repair Archives - Page 2 of 5 - Keld Ampworks Guitar Amplifier Repair

HH amp Repair

10/02/201710/02/2017 by rowan

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.

Dual Rectifier Tremoverb repair – Mesa amp repair

10/02/201710/02/2017 by rowan

This Tremoverb repair was for a customer who was attempting a combo to head conversion. It’s a lovely lovely sounding amp, but the 2×12 speaker box in which it was housed was too heavy for the owner. The owner performed the conversion himself but in doing so, the hand wired input jack became disconnected so the he brought it in for repair and basic service.

The Tremoverb input was easily and quickly fixed. My minimum fee is the 1 hour diagnosis period, so I proceeded to give the amp a full valve test in order to give best value for money.

The Valve test revealed that one of the power 6L6 valves was faulty and the others were out of spec. Most Mesa amps require a specific set of valves and this Tremoverb Repair is no different so I fitted a matched quad of Mesa STR-440s.

Whilst giving the amp a look over I noticed a very wierd bit of PCB layout. The Opto isolators that Mesa always used on amps (pre-late nineties) were stacked one on top of the other. I hope I never have to replace the bottom opto on one of these. As I’ve said before, Mesa really don’t think about repair when they’re designing. Pity, when they sound so awesome!

If you have a Mesa Tremoverb repair please get in touch.

MXR Dyna Comp repair

27/03/201708/02/2017 by rowan

The Dyna Comp is possibly the most famous of the compressors used on guitar. This Dyna Comp repair was similar in nature to the ESD fix that I’ve documented elsewhere in relation to the Carbon Copy pedals.

The issue is with the switching circuit – the FX does not switch in when the pedal is pressed.

There was a small complication in the Dyna Comp repair however – this unit uses through hole components which are now obsolete. It took a very steady hand to fit the 1mm wide body of the modern equivalent part into the massive space left by faulty component, but fortunately I’ve done this before many times in R&D work.

If you’re interested in the Dyna Comp, check out my analysis of the Behringer DC9, a clone.

UPDATE: 2017

The MXR ESD repair kit is now available for sale at www.rsdsound.co.uk. If you’re an experienced repairer and skilled with SMT repairs then you can purchase this kit. If in doubt, just post it to me and I’ll sort it for you. Note that some DynaComp are not SMT.

http://www.rsdsound.co.uk/product/mxr-carbon-copy-esd-repair-kit/

If you have a Dyna Comp repair with problems, please let me know.

Peavey Valve King Repair – VK100

21/06/201707/02/2017 by rowan

My customer brought this Peavey Valve King repair in to me before Christmas to get an opinion on its state of repair. The amp was blowing fuses.

The Valve King VK100 is a monster of an amp. Not fire breathing levels of gain like some Peaveys but a big and heavy brute with a classic sound.

I determined within the first hour that the fuses were blown due to a failure of the DC heater circuit. DC heaters are used to reduce the hum in high gain amps. Unfortunately the internal fuse was a soldered-in part, so I made temporary fix (pictured) to test my theory and quote for the customer, before fully disassembling the amp and replacing the part properly when the quote was accepted.

Whilst fixing the heater circuit I noticed that the area of the circuit board that I was working on had been repaired previously. Unfortunately they hadn’t told him what they’d done.

After fixing the DC heaters, I tested the units full output power. It’s a 100W amp, but was only putting out about 15W. More work to do! After a bit of further investigation, the amp output 87W. Not full 100W, but within the margins of dodgy advertising!
The amp needed a couple of valve changes and a couple hours work but the owner was pleased with the result.

If you have a Peavey Valve King repair in need of repair, please visit the contact page.

Carvin repair – Nomad

10/02/201707/02/2017 by rowan

This Carvin repair was completed for Simmonds music in Grantham. They received the amp in part exchange. The amp would occasionally drop to very low volume, with no apparent reason.

From the beginning it was obvious that the Carvin repair had been attempted by another tech in the amplifier’s past. The first valve stage had sustained some damage. Unfortunately it appeared that some damage had remained unfixed.

The amp also had a bad problem with a hum on the high gain channel which I was able to fix.

After replacing the plate resistors, the DC heater circuit, the cathode bypass caps and as number of other smaller parts, the amp was completed and returned to Simmonds in as-new condition with an Ampworks guarantee transferable to the new owner.

If you have a Carvin repair, please do contact me and I’ll get it working again!

Orange AD30R Repair – Valve amp Service

21/10/2016 by lois

This Orange AD30R Repair came in semi-urgently for a full service. The customer had a gig with his band at the Bodega in Nottingham on the thursday and he brought me the amp on Monday night. I do offer an urgent 24 hour turnaround service but fortunately the customer didn’t need that, just a 48 hour turnaround!

