Search found 12 matches

by adalogue
Tue May 31, 2022 6:30 am
Forum: JLM Audio Kits
Topic: BA500v2 Mic Pre Amp BUILD THREAD 500/51X
Replies: 39
Views: 52198

Re: BA500v2 Mic Pre Amp BUILD THREAD 500/51X

Joe Malone wrote:
Mon May 30, 2022 7:55 pm
The normal trimpot range is roughly centered for 0VU = +4dBu so not sure why yours is not adjusting correctly.
Joe:

Possible to get typical voltage values at VU buffer IC pins for +4 dBU output?

Adam
by adalogue
Mon May 16, 2022 3:40 am
Forum: JLM Audio Kits
Topic: BA500v2 Mic Pre Amp BUILD THREAD 500/51X
Replies: 39
Views: 52198

Re: BA500v2 Mic Pre Amp BUILD THREAD 500/51X

Joe: I believe my gain resistors are correct, I've verified 60.5 dB max gain @ 1kHz (Zin @ detent). Is it going to mess anything up if I change a resistor value in the VU meter buffer stage to reduce the signal level feeding the VU meter? Since the unit clips at about +28 dBU, I'd like to decrease t...
by adalogue
Tue May 03, 2022 4:07 pm
Forum: JLM Audio Kits
Topic: BA500v2 Mic Pre Amp BUILD THREAD 500/51X
Replies: 39
Views: 52198

Re: BA500v2 Mic Pre Amp BUILD THREAD 500/51X

Transformer output with no reference resistors to the ground means only the internal capacitance to the primary give a ground reference so you will always have what seems like different output levels on a floating transformer out until it has resistance on +out and -out to ground then everything wi...
by adalogue
Mon May 02, 2022 10:20 am
Forum: JLM Audio Kits
Topic: BA500v2 Mic Pre Amp BUILD THREAD 500/51X
Replies: 39
Views: 52198

Re: BA500v2 Mic Pre Amp BUILD THREAD 500/51X

Progress! Traced the issue back to J1 header. Desoldered J1 ribbon connection and GND short went away. Ohm’d the ribbon cable and found two shorts in the ribbon cable. Re-terminated the ribbon cable and GND short issue was fixed! Now getting nice balanced input impedance with good variation from Z p...
by adalogue
Tue Apr 26, 2022 2:20 pm
Forum: JLM Audio Kits
Topic: BA500v2 Mic Pre Amp BUILD THREAD 500/51X
Replies: 39
Views: 52198

Re: BA500v2 Mic Pre Amp BUILD THREAD 500/51X

The soldering pads below the green/black text have soldering going over the ground plane which is bad as any hole in the solder mask will give a dead short to 0v. Also a couple of the 10 pin black DI header soldering do the same by the looks. Is the black DI header also fitted the correct way aroun...
by adalogue
Mon Apr 25, 2022 3:14 pm
Forum: JLM Audio Kits
Topic: BA500v2 Mic Pre Amp BUILD THREAD 500/51X
Replies: 39
Views: 52198

Re: BA500v2 Mic Pre Amp BUILD THREAD 500/51X

One other thing I noticed, with DI jumpers in, if input pad switch is down, l get 440 ohms between xfmr green and 0v and still a short between xfmr blue and 0v. These tests were done without the pots plugged in. Some of the resistors got hot when I was trying to solder the switches in, I should have...
by adalogue
Mon Apr 25, 2022 3:03 pm
Forum: JLM Audio Kits
Topic: BA500v2 Mic Pre Amp BUILD THREAD 500/51X
Replies: 39
Views: 52198

Re: BA500v2 Mic Pre Amp BUILD THREAD 500/51X

I'm troubleshooting very low input impedance and no output. If you have 28ohms between green and red that is correct. Make sure black wire is not connected to anything. The input is balanced so the -in should not be low ohms to 0v. Pot wiring looks correct. Make sure the red and green wires are not...
by adalogue
Mon Apr 25, 2022 7:03 am
Forum: JLM Audio Kits
Topic: BA500v2 Mic Pre Amp BUILD THREAD 500/51X
Replies: 39
Views: 52198

Re: BA500v2 Mic Pre Amp BUILD THREAD 500/51X

I'm troubleshooting very low input impedance and no output. I have 28 ohms a crossed the input xfmr primary (between RED and BLK wires), this is the same in and out of circuit, and the same as what I read from between In(+) and GND at the edge card connectors. I have very low resistance between Vin(...
by adalogue
Mon Apr 25, 2022 6:41 am
Forum: JLM Audio Kits
Topic: VUPPM500 KIT Build Thread
Replies: 29
Views: 52160

Re: VUPPM500 KIT Build Thread

For the record this ended up being both a cold solder joint or two, both sides of meter now repsonding.
by adalogue
Sun Dec 26, 2021 11:20 am
Forum: JLM Audio Kits
Topic: VUPPM500 KIT Build Thread
Replies: 29
Views: 52160

Re: VUPPM500 KIT Build Thread

Email sent, thank you Joe. The PPM is not peak value of waveform but rather highest RMS value over a period of time? I though main VU was RMS and peak VU was waveform peak, if that’s not right then it explains some of my issues. Appreciate your help.
by adalogue
Mon Nov 15, 2021 2:41 am
Forum: JLM Audio Kits
Topic: VUPPM500 KIT Build Thread
Replies: 29
Views: 52160

Re: VUPPM500 KIT Build Thread

HI Adam Sorry I didn't get a notification for this post. That 0.1uF will be fine. What problem are you having with the calibration? Hi Joe. I went ahead and installed the two 1uF bypass caps since I had already ordered them, I also desoldered and flipped the trimmers since I stuffed them backwards ...
by adalogue
Wed Oct 20, 2021 8:59 am
Forum: JLM Audio Kits
Topic: VUPPM500 KIT Build Thread
Replies: 29
Views: 52160

Re: VUPPM500 KIT Build Thread

I seem to have lost one 1uF ceramic axial cap. I have a bunch of 0.1uF axial ceramic lying around for use as bypass caps, can those be substituted for the two caps under the CPU, or is 1uF required? I'm having some issues getting the unit totally calibrated, wonder if this might be influencing that....