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

[fdel]

Hey Guys.  First post here total noob.  So please be gentle hahah.  This is only my second Build.  Previous build was a VP28, an amazing Pre Jeff well done I'll be buying more of these I love the sound of that thing!

Loving the DIY So I thought I'd try a couple of BT-50's.  I completed the first one and when I put it in my 500 series rack  I can't get any signal/power through it.  It doesn't seem to be getting any power.  Its not the rack I've checked that already. 

I"ll swap the transformer out for the other one on the second unit (not yet built) and see if that's the issue and I'll run the microscope over the all the resistors and caps again to see if there are any shorts etc.  Are there any other things I should check?

Any advice would be greatly appreciated.

 

[fdel]

Update on my build. I managed to swap out the transformer and get power to it.  Yay!    And then there was the dreaded burning smell and it appears I still have a build error as I have melted  some resistors see photo.  Please help.

 

[jsteiger]

Update on my build. I managed to swap out the transformer and get power to it.  Yay!    And then there was the dreaded burning smell and it appears I still have a build error as I have melted  some resistors see photo.  Please help.

The output transformer will have nothing to do with getting "power" to the module. From the results its something else.

I assume the opamps are built by you? These smoked 6 R's are power damping resistors. 2 supply the 1st discrete opamp, 2 supply the 2nd discrete opamp and 2 supply all of the discrete followers. Burning all 6 means that you have a major error on each of the above locations.

The first rule of thumb is....you should never try to test a fresh module build with fresh opamp builds. In this situation you immediately thought it was the module but the smoking of the 10Ω power damping R's tells me it's the opamps. Here we also have the 10Ω's for the discrete followers smoked so I would look for incorrectly placed transistors there which is Q1-Q6. I'm not saying there can't be trouble on the module itself though.

PR1 and PR4 are for A1
PR3 and PR5 are for A2
PR2 and PR6 are for the discrete followers Q1-Q6

As for the gar2520 issues, you should visit that support thread.

Once you replace the 10Ω R's and get the Q1-Q6 parts sorted, you can power the module with no opamps to make sure the followers don't smoke their R's. Then use good known to be working opamps from another module to test this build.

 

[brianmatteson]

Hello,

I'm looking for some help troubleshooting a BT50 I just built.

Hi and Mid eq's work great, but the low band doesn't eq. Any boost I try to add on the low band just distorts the signal. Also, the high and low pass filters seem to not do anything at all. I've checked my work and am totally stumped, any help would be greatly appreciated!

****UPDATE*****

I had one transistor facing the wrong direction I fixed that and now the low band works-but only in shelf mode. In peak mode it doesn't seem to add any bass. Again, any help is greatly appreciated!

 

[brianmatteson]

Hello Again,

Jeff are you able to help me out? I've done builds and am fairly experienced that way, but there are gaps in my knowledge, especially with troubleshooting-is there a way I can test areas of the circuit to see what's failing? The low frequency peaking mode isn't working and it doesn't seem like the filters are either. Everything else works very well and I've checked all the other components over-specifically LC1-LC18 to make sure they are in the correct spots. Any help at all is greatly appreciated!

 

[jsteiger]

Hello Again,

Jeff are you able to help me out? I've done builds and am fairly experienced that way, but there are gaps in my knowledge, especially with troubleshooting-is there a way I can test areas of the circuit to see what's failing? The low frequency peaking mode isn't working and it doesn't seem like the filters are either. Everything else works very well and I've checked all the other components over-specifically LC1-LC18 to make sure they are in the correct spots. Any help at all is greatly appreciated!

If none of the freq's are boosting on the LF, I would look for (or just touch up all) a bad solder joint on the mini toggle SW3 or the Grayhill SW1.

As far as the filters, it may be hard to detect with ears only depending on the source. Running some tones and analyzing the output may be a better way of "testing".

 

[brianmatteson]

If none of the freq's are boosting on the LF, I would look for (or just touch up all) a bad solder joint on the mini toggle SW3 or the Grayhill SW1.

As far as the filters, it may be hard to detect with ears only depending on the source. Running some tones and analyzing the output may be a better way of "testing".

