trinityamps.com

Hi,

New to this forum, hoping someone can give me a hand with a VRM installation in a 5E3 kit.

The 5E3 kit I have is one from the Tube Doctor which is a Mojo kit from what I understand with Tube Doctor components.

Got a VRM kit from Stephen and the installation went OK with a couple of tweaks needed like making sure the wires are twisted and short as possible.

The VRM seems to do it's job OK in reducing the volume but when I start to turn the pot about a third of the way around I start to get a humming noise over and above the normal amp hum. As I continue to turn the pot to about two thirds of the way around the hum turns into a buzzing noise. After two thirds to full on the buzz goes away and the amp sounds like it normally does.

Stephen has been very helpful with suggestions but I still have the problem.

I have tried mounting the pot in place of the ground switch with the mosfet bolted to the side. I then replaced the on/off switch with the pot and mount the mosfet on the chassis close to the pot. Both locations had the same problem

The amp works fine with no extraneous hums or buzzes without the VRM kit installed.

Anyone any ideas what might be causing the problem?

Cheers.

Post some pics of your build, so we can see how everything is installed/wired.

I remember someone having a similar issue, maybe try doing a search here on the forum.

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http://pdfelectronics.com

Thanks for the reply.

I have taken the kit out as I wasn't sure if any damage was being done, by my installation not the kit.

I have done a search and found a similar problem but the difference was that in that instance the noise stopped when the pot stopped turning. In my problem the noise is always there.

I do have a recording of the humming but I can't upload an MP3 for some reason.

I have a picture of when the kit was installed on the side of the chassis.

Cheers.

PS - I've obviously posted this in the wrong area How do I go about moving it to the right board?

Post moved. Even that installation looks like it would be fine.
At this point, you've even tried aluminum shield around the control wires so a it of a loss. One thing I've never had to do was to put a filter cap ahead of the VRM to smooth out the DC before it hits the unit. But it would have to be the same size or less uf than the tweed filter caps.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Read on other posts that some do put a filter cap ahead of VVR kits.

Ordered a TAD 16uf 475v cap same size as the other filter caps in my Tweed. Worth a shot.

Let you know if it works!

Stephen,

Installed a TAD 16uf 475v cap on the rectifier pin 8 and to ground and the noise has gone!

Many thanks for the your help.

Cheers.

Quick question about the .1uf caps to stop the scratching noise.

I have seen a picture where the caps are soldered directly to the V1 pins and to ground rather than from the 68k junctions to the pins. Is it OK to do that as it will make the wiring a lot easier.

I don't intend moving the 1m resistors unless absolutely necessary!

Cheers.

The .1 needs to be in the signal path, not to ground. So it needs to go on the grid after the two 68k come together. Going to ground will not block any potential DC.




Recommend you do this as well. We've had it both ways and the tone is affected if they aren't moved. Try it and see for yourself.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Moving the 1m's is going to be a pain.

Will the scratching noise cause any problems or is just annoying?

Cheers.

The noise is a small amount of DC voltage on the pick-ups and/or controls in the guitar. A small amount may be OK.
Easiest way is to cut off the 1M on the jacks and put new ones on the sockets.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Ok, cheers.

All done.

Decided to pull out the inputs and re-wire them.

No more noises anywhere.

VRM works really well.

Cheers.

Well, that's good news. What inspired you to rewire the inputs?

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Sorry for late reply!

I had to move the 1M resistors and with the kit I have the resistors are soldered across a few tags across the sockets as per the original layout as far as I understand it.

On the Trinity layout the wiring on the inputs looked much simpler and easier to understand what was going on. Plus, if I ever needed to put the 1M's back on the sockets it would be much easier to do so.

Cheers.