A useful Laney LC 30 mk2 blog.

I promise this will be useful. Not to Mesa, Fender, Marshall, Valco, Hiwatt, Matchless, users/ owners of course. Nor will it be much good for those needing information on house training a rhinoceros. But there will be a smattering (you didn’t know I knew that one eh?) of almost interesting information.

This (the Laney LC 30 mk2) is a noisy amp to my mind. One reason for this is that the centre tap of the heater supplies is grounded (via a 2amp fuse) to chassis. Another reason is that the pcb is grounded via the pot screws to the front panel metal work.

One thing you really don’t want in an amp is ac currents through the chassis. It introduces noise at every stage. So the best way to ground the heater CT is at a star point at the incoming earth. (At the IEC mans input in other words.) Make only one connection to each section of the chassis and lead these wires back to the same ground star point. The ground to the pots is best hard wired, again to the star point.

Sorting that out will produce a significant improvement. You can’t do much with the heater wiring. AC heater wiring is traditionally twisted together; for good reason. The twisting produces a cancelling effect of the heater current-generated hum. In this amp the wiring is not twisted anywhere in it. This amp, it seems, had an optional pcb, that converts the heater supplies to dc. In that case (if it is done well) the heaters don’t generate hum. But if it’s not a good supply design it will generate 100Hz buzz. Oh well.

The third problem that you may be able to rectify, is the fact that the design omits two control grid leak resistors on the first and third preamp valves. If you connect a 220K resistor from the centre grounded pillar of the first valve to pin 7, and repeat the procedure on the third valve, the noise levels will be attenuated by a lot of db.

I thought this was a sort of responsible blog. But I don’t get a macaroon because I didn’t get a laugh out of it. And there are few things more significant than that.

Supro Thunderbolt Reissue (well, the box is pretty close anyway.)

When is a ‘reissue’ patently not a reissue?

Taking an extreme view, anything in a Vox AC30 box, would be unlikely to be called a ‘Fender Twin reissue’. I would be, I would guess, in serious trouble if I was selling a goldfish on ebay that was actually a rhinoceros. You can’t do that sort of thing because it must contravene a trades description thing. Mustn’t it? You surely see my point, even if it does emanate from a cynical old git. That’s me, in case you were in any doubt.

And so, on to the Supro Thunderbolt ‘Reissue’. Apart from the fact that in the original had the power amp in a completely different place (bottom of the case), a quite different preamp arrangement, totally different biasing circuit…..well, the reissue is just the same.

But this was a repair job, so I should be at least a bit more useful than that. It (the reissue) has three power settings on a four pole three way rotary switch. This switch, in the one I had in, had fallen to bits. It effects the power levels in two different ways, and there are two different biasing arrangements associated with this switch. The first position, 60 watt setting switches in a 270ohm 15 watt resistor into the cathode circuit of the 6L6 output valves, so this is cathode (or automatic) bias, and much like the original circuit. In the other two positions (5watt and 1watt if I remember right) the cathode resistor is switched out and the control grids of the 6L6′s have a negative bias voltage applied, which are the other two functions of the power switch.

I think if I owned this amp, I would be wary of switching the power settings without first switching off standby. Just a thought. And now another thought. Tea and a macaroon. Nice thought.

 

A Very Quiet Fender Twin Reverb

I hadn’t seen John for some years, but he turned up out of the blue with the Fender described above.

Even if I looked at the amp from a distance of a lot of miles I would have known it was a ‘Reissue’. I’ve just looked up ‘Reissue’ in ‘Ballooning for Aquatics’ and it said ”Consult ’Skiing for Quadrupeds’.” Which said ‘Consult “Brain Surgery with Lump Hammers”.’ So I finished up guessing. It must mean, I thought, something old brought out again, much later. Wrong.

What it really means is ‘Nick a label off a really nice amp and make a new one that’s nothing like it.’

The overriding problem with current reissues of ‘classic’ amps, is that it’s impossible to do unless you have a raft of prospective customers with bottomless back accounts. I’ve got one of those, but only because it has a big hole in the bottom. A reissue amp has to use pcb’s. If it used solder wells, tagstrips, turret board; as the original Vox, Hiwatt, Marshalls(old ones), Fender (old ones), Selmer, Supro, Carlsbro (old ones) etc….etc…. it would be monumentally expensive (there are still a few of this breed around) because people would have to do much of the building, as opposed to computers.

