API-312 48v noise when using DI?

[Spencerleehorton]

I have noticed lately that most if not all of my API-312 preamps when i use 48v and a Bo Hansen DI it introduces some static noise?, the Bo` Hansen DI which is the mod you can do to the API-312.
On my modded channels with the Bo Hansen DI in it, its completely silent apart from when you turn the gain up and get a little hiss, but no static?

Any ideas?

 

[Spencerleehorton]

well its seems changing the Led for a 3mm red one may stop the noise issue, i'll also try to tuck the wires on the XLR away from the led wires.

 

[Spencerleehorton]

I think I’ve found my problem, jacks are not isolated!!, will change and hopefully all will be sorted.

 

[Spencerleehorton]

nope still got noise? but it does get less static crackle after a few minutes?
could try replaceing transformer?

 

[JohnRoberts]

If the noise is only present when 48V phantom is in use the problem may be excessive DC leakage in the Phantom DC voltage blocking capacitors.
===
Back last century we ran into a bad batch of electrolytic capacitors that were noticeably noisy during production line testing. I ended up black balling the entire capacitor series. Sorry I do not remember the brand, we used lots of capacitors at Peavey.

JR

 

[Spencerleehorton]

Well the 100uf caps in there I’ll change and see if the static crackles go!!

 

[Spencerleehorton]

changed the 100uf caps for some new nicholon and static still there, if i turn off the 48v for a few seconds i get nice clean audio through the bo hansen DI, so i will change the other 10uf caps in there and work out why the THRU isnt working?

 

[Spencerleehorton]

changed the 10uf and no different, reflowed all joints and same, will check schematic and parts for something ive missed?

 

[Spencerleehorton]

Changed the transformer and it’s slightly better but still some signs of static/crackle?

 

[Matt Syson]

Transformers do not create static/crackle. People have to learn to define so called 'imperfections and be precise as well as understanding the possible failure modes of various components.

 

[Spencerleehorton]

i didnt know whether cheap chinese transformer i'd put in was an issue due to it not having a mumetal case and a seperate screen.

have tried this bo hansen di through a API and a neve and same problem so i know its not the source 48v.

could it be the transistors?
im using a 3mm red LED as specified, try a 5mm red?

any other ideas?

 

[ccaudle]

my modded channels with the Bo Hansen DI in it

Is the distinction you are making a pre-amp with a separately cased DI connected by cable, compared to a preamp which has the same DI circuitry internal to the preamp case?

get a little hiss, but no static?

Can you make a recording of what you are calling "static" so everyone is sure of what you are describing?

its seems changing the Led for a 3mm red one may stop the noise issue

I'm sure there are several people like me who have not memorized the Bo Hansen schematics. Could you provide a link to the schematic you are using?

 

[Spencerleehorton]

here is the bo hansen schematic


strangely i plugged a bass into the DI and didnt really notice any static yesterday, but i will try again today and record the static noise

 

[Spencerleehorton]

after all that changed XLR cable and get correct volatges and silent!!! so sorry to bother everyone!!!