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>
<control change (9)>
<volume control (7)>
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.
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.
All customer communications are paperless. This is the most efficient way of communication.
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.
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.
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.
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!
I’m just quickly leaving some infromation about a Philips MyLiving Fremont LED light repair in the hope that it will help someone else!
Ah, the joy of being a repairer. No sooner have I finished a hard week of repairing guitar amps than I must power up my soldering iron again to fix the broken kitchen light in our family home.
LED lights are indeed more reliable than their counterparts, but only if they’re made properly! I’m rather disappointed in Philips. We had one of the single spots replaced under warranty after a few months. Then two spots out of a four spot bar then died within warranty. This second time the unit was obsolete so Philips offered a completely different unit (different mounting and non matching appearance) as a replacement, which we declined, so we were stuck with them and I decided to repair them myself.
The first one was a nightmare to fix as I tried to reuse the original LEDs and then it took ages to find a suitable part. But the second one was relatively easy after I’d learned the lessons of the first. So here’s the right way for any other poor sucker who has bought one!
The LEDs that I used for the repair were the Lumileds L130-27800CHV00001. Specs below:
Colour Temp (CCT) 2700K
Colour index CRI: 80
Luminous flux: 107lm
Size 3x3mm (1210)
Having lived my whole career in the audio sector I didn’t even know Vf=48V LEDs were a thing, I’m used to them being Vf=2-5V parts! I determined that the drop through each was 48V by testing a working unit, results below.
The LEDs don’t seem to fail, the failure is in the solder connection connecting the LEDs. Because the LEDs are in series, one solder joint failure causes the whole light to go very dim (or off).
This is a potentially dangerous process, so only attempt if you know what you’re doing. The lights are VERY bright and can affect your vision. I wore sunglasses for testing. Really, I did!
Turn off mains and
Remove from ceiling
Check safety with multimeter
Disconnect L and N wires
Use a 2mm hex allen key to loosen the head of the light and thread the wires out, being very very careful not to snag the wires
Use a flat blade screw driver to gentle push back the metal springs holding the glass cover on and remove the cover
Use a flat blade to push the metal spring ring over the tabs and remove it completely
Unscrew the lens and remove the lens, and metal insert from the plastic case and thread the wires out. You may have to cut off the crimps if it’s a 4 bar.
Here’s how I diagnose which LED connection is at fault:
Use a 48 or 50VDC supply with some sharp multimeter probes. Set the current limit to 50mA. Make sure the probes don’t touch and short your supply!!
The PCB is well labelled. Prod the sharp positive probe into the Anode (A) pad on the PCB and the sharp negative probe into the cathode (K) pad. If the LED illuminates then it’s OK.
Test each LED in turn until you find the faulty LED connection.
The LED pads don’t touch the edge of the part so replacing them is tricky and not for the inexperienced. Here’s how:
Remove the LED using a hot air blower / chipquik or your method of choice. The LED pads don’t touch the edge of the part so this is tricky to do without damaging or discolouring the LED. Heated SMT tweezers might work if you use them to heat the pads rather than the component but they’re not ideal.
You could test the LED by laying it face down it on a small piece of clear plastic and using your 48V probes to illuminate it. It’s probably still working – all of mine were. If the LED is discoloured upon removal then bin it anyway – you’ll be able to see the discolouration through the lens and it might affect the colour – I’m not sure!
Clean the flux from the PCB (again, the discolouration is visible if you don’t).
Tin the PCB pads and tin the component pads, using only a VERY SMALL dab of solder.
Put a small dab of flux on the PCB pads
Heat up the larger cathode (K) pad on the PCB and very quickly place the component, observing orientation. Hold the part in place pressing lightly with tweezers until you can feel the solder melt and the part flow into place. It should be almost flush on the cathode side but there will be a small incline towards the anode because you tinned it.
Heat up the anode pad and add a small amount of extra solder. Due to its smaller size this pad should make the joint easily.
Test with your 48V probes.
If you’ve got a mains safety claw you could test the whole light on mains AC. Don’t do this if you’re not comfortable working with un-isolated mains.
Clean flux off the PCB again if necessary.
Hope that helps someone who needs help with a Philips MyLiving Fremont LED light repair. I’m not interested in repairing these for money, I’m an amp guy only. But I’ve got a few of the LEDs spare so if anyone needs them pop me a message and I can list them them for sale on www.rsdsound.co.uk .
