WEM Copicat Tape Echo Repair

Recently, I had the pleasure of completing a WEM Copicat tape echo repair on three different units, each presenting its own challenges. After years of use, they often require some TLC.

All three Copicats needed new tape loops, which are essential for achieving that classic echo effect. Additionally, extensive mains safety work was necessary to ensure safe operation. During the inspection, I discovered visibly leaking electrolytic capacitors in each unit, which I promptly replaced to prevent further damage.

One of the Copicats had a stiff arm that affected playback, so I carefully adjusted it for smoother operation. Another unit was extremely noisy, indicating potential issues with the tape mechanism; after thorough cleaning and adjustments, the noise was eliminated. Finally, one Copicat had a faulty channel 2, which I diagnosed and repaired to restore full functionality.

After completing these WEM Copicat tape echo repairs, each unit was tested and sounded fantastic, ready to deliver that iconic echo sound once again. If your tape echo needs some attention, don’t hesitate to reach out for a WEM Copicat tape echo repair!

Hughes & Kettner Switchblade Amp Repair

I recently repaired a Hughes & Kettner Switchblade amp that had a shorted mains transformer, causing power failure. Thankfully, I sourced a replacement transformer from a genuine parts supplier, ensuring top quality for the repair.

After installing the new transformer, I performed a full service, which included cleaning key components and checking all connections. I also replaced the old output valves with a new pair of EL34s to restore the amp operation.

Following the Hughes & Kettner Switchblade amp repair, I tested the amp at various volumes, and it delivered as expected. The owner was thrilled to have their amp back, ready for upcoming gigs.

If your amp needs attention, don’t hesitate to get in touch—your gear deserves the best!

AER Compact repair

AER Compact repair

Recently, I had the pleasure of repairing an AER Compact 60 amp that was experiencing frustrating audio dropouts. The owner had noticed that sound inconsistently faded in and out during performances, which can be a nightmare for any musician.

To diagnose the issue, I conducted a soak test—a method that involves running the amp at gigging volumes for an extended period. This technique helps reveal intermittent faults in the AER Compact that might not be evident during a brief test. During the AER Compact repair I monitored the amp, it became clear that the dropouts were linked to oxidized switches. These switches, often overlooked, can degrade over time, leading to poor connections and sound cut-offs.

After cleaning the affected switches and ensuring all connections were secure, I re-tested the amp. The result of the AER Compact Repair? A solid, consistent output with no further dropouts. The owner was thrilled to have their AER Compact 60 back in perfect working order, ready for the next gig.

If you’re facing similar issues with your gear, don’t hesitate to reach out for a repair!

Line 6 Helix Ground Loop issue when using the amp channel switcher

Line 6 Helix ground loop issue

Here’s a fix for a Line 6 Helix related ground loop problem I did for a customer a couple of years ago. He used the HX floor unit to control the amp channel switching and it created a really bad ground loop hum. It appears that the HX amp control sleeve is ground referenced, which is a pity on such an amazing unit.

You could modify a TRS cable to break the ground loop and it would work fine. On bigger stages though so the better is to build an adapter box to break the connection so that any length TRS cable can be used.

This isn’t a particularly common problem for Helix users, but it’s a real one that people occasionally come across.

The ground loop is caused by both pieces of gear. There’s a ground path running through the audio path of the amp and helix and a ground path running through the switching path of the amp and helix.

In some amps, the ground scheme will be such that noise is induced into sensitive parts of the audio path. The guitar amp designers won’t have paid much attention to this because most guitar amps with these sockets were designed before the advent of systems that share audio and switching functions, like Helix or GigRig. The amp designers were only expecting the user to plug in a latching footswitch to the jack. Latching footswitches don’t share an audio ground so no loop is created, so the designers didn’t need to control the ground currents. Thus the amplitude of the induced noise is determined by the amp grounding scheme resulting in different amps exhibiting the problem at different levels. Hope that makes sense. 🙂

It couldn’t happen if the Helix sleeve wasn’t grounded, it wouldn’t happen if the amp’s FX connector sleeve wasn’t grounded. 🙂

The opportunity to break the ground connection entirely is only available at the Helix or switcher end. Whilst an isolated footswitch design could be built in at the amp’s end, this would be awkward because it would require an industry standardised LV power source in switching systems to power a relay (or opto) in the amp. Worse, it would stop the footswitch socket working with the very common stand alone latching footswitches (which have no power). 🙁 No manufacturer is ever going to choose to do that. However it’s very easy to create a relay driver at the Helix end so that the sleeve is isolated from the audio ground (much like the GigRig remote switch options). 🙂

The noise level is also proportional to the amount of external noise as this is the external noise source that’s then picked up by the GND loop. In my workshop there’s plenty of external noise sources, just like in lots of venues. Studios, should hopefully be much quieter.

