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Author Topic: Buzz from preamp stops when touching chasis. HELP!!  (Read 14286 times)

Mike Bloomfield

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Re: Buzz from preamp stops when touching chasis. HELP!!
« Reply #10 on: March 07, 2011, 02:56:08 pm »

As is mentioned in my first response you may want to look into "pin one problem" . This may be an actual design problem in the original unit, but somebody will have figured out how to make it right by now.

JR
I read up a lot about the "pin-one-problem" and did everything I could to try to rectify it externally. I'm pretty sure the Trident S40 preamps are very quiet units and there is something internally wrong. I posted some samples of the noise it was making here (three scenarios recorded):

http://soundcloud.com/mdb/trident-s40-xlr-w-mic-tests
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Mike Bloomfield

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Re: Buzz from preamp stops when touching chasis. HELP!!
« Reply #11 on: March 11, 2011, 04:40:24 pm »

I got a call from the service shop and it is supposedly fixed now. So I will confirm that tonight when I pick it up and test it at home.
It needed the pots cleaned (knew that) and there were some internal ground connections that needed re-soldering. Here's hoping...
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Mike Bloomfield

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Re: Buzz from preamp stops when touching chasis. HELP!!
« Reply #12 on: March 14, 2011, 02:51:59 pm »

The shop did not fix the preamp although they claimed that they did so... forget them. I'll try it myself (even though I have no idea what I'm doing). I took it apart at home and there were two pieces of bare aluminum wire connected (soldered) across the top of the pots - one on the top row and one on the bottom row. There was also two pieces of green wire soldered to the negative terminal of the VU meter and attached to the nearest pot (connecting all the potentiometers in series to ground via the VU meter negative). These components did not look factory so I removed them (they were present before I took it to the service shop too). Am I correct and okay to do this? The pots are grounded to the chassis via their mounting nuts anyway and by removing the additional grounding some of the noise the amp was making has been eliminated (although it still gets noisy with the gain turned up high). The buzz is less when the EQ stage is engaged.

Should I replace all the caps and if I do, is the rated operation temperature of the caps critical? What about the type of cap (aluminum electrolytic, film, copper, poly, etc.)? I hear Panasonic are good, but they have so many different "series" of caps. Which ones should I pick? I really don't know anything about them, but I can operate a soldering iron. It can't hurt to change them although I've read changing them may change the sound (color) of the pre-amp.

These are the radial caps that I found in the preamp:

Main circuit board
2200 microF @ 16V x1
100 microF @ 50V(RE) x2
4.7 microF @ 63V x2
10 microF @ 50V(LL) x2
22 microF @ 35V x1
47 microF @ 35V x2

Power supply board
220 microF @ 35V x2
2200 micro-M @ 25V x2 **What is micro-M?
100 micro-M @ 63V x4
220 microF @ 100V(RE) x1
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John Roberts {JR}

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Re: Buzz from preamp stops when touching chasis. HELP!!
« Reply #13 on: March 14, 2011, 03:11:47 pm »

You are more likely to get a better response to a design issue question over at Bruno's forum where you appear to be running duplicate threads. I will respond over there.

JR
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Mike Bloomfield

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Re: Buzz from preamp stops when touching chasis. HELP!!
« Reply #14 on: March 14, 2011, 03:37:04 pm »

Ya, sorry for the duplicates, but I was getting two different sets of people responding and felt I had to update both.
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Scott Smith

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Re: Buzz from preamp stops when touching chasis. HELP!!
« Reply #15 on: March 14, 2011, 08:29:53 pm »

Are you near any RF sources?
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Mike Bloomfield

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Re: Buzz from preamp stops when touching chasis. HELP!!
« Reply #16 on: March 15, 2011, 01:22:45 pm »

Are you near any RF sources?
Just a CRT television, but even with that off I still get the noise. For a moment last night I had about a minute of pure silence with it and then when I engaged the 48V phantom power while the unit was on (probably should have turned it off first) the noise returned.
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Mike Bloomfield

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Re: Buzz from preamp stops when touching chasis. HELP!!
« Reply #17 on: March 24, 2011, 02:27:09 pm »

Thanks for all the help here. I felt I should update this thread in the even that someone else has the same difficulties with their preamp and is looking for a solution.

I sent the unit to Vancouver to a most excellent technician. I do not have the Trident back yet, but am confident it will be great when returned. There was some cold solder joints, oxidized input XLR posts (causing an ~800Hz oscillation) and no ground lift circuit on the PCB. Jumping a ground from earth to the XLR pin#1 stopped the noise.

While it's opened up I am also changing the original preamp with a THAT Corp 1512 pre IC and some of the opamps with Burr-Brown OPA2032's. I might be replacing the rest of the opamps with Burr-Brown OPA627 or with the OPA2227 ops, but it depends on whether the pins match and they can be fit onto the PCB. It may not come back sounding like a "Trident", but it will be the best sounding Trident S40 around!!

If you need something fixed, Steller Studios in North Vancouver is excellent!!
http://www.steller-studios.com
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ProSoundWeb Community

Re: Buzz from preamp stops when touching chasis. HELP!!
« Reply #17 on: March 24, 2011, 02:27:09 pm »


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