crackling noise

Fender Hod Rod Deluxe Repair

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Because the Hot Rod Deluxe is the world’s most popular valve amp [citation needed], I get a Hot Rod Deluxe Repair arriving quite regularly.

The amp has two common faults, which are well documented:

The most common fault is the Low voltage power supply (LT supply) failure. This powers the opamp driven reverb and effects loop. Fender create their 16V low voltage power supply from a 33V and create significant heat in the dropping resistors and zener. This heat then causes the copper to delaminate from the PCB, leading to crackles and bangs and occasionally complete signal dropout. You can see the heat issues on this picture, taken with my thermal camera. The dropper resistors are getting hotter than the power valves! (Update 2020: repair kit available here): Hot Rod Deluxe Repair Thermal

On older hot rod deluxe repairs there’s some PCB retracking work to do to repair the PCB damage. On newer amps I can just take preventative action – replace the 5W dropper resistor with a 5W part raised off the PCB with ceramic spacers and replace the replace the zener also raised off the board.

The second common fault is the grey ‘IC’ (Illinois capacitor) electrolytic filter caps which are prone to failure. Fender use these presumably because they’re the cheapest 450V axial caps around. In fairness to Fender, there are probably hundreds of Hot Rod Deluxe amps using these caps that are still working, but there are also a lot that fail. I use a mix of quality F&T (German) and Nichicon (Japanese) capacitors to replace these parts and I recommend replacement on all Fenders when I’m already removing the board.Hot Rod Deluxe Repair Caps

I overrate all caps significantly The cost increase is only a few pounds but leads to better performance and improved lifespan. The most important caps are C33 My preferred configuration is:

C36 (overrated by 100V)
C35 (Overrated by 50V)
C33 (overrated by 470V using 2 series caps!)
C31 (overrated by 470V using 2 series caps!)

Update Sept 2020: At the time of this post (2018), great quality Nichicon and F&T axial caps were still available. 2 years later, Axial caps are going the way of the dodo so I’ve switched to using high reliability radial RubyCons with a special adapter board  (which I’ve made available to others as a repair kit available here).

The other thermal ‘weak point’ is the footswitch circuit, which gets the same treatment as the other hot resistors in the LT supply.

If you need a Hot Rod Deluxe Repair, please contact me.

Hot Rod Deluxe repair Dropper resistorsHot Rod Deluxe Repair ZenerHot Rod Deluxe Repair Footswitch Dropper

Trace Elliot GP12 Repair – Keld Ampworks, Newark

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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

HH amp Repair 

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HH amp repair

I’ve seen and played most amps in my career in music retail and amp repair, but this HH amp Repair was a bit of a revelation. The clean channel is a thing of beauty.

It’s a full solid state oversized 1×12 combo with two independent channels. The tube emulation circuit seems to involve distorting a signal transformer. It’s OK but nothing special. The clean sounds on both channels are really great.

The amp needed repair because it was making a strange ticking noise when the reverb was turned up.

The reason for this turned out to be a lack of local decoupling on the reverb board. This is a fairly major design flaw, but the amp obviously ‘got away with it’ for the majority of its life, the problem only appearing as central filtering components aged.

Here’s a quick video of the HH amp repair, showcasing the crackling and ticking issue then the lovely clean sound when fixed.

If you have an HH amp repair job please get in touch.