After testing all the valves in my valve tester, I determined that the EL84s in the output stage were mismatched. It’s important to match output stage valves to ensure continued good amp health and reliable tone. Fortunately I hold stock of EL84 valves so it didn’t delay the service.

I confess I’ve had to use an Orange AD30R image from Google because I forgot to take a photo!

If you have a Orange AD30R Repair, please let me know and I’ll take a look!

Presonus Monitor Station Repair – Loud Buzz!

09/06/202321/10/2016 by rowan

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!

Laney speaker change – VC30

21/10/201620/09/2016 by lois

This Laney speaker change job came down from York last week. The Laney VC30s are great amps but sadly are supplied with quite bland speakers. My customer asked me to fit a Celestion V30 to replace the stock HH driver.

It’s owned by a professional guitarist who bought it as a spare – unfortunately the amp also had a bad case of ‘snap, crackle and pop’ so whilst en route to gig he brought it to me for investigation and a speaker change.

The speaker change was a success. Because I’ve had experience of microphonic howls in Laney amps, I was initially concerned about the V30’s greater magnet size and proximity to the valves, but this turned out to work well. You can hear the results of the speaker change below, a great improvement!

In another Laney speaker change, I had good results with an Eminence Legend, I’m afraid the audio isn’t as good on this one!

The crackling issue turned out to be the phase inverter valve, one if two 12AX7s which failed in my valve tester.

If you have a Laney VC30 speaker change or repair, drop me a message and we’ll bring your amp to life!

Orange Amp Repair – Rockerverb 100 MKII

20/09/201611/09/2016 by lois

This Orange amp repair is a particularly shocking example of an amp which someone has attempted to repair without really having an understanding of what they’re doing. The customer brought it to me with two issues: a broken reverb (victim of the botched repair) and an intermittently faulty gain channel.

I started out by performing a basic valve amp service upon the amplifier. This involves testing all the valves with my valve tester. 3 preamp valves were found to be faulty: this proved to be the cause of the gain channel dropout. This Orange amp repair didn’t require checking of the bias of the amp, because the Rockerverb MK II has Orange’s proprietary ‘DIVO’ power valve management, meaning that the amp biases itself. It’s the only system that I’m aware of that doesn’t require matched valves in the output stage, so when one of the EL34s was found to have a snapped key on its base, I installed a 6L6GC in its place! I also fixed the snapped key so it could be used.

Turning my attention to the spring reverb repair, I noted that one of the phono cables had a broken connection. The connectors had been made up without any strain relief and this had allowed damage to happen during normal use. This is an easy fix and after fixing the broken connection I resoldered the other reverb intact connector so that both had adequate strain relief.

Upon testing the faulty spring reverb I discovered that it still wasn’t fixed so I turned my attention to the unit itself. Worryingly, one of the sockets was surrounded with glue on the outside. When I opened it up I realised that some fool(!) had tried to fix the loose socket by flooding it with superglue. Worse, as you can see in the picture the glue had dripped inside the unit and fouled the springs quite badly.

I was able to remove the superglue, but they remained quite distended. The unit still works as a reverb so my customer decided not to have me replace the tank.

If you’ve got an Orange Amp repair or a spring reverb repair, please don’t bodge it, just get in touch!

Marshall JCM900 repair – Ampworks Newark

20/09/201604/09/2016 by lois

This JCM900 repair arrived after the owner found that it was lacking in volume.

It’s a 2009 unit, two channel, with a 2203 type circuit on channel A and a higher gain circuit on channel B.

The problem appears to have been with the amplifier bias. Although the valves were matched, the bias on this JCM900 repair was set very high. The bias set the dissipation at about 95% – Marshall suggest about 70%. This causes the output to compress much earlier than would otherwise occur. Fortunately this is easy to fix.

I then offered to soak test the amp which is a means of testing the amp in the conditions it would be in rehearsal or gig. This is great for revealing those hard to find problems that would otherwise missed. It revealed a minor fault with the preamp – a crackle appeared behind the note transients. Since this was a relatively minor problem, the owner chose not to have it looked into.

I sometimes have been known to complain that some amp manufacturers give little thought to ease of repair – mesa boogie have had some stick from me in other reports. Some marshall repairs – thinking the DSL range in particular – are a bit difficult because of their complexity but this JCM900 repair is a delight to work on. They’ve really thought things through both in terms of reliability and ease of repair. It’s probably the easiest channel switching amp to repair that I’ve seen.

Although the channel A had a great plexi type tone, the owner isn’t a big fan of the Drive sound in ChannelB – he’s thinking of modding the amp to acheive the fabled Silver Jubilee tone so stay tuned – this one might turn up again.

If you have a JCM900 repair, please do get in touch.