Unfortunately an ISO hum silencer box can’t fix it because this needs to respond to DC changes – the transformers in an ISO hum silencer will block DC. You could use one of those in the audio path to fix the problem by a different route (break the loop in the audio instead of the switching), but then that potentially messes with the audio path, so it’s not the best solution.

Above is a picture of the box I built for my customer. Very simple to make if you’ve got a soldering iron and a step drill. You can build one up yourself from the picture, or if anyone ever wants one building I can make one up at my usual labour rate.

Here’s the BOM to make your own:
Hammond 1590A style box.
Switchcraft 12B stereo metal jack socket
Neutrik NMJ6HCS or NMJ3HF-S or similar stereo plastic bodied socket
2 wires!

Here’s a video showing how it works:

Seymour Duncan Powerstage 170 Repair

Seymour Duncan Powerstage 170 repair

This Seymour Duncan Powerstage repair was a pretty simple job and was turned around next day for the customer on my express service. The customer was an American pop punk band, currently touring the UK.

Though he normally used a step down converter. Unfortunately the customer had inadvertently connected his 110V seymour duncan powerstage to UK mains (nominally 230V, really 240V) and it had blown up spectacularly.

The part that was blown up is a hifi poweramp, made by a subsidiary of Bang And Olufsen. They’re used in many amps nowadays, including Gallien Kruger, Acoustic Image, Fender Bassman 500 and Fender Tonemaster.

Icepower module replacement Seymour Duncan Powerstage 170 repair

Ironically, the unit has an internal selection for 110V/230V to allow the unit to be swapped very quickly between UK and US mains. I’m not giving details of what to do online as encouraging people to meddle with mains electricity is beyond the scope of this blog!

The band’s tour manager brought the unit in for repair and I got the new power amp module delivered on next day shipping.

I set the Powerstage back to 110V operation for the customer as had a spare for UK gigs but were touring US again immediately on their return.

If you have a Seymour Duncan Powerstage 170 that you need repairing, please do drop me a message.

Valve Amp Workshop Spec Suggestions

Roland RH-1 RH1 power supply for Roland JV2080 repair

I recently got a Roland JV2080 in for repair. The cause of the fault was the RH-1 power supply board. This is a switched mode power supply board that Roland use in a few products. Normally I’d be fine fixing a SMPS, but Roland can’t release schematics for this board as it was designed by a contract engineering company outside of Roland. That makes things difficult. Spare PCBs are also not available.

So I decided that the most sensible thing to do would be do design a replacement. I got part way through designing it when the customer decided it wasn’t something he wanted to proceed with. No hard feelings, he hadn’t actually authorised it. So it’s my lookout. But anyway. I’ve got a half designed Roland JV2080 RH1 power supply board. I’d be glad to finish the design for someone and get their unit running again!

Get in touch.

Midi For Guitarists

The MIDI standard that’s used to control loads of guitar equipment seems really complicated. Most devices will give you a painless way of programming your amp or equipment to avoid having to learn any of the codes, but occasionally there will be a device or occasion that requires a slightly more in depth look. The good news is that as a guitarist/ guitarists tech you can ignore nearly all of MIDI apart from program change and controller change.

The MIDI cable

It’s usually a 5 pin DIN cable, though others are possible. The midi cable has a send wire, a receive wire, and a ground. The other pins in a 5 pin are not connected. You shouldn’t need to know the pinout or which pin is which.

What is a MIDI communication?

Basically when you do something on a midi device, it sends 4 or three binary numbers down the send line. In a 4 number version, this is what the numbers are saying:

  • <this is what I’m gonna tell you (code 0-15)>
  • <but only devices on this special channel should listen to me (0-15)>
  • <some more detail about what I’m gonna tell you (0-127)>
  • <this is the data, usually a number between 0-127>

For example:

  • <control change (9)>
  • <channel 4>
  • <volume control (7)>
  • <56>

This all gets picked up by the receiving device(s) on channel 4 which act(s) accordingly. In this case, it will change the volume to 56 (out of a maximum 127).

Technically, I’ve oversimplified, as the first two 0-16 numbers are rather confusingly sent as one combined binary number (common practice in serial comms), but that’s the gist of it.

This explanation was written in response to a facebook query. Hope it helps some others too.

