This is as far removed from the current versions of Studiomaster, as politics is from sanity. They’re the same colour (Henry Ford’s colour; “any so long as it’s black”) and…errmm….they’re the same colour. That’s about it.
This a picture of the inside (?) of a ‘proper one’. It’s about here that the longsuffering reader pulls out every hair on his/her head because it sounds like I’m ‘talking down’. Not true. Anybody who fixes amps for a living is in no position to talk down to rodents, even. Some of my best friends are rodents. Most of them don’t know it, however. We digress. Back to picturesque landscapes of the inside of an amp.
In various places on this blog (mostly under ‘information’; a much maligned term if ever there was one) there is a lot of stuff on ‘what does what’ in an amp. This is more to do with ‘where does what’.
We’ll start with the circular lump that is unmissable. This is the mains transformer. This is often abrieviated to’TX’ and used to be called a ‘tranny’ in the days before transistor radios, which were also, not a little confusingly, called ‘tranny’s’. Don’t know where that came from. Anyway this is a particular design of transformer called a ‘toroidal’ and it has a particular property which is very useful in this situation (this situation being cramped.) It has very little magnetic flux, external to the transformer itself. This is very desirable in these circumstances, as magnetic flux at 50 hz is picked in up the electronics (especially in the preamp stuff) as hum; something we definitely want to keep down to a minimum. The reason it is there at all is to take the mains voltage in, and transform it to relavent voltages that the amp needs.
Across to the left of that are two flat green pcb’s (printed circuit boards; and no I’m not talking down as my best friends are rodents etc.etc). This actually looks like one pcb but they are two identical ones side by side. These are the power amp assemblies, and the bit we can see is the back of the switching modules. More of that in a bit. In between the tranny (?) and the power amps are some black cylindrical things which are smoothing/reservoir capacitors and are part of the power supply section most of which is on that pcb in the middle with the capacitors on it.
This little pcb is mounted on the back of the amp and houses the input jacks/XLR’s and has the preamp chips on it. These might be TL 072 chips (or sometimes BA4558) and the purpose of it is to amplify the input signal to a level that the power amps can deal with. just under that are a couple of spade tags which are fitted to the main bridge rectifiers; we can’t see those too well, but they rectify the transformer voltages to d.c. for the power amps. The power amps have two seperate voltage levels (pos and neg 45volts; and pos and neg 95volts) and there are one each of these rectifiers fitted to the bottom chassis. The flat cables you can see are ribbon cables and carry the signals to the power amps.
Here we can see one of the power amps. This top pcb is the switching amp, and this is physically connected via heat sinks to a lower pcb which is the power amp. The top board sorts out the voltages (between the 45v and 95v mentioned earlier) that go down to the power amp section. The flat black piece of plastic to the left of the power amp is the top of the fan which drives air through the heat sink tunnel.
The 1500d, 1500E, 1600E, and 2000E all look identical, except that the 2000E has two fans. If you take the top off any of the powered mixers (vision, horizon; 1200, 1500,) the bottom of the amp again, looks exactly the same. Some have the transformer higher up and the rectifiers lower. The very early models of the Powerhouse look different. There is no voltage switching pcb; it’s just a flat board where you see the green pcb’s. To get the 250-350 watts out, the switching approach wasn’t necessary.
Repair isn’t necessarily cheap. If a power amp goes down on you, it’s generally a rebuild of both boards of whichever side, left or right. Not cheap, but a lot cheaper than buying something of a similar quality, these days.
So what was the point of all this, other than to postpone my taking the dog for a walk? Just that, if we insist on getting lost inside one of these things, it’s nicer to do it with the odd recogniseable landmark.