This gets me (eventually) to John’s Fender Twin reissue. The almost insuperable problem of valves and pcb’s not being mutually on speaking terms rears its head. In this case the output valve bases (4x 6L6) are soldered directly through the pcb, and…… as the valves hang from the bases the heat rises and…..they get hot!!!! And if we heat up a solder joint a lot of times (it doesn’t even need to be all that hot; the melting point of tin is 232degrees c and lead is 327 c so anything over 232c burns off the tin and leaves the lead.) So it drives off the tin content of the joint and you finish up with lead. And usually cracked lead. The alloy of solder is usually 65%tin to 35% lead, and the resistivity of tin is 11,5 ohm.m whereas lead’s resistivity is 21,3 ohm.m. This means that the solder joint has twice the resistance when the tin has gone.

Another property of lead is that its flexibility is poor, and the expansion and contraction of the metal with heating produces cracks and poor contact with the joint. At its most extreme the joint can become an insulator, and your nice guitar sound has become nothing at all at the other side of this joint (which is known as a ‘dry joint’ or a ‘cracked joint’).

It’s about here when I wish I had a bit more interest in photos and things, because it would be useful. However….the fault with John’s amp was minimal, but as with a lot of pcb-based amps, not that cheap. To correctly replace a component in a pcb, you have to be able to get to the to the UNDERSIDE of the board. Pheeew! That can mean taking off wiring, marking where it came from, taking the pcb out, all to get to the track side of the pcb. If you don’t do that (it’s possible to cheat by cutting off the component and soldering to the resultant wire sticking out) you run the risk of dry joints, shorts to chassis and missing any burned tracks that might be under there. In the original version, the solder wells are visible, and the pcb dismantling zero, because there aren’t any. So the job takes five minutes, and the rest of the time can be usefully spent cleaning up and servicing.

Also, on this amp there are two wirewound dropper resistors (270 ohm if memory serves) that run hot. That’s ok, they drop the voltage from around +- 50 volts down to +- 17 volts to supply the chips and relays that the amp uses for channel switching. These two resistors are flat to the board (not ok), and so heat up the tracks underneath, and are also close to two 1000uF 35 volt capacitors which don’t like the heat. For an amp of this age (1994-ish and on) these components are ready for replacement and you need to have a good look and resolder all the joints under there.

Just as an aside, it’s interesting to note that any mortgage you might have taken out to buy a Mega-Hugely-Marvellous-Platinum Plated- Radar Controlled…..erm….guitar lead….would be a totally daft investment if you had a dry joint on the input socket.

To put this problem right would cost you 0.00000001% of your investment with Wonderful Guitar Leads Inc.

Which is but a small increase on my macaroon outlay for the decade. Tea.

 

Messages from the Virtual Idiot Dept

My partner has a phone. It looks like a spaceship. I have a phone that looks like a loofah. The difference between these ostensibly similar devices is that my phone does not work well in the bath either as a backscrubber or an underwater communication device; whereas I can’t make my partner’s do anything at all even standing next to EE’s gargantuan mast.

That’s because I’ve never worked out how to switch it on. By the same token I’ve never figured out how to switch it off either. She says it will make movies, take pictures, recite Shakespeare, jump up and down to the rhythm of the latest 007 Theme, act as a life raft in extreme circumstances. But I can’t ring anybody on it. Meanwhile, back at my loofah-phone, I can’t ring anybody on that either. I am told by nauseating folks at Vodaphone that it’s because I don’t put money in it. I bought it for ten quid twenty years ago; what more do they want?

I drool after those phones in the black and white ‘B’ films that people whir around with a middle finger, talk into a black stick-looking trumpet thing, and say something like “Give me Whitehall 1212, please operator”. Now, I have to key in a 54 digit, digitally secured code (that turns out not to be secure because some flea bitten company like Norton or Avast or somebody, wants to charge me a mortgage to ensure that I am secure) and after doing that I find I’ve straightened out the National Debt while waiting a day and a half in a queue for somebody from the phone company to come back off holiday to tell me how much I owe them.

So I now employ a completely revolutionary device called a ‘Hermit-o-phone’. By using this I don’t have to ring anybody at all. The first Hermit-o-phone I had I came across accidentally. I picked a banana up in Tesco and, lo and behold….it didn’t  ring! This is the phone for me, thinks I. There was also, I soon found, a bonus. I couldn’t ring anybody else, either. Another big advantage is that nobody has sent me a bill. For anything. I’ve tried this with various ‘apps’. A stick, a dog biscuit, a JCB tyre; they don’t ring you on them either.

