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

[jsteiger]

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

The small arrows on the side point to the negative end. If you look close there is a "-" sign inside each arrow. The positive end has a small groove around it. You won't have damaged anything but you should make it the right orientation.

 

[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.

Thanks!

Any ideas?

 

[jsteiger]

Any ideas?

Could be many things I suppose. I've never experienced this so don't have a definitive place to look. It's likely there is no silver bullet fix. Have you ruled out all outside potential causes like rack slot, patchbay, cables etc? The input of the BT50 in unbalanced so it's possible the device you have before it does not like being unbalanced? Maybe its the rack itself?

 

[mattk]

The input of the BT50 in unbalanced so it's possible the device you have before it does not like being unbalanced?

Yes!!!! That's it!!!!
I had checked cables, different slots, etc, I even disassembled the eq to triple-ckeck for errors but had only tried it as a hardware insert in PT (out of an Apollo 16 throgh the patchbay).
Thankfully I'm mostly going to use the bt50 for tracking (after a pre) so I'm good.
Thank you very much Jeff!

 

[CJBrain]

Hi Guys,

Was wondering if anyone had any feedback from my last post?

Cheers

Colin.

Hi Jeff

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

Cheers

Colin.

 

[jsteiger]

Hi Guys,

Was wondering if anyone had any feedback from my last post?

Cheers

Colin.

Colin, if you are good at TP3 and have lost signal by TP4 (with the low band gain switch set to 0 cut/boost) then you have a likely bad solder joint on one of the R's, LR5-LR9 or the lowest (F) deck of SW1 pins which would be FC1 and F1-F5. See the attached screenshot.

You could also pull R7 and if the signal comes back at TP4, then your issue is with the discrete follower network of Q1, Q2, R13, R14.

 

[myers1st]

Hi all,

I’ve just finished building a pair of BT 50s and one is working perfectly but the other has a weak output, perhaps 12 dB lower than the other one. The EQ functions seem to be working correctly. I have swapped op amps and rack slots and that is not the problem. Any ideas?

Thanks!
Steve

 

[jsteiger]

I’ve just finished building a pair of BT 50s and one is working perfectly but the other has a weak output, perhaps 12 dB lower than the other one. The EQ functions seem to be working correctly. I have swapped op amps and rack slots and that is not the problem. Any ideas?

Since you have one working properly, inject a sine wave and notate the ACV at all of the Test Points going thru them in order. Then move to the troubled unit and see where things go sideways. That will help pinpoint where the problem is. Otherwise its a needle in a haystack.

 

[myers1st]

Hey Jeff, thanks for the quick reply.

Rookie mistake, had pink and red swapped on the Litz.  Switched them and all good.  These sound superb by the way!

 

[jsteiger]

Rookie mistake, had pink and red swapped on the Litz.  Switched them and all good.  These sound superb by the way!

Oh good, that was an easy one 

 

[Thekahn]

Hi guys!
Just built my first BT-50 and everything works amazing, except the shelving on the low frequencies doesn't do anything when engaged. (The peak mode works perfectly on all frequencies).

I'm assuming I should reflow the solder joints at the mini toggle switch. Anything else I should look at specifically?
Thanks,
Chris

 

[jsteiger]

Hi guys!
Just built my first BT-50 and everything works amazing, except the shelving on the low frequencies doesn't do anything when engaged. (The peak mode works perfectly on all frequencies).

I'm assuming I should reflow the solder joints at the mini toggle switch. Anything else I should look at specifically?

Chris, sounds like a cold solder joint on the mini toggle and/or the LF Grayhill, and/or one of the low filter caps.

 

[Thekahn]

Chris, sounds like a cold solder joint on the mini toggle and/or the LF Grayhill, and/or one of the low filter caps.

Thanks for the response Jeff,
I reflowed the mini switch, all low frequency caps and any of the gray hill pads that looked at all suspect (honestly they looked pretty good to me), to no avail.  It's almost as if when in shelving mode the signal isn't passing through any of the LF components, but in peak mode everything sounds glorious. Any way I can inject a sine wave or do a continuity test to help? Thanks!
Chris

 

[jsteiger]

Thanks for the response Jeff,
I reflowed the mini switch, all low frequency caps and any of the gray hill pads that looked at all suspect (honestly they looked pretty good to me), to no avail.  It's almost as if when in shelving mode the signal isn't passing through any of the LF components, but in peak mode everything sounds glorious. Any way I can inject a sine wave or do a continuity test to help? Thanks!
Chris

Using the attached screenshot as a guide...

1. With DMM continuity, make sure you do not have a direct short from Grayhill SW1 wiper pad EC1 to ground.

2. When in shelf mode, the middle wiper pin #2 of mini toggle SW3 should be directly connected to Grayhill SW1 wiper pin EC1.

3. Grayhill wiper pin EC1 goes to ground thru the resistor string LR18->LR19->LR20->LR4->LR3->LC8->GND, depending on the cut/boost position. So, if +/-12dB you should have 6k34 DCR between the wiper of SW3 and the right end of LR3.

