Mesa Boogie DC5… with distortion fit to drill teeth

Without doubt, Mesa Boogie are a class act. But you will be very daft to try to repair one. I’ve had a better time pulling out my own toe nails.

 

 

 

Here’s the inside of one of these legendary DC5 machines.

You really have to take a lot of things to bits to get anywhere near a repair. Anyway, not to carp on. (For once.) This one had a more distorted view of the world than Hitler. There was nothing you could do to get a clean sound. Except maybe drop it out of a plane. As I don’t know anybody with a plane, I had to fix it.

This is me looking intelligent. The thing that I am asleep on, is a schematic of the preamps of the two channels

Each round looking thing (not me) is one half of an ECC83 (12AX7 across the water). Looking from left to right the three gain stages of this clean channel lead one to another (it’s called ‘cascade’) finally leading to the switch on the far right. The lower channel does the same thing except through four gain stages. The tone filters are a different arrangement but they’re essentially doing the same thing. That also leads to the switch, and this is the channel switch footswitch socket.

This is the next schematic in the series, and the output from the switch of the previous sheet arrives at the arrow at the far left of this drawing. There are then four more round things. These are different, they’re transistors. What happened here, was that although everything looked fine and dandy up to the input of this stage (which drives the fx send signal) at the send output it looked like something Salvador Dali might have cooked up. This is obviously referring to oscilloscope displays.

All the transistors in this section need replacing. This is where they are in the amp.

The four little black things in the centre of the picture are the culprits. MPSA 70 (two of) MPSA63, MPSA20. Cost about ten quid all told.

This is a fault that you could spend a lot of money on (revalve etc.) after which you find its exactly the same. Depressing.

Anyway, it’s tea time. Might have to consider a macaroon.

 

 

 

 

Korg SDD3000 (The old one).

I like rack mounted effects units. I know the hot fashion for little boxes that sit on the floor and you stamp on them. But they really don’t do your stage persona much good when you’re grubbing around to find a three millimetre diameter knob amongst a wash of Carling Black Label and fag ends. Still, each to his own, live and let live, and all that.

    

This is the inside of the rack mount Korg SDD3000. Unfortunately I was too late to do a ‘before and after’ thing on it. I’d done the job before I caught up with the brain cell that deals with ‘before and after’.

This is the battery that was in there before the thing I replaced it with. Sorry ‘with which it was replaced’. I could do it in Italian, but I don’t know any. This original one was a NiCad, rated at 250 mAh @ 3.6 volts. The mAh (miliampere-hour) rating tells you that it will put out 250mA for an hour. Or 500mA for half an hour. You get the idea; it’s the capacity of the battery to store charge. It’s not that important electrically, especially in this context, where the current draw is minimal. In other words they last a long time. This particular battery had drained to about 2.6 volts. With an old unit like this, checking the backup battery is first job.

But the voltage is important. And in this case, if the battery voltage drops too far, not only do you lose your custom settings, it also doesn’t work. At all. Dave’s unit came in to be checked over and serviced. Servicing is generally straight forward. Separate all internal connectors and spray them out with something like Servisol 10 (NOT WD40). Same with pots and switching and jacks.

Here’s also a timely warning. There are various static sensitive (Cmos) devices in here. They don’t like fingers much. Strictly speaking, these blogs are not a sort of instant-do-it-yourself-manual. Sometimes they might save you a few quid, but often they are just interested in informing.

The only battery I could find that was 3.6 volts and would fit in (with a shoe horn) was an AA size lithium battery. It did fit in with the correct clip, the only other mod being moving the 100 ohm current limit resistor. The custom presets had to disappear because the original battery voltage was too low to hang in a temporary d.c. supply, but Dave was ok with that.

There was another problem waiting to happen on this one.There are two separate bridge rectifier networks in this. The four diodes in the pic have replaced the originals. There was nothing wrong with the originals, but they had obviously been running hot for a long time, and joints underneath them had dried/cracked and the pcb was discoloured. I replaced these because with the longer leads they can be spaced off the surface of the pcb and dissipate heat, so that future dry joints won’t happen.