Argh! The internet! The most frustrating thing as a professional amp repairer is seeing so much misinformation spread about guitar amp faults. Every time a poor soul with a broken amp pops up on a facebook group there’s a chorus of very confident replies. It’s the caps! It’s the output transformer! Etc etc.
You’ve probably seen these guys below. Don’t get me wrong, I know people are only trying to be helpful, but they aren’t. Not because of their lack of expertise, but because they don’t possess psychic powers. Despite 10 years experience and a very high success rate in amp repairs, when someone brings me an amp, I usually don’t have a clue what’s wrong until I’ve got it on the bench, run a signal through it and stuck some probes inside!
“Sucks to be you mate, it’s an output transformer failure!”
This is the most bizarre one. Output transformers very rarely fail. I repair about 200 amps a year and see maybe one or two output transformer failures. It just doesn’t happen very often!
“Sounds like BAD CAPS to me!”
“It is a truth universally acknowledged that an amp in possession of a fault must be in want of a recap.” So said Jane Austen in her ill-fated 1817 comeback attempt ‘Caps and Incapacity”.
Caps (capacitors) do cause failures. Most commonly issues are related to the electrolytic capacitors that filter the power supply. Electrolytic capacitors have a dielectric that dries out over time.
I’ve heard various rules of thumb – they should be replaced after 5 years, 10 years, 20 years, 40 years or never at all (argh!).
Cap lifespan is definitely a subject for another post. I don’t go by a rule of thumb. I know that there are certain designs where the caps have been designed close their ratings where replacement is advisable. I know that there are certain brands that *nearly always* leak. I still see plenty of working amps with 40 year old caps in them but yes, I do always recommend that they’re replaced at that age. There are some cap brands in some designs that don’t ever seem to fail around the the 20 year mark so I give that honest opinion to the customer and they can choose whether they want to future proof the amp. There are some amps *cough cough* modern Fender *cough* where I recommend that they’re replaced after no more than 5 years as they’re so darned lousy.
“My Vox crackled too. I put new power valves in and it was fine.”
Two amps with the same symptoms will not have the same root cause. Right now, in the workshop, I’ve got a crackling Hot Rod Deluxe caused by an overheating LT supply, a Jet City with a crackling preamp valve and a Mesa with crackles caused by FX loop oxidation.
Add to that the huge difference between various designs. An AC30 runs the valves *hard* and goes through EL84 power valves regularly. A Peavey 5150 biases the power stage very cool and doesn’t wear out power valves anywhere near as often.
So what’s the right way to do it?
There’s no one way to do it, but let’s take an example. I’ve got a Blackstar in at the moment with a hum issue. This is what I’ve been doing.
Test all the valves. They’re all fine. Replace the valves.
Turn the master volume down. The hum didn’t go away, so we’re looking at a power amp issue.
Remove the phase inverter. Hum goes. This amp has no NFB so we’re looking at a phase inverter issue.
Check pin voltages on the valve. Anode voltages are radically different.
Remove valve and retest. Anode voltages still different. Smoking gun, this looks like an anode resistor.
With the amp off, meter the anode resistors, one is way out of spec. Replace it.
Turn amp on. Situation is better, but anode voltages are still different. The valve passed test, but maybe the tester missed something. Replace it
Anode voltages fine.
Test with speaker again. Hum gone!
Check bias. It’s way too high. Fix and recheck.
Check output power.
Listening test with guitar
Soak test the amp.
Listening test again.
That said, there are times when it is possible for an experienced guitar amp repair to predict the cause of a failure. This is usually where there’s a flaw in the design that causes repeat failures. Some examples are:
Aiming to bring some objectivity to a much debated topic, this time we’re talking about lead free solder in guitar amps.
“Do you use Leaded or Lead free solder at Keld Ampworks?”
In products that were built using lead solder I use lead solder. From a health/product recycling point of view it’s pointless to do otherwise.
In products that were built with lead free solder I use lead free solder. I DON’T use lead solder for these because if the two solder types are mixed they don’t flow together properly. They cool at different temperatures causing cracks in the solder and leading to long term reliability issues. If someone is repairing your amp and they’re using lead solder to ‘fix’ the lead free solder then they’re making it worse. Hope that hasn’t happened for you.
