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

Help Support GroupDIY:

theblastedman

Member
Joined
Jul 8, 2020
Messages
5
Hi Jeff/All, I'm building a BT50 and all has been well so up until I just snapped a lead off one of the 6 deck grayhill switches. I'm having a bear of a time trying to find the correct replacement part to order, can anyone offer some guidance on how to narrow this down on mouser? Thank you in advance.
 

myers1st

Active member
Joined
Sep 12, 2017
Messages
42
Location
Prague
You can actually disassemble those grayhills... depending on which deck it’s on (hopefully away from the switch) you *might* be able to solder on a super fine like cat5 cable or cut resistor lead to extend it down to the PCB.  I know those pins are small so it might be tough.  It’s be a shame to have to replace that as they’re really expensive.  Also it’s next to impossible to find Grayhills right now, I think they have prioritized their production for medical equipment currently.

Anyway, I hope you sort it, the BT50s are freaking amazing, I rue the day I ditched 500 series and sold mine...
 

theblastedman

Member
Joined
Jul 8, 2020
Messages
5
Well it seems like it's going to be OK! I chipped away some of the grey plastic around the broken off lead, exposed enough to get some solder onto, installed the switch, and passed through a bit of trimmed off lead, flowed some solder down there and it seems to be good. The same position produces continuity from my hacked lead to the pole as it did for the rest of the rows. Thank goodness!
 

Attachments

  • IMG_1736.JPG
    IMG_1736.JPG
    1.8 MB · Views: 19

theblastedman

Member
Joined
Jul 8, 2020
Messages
5
Another update, got it all assembled and it works like a charm! This thing sounds seriously good. Need to build another as soon as they come back in stock. Thanks all!
 

critterkllr

Well-known member
Joined
Nov 5, 2010
Messages
311
Location
Dearborn, MI
Has anybody modded their BT50s? I LOVE the weight it gives me on kick, but I'm only finding two of the eq bands useful for me in this application. I was wondering if somebody could point me in the right direction on figuring this out.

I'd like to:

1) Change one of the High Frequency options to 3khz (preferably 15khz since I can't imagine using that on kick ever). I'd like to know which caps are responsible for each frequency in the high frequency switch.

2) Widen the Q of mid frequency range for -6db, -9db, and -12db. Which resistor/s are responsible for this? Am I right in thinking that I could raise the resistance of MR2, MR3, MR15, and MR5? I'd like to have a larger Q for scooping out 400hz.
 

critterkllr

Well-known member
Joined
Nov 5, 2010
Messages
311
Location
Dearborn, MI
One of the great things about this design is the ease of recall, and that you can undo any eq decision you made by reversing. I decided to make a recall sheet for my projects. Hopefully this will be helpful to somebody. If you want just a single channel, let me know and I'll attach it.
 

Attachments

  • BT50 Recall Sheet.pdf
    1.2 MB · Views: 14

brianmatteson

Member
Joined
Aug 7, 2017
Messages
5
Hello, Ive got a pair of BT50's I built a few years back. They're great! The issue I'm having is that I built 2 and they have slight level differences and also one seems to have a permanent hi and low frequency roll off. I can see it in Qclone even when the eq is not engaged. Any ideas what could be causing this? For clarity, it's less of a cut than when the filter buttons are engaged and yes, the filter buttons do still seem to work normally.

I also have a pair of LC 40's I built at the same time and they're identical in Qclone, which makes me think I have an issue with one of the BT50's.  Any help is much appreciated!

***Update***

I have realized that I had a dysfunctional op amp.
 
Joined
Apr 11, 2021
Messages
5
Hi all, I ran into a BT50 issue on my 4th build.  The first three all worked great.  This last BT50 has a very bad distortion/fuzz that happens even in bypass after a preamp.  The fuzz actually gets slightly better when the BT50 is engaged.  It sounds like a massive overload, like just an awful fizzy distortion.  The distortion gets worse when the cut/boost knob is increased, so, more boost = more fizz.  Additionally, there is a 50% volume drop no matter if the bad unit is bypassed or engaged.  So, assuming the preamp stays consistent:

Preamp  -> bad BT50 (not IN) -> DAW shows a 50% volume drop
Preamp -> bad BT50 (IN) -> DAW shows a 50% volume drop
Preamp -> good BT50 (IN or not IN) -> DAW shows normal volume

So, it looks like even having the bad BT50 in the signal chain causes a volume drop. 

I've swapped out opamps with known good ones, and the exact problem persists.  The original opamps were placed into one of my working BT50 and everything sounded normal.  So I'm pretty confident I don't have a simple/typical opamp issue.  If I need to start tracking down my signal, can anyone point me in the right direction - like what tools do I need?  I don't have an oscilloscope or anything like that, just a soldering iron and multimeter.  Did I miss the BT50 test point documents?

I'm currently checking all my resistors, solder joints, etc. 

Any ideas?  Thanks!
 

Potato Cakes

Well-known member
Joined
Jul 1, 2014
Messages
1,886
Location
Nashville, TN
EyeByTwoMuchGeer said:
Hi all, I ran into a BT50 issue on my 4th build.  The first three all worked great.  This last BT50 has a very bad distortion/fuzz that happens even in bypass after a preamp.  The fuzz actually gets slightly better when the BT50 is engaged.  It sounds like a massive overload, like just an awful fizzy distortion.  The distortion gets worse when the cut/boost knob is increased, so, more boost = more fizz.  Additionally, there is a 50% volume drop no matter if the bad unit is bypassed or engaged.  So, assuming the preamp stays consistent:

Preamp  -> bad BT50 (not IN) -> DAW shows a 50% volume drop
Preamp -> bad BT50 (IN) -> DAW shows a 50% volume drop
Preamp -> good BT50 (IN or not IN) -> DAW shows normal volume

So, it looks like even having the bad BT50 in the signal chain causes a volume drop. 