Time for tea. And maybe a macaroon, to celebrate something.

 

 

 

 

Let’s Hear it for Mesa Boogie and Traynor!!!!!

Yes, it’s true! You haven’t inadvertently flipped over to an American Evangelical site selling you a place on the Bus to Heaven!

I sat down in front of this hated machine this morning, ready to do battle with the Lords of Rock Surveillance and their Secret Minions. (You know, Roland and Soundcraft and Laney and just about everything Chinese and….well you’ve got the picture long before this.) Yes, the shock was nearly as dramatic as finding out that Marc’s strange AEI amp had 415 volts on the ground of a line in. I measured it out of curiosity after it had killed me. A tricky proposition but clearly not impossible. I had paid my subs to the Heavenly Bus Co. however.

To return to the topic. That’s a fresh approach, at least. I typed into my WEB BROWSER (I had to put that in capitals because I only just found out what one is) YCV20, and within half a minute I had a complete set of schematics for this Traynor amp. A SERVICE MANUAL, no less.

And then (shock horror!!!) I did the same with a Mesa Boogie DC5 and the same thing happened. I had clearly caught Heavenly Bus. Ecstatic!!!!!!!!!!!!

Please take note. I did say ‘half a minute’ and not ‘half a month’. If I’d been looking for a new Wharfdale or a new Carlsbro, I wouldn’t have been able to see the screen without having had two haircuts.

So the flag outside the workshop now says ‘Mesa Boogie and Traynor are Brilliant’.

I’m now off to catch the Heavenly Bus to a cup of tea.

Dedicated to Dave and Marc, the two readers of this blog

I heard, in person, face to face, unequivocally (didn’t think I knew that one, did you?) first hand, that there are two gentlemen who actually read this junk. I mean ‘these literary expositions’. So that they do not lose their respective jobs for their rank bad taste in reading these literary triumphs, they will be forthwith referred to in code as ‘Dave and Marc’. Ooops.

So here is blog of your very own, kind sirs. It’s actually a short story about Dick Big and Barney the Stoat, private dicks. When I get tired of writing this blog bollox, I turn my attentions to……writing some more bollox! What else?

 

                    The Dick Big Detective Agency. 

For best effect, recite through a mouthful of gravel, preferably in a down-market bar. If the venue is misjudged, the recitation may be improvised through a mouthful of loose teeth.

 

            Dick Big was suspicious. That was o.k. It was Dick’s job be suspicious. And to talk in short sentences.

Sometimes. Very short. Sentences. (Breathe here.)

            Barney was his sidekick; but he was starting to show the bruises. Dick would have to kick him with the plimsoll.

            It all started on a usual, short sentence. Day. But Dick knew that something big was up. Not enough roughage. Barney scratched a match along the hatch, and catched; sorry, ‘caught’; a cheroot with the side of his mouth. That was side that had a lot of blisters. He needed the practise.

            “O.k. Barney, this our big break. We get the lowdown on this trip and we’re fixed-up floosied for good.” Dick didn’t know what any of this meant, but it sounded helluva good. He was going to have to look up ‘helluva good’ in Roget’s Tyrannosaurus.

            The dry, dead, sylvan carpet sounded loud as a erm, stoat, in the still night mist of the forest, leaves of the twisted birch rustling their rhythmic salsa underfoot, and the owls owling their percussive pizza. Otherwise all was quiet. Except for the M63 in the background; delicately humming its low harmony; its irritating drone; its intolerable blood-curdling roar, driving the innocent to maim and kill and murder and COMMIT HORRIBLE CRIMES AGAINST HUMANITY………

Other than that it was quiet. Too quiet. It must have been because Dick Francis said so somewhere. So did everybody else for that matter.