“But I’ve heard lead free sucks!?”
It’s probably worth addressing some claims regarding the use of lead free solder in the audio industry. Ten years ago I used to be a “lead free sucks” kinda guy too! But my understanding of the subject and my soldering skills have improved and so has the lead free technology – I no longer believe that modern lead free does “suck”. This post may border on a rant, so apologies in advance.
I’ll try and talk in general terms. This post’s intended audience is a guitarist with a soldering iron.
Solder is commonly made from a combination of Tin (Sn) and a mix of Lead (Pb), Silver (Ag), Copper (Cu), Nickel (Ni) in different ratios:
There are three common combinations:
SnPb – Leaded solder was common worldwide until the 21st century. As I understand it is used for internal markets in the USA and China.
SnCu – ‘Cheap’ Pb-free solder. Commonly used in budget Pb-free applications.
SnAgCu – ‘Good’ Pb-free solder. The silver helps the solder to flow. Used in ‘good’ Pb-free applications.
For a number of health and recycling reasons, the EU (…pause whilst normally reasonable people from all political spectrums start fighting for no apparent reason…) introduced legislation in 2003 that had to be enacted by 2006. This legislation was called RoHS (Restriction of Hazardous Substances). As you’d expect because of purchasing cycles, some manufacturers switched before the introduction date. Others didn’t prepare, or didn’t know how to.
The early days of Pb-free adoption (early 2000s) saw some serious problems, especially using lead free solder in guitar amps. Lead solder had been around for 100 years. Problems were to be expected in the first few years of a new technology. In our small industry, many brands build their products in house rather than paying specialist electronic assembly subcontractors companies to build their products. This meant that the music industry was slower to fix lead free issues. They couldn’t afford to buy better machines, they couldn’t afford to hire expensive Pb-free transition consultants. So audio electronic products from the early 2000s had some problems, the results of which are still turning up on my bench now.
But this was almost 20 YEARS AGO. Machines got better, process control got better and these problems no longer really occur when using lead free solder in guitar amps (modern guitar amps). This is my own experience and also the opinion of the vast majority of assembly houses and manufacturers. I’ve been doing repairs since 2008. The early crop of Pb-free failures were already surfacing. As time has passed, the Pb-free related issues I’m seeing mostly stem from that early crop of amps. Later (post 2010 to be cautious) Pb-free units don’t seem to have any more problems than their older SnPb relatives.
“Lead Free Causes cold solder joints!”
The risk of cold solder joints in Pb-free was higher in the early days of Pb-free tech. But changes in manufacturing process and process control have now fixed those issues.
At first, some manufacturers simply tried to ‘turn up’ SnPb machines to a hotter temperature to use with Pb-free. This didn’t work and bad joint issues appeared *cough* early JCM2000s *cough cough*. Just ‘turning up’ the machines didn’t work because you need to make changes to the heating up process – a few extra degrees of board preheating, changes to timings etc. Over time all those old machines have been replaced with machines with temperature control loops that can cope with lead free tech.
In another life I worked with several sub contract PCBA companies who made lead based and products alongside lead free. Every one of them has voiced the opinion is that the joints on modern Pb-free tech are on a par with those on modern SnPb tech and are BETTER than those of older SnPb tech. Almost 20 years into RoHS, this is to be expected. If you’re working with a manufacturer and they’re telling you to use lead free to improve reliability, then ask yourself what else they’ve missed from the last 20 years.
“Lead free solder in guitar amps causes Tin Whiskers”
This is a piece of largely irrelevant doom mongering. Tin whiskers are a real thing, but they’re not a significant risk in properly made guitar products in 2020.
The actual cause of tin whiskers is unknown, but they have always existed in tin based electronics – they happen in lead based products too. Anything with tin with impurities can have tin whiskers. Once again tin whiskers problem got much worse when Pb-free tech was in its EARLY stages. Those issues have once again been overcome by changes in process control. It transpires that if you change the rate at which lead free solder cools (annealing) then the risk of tin whiskers is substantially reduced. Tin whiskers still happen and are still slightly more common in Pb-free, but the serious cases relate to early Pb-free tech.
