LA500A opto comp MAY 2021 BUILD THREAD 500/51X

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bramble
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Re: LA500A opto comp MAY 2021 BUILD THREAD 500/51X

Post by bramble »

I've completed my LA500A and am having trouble getting it working. I've isolated the problem to the following on the Side Chain board:

Applying a +4dbu 1khz balanced signal to the unit, threshold has no effect at all on GR. I've isolated the problem to the diode bridge D1-D4. With the Threshold set full CW is I've measured 0.452VAC/RMS(+0.72VDC) across the LED of U1. I believe this is still below the LED's forward bias. The output from pin1 of IC1 is -8dbu which is the same signal strength after R1.

Top trace is the input signal. Bottom is the test point. Both set to 1V/div.
Image 1 is the signal at the D1/D3 Cathode
Image 2 is the signal at the D2/D4 Anode
https://imgur.com/a/IDFV3w8

I have removed from the circuit and confirmed all of the following components are working: IC1, D1-D4, U1, Balance trim pot, Zero GR trim pot. I have also re-flowed every solder point on the SC board.

I am at a complete loss on this. Anyone have any ideas on where my problem might lie?

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Re: LA500A opto comp MAY 2021 BUILD THREAD 500/51X

Post by Joe Malone »

bramble wrote:
Wed Feb 08, 2023 5:35 pm
I've completed my LA500A and am having trouble getting it working. I've isolated the problem to the following on the Side Chain board:

Applying a +4dbu 1khz balanced signal to the unit, threshold has no effect at all on GR. I've isolated the problem to the diode bridge D1-D4. With the Threshold set full CW is I've measured 0.452VAC/RMS(+0.72VDC) across the LED of U1. I believe this is still below the LED's forward bias. The output from pin1 of IC1 is -8dbu which is the same signal strength after R1.

Top trace is the input signal. Bottom is the test point. Both set to 1V/div.
Image 1 is the signal at the D1/D3 Cathode
Image 2 is the signal at the D2/D4 Anode
https://imgur.com/a/IDFV3w8

I have removed from the circuit and confirmed all of the following components are working: IC1, D1-D4, U1, Balance trim pot, Zero GR trim pot. I have also re-flowed every solder point on the SC board.

I am at a complete loss on this. Anyone have any ideas on where my problem might lie?
Sent a reply to your email thread as it was too long to reformat to make sense on here.
Joe :-)
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noahraimy
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Re: LA500A opto comp MAY 2021 BUILD THREAD 500/51X

Post by noahraimy »

Had a blast building this but am really just stumped with figuring out how to get a proper test tone going through the box. Apologies this is kind of a dumb question, I've just never calibrated a VU meter before.

At the moment, I only have a laptop with a headphone jack and a MOTU interface with stereo set of TRS out put jacks. I have not been able to get a reading higher than 0.1vac in any configuration from my lunchbox's output or from the cable going in to the lunchbox.

I tried using my outs on my interface with output volume cranked and then out of my headphone jack as well. I tried running cables into a DI box, then into a converter jack thing. Now I've tried running balanced cables and still no luck. My interface is rated for up to 20dbu on the output so clearly I'm doing something wrong with my connections or measuring.

I'm not sure what else to try with my connections, I was initially using alligator leads clipped to the pins which was a bit awkward and then took apart one of my XLR cables so I could clip my leads directly to the wire. I wasn't sure if it was a multimeter issue because I recalled having a problem in the past, and borrowed another one and both gave more or less the same readings.

Is there anything else I should try or anything I stupid I am missing? Apologies I'm fairly new to this and might be a bit in over my head.

Thank you!

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Re: LA500A opto comp MAY 2021 BUILD THREAD 500/51X

Post by Joe Malone »

noahraimy wrote:
Tue Aug 29, 2023 7:17 am
Had a blast building this but am really just stumped with figuring out how to get a proper test tone going through the box. Apologies this is kind of a dumb question, I've just never calibrated a VU meter before.