            Dick Big had a clue. It was the first one. He was, generally, clueless. As they walked together towards the ancient chapel, the flicker of a bloodied candle stabbed the forest through a cracked finger-nail. They dived into the ditch at either side of the forest trail as the hooded figure in flowing shawl slunk from the ancient chapel of devil-worshipping hamsters, and writers who put far too many words in a sentence and should be dismally ashamed of themselves; casting hunted glances, the ceremonial axe at its back dripping ceremonial blood, that whipped up in a petulant wind like a erm, stoat. The sleek furry creature followed closely and silently; and moving swift and deadly leapt at the back of the fleeing figure in black, ripping at the cowl like a, erm, stoat. (“Have I done that one already?” “Yes. To death, actually”)   There was the sudden wail of a screaming banshee through the catacombs of death. Or Waitrose car park at 2.00 am. The difference is a subtle one. 

            “I’ve broke my fuckin’ ankle”. It was Barney. He had. It was bad. They were back to short sentences again. Dick was supportive;

            “With all those bruises I’m surprised you noticed a broken ankle.” Fortunately for Barney, Dick was no good at first aid. He sympathetically levelled things up by breaking his other ankle.

            “That should hold it, till we can get help.”  He looked up. Quickly. Very quickly. In fact. The stoat was expanding in a very unstoat-like fashion, standing over the prone figure of the skeleton monk and hacking indiscriminately with the bloodied ceremonial axe.

            This was Dick Big’s big chance. He threw his plimsoll in the air.

            “O.k. Barney. If the shoe hits the ground, you go take the monster out. If it doesn’t, I go. Fair’s fair.” The shoe floated around at head height. Barney turned around. Dick had gone. Back to short sentences.

            “You bastard.” Barney slipped in this short sentence of his own. But Barney was made of stern stuff. He had a well-stuffed stern. Drawing himself up to his full height, he dusted off the dead leaves and stared into the alien’s kneecap.

            “Growl!” it said using the first exclamation mark in the whole piece. The axe sang through the night and hacked Barney’s head off.

            “Barney!” shouted Dick, extravagantly wasting another exclamation mark. “It wasn’t ‘heads you lose’.

            “Growl” said the blood-sucking vampire alien from planet zgrvtrblblet.

            “Growl” said the M63.

            “There’s only room for one blood-sucking alien in this piece and I’m it, buster” said the blood-sucking alien from planet zgrvtrblblet (which we will, for convenience sake, call Brian), running onto the M63 in a rage and no safety first procedure and was squashed flat by a Virgin; er…Virgin Express, having taken a wrong turn at the Maidenhead junction. And now back to short sentences.

            Dick Big was benighted. Barney had a head transplant from a stoat.  Everybody lived happy ever after. Except Brian who was dead.

 

                                   Nearly The End.

 

Well, there we are. The literary firmament has hit a new low. But only because it hasn’t yet read the continuing saga of Dick Big and Barney the Stoat.

Tea time. And I hope Dave and Marc imbibe also. It might improve the after taste.

             

             

More Members of the Secret Police

Don’t get too excited about this. There won’t be too much information in it. But even if there were none at all it would be (usually) a 100% more than the average amp/instrument manufacturer wants you to know about.

This last insult to the musician’s intelligence was from Roland. Here’s a little test for you. Have a go at finding a schematic for a DB500 bass combo. They’ve probably been around for twenty years (a guess). It would be a simpler proposition to find a flowering begonia shrub on Pluto. After an hour or two of brain-numbing frustration, I came across a random piece of information. ‘Random’ is the key issue here.

The Secret Police of selected Amp Companies would never be party to helping you get your amp fixed. Unless you wanted to take it to Japan, or Korea (or Pluto?).

Here’s the sacred phrase. The DB500 is, apart from minimal output device modification, EXACTLY THE SAME AS THE DB700.

This one you can find schematics for, if you are sufficiently bloody-minded. Which I definitely am.

So I was able to sort out the DB500, which turned out to be a blown resistor/zener diode power supply fault. The bits were about 20 pence.