I've swapped out opamps with known good ones, and the exact problem persists.  The original opamps were placed into one of my working BT50 and everything sounded normal.  So I'm pretty confident I don't have a simple/typical opamp issue.  If I need to start tracking down my signal, can anyone point me in the right direction - like what tools do I need?  I don't have an oscilloscope or anything like that, just a soldering iron and multimeter.  Did I miss the BT50 test point documents?

I'm currently checking all my resistors, solder joints, etc. 

Any ideas?  Thanks!

Take a multimeter and test for shorts between your power, audio, and ground connection points on the gold fingers of the edge connector on the PCB. Also test the voltage a the DOA sockets with no op amps installed. It sounds like one of the op amps is not getting enough voltage or missing one side. Also double check your transformer wiring in regards to level drop.

Thanks!

Paul
 
Joined
Apr 11, 2021
Messages
5
Thanks Paul!  I'm still learning here, so I dug through some of your older/related posts and will give it a go.  Had to order a testing Jig from Jeff, so as soon as that arrives, I will get rolling.  It will probably do me good to take a few days and read through all the info. 
 
Joined
Apr 11, 2021
Messages
5
Potato Cakes said:
Take a multimeter and test for shorts between your power, audio, and ground connection points on the gold fingers of the edge connector on the PCB. Also test the voltage a the DOA sockets with no op amps installed. It sounds like one of the op amps is not getting enough voltage or missing one side. Also double check your transformer wiring in regards to level drop.

Thanks!

Paul


I checked the faulty unit transformer wiring a few times just to be sure (I'm a bit colorblind which makes all of this stuff extra fun).  The wiring is correct and matches that of my functional units.  So I think I'm ok there. 


I set up my system like it suggests in the VP28 test point guide using Pro Tools and its signal generator plugin with the 400Hz signal at +4dBu, 1.228V.  I wasn’t too sure initially if I was doing things correctly, so I tested a functional Gar2520-loaded VP28 at all the test points and basically replicated all the values listed in the Proper Results section of the VP28 guide.  So, I’m guessing I was on the right track.

I unhooked the VP28 from the test jig and switched over to a fully functional Gar1731-loaded BT50 without changing anything on my DAW/signal generator.  So, like the VP28 test points, these were from the AC voltage reading.  Got the following results:

TP1: 0.311V
TP2: 0.311V
TP3: 0.311V
TP4: 0.306V
TP5: 0.306V
TP6: 0.304V
TP7: 0.303V
TP8: 0.299V
TP9: 0.459V
TP10: 0.300V
TP11: 0.298V
TP12: 0.300V


I then looked at the faulty BT50.  I first took the Gar1731s out of the previous BT50 and stuck them in this one.  The faulty BT50 gave essentially the same test point results except at TP9, which read 0.500V (versus the 0.459V in the functional unit).  I removed the opamps and checked the DC voltage at the +V and -V sockets and got 15.05V and -14.40V.  I checked the functional BT50 and got the same readings, 15.05 and -14.40 on that unit. 


I measured the total V output from an XLR cable exiting the back of my 500 Lunchbox, and there was a big difference here.  The functional BT50 had 1.36V out versus the non-functional at 0.166V.  For the sake of comparison and to check my technique, I ran a similar check using the same slot and cables and using a functional VP28 and got 1.298V which is essentially spot on with the VP28 test point docs.

I also have tried to check the transformer, but don't know if this method was correct.  However, I did see some differences.    I have the Litz version already installed.  I'm guessing that you check the adjacent wires for resistance.  That seemed like what people had done for similar checks on the VP28 thread.  I'm seeing:

Functional BT50:

orange-purple  8.8 Ohm
Pink-grey        8.9 Ohm
yellow-white    8.9 Ohm
red-black        8.8 Ohm


Malfunctioning BT50:

orange-purple    8.7 Ohm
Pink-grey          4.5 Ohm
yellow-white.    4.5 Ohm
red-black          8.7 Ohm




I spaced and forgot to check the shorts at the edge pin connectors.  I’m a bit confused to the best way to do that, any advice?  In the meantime, I will do some digging.  Gonna head back to the studio tomorrow and try some things. 

Thanks for any advice or critiques!
 
Joined
Apr 11, 2021
Messages
5
Just an update – the output transformer was bad, as was a frequency selector toggle switch. Double trouble! The remaining components and opamps were all assembled and installed correctly, and nothing was misplaced.

Quite a frustrating experience all around that was eventually, to some extent, made right, and I will leave it at that. But hey, after the faulty pieces were replaced, this BT50 works fine now.
 

Potato Cakes

Well-known member
Joined
Jul 1, 2014
Messages
1,886
Location
Nashville, TN
Bad transformers are pretty rare in my experience, but they do happen and it's usually the last thing that one would suspect would be the culprit in a build. Glad you found the problem and are up and running. The BT50's are fantastic EQs.

Thanks!

Paul
 
Joined
Apr 11, 2021
Messages
5
Can't take all the credit for finding the problem. You certainly pointed me in a direction, but I also had a lot of help from people outside of this forum.
 

LakeCountry

New member
Joined
Jan 5, 2021
Messages
1
Hey folks, just finished two BT50 from this recent run. They work and sound great. All the bands and filters sound identical on both,
BUT one of the units is 2dB down from the other. Jumpered the same. Tried different slots, routing, converter channels, cables, and swapped op amps - no change and still 2 dB down. It's a somewhat manageable issue for mono sources/inserts, but for guitar or drum bus or something it obviously wont work without trimming one side up or down. Any thoughts, anyone had a similar issue?
 

Latest posts

Top