltages on all of my transistors check out.
I feel like it's either an issue on the ratio board, or an issue with setting the qbias. My qbias, set according to mmats directions and also double checked using Hairball's directions, puts about -1.5 VDC at pads 7&18 with my black probe on CT/ground lug. My trim pot maxes out at about -3 VDC, so I usually go through half it's range before I see any volume drop.
It's hard to tell if my ratio switch is working since I'm getting no GR. But when I switch between the normal ratios I see the vu meter needle twitch as I'm used to seeing on my Hairball Rev A. However, when switching to 'all' mode I don't see any needle movement. It stays over zero instead of slamming hard right which makes me think an issue might be there, or is perhaps indicative of a problem elsewhere.
I'm probably going to check out the ratio board a bit closer when I get home to see if there are any major issues.
Any help would be greatly appreciated. The unit passes audio just fine, and both input and output controls with as I would expect them to. I feel like I'm so close to finishing this unit and getting into the rack
I've been looking around the forum, especially the official build thread for this unit, and so far I haven't found a solution, though I am a little farther along than I was.
So right now, on channel 2 of my stereo build with rotary switches, I'm able to complete calibration steps 1&2, but I can't complete the final step because my unit seemingly has no gain reduction, and I can't figure out why. I've re-flowed solder into all of my solder joints, and the voltages on all of my transistors check out.
I feel like it's either an issue on the ratio board, or an issue with setting the qbias. My qbias, set according to mmats directions and also double checked using Hairball's directions, puts about -1.5 VDC at pads 7&18 with my black probe on CT/ground lug. My trim pot maxes out at about -3 VDC, so I usually go through half it's range before I see any volume drop.
It's hard to tell if my ratio switch is working since I'm getting no GR. But when I switch between the normal ratios I see the vu meter needle twitch as I'm used to seeing on my Hairball Rev A. However, when switching to 'all' mode I don't see any needle movement. It stays over zero instead of slamming hard right which makes me think an issue might be there, or is perhaps indicative of a problem elsewhere.
I'm probably going to check out the ratio board a bit closer when I get home to see if there are any major issues.
Any help would be greatly appreciated. The unit passes audio just fine, and both input and output controls with as I would expect them to. I feel like I'm so close to finishing this unit and getting into the rack