bababouy
Member
Hi, just finished my first BT50. I'm not getting any output, bypass on and off.
I did verify the opamps (CA-0252) work on a separate preamp.
I did verify the opamps (CA-0252) work on a separate preamp.
[Build] CAPI BT50, 500 Series EQ (a la 550), Official Support Thread
- Thread starter jsteiger
- Start date
Help Support GroupDIY Audio Forum:
We need to know where the signal stops. To find this use a signal generator to send a +4dBu 400Hz signal to your EQ. If you don’t have a dedicated signal generator, send the 400 Hz signal from your computer (about -14 dBFS). Record the AC voltage at each test point, then post the results here.
If you haven’t cleaned the bottom of your board thoroughly, do that first.
If you haven’t cleaned the bottom of your board thoroughly, do that first.
bababouy
Member
Recleaned the bottom of the board, and double checked for any solder bridges.
Sent a tone generator to the EQ (400 hz, -14 dBFS), EQ bypassed. The output is very low, just above the noise floor.
Test Point Results:
TP1: 0.0 V
TP2: 0.1 V
TP3: 0.1 V
TP4: 0.1 V
TP5: 0.1 V
TP6: 7.0 V
TP7: 27.6 V
TP8: 22.5 V
TP9: 3.2 V
TP10: 1.1 V
TP11: 1.4 V
TP12: 1.7 V
Sent a tone generator to the EQ (400 hz, -14 dBFS), EQ bypassed. The output is very low, just above the noise floor.
Test Point Results:
TP1: 0.0 V
TP2: 0.1 V
TP3: 0.1 V
TP4: 0.1 V
TP5: 0.1 V
TP6: 7.0 V
TP7: 27.6 V
TP8: 22.5 V
TP9: 3.2 V
TP10: 1.1 V
TP11: 1.4 V
TP12: 1.7 V
Are those voltages AC? They look WAY off.
Here’s an example of voltages from a working unit that someone posted earlier:
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
This is pretty typical. You should at least have 0.3ish VAC at TP1.
bababouy
Member
Yes, AC voltage. I thought it was way off as well, so I remeasured ( I had the leads reversed). Still rather low.
TP1: 0.1 V
TP2: 0.1 V
TP3: 0.1 V
TP4: 0.1 V
TP5: 0.1 V
TP6: 0.0 V
TP7: 0.0 V
TP8: 0.0 V
TP9: 0.0 V
TP10: 0.0 V
TP11: 0.0 V
TP12: 0.0 V
edit:
I checked the DC voltage at the opamp -V and +V sockets. I measured -14.6 and 14.3 respectively. I resoldered the pins and got -15.2 and 14.8.
Last edited:
TP1 is immediately after the input amp so if you're low there (which you are) its either the way the signal is being applied to the module or the input amp A1.
The BT50 has a historically unbalanced input. What device is feeding the sine wave to the module? Maybe it doesn't like being unbalanced with the negative side going to ground?
The BT50 has a historically unbalanced input. What device is feeding the sine wave to the module? Maybe it doesn't like being unbalanced with the negative side going to ground?
bababouy
Member
I'm using the Cranborne 500R8. There is another in this thread where someone was using the Cranborne 500ADAT. I tried using the Konsole 6 with the MIDAS Legend 6 as well, no luck. Trying unbalanced cables next.
I was more wondering about the preceding device not the rack. Unbalancing the output of some converters can be interesting. A device with an output transformer won't care.
bababouy
Member
The Cranborne 500R8 in this case is the converter AND the rack. Curious if anyone has gotten the 500R8 to work with this EQ.
If you have a piece of gear with transformer output, place it before the EQ and see if it makes a difference.
Hi capi gurus,
I’ve got a Bt50 that produces a 5k tone at all times even in bypass. It seems to modulate the freq when I change the LF selection or filters. And goes up to around 10k. I have a twin bt50 that doesn’t do this.
Swapped 1731 opamps no change.
Does anyone have a suggestion how to fix this it sounds fine everything works but this constant tone is making it unusable.
Thank you for your reply
I’ve got a Bt50 that produces a 5k tone at all times even in bypass. It seems to modulate the freq when I change the LF selection or filters. And goes up to around 10k. I have a twin bt50 that doesn’t do this.
Swapped 1731 opamps no change.
Does anyone have a suggestion how to fix this it sounds fine everything works but this constant tone is making it unusable.
Thank you for your reply
That is new one. Its has to be a build error of some sort. I'd very carefully compare the good build to the bad build. Might also be a solder bridge somewhere on the build.
I’ve checked over both and found one questionable solder joint but the problem persists. I made a short vid demo.
View attachment IMG_2534.MOV
I have already told bababuoy in a dm that I have built the BT50 and have installed it in my Cranborne 500R8 successfully, fully functioning. Just mentioning it here in the event someone else is also curious about this situation.
Volume11
Well-known member
I have two in a Cranborne audio 500r8 as well, they work perfectly. Building two more now
Hi guys. @jsteiger . I've made 10 BT50 Litz....I have some trouble with one. I have a loss of 4 db. The EQ works well, but with 4 db loss. No shortcut . Even if you swipe the jumper for +6 works but with the 4 db loss.
Testing tone 1Khz near -14db. running tone from laptop. Eq out. (not engaged)
For that level of input All TP's are near 0,37v AC, only TP 9 is 0,52v.
In a working fine unit those values are the same for that input level.
With Eq IN (engaged) and gain full in the 3 bands, the TP's go higher in value cause the gain add in each band.
But the TP 2 stay the same value as the eq wasn't.'t engaged like 0,37v.
Could this indicates a problem?
could any of the transistor go bad?
thanks in advance
cheers
Pedro
Testing tone 1Khz near -14db. running tone from laptop. Eq out. (not engaged)
For that level of input All TP's are near 0,37v AC, only TP 9 is 0,52v.
In a working fine unit those values are the same for that input level.
With Eq IN (engaged) and gain full in the 3 bands, the TP's go higher in value cause the gain add in each band.
But the TP 2 stay the same value as the eq wasn't.'t engaged like 0,37v.
Could this indicates a problem?
could any of the transistor go bad?
thanks in advance
cheers
Pedro
Last edited:
TP2 is after the boost resistor-cap network in the feedback loop of A1. LR10-LR14 are the resistors.
All active components are in the signal path no matter if the EQ is in or out.
Can you post a few pics of the top of the board so some resistors can be verified?
Can you post a few pics of the top of the board so some resistors can be verified?
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