Tin whiskers are very very very small. They’re referred to as spanning ‘long’ distances in technical documentation and science journalism, but that’s because to someone who spends their technical life looking at PCBs under a microscope 0.5mm is ‘very long’. The very extreme cases are a couple of mm or so. ‘Normal’ lengths are micrometers long and they primarily affect fine pitch SMD. But the “lead-free sucks” adherents usually consider SMT to be against their religion anyway. 😀
For manufacturers still worried about tin whiskers, then the solution regardless of whether you use SnPb or Pb-free is to conformal coat the board. Conformal coating is like a sort of PCB varnish. It isn’t a nice process and should only be attempted with appropriate PPE, but as well as being a good way of reducing tin whisker growth it has the more useful advantage of water-proofing the PCB. An audio product is significantly more likely to die from beer than tin whiskers so this is of real benefit to our products.
“What is a good Pb-free solder?”
The important things are to get a Pb-free that is SnAgCu (Tin, silver, copper) rather than just SnCu (cheap option). The addition of silver helps it to flow. Also lead free requires a higher flux content (2% or greater, by weight) to wet properly. Because they’re higher flux content is makes sense to use a solder with a no-clean flux.
Other than that, just look for a known brand sold by an reputable electronics company so that you know that what it says on the label is actually true. So Kester, or Loctite, Multicomp from Farnell, RS Pro from RS etc will be fine provided they’ve got the above specs. Amazon or eBay or Aldi or Lidl ( 😀 😀 ) may not be!
I use SAC305. This contains 96.5% tin, 3% silver, and 0.5% copper. My Pb-free solder has 2.2% no clean flux.
Nope. May as well be honest about that. If soldering is your idea of fun then Pb-free does indeed “suck”. But it is electrically fine. Using SnAgCu helps, as does higher flux content.
“The Military/Aerospace won’t use lead free because it sucks, so why use lead free solder in guitar amps”
OK, ignoring for a minute the absurd idea that a guitar amp should be designed to the same spec a rocket.
At the end of their product lifecycle, Military, Medical and Aerospace electronics have their decommissioning dealt with by experts in their fields. This is why they are exempted from legislation. Those experts know what’s in the products they’re decommissioning so it essentially doesn’t matter what they’ve got in them (within reason!). When processing consumer waste at your local recycling centre the processor doesn’t have that info so they need to be able to make assumptions about what chemicals are in a guitar amp. So if a guitar amp is CE marked then it’s assumed not to have lead in it. If it’s not CE marked, then it’s assumed to have lead in it.
This is why if you go down to your local dump then you won’t find the SpaceX prototypes lying around. I know you’ve been looking.
“It kills soldering iron tips”
True. Tips will degrade faster because the higher tin content reacts with the iron plating on the tips.
There seems to be some confusion about mains voltage in the UK: whether the UK is on 230VAC mains or 240VAC. The answer is both, kinda. We’re on 230VAC on paper and 240VAC in practice. It’s not a hugely interesting topic, but it has some implications for modern guitar amps in the UK. Although this article is written in July 2020 (the UK is currently in a transition period, having left the EU), there’s been no suggestion that we’ll move back to the 1980s 240VAC standard.
What happened to mains voltage in the UK and the EU?
The UK has always had a nominal 240VAC power grid. Many European countries ran nominal 220VAC. It’s important to understand that these were only nominal voltages. The actual voltage coming out of the wall varied around the nominal voltages. The variance in most countries was around +/-6%. In 2003, mains voltages across the EU (which then included the UK) were standardised to 230VAC +/- 10%.
(Actually this is a slight over simplification. The harmonisation was staged through the 90s and 2000s and there are localised sublimits (-10%/+6%) for the voltage coming out of the wall, but the product harmonisation is for +/-10%).
At a similar time, Australia (the other economically ‘big’ 240V country) also standardised to 230VAC.
From the table below we can see that the new harmonised limits allowed every country to keep their wall voltages basically the same.
Lower limit Vrms
Upper limit Vrms
Old UK 240V (1988)
There’s no practical change to wall voltage. We’re still running 240VAC nominal through the grid, they’re still running 220VAC nominal. Everyone’s happy (except Nigel, of course).
There’s no change to mains voltage at the grid, so what’s the point? Why did they do it?
Because it makes it easier for manufacturers. Rather than having to make and hold stock of nominal 220V and 240V equipment, the manufacturer only needs to hold stock of nominal 230V equipment. It’s then the manufacturer’s responsibility to make sure that their product works reliably between 207-253 volts.