Instead of being led by the nose by Roland to buy their latest offering, for several hundred £, the gentleman paid me a few quid to get back his amp, which he didn’t want to change anyway.

The next time you happen to be looking round at a prospective new purchase, at the bottom of all the bullshit, insert a little phrase of your own: “but don’t expect to be able to get it fixed out of the year’s warranty”.

Tea time.

‘Attention Span is Now About’…. erm, where was I????

This is another of those rather daft blogs in which I get to SHOUT AT SOMETHING. Let’s face it, there’s plenty to pick from. So who is it that might be the unwitting butt of my ire? Will they care? Will they even notice?

In reply to the latter two questions the answers are:- ‘no’. And ‘no’. And the answer to the first one is ‘nobody in particular, but GOOGLE and HOTFROG will do as the whipping post’. Now I have your full attention (all eight seconds of it) we shall investigate the reasons for this jacking up of my blood pressure.

I received in a circular from Hotfrog (who must be a subsidiary of Google, because everything is), the salutary bit of information that ‘the attention span of the average human being’ (whoever that is) ‘has now shrunk to eight seconds.’ Or something distressingly like that. Effectively, this means that we are generally educated to be up to writing a cross at the bottom of an IOU that we can’t read. About the same as a goldfish, except that we still stay ahead of them by being able to write the cross at the bottom.

The degree of concern shown by these folks who were happy to disseminate this depressing fact was….. none at all. Their concern was entirely that business would have to lower it’s marketing sights in order to continue to sell stuff.

This concern I interpreted in this way. That if you’re selling breakfast cereal your advert says ‘BUY THIS’. If you might be selling mobile phones your advert says ‘BUY THIS’. Maybe you’re selling a car? ‘BUY THIS’. Words of three or four letters should be enough for anybody, so long as they’re in primary colours But not for somebody who wants to think for themselves.

This is no great direction for the evolution of the human race. Personally, I take solace in the fact that the entire ‘digital domain’ could disappear in an instant.

We would really need to be able to think then. It will take us a lot longer than eight seconds to learn to do that, though.

My little blog only exists to blast at bullshit. A little knowledge is great piece of armour.

Tea time.

 

 

 

 

 

 

 

 

 

Binson Echorec…more of the same

The story so far ……

We were left in Dracula’s castle with the blood sucking tortoise attacking (in slow motion, obviously). Meanwhile, back at the ranch, Butch Blair and The Sundance Cod were fighting it out at the Oh Dear! Corral and……….what am I talking about?

Here’s a nice picture of a Binson Echorec. To anybody of a musical disposition, this is as calming as a nice Constable (artist not policeman).

This bit of it is pretty much the same for all Binsons. Back on the subject of half-century old Echorecs that have been stored in the coal shed forever, this picture shows another reason not to switch it on. The reason given in part one of this, was danger of electrocution. Coupled with that, there is also the possibility that you could render the poor thing a pile of scrap. If the heads have been unwisely shifted about, they can shred the recording material from the disc, which means you get a lot of noise and not much echo.

If get our bearings from the pic, the heads are positioned around the disc edge, as shown. They should not rub (or touch) the disc; so this is the subject of this little diversion. If you upend the unit you will find the bearing cylinder sticking out under the top plate. There are two screws on it. One big one at the bottom (which you will hopefully not need to touch) and a slotted head screw in the side. If you unscrew this a few turns, the disc will be removable, and from the top you’ll see the tube that the disc bearing fits into. You need to clean off all the grease/oil/crap from the socket and also the disc shaft. Blast contact cleaner in the socket and onto the shaft. Then you need to replace the oil you’ve taken off, using the stuff supplied in the little bottle in the clip. If that’s not there, a light oil like say 3-in-one, will be ok.