So I’m stretched out on my blow-up mattress watching the rain outside my shed, banana on the one hand, tea and macaroon on the other.

I might have a peaceful conversation by macaroon, shortly. You’re never alone with a macaroon……..

In Praise of People we Pay Good Money to Break Things For Us

The latest in a long line of parcels that arrived as a shovelful of bits in a box that was once square-ish and had metamorphosed into some distant cousin of the arthropod species,  convinced me that sending anything to climates more distant than next door is seriously questionable. And if you got through that sentence without retching, you are made of stern stuff, and I doff my hat.

I would have to say, in the interests of fair appraisal, that my curiosity in any place more distant than arm’s length, on the Richter Scale of zero to ten, is about minus five hundred and seventy three. And you can multiply that by a lot if it’s raining.

Even taking this into consideration, I have toyed with the idea of stowing away in one of my parcels booked in for shipping (pick your own company; in my experience their records of losing/ breaking/ delivering to people I’ve never heard of, are remarkably similar), with my trusty machete and Heckler and Koch automatic. Unfortunately, I would have to be built of sheet stainless steel to survive the journey. So I shelved that plan.

So what is the most effective packing for a piece of valve equipment? Bearing in mind that there are few materials (in this Universe at any rate) that will stand being run over by a fork truck, this gets to be a problem that Einstein might balk at. So I phoned him.

“Is your name Einstein?” I asked.

“Yes” said Einstein.

“Would that be Albert Einstein?” I asked.

“It’s actually Einstein Trimblestrop; actually” said Einstein.

“I’m sure you’ll do” I said hopefully. “How would you pack a parcel to be delivered by courier to Spain? Or anywhere, really.” I asked.

“I wouldn’t send it at all” said Einstein. He thought a bit. “I did send a Victorian cast iron commode to Venezuela once. They said it looked like a toilet when it got there. I suppose that was near enough.”

“How did you pack it, Mr. Einstein?”

“I dropped it on the courier’s foot and he packed it in his plaster of Paris splint.”

So that’s solved that one. I’m now looking for my brand new packet of Macaroons shipped from Venezuela.  Easily mistaken for a box of nails when shaken.

Reconstituting smashed Venezuelan macaroons is an extended project, I can tell you. Almost as bad as repairing a new Studiomaster Powerhouse.

Now, where’s my brand new packet of tea from Venezuela………?

 

Universal Audio S-610 preamp

This is brief set of impressions regarding a nice American made valve preamp. This one blew fuses, so not quite as nice as it should have been.

On the back of the unit there is a lot of blurb about which fuse to use for which mains voltage. What it is less than clear about is that you don’t just swap the fuse and everything is ok for the different voltage. What it says is that a 250mA fuse is for 110 volt operation and a 120mA fuse is for 240 volt operation. What is not obvious is that there has to be changes made inside the unit to effect the voltage change. You might notice that if you trawl through the user manual, but not necessarily.

There two four pin connectors mounted on the internal pcb near to the IEC input, and the free plug that fits these (looking from the back of the unit) needs to be on the left hand one for 240 volt operation or the right hand one for 110 volt operation.

Unfortunately, if you’ve bought one of these units, and it was internally set for 110volt operation, and have plugged into 240 volt mains, it will have blown the fuse in the IEC socket. You might be lucky and after changing the voltage setting to 240 it might be fine. But the electrolytics in there will have been subjected to a high over-voltage and it would be sensible to check these.

 

 

Extra terrestrial messages from an endangered species

Well, alright, it’s me really. But I am.

“What is that daft old git talking about?” You would be well within your rights to make that comment, even if it is fairly disrespectful. “So, explain yourself!” you ejaculate (?).

Alright, I will. On your own head be it. Whatever ‘It’ is.

There are few weeks go by that I don’t look inside an amp and wish for x-ray vision. Or at least an electron microscope. You can at this point visualise me (not a pretty sight) squinting at a piece of circuit board with 574 components on it. That will easily fit in my tea cup. It’s about at this point that I go to the many sites on the Wonderful Web that stack up schematics. An hour after that I’ve pulled all my hair out and am just starting on my toenails. Shortly following that, the innocent-looking pcb is in the fire bucket and I’m stomping off kettle-wards.

I started my apprenticeship in 1963. It lasted five years but I had expired well before that. (“In your dreams, mate”). It was intended to be an electrical engineering apprenticeship at the outset, but fate stepped in and after two shakes of a dead lamb’s tail it became an industrial electronics apprenticeship. This was in spite of the fact that industrial electronics and electrical engineering are as mutually compatible as bulldogs and arses.

