Hey Jeff, having an issue on my latest build. I began to do the pre calibration step (with no op amp installed) and when I powered it up, all the LEDs went on, and when I flipped the SC HPF switch, PR2 smoked. I don’t see any polarity issues with any of the capacitors or diodes. Anything I should look for? I have a working FC526 I’m comparing with
[BUILD] CAPI FC526~500 Series~FET Limiter Kit~Official Support Thread
- Thread starter jsteiger
- Start date
Help Support GroupDIY Audio Forum:
Look for incorrectly placed transistors or resistors in the bottom left corner area of the main PCB.
Hi Jeff, I just completed my FC526-XFMR build and followed the calibration procedure. It passes signal, but I'm getting some strange results. When I apply a 1kHz sine wave @ -30dBu to the input, with the input and output pots at maximum, the output is around +7dBu like it should be. But the voltage at TP1 and TP2 is about 3x what it should be, 18mV AC instead of 5.8mV AC and 377mV AC instead of 117.7mV AC. I'm getting compression when I switch to 12:1, 20:1, or ABI, but no compression at all at the lower ratios.
The -10v DC rail is normal. I'm using a known working 990 opamp because my 2520 opamp isn't working.
I saw the earlier post with a similar problem and checked R31, R69 and R70. Values are correct, no solder bridges. Anything else I should check?
The -10v DC rail is normal. I'm using a known working 990 opamp because my 2520 opamp isn't working.
I saw the earlier post with a similar problem and checked R31, R69 and R70. Values are correct, no solder bridges. Anything else I should check?
Does anyone have any good/clear pictures of a correctly completed main board and also meter board (separately) of the XFMR?
I can’t find any good resolution pictures that I can refer to in order to compare with my build (resistors, capacitors, diodes, etc...) My test points and calibration isn’t quite going right.
Thanks in advance!
I can’t find any good resolution pictures that I can refer to in order to compare with my build (resistors, capacitors, diodes, etc...) My test points and calibration isn’t quite going right.
Thanks in advance!
@jsteiger Hi,
I have built a pair. All IC's, transistors, CR's and FET's are on sockets, so I can remove them easily. One on the pair also has the DTO5 on sockets.
Before fire up I check for bridges on +V and -V pins of DOA. --> no
I then checked voltages +V and -V, without MTR PCB connected and any quad IC/transformers/ etc.
+16VDC and -15.9VDC.
Did the same again, but with all parts placed on sockets, all but the VVR and MTR FET's and no DOA.
Then, when I placed the FET's and turned on, no LEDs and smoke... (Still no DOA placed).
The other one has LEDs lights up and no smoke. I compared polarized parts on both and they are placed identical to the PCB overlays. DTO5 has no mistakes. All diodes and elec. caps are orientated correctly. I have replaced the burnt resistors PR1 (MTR PCB) and PR2 (MAIN PCB), 10Ω, but with metalized ones; I don't have the other type.
From post #388:
Here are all of the PR uses:
PR1=A1 +V and feed to meter board
PR2=A1 -V and feed to meter board
PR3=DTO5 +V
PR4=DTO5 -V
PR5=2520 -V
PR6=2520 +V
PR7= Discrete follower (Q1 &Q2) +V
PR8= Discrete follower (Q1 &Q2) -V
So something went wrong with -V PR2 on main PCB burnt, which also burnt PR1 on meter PCB and possibly IC TL084.
Where should I check next? Same steps, and maybe use IC's/ mtr pcb from the other build?
I have built a pair. All IC's, transistors, CR's and FET's are on sockets, so I can remove them easily. One on the pair also has the DTO5 on sockets.
Before fire up I check for bridges on +V and -V pins of DOA. --> no
I then checked voltages +V and -V, without MTR PCB connected and any quad IC/transformers/ etc.
+16VDC and -15.9VDC.
Did the same again, but with all parts placed on sockets, all but the VVR and MTR FET's and no DOA.
Then, when I placed the FET's and turned on, no LEDs and smoke... (Still no DOA placed).
The other one has LEDs lights up and no smoke. I compared polarized parts on both and they are placed identical to the PCB overlays. DTO5 has no mistakes. All diodes and elec. caps are orientated correctly. I have replaced the burnt resistors PR1 (MTR PCB) and PR2 (MAIN PCB), 10Ω, but with metalized ones; I don't have the other type.
From post #388:
Here are all of the PR uses:
PR1=A1 +V and feed to meter board
PR2=A1 -V and feed to meter board
PR3=DTO5 +V
PR4=DTO5 -V
PR5=2520 -V
PR6=2520 +V
PR7= Discrete follower (Q1 &Q2) +V
PR8= Discrete follower (Q1 &Q2) -V
So something went wrong with -V PR2 on main PCB burnt, which also burnt PR1 on meter PCB and possibly IC TL084.
Where should I check next? Same steps, and maybe use IC's/ mtr pcb from the other build?
