BHC Speedball - High OB voltage on Large Board

[ng5921]

Hey yall!

Today I decided to do the Speedball upgrade on my stock BHC. The BHC was fully functional prior to the upgrade, with all voltages within the limits defined in the manual.

I am running the stock 12AU7 and 6080 that came with my BHC kit.

Small board installation went without issue, and I got the following voltages:
OA 90.1V
IA 197V
B-A/B 0.3mV
IB 197V
OB 85.1V

Large board voltages are not perfect:
OA 115
G 0.3mV
OB 175V
B+ 197V

Concerned about the high OB voltage.

I also noticed that upon disconnecting power to the amplifier, the OB voltage never seems to drop. Whereas B+ and OA voltages fall to <2V very quickly.

All LEDs on the small and large board light up.
There is no sound output from the LEFT channel.


Any guidance is greatly appreciated!

[Paul Birkeland]

First things first, it's really, really, really important not to try to use an amp that doesn't pass its voltage checks.  Not passing the voltage checks tells us that the amp isn't working properly, and an amp that isn't working properly can destroy your headphones.

Could you post some photos of your build?  Are you certain that the wire leaving OB is going to the correct place?

You could get very high OB voltage also from a poorly soldered R1 resistor on the larger Speedball board.

[ng5921]

Hi Paul,

They were just 99 cent IEMs that I use to see if things are working

I triple checked the wire leaving OB is correctly going to the terminal 7U. I also resoldered the R1 resistor on the large speedball board. I did purchase this Speedball used and pre-built by someone else.

Another strange behavior I noticed is that the output capacitor attached to 7U will not discharge on its own after powering down the amp.



Best,
Nik

[Paul Birkeland]

Can you remove the large Speedball board and flip it over to get a picture of the soldering on the bottom?

Do you see DC voltage at terminal 6 or just lingering DC voltage at terminal 7?