Replace the disc, and gently move it up and down while tightening the screw you slackened off earlier. There’s nothing more to do with the disc, but the interwheel/idler drive might need attention. That’s the rubber drive wheel marked in the pic. The problem with this is that it rests on the capstan and over a long time creates a notch in the rubber surface. If that has happened it will sound like Pavarotti sliding over a cattle grid. Whatever turns you on, I suppose. The best remedy is to throw the wheel away and fit another. Dead easy, just one screw holds it. But, if you can find one, it will cost all your limbs and a few of somebody else’s. Probably. Here’s a couple of alternative possibilities.

If you know a feller handy on a lathe, you get him to take off a few thou (thousandth’s of an inch) from the edge of the wheel until the dint in the edge has gone. The best way to do this is to freeze the wheel. Then it doesn’t distort during the turning process.

The other alternative does work, but it takes a fair bit of patience, and you can’t do it until the heads have been set up. You run the disc and place a flat needle file gently on the edge of the rubber wheel and keep it going until you can’t feel the ‘bump’ as the indentation passes under the file.

To set the heads it’s best done with a scope, but can be tolerably ok without. All the following is done with the disc stationary. You need a small spanner, about 8mm if I remember right. There is a hexagonal mounting pillar for each head; you look down at the gap between the disc face and the head face. A torch underneath helps. If they touch, you need to back the mounting pillar off with the spanner, clockwise, just a tweak. Then you need a piece of thin paper. You slide this between the head and the disc face and then tweak the pillar back again until it just (only just) traps the paper. Remove the paper and you should see a slight gap between the head and the disc.

You go through all the heads like that. After doing all that (and having replaced the wiring as in part one) you can switch it on.

Then you’ve gone far enough to find out whether it works or not.

Tea time.

Binson Echorec…..well, nearly.

Around the late ’70′s-early ’80′s the Binson company built units for Guild and Sound City; both very big names of the time. Don’t quote me on the dates. According my history books Oliver Cromwell lived next door to  Nova Scotia.

There was a very considerable difference between the gear with ‘Echorec’ marked on it and those we’ve just mentioned. The Guild and Sound City versions were transistor machines and Binson’s usual designs were all valve. The ‘Echomaster’ was Sound City’s incarnation,and that’s what this is.

You have to admit, it looks very cool; they all do. I think they could have knocked one up out of washing up liquid bottles, and they would still have looked cool.

Although this model is so different from the usual Echorec models, in some ways they are exactly the same. With many of the same problems. The idea behind any mechanical analogue echo, is that the signal (sound) is recorded via a record head, onto a moving medium; might be a tape loop or a cassette loop of some sort. This sound on the tape then passes across playback heads and this means that the sound will be played back later and at different times from the original sound. There are a variety of ways these repeat echos are processed afterwards, but that is basically the arrangement.

The Binson is different. The recording medium is a steel disc which revolves past the heads, and has a recording surface on the edge. Not many designs use this. Schaller did one, and that’s the only other that I know of. The idea is still the same as the tape, though.

So that’s a very approximate overview. Should you be so fortunate as to acquire one of these brilliant pieces of coolness (coolity?) from your neighbour who has kept it under a sack of spuds for a half century you should be very cautious about switching it on. Best done with a long stick from behind a wall of sandbags.

The coloured cables are the reasons why. They are the originals and the insulation often rots away, so you get bare copper exposed. I don’t know what the insulation was made from, but it could be a rubber-based material and that would perish, so it makes sense. The high voltage stuff is also made of the same materials. The pic shows the job part-way through. The black screened cables have replaced some of the original wiring, but it was all replaced in due course.

You have to do (or at least visually check) this wiring BEFORE YOU SWITCH IT ON. Or make sure you get your solicitor to check that your fire insurance is up to date. That means the signal cables and the mains/ HT wiring. It’s a time-consuming job before you’ve even thought about whether it works or not.

I’m going to continue with the procedure for setting up the heads and disk on the next blog. Otherwise these things start to look like an unexpurgated big letter version of ‘War and Peace’ and nobody will read it. So what’s new?

Time for tea.

Read a Schematic? A piece of poop.

