[Build] CAPI BT50, 500 Series EQ (a la 550), Official Support Thread

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Barklay

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jsteiger said:
Check continuity from each of the LF Grayhill wipers (the metal tabs that stick out of the switch body) to ground. You are looking for a short or very low Ω reading.

Ok, i’ve checked. Three of 8 were about 30 ohms. As Jeff posted earlier to Jan, i’ve de-soldered them and slightly bended, then re-soldered. After all, it works correctly
 

jona

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jsteiger said:
Might be opamp related or cabling outside of the rack?
thanks  for the reply jeff..
i used red dots as for some of my other builds too.. i dont think it has to do with cabling.. i tried it in different slots and even in a different rack.. none of my other modules have this problem.do you have. any other  idea ? the strange thing is both bt50 have the exact same problem...
 

attisma

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Hello Jeff,

I just built a pair of BT50's. I'm using known working gar2520's. My current issue is that when I run audio thru them, and with "IN" in either position, and all frequencies set to 0, I'm getting what sounds like a low cut filter.  If I boost/cut low LF, they seem to filter but I would expect the sound to be unchanged when positions are at 0.  Can you advise the best way to troubleshoot.

I've already spot checked and re-soldered my joints for good measure but to no avail.

Any help is appreciated.

Thanks
 

jsteiger

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attisma said:
Hello Jeff,

I just built a pair of BT50's. I'm using known working gar2520's. My current issue is that when I run audio thru them, and with "IN" in either position, and all frequencies set to 0, I'm getting what sounds like a low cut filter.  If I boost/cut low LF, they seem to filter but I would expect the sound to be unchanged when positions are at 0.  Can you advise the best way to troubleshoot.

I've already spot checked and re-soldered my joints for good measure but to no avail.

Any help is appreciated.

Thanks
How are you testing them? What device is just before them? The BT50's input is unbalanced (like the vintage counterpart). Is it possible that whatever you are feeding them with does not like being unbalanced by shunting its XLR pin 3 signal to ground? Maybe try a quick test with a transformer output device before them.
 

attisma

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jsteiger said:
How are you testing them? What device is just before them? The BT50's input is unbalanced (like the vintage counterpart). Is it possible that whatever you are feeding them with does not like being unbalanced by shunting its XLR pin 3 signal to ground? Maybe try a quick test with a transformer output device before them.

I was using a balanced cable. Problem solved!!

Thanks Jeff!!
 

Ngr

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Hello Jeffrey,
I just built a BT-50. Everything is working fine except for the bypass switch. The eq is always on, no matter if the IN button is depressed or not. Where do I have to look at?
Thank you
 

jsteiger

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Ngr said:
I just built a BT-50. Everything is working fine except for the bypass switch. The eq is always on, no matter if the IN button is depressed or not. Where do I have to look at?
I would look for a short/solder bridge on the bypass switch itself or the 6-pin header that connects the switch PCB to the main PCB.
 

Ngr

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jsteiger said:
I would look for a short/solder bridge on the bypass switch itself or the 6-pin header that connects the switch PCB to the main PCB.

No bridges, or shorts. I checked the switch pads and they appear to be all shorted within themselves when the IN button is pressed. When button is depressed only the first two pins ( looking at the board top side from left to right ) are shorted. On the 6 pin header there's a short between pin 1 and 3 when button is depressed, a short between 2 and 6 when it is pressed. Is that correct?
 

staylor200

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Hi, Jeff. Just completed a clean BT50 (with gar 1731's) and need some help. First power on and some of the 10ohm power dampening resistors started to smoke. I swapped in other 2520 opamps and no smoke. I checked the two gar 1731's and it looks like r14 & r15 on both 1731's slightly started to burn up.

thank you
 

Potato Cakes

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Check to see if the 10R resistors are still reading 10 ohm. If not replace and then try again with the different op amps and see if there is still no smoke. If they are still measuring good and the unit is working fine with the different op amps then you have an issue with the gar1731's and that should be addressed on the that particular build thread.

Thanks!

Paul
 

staylor200

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Potato Cakes said:
Check to see if the 10R resistors are still reading 10 ohm. If not replace and then try again with the different op amps and see if there is still no smoke. If they are still measuring good and the unit is working fine with the different op amps then you have an issue with the gar1731's and that should be addressed on the that particular build thread.

Thanks!

Paul

Thank you, Paul. Forgot to mention BT50 works and sounds great with a gar2520 & rogue five in it.
 

gzpz

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Hi- Just finished one of two BT50's and it's working great, but I wanted to give a heads up about the blue knobs.  Two out of three had holes that were too small.  I'm surprised I didn't break a Grayhill trying to force the knob on!  I had to use a drill to increase the size of both knobs.  The third knob was perfect, so it must just be unit variation.  I used a 1/4" bit to fix the problem.
 

stribor1

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gzpz said:
Hi- Just finished one of two BT50's and it's working great, but I wanted to give a heads up about the blue knobs.  Two out of three had holes that were too small.  I'm surprised I didn't break a Grayhill trying to force the knob on!  I had to use a drill to increase the size of both knobs.  The third knob was perfect, so it must just be unit variation.  I used a 1/4" bit to fix the problem.

