Problem with Trident S20 preamp.

[imloggedin]

i bought this used off craigslist and it works exactly how it should with a condenser but if i try and use dynamic mics its terrible, anything above about 40db of gain and you hear horrible noise. if you ground the mic with your hand it stops. also if you touch the gain pot (without grounding the mic) the sound pops and the noise changes. it works as it should if you ground the mic by gripping the mic with your hand though.

heres a file (24bit wav) that shows this. the first part is with NO mic plugged in and the gain up all the way. the 2nd part of the file is with a sm7 plugged in and the gain all the way up. then i started touching the gain knob off and on (you'll hear it)

what could be causing this? my other preamps dont do it.

 

[imloggedin]

took the top off and jumpered pin 1 on the xlr input to the case and the noise goes away. what to do what to do

 

[imloggedin]

i took this apart and pin 1 is not connected to the chassis anywhere. it goes directly to the transformers (-) on the power supply. nothing on the power supply is connect to the chassis. the only thing connected to the chassis is IEC ground. humph. i guess ill ground pin1 to the chassis. hopefully it wont interfere with phantom power since 48v (-) is not connected to the chassis.

 

[thegoldenrulers]

I seem to be having the same problem that you are describing. It is only with dynamic mics. Did this solution work for you? And would you be willing to describe the process a bit for me as I have never worked on a mic pre before? Thanks in advance for your time.

 

[Whoops]

I seem to be having the same problem that you are describing. It is only with dynamic mics. Did this solution work for you? And would you be willing to describe the process a bit for me as I have never worked on a mic pre before? Thanks in advance for your time.

It seems that neither Pin1 on the Input XLR socket or the PSU connect to the ground at any point.

Please send pictures os the inside guts of the mic pre, top view, XLR connectors and PSU and I can draw you on the pics what you can do

 

[thegoldenrulers]

Thanks so much for being willing to look at this. Here are the pictures.

 

[thegoldenrulers]

And the inputs

 

[thegoldenrulers]

PSU

 

[thegoldenrulers]

Another view. Let me know if you need more. AND THANKS!

 

[Whoops]

Hi,
not a lot circuit there to troubleshoot.
this preamp is quite cheap and simple.

Do you have the schematic?

You have an Relay and an 2  IC's per channel, can you change the IC's to see if the problem goes away?

Do you have a signal probe? if not you should make one for yourself,  and use that to troubleshoot the signal flow

What could be bad that would work with a condenser Mic but not a Dynamic mic?

 

[pucho812]

This is a John Oram product that he made when the former owners of the trident brand were not doing anything with it. He just started to make things with trident on them. ThentThe brand was sold and that changed real quick  as the current owners are doing a lot with trident.

circuit looks to be a ina217 burr brown preamp chip with  5532 to offer a balanced output and then metering.  It's transformerless  I/O. 

I would bet that  the INA 217 part  is right of the data sheets for said preamp chip.  That makes a drop in replacement and so does analog devices. The that and the burr brown version sound very close to each other , the analog devices does not.

48VDC? how is it connected  from the description it sounds like it's floating, unless there is something I am missing.

 

[thegoldenrulers]

Yep, correct. INA217 and 5532.

I'm sorry I don't understand this question (my apologies, I am new to this): "48VDC? how is it connected  from the description it sounds like it's floating, unless there is something I am missing." This unit is being run at 115v and the phantom power works fine, but I bet I didn't answer your question at all. Here is a picture of the power supply.

And to reiterate, the problem only occurs when I have to crank the gain higher (like with a dynamic and/or ribbon mic).

 

[thegoldenrulers]

Hi Whoops,
I do not have the schematic.

"You have an Relay and an 2  IC's per channel, can you change the IC's to see if the problem goes away?" So you think this does not have anything to do with grounding? I will look into changing the IC's.

I don't have a signal probe, but I will start googling

"What could be bad that would work with a condenser Mic but not a Dynamic mic?" That is what brought me to this thread. In earlier posts, it seemed that others with this problem were able to fix it by grounding the unit. Not sure of the answer or how to do that.

 

[pucho812]

When i asked how it was connected I was referring to the following...

Power supply design usually has a floating output v+ and v- if I ground v- I would end up with a positive VDC output.  If i ground the V+ then I would end up with a negative VDC output.  so to get the +48VDC they have to be grounding out the negative of the floating output.

 

[thegoldenrulers]

I have no idea how to even answer, sorry. Thanks for trying to help me, but I am not even sure I can answer the simplest question on this. I was hoping it would be a matter of soldering a ground wire somewhere within this unit.