Let’s face it. It can’t be very hard to do; or I wouldn’t be able to do it. No. Reading one is EASY. You need to be able to remember what a line looks like. And what two parallel lines look like. And what a wiggly line (or a rectangle) looks like. And a triangle looks like.

There are, maybe, a dozen or so symbols that represent components: resistors, capacitors, transistors, IC’s. They connect together with lines. None of this represents where they are in an amplifier, just how one component connects to another. So the whole technique of reading a schematic diagram involves following lines and finding where they go to. SIMPLE. But……

Why do engineers take so long to learn their job, if it is so simple? It’s because the reading is the simple bit. INTERPRETING…..well….that’s something else.

So your line (track/wire) goes to this transistor. Fine. But the amp doesn’t work. Not fine. So what can be wrong? what is it supposed to do, just there? Why is this voltage high? why does this chip put out dc? These are questions that happen all the time, and the schematic won’t help you to solve them. It tells you what connects to what, what the ‘what’ is. It doesn’t tell you what it is supposed to do or why it isn’t doing it. Now that is the hard bit.

I read some time ago that ‘a good engineer doesn’t need a schematic’. It was written by either a hyper-optimistic or woefully inexperienced bloke. Although I wouldn’t argue with the fact that we can repair without schematic diagrams, (carrying around a lot of generalised ones in our heads) I would argue that the customer will be charged a lot of money for the privilege, and that is an irresponsible attitude on the part of the engineer. It will take much longer without our trusty schematic. Which is why I frequently rail against secretive attitudes of  amp manufacturers.

Tea time.

 

The Vox AC 30

“You’ve done this one already” you might say. True, but there are a lot out there and they keep turning up at my workshop. This particular one was another result of a ‘GAS attack’ of Marc’s. He does suffer, does that gentleman. It did throw up a few issues that might be of use to those unwary enough to delve into these things. It also broached the subject of just how much we should pay for…well, anything, really.

 So, for a start what do I mean by that? Well, the bits inside an amplifier cost the manufacturer 77 pence. (Approximately.) The folks who put it together are mostly robots and their oil bill for the century is about the same. Or it’s made in China or somewhere else they eat rice and where 38.5 amplifiers = 1 bowl of rice. So that is another 77pence. (Approximately.) That works out to 2 pence per amplifier. Even given the benefit of any doubt that might be lurking, the amp cost a bit less than a quid to produce. (Approximately.)

Now we get to the really expensive bit. For every bloke/robot in the shed actually knocking these things out there are at least 174 blokes in designer sunglasses selling ‘em. It’s called ‘Marketing’ and that’s where our money goes. So we buy things to be persuaded to buy things.

This is the underside of the power section of the Vox AC30. Pretty much original but the mains transformer has been swapped in the past.

 

 

This was after I got hold of it. I often use solid copper ground rails where they once relied on the metalwork of the chassis. The contact to the frame deteriorates, and you can clean them up as much as you like in a year or two they’ll be back causing you problems again.

The output valve bases were replaced with lacquered ceramic bases. They hardly ever track and the gold contacts are very robust. Anyway that’s all pretty specific, but the generality interest comes with actually switching on an old amp that has been in retirement for a long time that has a valve rectifier. Don’t do it.

Here’s what really needs to be done. Take the rectifier valve out. Solder a couple of diodes (say 1N4007) to the valve base. The sides with the silver band are connected together and soldered to the HT output (the single wire that goes to the first capacitor) and the other sides go each to the transformer connections. Then put a capacitance meter across that first capacitor. An ohm meter reading is better than nothing. This one was a short. Had I switched that on, the rectifier valve would have blown and it could possibly have taken out the mains transformer. Best to be cautious. As it happened the rectifier valve also had a short, so that would have been a total disaster. You can check out the whole of the amp leaving in the two diodes. If anything nasty happens, your 20pence diodes will survive, and your nice new £15 worth of GZ34 probably wouldn’t.

Tea time.