Solarbird (solarbird) wrote,

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studio buildout, part 3: playback amps

Woo! We’re Newfoundland and Labrador Folk Festival official photos page. Wait for it and you’ll see Anna and me both! Front page! 😀 We’re in fact in several photos here – one where I’m performing solo (my extended version of Ten Finger Johnny) and later with Anna in session. 😀

(Sadly, the photos – by Rick West – were taken down in when they redid their website)

Newfoundland music on Newfoundland soil. That’s called the correct way Even if I do have an uncanny ability to blink just in time for the photo. XD

But now, back to business.

Last time, we talked about monitor speakers; what to look for when you have no money, characteristics to seek out, simple mods to improve their behaviour, and so on.

But unless you went with powered monitors, you’re going to need amplifiers to drive those monitor speakers. Since you’re reading this, you probably aren’t going to just go out and pay full retail for some very nice new equipment; let’s talk DIY!

First, I need to repeat something I said last time:

The cheap but rebuildable equipment you want mostly comes from the 1970s… There are a couple of key reasons for this: 1. By this time, transistor audio technology had settled down, and no longer sounded like ass. 2. The state of the art was finally good enough (in transistors) that the then-goal of broad and equal frequency handling – meaning, flat audio reproduction curves – became realistically attainable, and people were still trying really hard for it.

This is true in amplifiers, too. Some would argue that in amps, you want to stick to the early 70s. I don’t particularly agree, but be careful when you get into the early 80s, just because of audio fashion trends being what they were.

You can also step back a bit into the 1960s, if you’re willing to learn vacuum-tube equipment. In some ways, that’s easier to work on, and you’ll get fantastic bang-per-buck. Look for EICO, Dynaco, Harmon-Kardon, just for examples; and research tubes first, to see what’s back in production.

Tube equipment has downsides, though: you can’t tip them on the side, they use a lot more electricity, need more ventilation space, generate a lot more heat, and most importantly of all, the power rail tends to be hanging out in the 450 volt range. Careful with those pliers!

Think of it as the advanced class

So unless you’re okay with that, stick to the transistor era.

If you poke around, you can find a pretty good number of old 70s component-stereo-system amplifiers for very little money. Don’t buy the combined units, with turntables and tape decks built in; those were junk then, and are junk now. You’ll see nostalgia for some of that era, and entertaining tho’ that might be, it’s not our goal. Look for something that’s just amplifier and pre-amp – preferably a unit without even a radio.

Undeniably groovy, but still kinda terrible

Pioneer is usually a good, safe bet, as brands of the era go; it’s right in that sweet spot of quality and commonality. So is Harmon Kardon. Sansui, Kenwood, and Marantz are often excellent, but tend to cost more even now. My general approach is to keep an eye open and when I see something of the right sort, then search the web for it and see what people have to say. AudioKarma and Gearsluts are both pretty good data sources in this regard.

My current studio monitor amp is a Pioneer SA-5200. It was made for all of three years (1972-1975) and I picked it up at a thrift shop for all of $5. They go for under $35 on eBay, working to various degrees.

Not mine, but same model. Not so groovy, but far more competent.

It has no power to speak of (20w), but you don’t need it for this application; most importantly, it’s noted for being a very clean amp; very low distortion and very low noise, at least as it shipped from the factory. And it has enough power to drive all my mains, and reference headphones.

That said, it sounded pretty terrible when I bought it, and got worse over time. This is where you need to know something which may and may not make any sense to you, depending upon how much you know about electronics: electrolytic capacitors age and die. And every audio chain you’ll find in any of these amps uses lots of them.

You’ll have to rip out and replace every one.

I’ve talked often about how the most important item in your studio toolkit is the soldering iron. Amps of these vintage can be rebuilt, without complex tools. The parts are large and relatively easy to access. You’ll want a low-wattage soldering iron, so you don’t damage the board with too much heat. You’ll want direct-value replacement swaps on those capacitors, in terms of uF rating. (You can go higher in voltage if you want; that’s a matter of how much the capacitor will tolerate, so replacing with higher voltage is safe.)

The electrolytic capacitors look like this, on the circuit board:

Or Doctor Who. Are you The Doctor? No? Don’t reverse polarity.

Coming out of the bottom of each of those cylinders are a pair of metal wires. Those go through the circuit board and are soldered into place, making contact with the printed circuit on the other side of that board. You’ll need to de-solder those connections, pull up the capacitor, and replace it with caps of the same capacity.

As a side note, these are not the only kinds of capacitors. You’ll see many flat discs; those are ceramic capacitors. Barring physical damage, you’ll never need to replace one. Similarly, you’ll occasionally find flattish rectangular capacitors. Those are usually film, and again, leave them alone, they’re fine.

Doing all this is kind of a pain in the ass, but you generally need to do it in equipment of this vintage. Here’s a bit of a map:

It’s dangerous to go to Toshi Station alone! Take this.

Any stereo amplifier is really two amplifiers combined together into a single box, one for the left channel, one for the right channel. You can see above how this results in symmetrical layout of components! Anywhere you have that kind of symmetry, you’re dealing with the left and right channels, duplicated. Anywhere you’re not seeing symmetry, you’re probably looking at power circuits.

Advanced students will want to bypass the tone controls. There’s no single way to do that, so I’m not going to post pictures. But I will explain why: it’s because, as with the monitor speakers, you don’t want help. You want flat response, or as close as you can get to it. The ideal studio monitor amplifier would be a wire, with gain – that is, a wire that magically changed nothing about your sound other than volume.

Tone adjustment knobs and systems, by definition, deviate from flatness. They’ll also add noise, so just bypass them. It’s also one less set of components to rebuild, so saves you time!

And that’s how to get a quality monitor amplifier on the smallest budget – at least, that I’ve found so far. Next week: I dunno! Microphones, or possibly digital audio workstation software and computers to run it on. One of those. Happy rewiring! ^_^

ps: Let the kitty help!

No, no, not wire snips – can opener! Here, I’ll get it.


This post is part of The DIY Studio Buildout Series, on building out a home recording studio.</p>

Mirrored from Crime and the Blog of Evil. Come check out our music at:
Bandcamp (full album streaming) | Videos | iTunes | Amazon | CD Baby

Also posted to ソ-ラ-バ-ド-のおん; comment count unavailable comments at Dreamwidth.

Tags: diy, studio, tours
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