It also means that it’s not necessary to have a flimsy rotary switch (Silverface Fender) on the back of the amp that can easily be knocked into the wrong voltage as it’s being loaded in and out of the band van, or a dubious pull out voltage selector that allows access to hazardous voltages (JMI Vox), or an unreliable pull out voltage selector (plexi Marshall).
What does this mean for guitar amps and valve amps?
That depends on how savvy the manufacturer is. (I don’t want to generalise too much, but I’m afraid some of the North American manufacturers haven’t quite grasped the implications of this.)
The ‘wrong way’ to do it
As an example of what NOT to do, Fender now ship their ‘modern’ export valve amp products (OK, toob amp products) as 230VAC products. That’s fine. It’s better than those dodgy red switches on the back of Silverface amps.
In the UK, the amps see a 10% increase in mains voltages when the mains voltage is 253V. Taking the Blues Junior as example, this 10% increase increases the anode voltages and screen grid voltages on an already over biased EL84 until the valve burns out (often literally causes a fire). Not good.
Taking the Hot Rod Deluxe as another example, the 10% increase causes the cheap electrolytic filter caps they use to be close to their rated limits leading to many filter cap failures. The mains increase also increases heat dissipation in the dropper resistors that they use for powering the FX loop and the reverb circuits leading to PCB damage in most UK Hot Rod Deluxes. Not good.
In a bizarre twist Fender have included a legacy 240V tap to the transformers on these products but they always wire to 230V. Fender have said ‘thanks very much’ to the single stocking EU models but ‘no thanks’ to putting in the minor R&D effort to make their amps reliable across the EU/UK/Australia on the 230V tap. A good UK/Aussie tech will always rewire a 230V Fender to be 240V for use in the UK. But clearly this shouldn’t be necessary, these are existing design issues that are compounded by the mains variation and they could be fixed so that the amps can always work across the 207-253VAC rage.
Just in case it’s not clear, this is not a problem with the standardisation, it’s a problem with the design.
The ‘right way’ to do it.
The sensible thing to do would be make sure that all amps will still be running under conditions that make them reliable at all extremes.
You don’t want an amp that drops out at 207VAC on a heavy load day in Germany and you don’t want an amp that burns up with 253VAC on a light load day in the UK. Ideally, the amp will run it’s rated power at 230V nominal and then the UK customers will get a slightly more headroom on their amp, whilst the EU customers will get something a tiny bit more crunchy. The manufacturer must run reliability tests on their units at 207VAC and at 253VAC.
If you want to know the difference in ‘tone’ that this will result in, then I’ve made a handy video below!
Valve amp filaments don’t like to be overpowered OR underpowered. By coincidence they’ll tolerate a +/-10% deviation from their 6.3V nominal. So if a manufacturer gets the 6.3V bang on at 230VAC, then the filaments will be happy anywhere in the EU.
To fix that Hot Rod Deluxe we’d increase the dissipation of the dropper resistors to allow for the amount of heat they’d have to dissipate at 253VAC and raise them away from the PCB and we’d use better filter caps or a series cap arrangement such as the one they use in the Hot Rod Deville. To fix the Blues Junior they should reduce the anode and screen grid voltages so they’re not going to burn out the valves and adjust the output transformer accordingly. If they have to reduce the rated output from 15W to 14W, who cares?
Is there an impact upon tone?
The million pound question… Yeah there’s a subtle impact. Here’s video with a Laney Lionheart running the 230V rated amp from 207VAC to 253VAC.
That is a 5W cathode biased Class A amp. Other amps will respond differently. It depending on the bias method, the screen grid resistors and tens of other things. Honestly, it’s one of the less significant things you can do. You’ll get more difference from changing string gauge, or moving your guitar volume a fraction, or a subtle boost pedal.
I’ve got a Fender amp in the UK, how can I change it to 240V?
I’m afraid this is one of those questions where if you have to ask, it’s not safe for you to try. These are lethal voltages and I’m not going to give any advice about doing this, either on this page or by email. My advice is to take it to a qualified amp repairer.
If you have a Fender amp in the UK, bring it to me (or another competent engineer) to get the transformer tap changed to 240V so it works better with mains voltage in the UK. Depending on the model, if the amp is brand new then this might be all that’s necessary for now, but if it’s a few years old then other work may be necessary to rectify issues with the amp.