At the moment, I only have a laptop with a headphone jack and a MOTU interface with stereo set of TRS out put jacks. I have not been able to get a reading higher than 0.1vac in any configuration from my lunchbox's output or from the cable going in to the lunchbox.

I tried using my outs on my interface with output volume cranked and then out of my headphone jack as well. I tried running cables into a DI box, then into a converter jack thing. Now I've tried running balanced cables and still no luck. My interface is rated for up to 20dbu on the output so clearly I'm doing something wrong with my connections or measuring.

I'm not sure what else to try with my connections, I was initially using alligator leads clipped to the pins which was a bit awkward and then took apart one of my XLR cables so I could clip my leads directly to the wire. I wasn't sure if it was a multimeter issue because I recalled having a problem in the past, and borrowed another one and both gave more or less the same readings.

Is there anything else I should try or anything I stupid I am missing? Apologies I'm fairly new to this and might be a bit in over my head.

Thank you!
First check your multimeter is switch to AC volts and range like 2v and are measuring between pin 2 & 3 of the output XLR. If you need more level you can turn up the makeup control. If you still cannot get the correct 1.23vac then attach some photos of the meter and comp build
Joe :-)
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noahraimy
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Re: LA500A opto comp MAY 2021 BUILD THREAD 500/51X

Post by noahraimy »

Joe Malone wrote:
Tue Aug 29, 2023 8:14 am
noahraimy wrote:
Tue Aug 29, 2023 7:17 am
Had a blast building this but am really just stumped with figuring out how to get a proper test tone going through the box. Apologies this is kind of a dumb question, I've just never calibrated a VU meter before.

At the moment, I only have a laptop with a headphone jack and a MOTU interface with stereo set of TRS out put jacks. I have not been able to get a reading higher than 0.1vac in any configuration from my lunchbox's output or from the cable going in to the lunchbox.

I tried using my outs on my interface with output volume cranked and then out of my headphone jack as well. I tried running cables into a DI box, then into a converter jack thing. Now I've tried running balanced cables and still no luck. My interface is rated for up to 20dbu on the output so clearly I'm doing something wrong with my connections or measuring.

I'm not sure what else to try with my connections, I was initially using alligator leads clipped to the pins which was a bit awkward and then took apart one of my XLR cables so I could clip my leads directly to the wire. I wasn't sure if it was a multimeter issue because I recalled having a problem in the past, and borrowed another one and both gave more or less the same readings.

Is there anything else I should try or anything I stupid I am missing? Apologies I'm fairly new to this and might be a bit in over my head.

Thank you!
First check your multimeter is switch to AC volts and range like 2v and are measuring between pin 2 & 3 of the output XLR. If you need more level you can turn up the makeup control. If you still cannot get the correct 1.23vac then attach some photos of the meter and comp build
I deleted a few replies because I managed to get the correct voltage! Through plugging in and unplugging everything multiple times trying to troubleshoot I made a stupid mistake that I didn’t notice until just now. Initially I believe I was just using a bad cable adapter but after finding a better one (and using the right ins and outs :roll:) everything is fixed. Oops!

I will probably be back on this thread later when I have a chance to properly run through the calibration and test the unit later. Again thanks for your help!!!

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Re: LA500A opto comp MAY 2021 BUILD THREAD 500/51X

Post by Joe Malone »

noahraimy wrote:
Wed Aug 30, 2023 8:03 am
Joe Malone wrote:
Tue Aug 29, 2023 8:14 am
noahraimy wrote:
Tue Aug 29, 2023 7:17 am
Had a blast building this but am really just stumped with figuring out how to get a proper test tone going through the box. Apologies this is kind of a dumb question, I've just never calibrated a VU meter before.

At the moment, I only have a laptop with a headphone jack and a MOTU interface with stereo set of TRS out put jacks. I have not been able to get a reading higher than 0.1vac in any configuration from my lunchbox's output or from the cable going in to the lunchbox.

I tried using my outs on my interface with output volume cranked and then out of my headphone jack as well. I tried running cables into a DI box, then into a converter jack thing. Now I've tried running balanced cables and still no luck. My interface is rated for up to 20dbu on the output so clearly I'm doing something wrong with my connections or measuring.