Keld Ampworks’ Fluffy Green Policy

I write this post with some trepidation. As public and government figures finally start to take heed of the dangers around climate change and linked environmental issues, some have started to view what is essentially a scientific theory, backed up by decades of real world evidence and proven hypotheses, as a political issue. As a very small business, it’s very risky to engage in political discourse and risk alienating customers. So let me be clear, this is isn’t a political post. I’m an engineer, and Keld Ampworks is an engineering company. Climate change is a problem. The problem was (and continues to be) created by the actions of engineering industries. The problem is identified and rigorously quantified by scientists. With a growing human population, the problem is one of efficiency. Efficiency is the engineer’s domain. The solutions lie within engineering.

With that in mind, all of my fluffy green policies are about Keld Ampworks’ commitment to making the rational engineering efficiency choice, they’re not about economic efficiency.

What can Keld Ampworks do about it? At the end of the day, I’m a tiny tiny company with very little financial power. Only little things.

Repairs are the ‘Green’ choice.

The core of the Keld business is in repairs. Every unit that’s repaired here and at all the other repair shops across the world is a unit that does not need to be scrapped and replaced. Landfill is reduced, waste is reduced.

Repair is nearly always the choice of best engineering efficiency, however it’s frequently not the choice of best economic efficiency. Unlike many repairers, I don’t have a ‘no cheap amps’ policy. I’ll offer a quote even on a cheap 90s solid state amp where the cost of repair is equal to the economic value of the amp. I’ll always be honest with the customer about the economic side of things. I’m not trying to dupe anyone.

WEEE, RoHS and Solder

All components removed from amplifiers are disposed of through the WEEE scheme. All CE marked products are repaired with RoHS components. All CE units are repaired with Pb-Free solder. As well as being a legal requirement, this is also the choice of best engineering efficiency: a mix of Lead and lead free causes a solder joint that is weaker than either a Pb or Pb free joint, resulting in a less reliable amp. A less reliable amp is not an efficient engineering outcome. I expand upon this here. But there’s a big caveat here…

RoHS and Pb-Free exceptions.

HOWEVER in units that predate RoHS regulations I use lead solder exclusively. Using Pb-free has no environmental advantage in a unit that is already non-RoHS and the solder mix reduces the reliability as described here. I will also use non-RoHS components in non RoHS units. It would be a poor engineering efficiency choice to scrap a unit, rather than use a non-RoHS component.

Paperless

All customer communications are paperless. This is the most efficient way of communication.

Finance

Keld Ampworks uses a paperless bank with a commitment not to invest in fossil fuel based energy. Fossil fuels may be an economically efficient way to generate electricity, but it’s not an efficient engineering choice.

Component reuse

In general, it’s a poor engineering choice to reuse old components. However there are some exceptions. I routinely save transformers and knobs, heatsinks and obsolete components from amplifiers that weren’t repairable. These are then used in other repairs.

Packaging reuse

I get several component orders every week as well as getting repair work in by post. All packaging is re-used for items that are posted out to customers. Packaging that I can’t make use of is donated to another Newark based business for reuse. Any remainder is recycled.

Design for longevity

Much of Keld Ampworks design work is done with Class D amplifiers. In this, we again have to think about engineering efficiency, not just in use, but over the lifetime of a product. Class D products are often designed using monolithic chips that are unrepairable and go obsolete. My Class D designs use discrete MOSFET devices – replacement parts will always be available, meaning that the amps will always be repairable.

Behringer XR18 repair (digital mixer repair)

This Behringer XR18 repair was a digital mixer repair performed for a local secondary school – the Minster school in Southwell. The unit is in constant use at the school. I’ve previously done some PA repairs for them.

The power light began to flicker and the unit would no longer connect via WiFi.

Upon opening the unit I noticed a number of slightly venting electrolytics. These were CapXon 85 degree capacitors. They’re not great quality parts! Electrolytics degrade with temperature and load life (usage).

Testing the power supply off load the voltages seemed stable, however when the unit was loaded with the current draw from the digital section the 5V rail dropped to a very unstable 2.8V. This is no where near enough voltage for the

I gave the customer the option of replacing the power supply board with a new one from Behringer or upgrading the electrolytics on the board to some better quality 105 degree RubyCons. The new board from Behringer would presumably have had the same CapXon caps installed so the customer chose the latter option, which is probably the best choice for a unit that’s going to be on for many hours at a time in a school.

We replaced the electrolytics in the 15V and 48V supply, as well as in the 5V supply that had been drooping. The 15V supplies are used for the mic preamps and the 48V supply is used for the phantom.

After repair, the power light remained on constantly and the unit connected to WiFi. It took a moment to work out how to get the software to work, but other than that it was pretty painless!

The whole job was turned round in 24h to enable the school studio to get up and running again. Success!

Update May 2022: It was a bit of a faff to find the parts for this repair, and I’ve had enquiries from around the world on this subject, so I’ve put together a pack for the repair on my other website here.

If you need a Behringer XR18 repair, please get in touch.