The reason for this metamorphosis was pig ignorance by those leading the way for the electrical department, coupled with my own brand of pig ignorance. Not forgetting that electronics gear was flooding through the doors like a blizzard and there was nobody in the factory knew any more about it than how to fit a plug on the end. So I finished up at Chesterfield Technical College for seven interminable years.

So how does that equate to anything relevant to the topic? In 1963 valves (which had been around for, say, forty years plus) were being gradually supplanted by semiconductors. At the time transistors were mostly germanium and blew if placed near a stiff breeze. Whereas, valves had evolved about as far as they were going to. (The duodecatron valve was about the most complex and the mercury-arc rectifier the most powerful. In a darkened room the mercury-arc looked like something Frankenstein might have relaxed in.)

The point being (There’s a point?) that the folks who had the misfortune to be involved in electronics at the time, and also throughout the following sixty years or so, found themselves on a technological ice flow whose shape and constitution was changing almost week to week. There was no way anybody could usefully design a course to accommodate electronics servicing, because for the next decades it was changing in ways that few people could guess the direction of.

And the motivation for these technological changes was largely the pursuit of excellence. Most pursuits currently in vogue are running after greater and greater….errm…profit margins. And compared to those decades just mentioned, the changes that happen these days are painfully slow and usually restricted to being able to put more pins on a chip you can scarcely see. The ideas don’t change much at all.

I have designed a spectacularly useful electronics service course though, for current electronic repairs. I’ve called it ‘How to Plug In a New PCB”. You can do an endorsement to this which I’ve called “How to throw it Away and Buy Another One.” To keep abreast of current new ideas, we have the course entitled ‘How to Paint it a Different Colour’.

It’s very obvious that the situation will never again exist that involves living and learning through the changes that had so many ideas developing at such an extraordinary rate. The digital age has solidified like grease in a chip pan and its developments (personal opinion) are shams of convenience. But we can always expect something faster; and paint it a different colour.

There must be a kettle round here somewhere. And….a macaroon?

 

 

 

 

 

Put the ‘Cuffs on, Mate, I did it….!

This is a layman’s guide to how to get away with murder. Or close to it, anyway.

Let’s (just for a minute) consider the terrible repercussions of my stealing a box of matches. Not a robbery, you understand; just a slight misappropriation of funds. Call it creative accountancy, if you like. I did not (yer honour) waft a firearm about with abandon; neither did I threaten bodily harm, nor even the slightest suggestion of a frown did pass my forehead. I just nicked the box of matches. Displaying a certain skill, I might modestly add.

Now let’s consider the Countess of Canterbury’s diamond necklace. Using similar levels of skill and identical nonviolent techniques, I nicked it. Yer Honour. Is this a more serious felony than my nicking (in exactly the same circumstances) Cyril Crabtree’s box of matches? If the long plonker of the Law comes down harder on the diamond necklace felony than on the box of matches felony, surely the Law is more concerned with the irrecoverable nature of the knocked off goods than the crime. Will I get six months in Dartmoor for the theft of a fiver and ten years for the theft of a hundred quid? If not, why not? Which gets us to my theory that most folks on the internet should be doing time, in a big way.

“Why” quoth the affronted internet population “should’st thou level that one at us, o varlet?”

It goes like this. The real reason that the diamond thief might have got strung up in days of yore, and got a mere ducking in the village pond for half-inching Cyril’s box of (damp) matches, is relative to the ease that the contraband would be replaceable.

The most irreplaceable possession any of us has? TIME. TIME. TIME. You just cannot get it back if somebody wastes it for you.

So the next time you read some brain-dead Tweet, twitter, twatter, facebook, bong, don’t just suffer it. Send ‘em a bill. Or better still, a summons of court.

If dealing with official bodies? Send ‘em a bill. Multiply it by a few thousand.

Better still, accumulate a load of their pamphlets, circulars, polls, customer reviews, opinion polls, and post them to a deserving cause. The council, say. It doesn’t matter which one, just steal their TIME. They can’t touch you for it; sadly.

I need that cup of tea. Preferably cold , to dowse the steam blasting out of my ears.

Ampeg (i.e. Loud Technologies) BA300 115

If you happened to be one of those few misguided folks who followed this blog, you may have noticed that….there hasn’t been any for quite a while. My excuse is that I have to get enough steam up to vent my spite on unsuspecting pieces of electronic equipment, and, more often than not, their manufacturers.

