Polytone Minibrute Repair (Minibrute III repair)

Polytone Minibrute repair

This Polytone Minibrute Repair came in from a Lincoln customer with an obnoxious hum problem. This unit is probably form the 1980s

The issue was solved by adjusting the output stage bias point and improving the connection between the screw mount power supply capacitors and the power amp stage.
polytone minibrute iii repair
The amp is a bit of an oddball in terms of construction, with the preamp contained in the top of the amp, and the power amp in the base of the unit. The power amp unit is held together by the capacitor screws and two large heatsinks.

If you need a polytone minibrute repair, please get in touch.

Trace Elliot GP12 Repair – Keld Ampworks, Newark

Trace Elliot GP12 Repair

The symptoms exhibited by this Trace Elliot GP12 repair were a loud hum and distortion evident during note decay. Unfortunately I wasn’t able to replicate the customer’s problem which makes repair difficult, so I took a number of steps.

I left the amp on soak test for 2 hours, which involves heavily driving the output stage – this normally shows up faults that are temperature or power supply related.

What I did find was that one of the internal IDCs was causing audible noises when manipulated. I’ve seen this before with another Trace Elliot GP12 repair Mostly crackles, although there was a slight increase in hum sometimes which matched the symptoms described. Cleaning the IDC fixed this and that connection is now stable. I also cleaned the FX loop sockets because unused FX loops are a prime candidate for noises such as those described.

As part of a general service I also cleaned the Graphic sliders as there were a few little crackles – nothing to do with the described fault.

The next step in hum busting would have been to replace the reservoir caps. I avoided this because it adds significant cost and I had no concrete reason to suspect them. The description of the distortion on the note tail does sound a bit like caps, but the soak test didn’t reveal any problems with them.

The amp was returned to the customer. When I contacted him again the next month, the amp was still working well, another successful repair!

Note that the image is an old image, not the amp in question, it’s actually

If you are in need of a Trace Elliot GP12 repair, please get in touch via the contact page

Presonus Monitor Station Repair – Loud Buzz!


This presonus monitor station repair was posted to me by a customer who’d read my report on another presonus repair. The original unit exhibited a constant buzz and the customer reported similar problems here. Upon testing the unit, the problems I experienced on testing the unit were less severe, fortunately the experience with the previous Presonus Monitor Station repair led me to go straight for the power supply section of the circuitry and I noticed the same area of internal circuitry was showing signs of damage. The repair was completed within the first hour, keeping the costs low for the customer.

As you can see in the video below, it’s working well now!

Update June 2023: I’m now selling a capacitor kit, so you can fix your presonus yourself. More info here

If you have a presonus monitor station repair, please get in touch, I’m getting quite used to them!