At this time I’m still open and accepting repairs. Thank you to all customers who’ve continued to use my services in this difficult time. I encourage customers to use courier services to send me equipment wherever feasible. I’m happy to advise or help with this.
I decided continue non contact drop offs for a month and a half beyond the government’s July 19th opening up date. However now I’m back to ‘normalish’.
Please note the following changes to services:
I’m now open for collections and drop offs, with customers free to enter the workshop.
If you’d like a non contact drop off or collection that’s totally fine, just let me know and you can drop the amp outside and return to a safe distance.
I am fully vaccinated.
I’d encourage you to wear a face covering.
However, please note that I will NOT be wearing a mask or face covering. I feel I ought to say that this is not because I’m a ‘denier’ or ‘anti mask’. The risk of injury or death as a result of wearing steamed up glasses in my line of work far far outweighs the Covid risk to myself or customers.
Same day and next day services are back up and running.
As with any social interaction in these trying times, there is a risk of contagion. Enter at your own risk.
Stay safe, everyone.
Collections and drop offs are strictly on a non contact basis, please message for details.
All repair items are cleaned twice with Iso Propyl Alcohol, once when they arrive and once before they are returned to the customer.
All repairs are quarantined for 24 hours after arrival, so same day and next day services are cancelled.
Payment by Bank Transfer only.
I now request advance payment for parts costing £20 or greater, including valves. With so many jobs uncollected this is the only way I can operate.
As I’m sure you know, Covid-19 and the associated closure of venues, clubs and pubs is disastrous for our Music Industry. If there’s any way in which I can help, even if it’s just sharing your lockdown livestreams then please let me know.
I don’t get many ENGL amp repair, so I was a bit annoyed with myself for not photographing this one. I’m grateful to the owner for helping me out by sending me a photo.
Here were the symptoms, in the words of the customer:
Overly noisy (hissing / popping) on both clean and overdrive channels at all times (with guitar plugged in or not)
A couple of noisy (scratchy) pots e.g. Clean and Lead Volumes
Loss of top end frequencies
Clean channel intermittent partial volume reduction coupled with distortion.
The first three symptoms were caused by the 12AX7 (ECC83) valves in positions 1 and 2, which were leaking DC onto the valve grid. This was also causing the scratchy pots.
The fourth symptom didn’t show up obviously during bench tests until I checked the output power. The amp delivered just under 50W into 16 ohms via the 16 ohm transformer tap, but only about 10W into 8 ohms using the 8 ohm tap.
I ordered a new output transformer from ENGL. I fitted it the day that it arrived and this fixed the problem completely. The amp was then soak tested for 90 minutes at gigging power levels.
After some discussion with the customer upon collection, it transpired that he was running two eight ohm cabs in parallel into the 8 ohm speaker tap. This would cause a higher current in the transformer secondary, which may have caused the failure. The correct way to run two eight ohm cabs with this amp is to connect them into the series sockets on the 16 ohm tap.
If you’re in need of an ENGL amp repair, please contact me
This LabGruppen repair was actually for me! As is often the case with people in this trade, I never quite get round to repairing my own gear because I’m so busy with customer’s work. This LAB1200C power amp died with a spark and blown fuse at a New Year’s Eve gig with Newark soul and motown band, the Acetones. Fortunately, a friend bailed me out during that gig and was good enough to lend me an (almost) identical amp to aid with diagnosis.
The amp is a four channel class AB amp, but runs from a switch mode power supply to reduce weight. Cunningly, the Switch mode power supplies can be configured by an ‘MLS’ button to provide ~64V rails for 4 ohm operation, or ~82V rails for 8 ohm operation.
This looked at first like a simple fault – In a SMPS the mains voltage is rectified into DC before the isolation transformer and there were dry joints on the primary side capacitors. This accounts for the symptoms. However after repairing this, the unit powered up but the fans were running at maximum speed. At this point the job was shelved for a significant period of time as customer’s work became a priority.
The construction of the amp is quite complicated, but upon returning to the job, the fix was actually quite simple. A transistor in the heat controlled fan circuit had failed, fooling the circuit into thinking the amp was overheating. After replacing this the amp was fine and passed soak test
All amps are soak tested after completion to ensure sustained high volume performance.