Attachments
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Measurements with not installed: FETs (VVR&MTR); DOA, Meter PCB
VDC PINS TL084 (NO IC PLACED) identical on both builds
1 1OUT -0.6
2 1IN– -0.6
3 1IN+ 0.0
4 VCC+ +15.2
5 2IN+ -0.8
6 2IN- -10.0
7 2OUT -9.6
8 3OUT 0.0
9 3IN- -0.5
10 3IN+ 0.0
11 VCC- -15.2
12 4IN+ 0.0
13 4IN- -0.6
14 4OUT -0.6
Measurement on a fully calibrated unit for reference:
VDC PINS (IC PLACED) no FETs installed
1 1OUT 0.0
2 1IN– 0.0
3 1IN+ 0.0
4 VCC+ +14.9
5 2IN+ -0.5
6 2IN- -1.5
7 2OUT +14.2
8 3OUT 14.4
9 3IN- -0.5
10 3IN+ 0.0
11 VCC- -14.9
12 4IN+ 0.0
13 4IN- 0.0
14 4OUT 0.0
These are the same on my built pair when I place the non burnt IC on both.
I’ll continue from here on with placing all parts etc. and when all is good, in the end will use a TL074, I have plenty of those, for the burnt TL084. I don’t have a spare TL084. Anyway, TL07X series are low-noise version of TL08X series from what I understand from the manufacturer website.
rtg603
Member
Hi everyone,
I am having the most difficult time attempting to calibrate this unit. I am totally new to calibrating and I'm having a difficult time wrapping my head around the process. I have my interface and 500-series chassis alongside Pro Tools. I have my FC526 in slot 1 of my chassis. I have Output 3 of my interface going into the input of the chassis and the output of my chassis going into Input 3. I opened Pro Tools and created 2 Mono audio tracks, one as a tone track and one as a receive track. I added a tone generator on Track #1 (TONE), and set it's output to Output 3 of my interface. I then set the FC526 receive track to Input 3 and then a different output. I enable Input monitoring and record enable, but nothing comes through when the unit is in bypass. I saw on the guide that it should be what goes in comes out. I am getting tripped up at step one and feel really dumb.
Hoping someone can help.
I am having the most difficult time attempting to calibrate this unit. I am totally new to calibrating and I'm having a difficult time wrapping my head around the process. I have my interface and 500-series chassis alongside Pro Tools. I have my FC526 in slot 1 of my chassis. I have Output 3 of my interface going into the input of the chassis and the output of my chassis going into Input 3. I opened Pro Tools and created 2 Mono audio tracks, one as a tone track and one as a receive track. I added a tone generator on Track #1 (TONE), and set it's output to Output 3 of my interface. I then set the FC526 receive track to Input 3 and then a different output. I enable Input monitoring and record enable, but nothing comes through when the unit is in bypass. I saw on the guide that it should be what goes in comes out. I am getting tripped up at step one and feel really dumb.
Hoping someone can help.
Mike from Hairball Audio has a nice video instruction for calibration with just a DAW and a multimeter. I know it's a different product, but it's basically the same principles here. Check the first 5 min to get started. Hope this helps.
Also handy, a units converter for dBu (calibration guide) and Volt (RMS) (multi-meter):
https://sengpielaudio.com/calculator-db-volt.htm
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I had the same issue with missing resistors and caps in four LC25 and LC40 kits. You can always ask Jeff.
But for me, it was not worth it to ask him, because in my case I would still be charged import fees where I live, even if it's $0 value.
Try to find two resistor that give you the desired value in parallel.
Measure with a DM if you have other resistors at hand or use this calculator to find a combination with common values that you do have locally:
https://www.electronics2000.co.uk/calc/series-parallel-resistor-calculator.php
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Thats actually a great idea. I did some combinations with two resistor values in parallel...ended up getting close to the desired value (about 3-4 ohms difference). Hopefully that will work in the meter PCB
Johan Olof Andersson
New member
- Joined
- Sep 1, 2023
- Messages
- 2
I am calibrating. First step test points, but not at full input.
I get good readings on TP2 118mV, TP3 963 mV and output 1.902 V.
TP1 though is at 0 V, no value.
When I follow the steps in the Calibration guide and set the bypass to active and full input, I get output 4.25 VAC, which is to much.
I get good readings on TP2 118mV, TP3 963 mV and output 1.902 V.
TP1 though is at 0 V, no value.
When I follow the steps in the Calibration guide and set the bypass to active and full input, I get output 4.25 VAC, which is to much.
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AndyKolp
New member
I'm sure you've got it handled already, but I just had the exact same problem. I found that diodes D1 and D2 were installed backwards. PR3 and PR4 were bad as well and needed replacement.
Andy! you've really saved the day here. I hadn't had it sorted yet. I had got pretty discouraged ,but low and behold, PR3 and PR4 are bad, I didn't notice. Thanks so much!!!
KP
If PR3 and PR4 smoke then there is a fatal error on the DTO5 build. Like Andy said, backwards diodes can be the cause. Misplaced transistors can do it as well.
Jeff! Thanks so much for responding. Aside from a snafu on a vp28, this is the first module that’s given me an issue out of the 10 I’ve built(6 vp28s, 3 bt50s and all op amps)
When I first built the unit, it was passing audio in bypass mode, and was passing audio and trying to compress when activated. Meters were working too.
I wasn’t sure how to cal it back then, just wanted to make sure it powered on without smoking. No smoke.…then when I got it on the test jig, it started acting weird. Long story short, i powered on lots of times to try and figure it out and there was no smoke. Then one day, when plugged into my APi rack, it started smoking.
For starters, I realized I had one connector on my test job backwards. So I’ll remedy that.
PR3 seems fine, but PR4 is slightly burnt. They both still read 10r. Should I replace them anyways?
D1 and D2 are installed correctly
As for DT05, R5 and R6 smoke immediately as soon as power hits it…..I’ll triple check the DT05 for build fails. I’ll try and add a pic when I get home
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