I'm not sure what else to try with my connections, I was initially using alligator leads clipped to the pins which was a bit awkward and then took apart one of my XLR cables so I could clip my leads directly to the wire. I wasn't sure if it was a multimeter issue because I recalled having a problem in the past, and borrowed another one and both gave more or less the same readings.

Is there anything else I should try or anything I stupid I am missing? Apologies I'm fairly new to this and might be a bit in over my head.

Thank you!
First check your multimeter is switch to AC volts and range like 2v and are measuring between pin 2 & 3 of the output XLR. If you need more level you can turn up the makeup control. If you still cannot get the correct 1.23vac then attach some photos of the meter and comp build
I deleted a few replies because I managed to get the correct voltage! Through plugging in and unplugging everything multiple times trying to troubleshoot I made a stupid mistake that I didn’t notice until just now. Initially I believe I was just using a bad cable adapter but after finding a better one (and using the right ins and outs :roll:) everything is fixed. Oops!

I will probably be back on this thread later when I have a chance to properly run through the calibration and test the unit later. Again thanks for your help!!!
Cool let me know how the cal goes for you.
Joe :-)
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noahraimy
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Re: LA500A opto comp MAY 2021 BUILD THREAD 500/51X

Post by noahraimy »

Hey Joe!

Got everything calibrated and the process went smoothly.

When demoing the comp everything works as expected except for the threshold control and the compression itself. The threshold has no noticeable effect on the signal until turned about 3/4 of the way where it begins to introduce a high pitched squealing distortion like oscillation sound which sweeps with the control until turned all the way to the right where it disappears. The instrument signal cuts out before coming back when turned all the way. The squeal also increases in volume in relation to makeup gain. There isn't much noticeable volume reduction and the signal going in doesn't seem to move anything on the VU meter not affect the level of gain reduction. Just trying it now, the meter reads -7 and jumps back to zero when I strum and makes a sort of shew shew stepped sound as it goes back to -7. The distortion also changes based on the ratio setting.

Any ideas? I should note I am sending a guitar through a DI box into the comp, and I don't have access to a preamp at the moment. I've attached some pics I took earlier and a video I took showing the sound. I took this video before I calibrated so if the VU meters look off it is bc of that. I didn't mention it earlier because I wanted to take everything one at a time and wasn't 100% sure if calibration would have an effect on it.

Here's an album of pics
https://drive.google.com/drive/folders/ ... AWZXZ-VXXd

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Re: LA500A opto comp MAY 2021 BUILD THREAD 500/51X

Post by Joe Malone »

noahraimy wrote:
Thu Aug 31, 2023 7:36 am
Hey Joe!

Got everything calibrated and the process went smoothly.

When demoing the comp everything works as expected except for the threshold control and the compression itself. The threshold has no noticeable effect on the signal until turned about 3/4 of the way where it begins to introduce a high pitched squealing distortion like oscillation sound which sweeps with the control until turned all the way to the right where it disappears. The instrument signal cuts out before coming back when turned all the way. The squeal also increases in volume in relation to makeup gain. There isn't much noticeable volume reduction and the signal going in doesn't seem to move anything on the VU meter not affect the level of gain reduction. Just trying it now, the meter reads -7 and jumps back to zero when I strum and makes a sort of shew shew stepped sound as it goes back to -7. The distortion also changes based on the ratio setting.

Any ideas? I should note I am sending a guitar through a DI box into the comp, and I don't have access to a preamp at the moment. I've attached some pics I took earlier and a video I took showing the sound. I took this video before I calibrated so if the VU meters look off it is bc of that. I didn't mention it earlier because I wanted to take everything one at a time and wasn't 100% sure if calibration would have an effect on it.

Here's an album of pics
https://drive.google.com/drive/folders/ ... AWZXZ-VXXd
The comp is looking for a pro level signal of +18dBu. Run some music into the input at +4dBu levels. A DI from a guitar needs to go to a mic pre before going to the comp.