The Ampeg BA300, whether in the 1x 15″ or the 2x 10″ versions, seems, from the various forums I’ve read, to be leaving a trail of very disgruntled musicians in its wake.  Many of them having had these amps switch themselves off, mid-phrase. The amp then switches itself back on again after a leisurely 10 seconds or thereabouts, and then, if the volume settings remain the same, does it all again. Although the amp itself seems not to suffer any embarrassment, the same cannot be said of the bass player.

I’d like to be able to say I’d successfully repaired one of these, but the honest statement is that I’ve done no such thing. But I have spent many hours inside one, and can let you in on a few conclusions.

The first mystery is why any builder of amps can think that it’s a great idea for the amp to switch itself off if too much power is demanded of it. The traditional answer to that problem is that the amp goes into clipping distortion, the player hears that, (not pleasant) and turns it down. If the music demands a heavy distortion, the amp just doesn’t go any louder if turned beyond it’s rated power output.

This amp is a ‘clever’ amp. This means that it’s complicated, not necessarily for any good reason except for, maybe, profit boosting purposes. It is a ‘class D’ amp. The ‘D’ stands for ‘dismal’ in my book. But it actually means that it uses a modulated carrier signal (of about 450 kHz if memory serves). There are different versions of the modulated carrier technique; this one uses ‘pulse width modulation’.

They also use a switchmode power supply. It’s a lighter alternative to a traditional isolating transformer, but it has its own problems.

The power amp section is unusual, and not a bad idea. It uses a bridgemode technique, which means that the speaker is driven from both sides, instead of the usual hot drive to positive and ground to negative. The power rail voltages can be much lower than in the traditional configuration, and this results in better efficiency in  the power amp section.

There were two faults showed up on this amp. The first was easy and fairly obvious. It didn’t work. With certain faults in mosfet devices, (these are !RF640 used in a push-pull configuration) an output signal can be produced which disappears when there is no load (speaker) connected. This amp has four !RF640 mosfets. Each pair produces a push-pull output, and the two pairs are out of phase; and applied to the speaker at either side. This was the bridgemode arrangement described earlier.

These devices were replaced and…It worked!

Un…fortunately I found out that a transient (a ‘pop’ or a slap on bass) switched it off. It returned after a delay and would do the same thing again. Etc…etc…

The ‘protection’ (if that’s what it is; one could argue that it’s musical assassination) switches off the carrier signal mentioned earlier.

Clever? Yes, but not very sensible.

Time for tea.

The Unfortunate Case of the Roving Vox AC30TB

There is a short but entertaining story to this, which deals with a range of matters from lack of respect for quality to wanting to kill people from a distance to destroying irreplaceable artefacts to dealing with insurance companies to fixing the unfixable to boldly going where……you get the idea.

This little story, although sort of entertaining, was definitely not so for Marc; who shall otherwise remain anonymous. He sold his lovely old (mid sixties) Vox AC30TB to a bloke in Spain who desperately wanted to buy it. My own involvement up to that time was that I had rebuilt the output stage for him a couple of years earlier. Although you could have bought one of these new in 1965-ish for a hundred and twenty quid or so, you certainly can’t now. So, the deal was done and the lovely Vox sailed away to Spain having been packed and cased by Marc, who is the soul of conscientiousness. So it would have been very securely shipped.

After a week or so, the Spanish bloke decided that he wasn’t actually as keen on buying as he had been, and took this up with Paypal. He had a full refund, and sent the amp back. All this, although a sad indictment on honourable dealings seems (to the modern mind, at least) alright. But it didn’t stop there. The lovely Vox AC30TB came back in the in same box without any packing. I did mention ‘lack of respect for quality’ did I? It was, unsurprisingly, very much the worse for its journey, with the front baffle and casework badly damaged. It also appeared to have had less than expert hands inside it, than it deserved. It’s about here where I get involved again. Marc needed an estimate for repair for Paypal as he was making a claim for damage in transit.

The big problem with an estimate in this situation (i.e. major accidental damage) is that you need to do all the repairs to find out what it will cost. There is so much in an amp that might look (and test) alright, that actually isn’t. Not reliably so, anyway. The valves would all need to go, for a start, whether or not they tested ok.

The result of this was that the amp was a write-off, mainly because the speakers  (original Vox Blues) were damaged, and therefore it would not have been possible to bring the amp up to original spec.

What a shame. These amps should be treated with kid gloves, not hobnail boots.