 

[Thekahn]

Using the attached screenshot as a guide...

1. With DMM continuity, make sure you do not have a direct short from Grayhill SW1 wiper pad EC1 to ground.

2. When in shelf mode, the middle wiper pin #2 of mini toggle SW3 should be directly connected to Grayhill SW1 wiper pin EC1.

3. Grayhill wiper pin EC1 goes to ground thru the resistor string LR18->LR19->LR20->LR4->LR3->LC8->GND, depending on the cut/boost position. So, if +/-12dB you should have 6k34 DCR between the wiper of SW3 and the right end of LR3.

Jeff,

1. I have confirmed when I put one probe on ground and one probe on SW1 EC1, there is no continuity.

2. I have confirmed when on shelf mode, there is continuity between pin #2 on mini toggle SW3 and SW1 EC1.

3. When I try measuring resistance from EC1 to pin 2 of LR3, it keeps climbing up and up, upwards of 12 mega ohms and doesn't really stop. Do I need to desolder that leg of LR3 to measure it properly(IE to pull it out of the circuit) ? Or does the data above give you the info you were looking for? 
Thanks,
Chris

 

[jsteiger]

3. When I try measuring resistance from EC1 to pin 2 of LR3, it keeps climbing up and up, upwards of 12 mega ohms and doesn't really stop. Do I need to desolder that leg of LR3 to measure it properly(IE to pull it out of the circuit) ? Or does the data above give you the info you were looking for? 

No you should not have to desolder anything. I just checked on a good unit here with the mini toggle set to shelving and full boost of low band and I get appx 6k34 from the wiper (pin #2) of the mini toggle to the right end of LR3. It takes a second or 2 to settle but goes right there and stays. That is telling me you have a cold solder joint(s) on the string of R's I posted above or one or more of the switch pins of the E deck of the Grayhill.

 

[Thekahn]

No you should not have to desolder anything. I just checked on a good unit here with the mini toggle set to shelving and full boost of low band and I get appx 6k34 from the wiper (pin #2) of the mini toggle to the right end of LR3. It takes a second or 2 to settle but goes right there and stays. That is telling me you have a cold solder joint(s) on the string of R's I posted above or one or more of the switch pins of the E deck of the Grayhill.

Hi Jeff,
There is definitely  no connection from EC1 to any of the E deck pins on the gray hill, nor the resistors mentioned above. I can track resistance values all down the E deck of the gray hill all the way down to the right side of LR3, but when I put it on EC1, it turns into mega ohms and keeps rising and rising. Is it possible my grayhill is broken internally? I get 25 ohms of resistance from the wiper of SW3 to EC1 on the gray hill, but like I said, it's as if EC1 stops there. Any ideas? Thanks again for the help.
Chris

 

[jsteiger]

Hi Jeff,
There is definitely  no connection from EC1 to any of the E deck pins on the gray hill, nor the resistors mentioned above. I can track resistance values all down the E deck of the gray hill all the way down to the right side of LR3, but when I put it on EC1, it turns into mega ohms and keeps rising and rising. Is it possible my grayhill is broken internally? I get 25 ohms of resistance from the wiper of SW3 to EC1 on the gray hill, but like I said, it's as if EC1 stops there. Any ideas? Thanks again for the help.
Chris

I would reflow the solder on the EC1 pad. Its possible the switch is bad but very unlikely. Try checking continuity from the EC1 metal wiper that that comes out of the Grayhill switch body to the associated E deck pins. They should beep out as you turn thru its rotation.

 

[Thekahn]

I would reflow the solder on the EC1 pad. Its possible the switch is bad but very unlikely. Try checking continuity from the EC1 metal wiper that that comes out of the Grayhill switch body to the associated E deck pins. They should beep out as you turn thru its rotation.

Hi Jeff,
There is no continuity from any of the E deck pins from EC1, even when I turn the gain knob and freq knob to different positions. I have re-flowed EC1 many times, and I even checked for continuity from the top side of the wiper pin at the grayhill body when checking the E deck pins.  What's odd is that I get continuity from the SW3 wiper to EC1 but no continuity from EC1 to any of the  E deck pins or related resistors. I'm thinking its a bad switch but I can't tell for sure.  Not really sure what to do now.  Any help would be great.
Thanks,
Chris

 

[jsteiger]

Hi Jeff,
There is no continuity from any of the E deck pins from EC1, even when I turn the gain knob and freq knob to different positions. I have re-flowed EC1 many times, and I even checked for continuity from the top side of the wiper pin at the grayhill body when checking the E deck pins.  What's odd is that I get continuity from the SW3 wiper to EC1 but no continuity from EC1 to any of the  E deck pins or related resistors. I'm thinking its a bad switch but I can't tell for sure.  Not really sure what to do now.  Any help would be great.
Thanks,
Chris

Chris, send me an email thru the store.