Same here, problems with a too tight fit of the blue knobs, particularly on the mid-band grayhill which seems to be a little wider than the other two band selectors. Nothing a drill couldn’t fix...
 

Fuzz Face

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I had the same thing with the blue knobs fitting too tight but it was an easy fix. For what it’s worth I think the problem is the tolerance of the Grayhill switches, not the CAPI knobs

At any rate those knobs are sexy and I love love love my BT50
 

jsteiger

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Its odd. We have built a bunch of them here and never had that issue. Sometimes one tiny little piece of aluminum hanging off the edge of the setscrew hole can be enough to hold things up.
 

AntonioAnz

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Hey Jeff,

Having issues getting this EQ to pass signal. Oddly, I've built countless opamps and the FC526 without issue.

I loose ACV signal at TP5, any idea what part of the circuit that narrows this down to?

Thanks!
 

jsteiger

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AntonioAnz said:
Hey Jeff,

Having issues getting this EQ to pass signal. Oddly, I've built countless opamps and the FC526 without issue.

I loose ACV signal at TP5, any idea what part of the circuit that narrows this down to?

Thanks!
Sorry for the delay. I meant to do this when I saw it but time got away from me and then I forgot. I run ARES with a windows virtual machine on my Mac so getting to a PCB layout is a small chore that I can't do quickly. I need to carve out a few minutes, which I wasn't able to do right away and then it slipped away...

Anyways, if you are good at TP4 and not at TP5, you need to look at R7 (series R), R8 (shunt) or the first discrete follower which is R13, R14, Q1 and Q2.

Another thing to check with no power connected, make sure TP5 is not shorted to ground. From the follower and TP5, the trace goes to J2-5 and onto the mid band board. The adjacent J2-4 is ground so make sure you have nothing shorted. If it does measure as a direct short, unplug the mid band board and see if TP5 is still shorted. Then you'll know where your short is.
 

AntonioAnz

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jsteiger said:
Sorry for the delay. I meant to do this when I saw it but time got away from me and then I forgot. I run ARES with a windows virtual machine on my Mac so getting to a PCB layout is a small chore that I can't do quickly. I need to carve out a few minutes, which I wasn't able to do right away and then it slipped away...

Anyways, if you are good at TP4 and not at TP5, you need to look at R7 (series R), R8 (shunt) or the first discrete follower which is R13, R14, Q1 and Q2.

Another thing to check with no power connected, make sure TP5 is not shorted to ground. From the follower and TP5, the trace goes to J2-5 and onto the mid band board. The adjacent J2-4 is ground so make sure you have nothing shorted. If it does measure as a direct short, unplug the mid band board and see if TP5 is still shorted. Then you'll know where your short is.

Hey Jeff,

No worries, thanks for the reply. So I'm seeing nothing is shorted, but signal does get lost at Q2... I'm seeing voltage at the base of Q2 from the adjacent transistor (Q1's emitter) but nothing at the collector or emitter of Q2, looks like that's the problem! I'm going directly to each leg so it must be a faulty transistor - not a trace error as I initially expected. I'll be reaching out soon for a replacement transistor. Thanks again!
 

AntonioAnz

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jsteiger said:
Sorry for the delay. I meant to do this when I saw it but time got away from me and then I forgot. I run ARES with a windows virtual machine on my Mac so getting to a PCB layout is a small chore that I can't do quickly. I need to carve out a few minutes, which I wasn't able to do right away and then it slipped away...

Anyways, if you are good at TP4 and not at TP5, you need to look at R7 (series R), R8 (shunt) or the first discrete follower which is R13, R14, Q1 and Q2.

Another thing to check with no power connected, make sure TP5 is not shorted to ground. From the follower and TP5, the trace goes to J2-5 and onto the mid band board. The adjacent J2-4 is ground so make sure you have nothing shorted. If it does measure as a direct short, unplug the mid band board and see if TP5 is still shorted. Then you'll know where your short is.

Hey Jeff,

Thanks for that replacement transistor; unfortunately I'm running into the same problem as before - no signal at TP5. This transistor (Q2) is still seeing voltage at the base but nothing is getting through to the emitter or collector. I measured all the resistors you suggested (R7, R8, R13, and R14) but they are within spec, and none of these components (besides R8 like it's supposed to) are shorting to ground. Any idea what could be going on? Seems like it could be a bias issue but I'm not sure.
 

mohausler

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Feb 27, 2017
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Hello

Does anyone here have a good suggestion to what the cleanest way would be to keep my signal balanced up till it hits the BT50s, convert it to unbalanced just at the rear of my 500 rack?

I am getting a lot of noise and crosstalk between my two BT50s and I suspect this is caused by the lines / patchy, rather than the units themselves

Thanks!
 

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