Thank you for your reply! I will look at those specifically and report back.

 

[brianmatteson]

Hey Jeff-I think it must have been a bad solder joint or something...everything seems to be working now. Thanks for the help!

 

[CJBrain]

Hi Guys

Just finished building a pair of these and while one of them is working perfectly,  i'm having some strange issues with the other one.

It only passes signal through when the LF cut/boost pot is turned two clicks anti clockwise and onwards. As soon as I turn it anywhere else, the signal cuts out...

Not the easiest thing to explain in words so I can record a short video and send it to anyone who is willing to help me try and fix this issue.

Cheers

Colin.

 

[jsteiger]

I would first look for shoddy cold solder joints or bridges on the Grayhill switch pins.

 

[CJBrain]

Hi Jeff,

Thanks for your reply.

Had a look this morning and re-soldered any suspect points. Still the same problem though....

Cheers

Colin.

 

[jsteiger]

Had a look this morning and re-soldered any suspect points. Still the same problem though....

Since you have a good working unit, I would inject a sine wave on the good one and write down all ACV at the test points and compare. Go in order on the bad unit. Once you see a major discrepancy tell us the TP # and that'll help me narrow down what to look for.

 

[Mario_checchia]

Hi all. Just completed one of my two BT50s. It works at first but then crackling and popping begins to pick up until after about 20 seconds the output drops significantly while the crackling gets so loud it drownds it out.

I thought maybe a component was cooking; however, upon inspection nothing appears to have overheated, nor is there smoke or a smell. I plugged it back in and it worked for another 20 seconds until it suffered the same result.

Any ideas what this may be? Aside from touching up solder points I am unsure how to troubleshoot.

 

[jsteiger]

What op

Any ideas what this may be? Aside from touching up solder points I am unsure how to troubleshoot.

What opamps are installed and who built them? Are they fully seated?
http://capi-gear.com/catalog/DOA_Install.php

 

[Mario_checchia]

What opWhat opamps are installed and who built them? Are they fully seated?
http://capi-gear.com/catalog/DOA_Install.php

I have built and installed the GAR1731 opamps. I ensured the millmax pins are fully seated. A bit of resistance at first but eventually they dropped in nicely.

 

[jsteiger]

I have built and installed the GAR1731 opamps. I ensured the millmax pins are fully seated. A bit of resistance at first but eventually they dropped in nicely.

Maybe its the opamps that are built wrong? Maybe the problem is on the BT50? No real way of knowing. These EQ's should ONLY be tested with known to be good working opamps.

It is likely an active part of the circuit so I would first suspect the opamps.

 

[Mario_checchia]

Maybe its the opamps that are built wrong? Maybe the problem is on the BT50? No real way of knowing. These EQ's should ONLY be tested with known to be good working opamps.

It is likely an active part of the circuit so I would first suspect the opamps.

Jeff,

Thanks for the quick reply! I will swap in a pair of known working opamps and determine if I can deduce that it is in fact the opamps that are the issue. Can’t rule out my soldering of the opamps as the source of the problem! I will report back when I have the chance. Thanks again.

P.s. these things are sweet to look at. Can’t wait to say how sweet they are to listen to.

 

[CJBrain]

Since you have a good working unit, I would inject a sine wave on the good one and write down all ACV at the test points and compare. Go in order on the bad unit. Once you see a major discrepancy tell us the TP # and that'll help me narrow down what to look for.

Hi Jeff

I've attached a table showing the ACV test point results for each unit.

Cheers

Colin.

 

[mattk]

Hi! Just finished building my first BT50! (Litz+RedDots) 

All went super smoothly, pictorial build guide was really helpful and, in general, I managed a pretty "clean" build, no solder excess etc, except for some flux here and there...

All works fine, except there is a  very noticeable, constant buzz, whether the unit is on or off. Apart from that, the eq works perfectly.
Any idea what could be causing this?

Thanks!

 

[mrmike186]

It appears I have installed the blue 470 electrolytic cap backwards. The unit has been working fine but could I have possibly damaged something?

I will switch it but is there any rule to what side is negative? Maybe the direction arrows or the indented side is the positive side? I did it this way because there was no black stripe but the end is black