Please keep answers as short as possible, otherwise, I may not get time to read them during the week.

With threshold and makeup fully CCW is the level the same when you switch from off to GR and VU?? Y / N

Did the comp do the -5dB cal from VU to GR correctly?

Are the opto dots in the correct places? Square pad on U1 & U2

What fault did you find and fit that you could finally align the comp?

Your videos and photos are too blurry to see. I need clear in focus well-lit top and bottom photos of each PCB to check all soldering and parts placement. Remove JLM99v opamps so I can see the parts underneath. But answer above questions first to see if I can narrow down what is wrong.
Joe :-)
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Alex1990
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Re: LA500A opto comp MAY 2021 BUILD THREAD 500/51X

Post by Alex1990 »

Hi!

A unit I built recently when engaged has a 9-10db volume boost, with the make-up gain pot not having a massive overall effect. It’s as though the minimum gain on the pot is set that much higher somehow. Any thing I can look out for/measure? Unit sounds good otherwise.

All the best!

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Re: LA500A opto comp MAY 2021 BUILD THREAD 500/51X

Post by Joe Malone »

Alex1990 wrote:
Thu Oct 19, 2023 5:38 am
Hi!

A unit I built recently when engaged has a 9-10db volume boost, with the make-up gain pot not having a massive overall effect. It’s as though the minimum gain on the pot is set that much higher somehow. Any thing I can look out for/measure? Unit sounds good otherwise.

All the best!
HI Do the link and slow attack leds light up when pot switches pulled outwards?
Attach a clear well lit in focus photo of the top of the BIO500 pcb to start with 99v opamp removed so I can check resistors are in the correct place.
Joe :-)
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Alex1990
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Re: LA500A opto comp MAY 2021 BUILD THREAD 500/51X

Post by Alex1990 »

Thanks!

Yes both LEDs light up.
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Re: LA500A opto comp MAY 2021 BUILD THREAD 500/51X

Post by Joe Malone »

Alex1990 wrote:
Thu Oct 19, 2023 8:41 pm
Thanks!

Yes both LEDs light up.
Ok so when you switch to off the level is unity but in GR or VU the level jumps up 9dB with no makeup added?

Ok that looks fine. So best to remove the bio ribbon cable from la500a sc pcb and fit 2 wire links as shown in first post and attached here to see if the bio pcb then gives you unity in and out
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Alex1990
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Re: LA500A opto comp MAY 2021 BUILD THREAD 500/51X

Post by Alex1990 »

Hi Joe - correct.

Can confirm the unit stays at unity gain with bypass wire in/out so the problem must not be on BIO PCB.

all the best!

noahraimy
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Re: LA500A opto comp MAY 2021 BUILD THREAD 500/51X

Post by noahraimy »

Hi Joe

Been a while but was able to test compressor with proper level input signal and things were still not functioning as expected.

The compression does not increase smoothly when turning the pot. There isn't much audible compression until 3 o clock on the pot, then the level is sharply reduced and the signal is sort of distorted when brought back up with make up gain. When turned the rest of the way to the right the signal sounds roughly the same as when no compression is dialed in. It behaves this way with varying intensity according to the ratio level set. The VU meter also shows what I am hearing. Make up gain, LEDs, and all switches function as expected.

I tried to take better pictures showing each PCB and the traces. Please let me know if there is anything else I can share/show to help diagnose. Thanks for your help.

Forgot to answer your previous questions:
Yes VU was same when GR and T were CCW.
I don't recall any issue with the GR calibration but I will reassemble and try again.
Optos are in correctly
And I was using a bad cable so calibration issues were not from the comp itself

https://drive.google.com/drive/folders/ ... sp=sharing

Alex1990
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Re: LA500A opto comp MAY 2021 BUILD THREAD 500/51X

Post by Alex1990 »

Alex1990 wrote:
Sun Oct 29, 2023 10:01 pm
Hi Joe - correct.

Can confirm the unit stays at unity gain with bypass wire in/out so the problem must not be on BIO PCB.

all the best!
Sorry - just wanted to nudge this! :)

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