( 
)This is not so much a guide as a suggestion.
When building a DIY (do-it-yourself) project, a major part of the work is often the cabinetry and controls - which, for a preamp, may include a cabinet, knobs, and switches. Some of us, unfortunately, are 'woodworking challenged' or 'metalworking challenged'. I personally enjoy DESIGNING circuitry. I don't mind building or designing PCBs or doing point to point or prototype board wiring, but I really hate metalworking and woodworking (which is probably why I'm not very good at them). You've also probably noticed that those nice pre-fab cabinets (where you just have to drill a few holes and you're done) are rather expensive. They look great, and do allows folks like me to produce a nice looking finished product without too much pain, but sometimes they cost almost as much as a working piece of used equipment.
My suggestion is that it is often much easier to buy a vntage piece of equipment and reuse the case and controls. For example, the Dyna PAT-4 is a terrible preamp, but it has a reasonably decent cabinet, a nice aluminum faceplate, and really nice aluminum knobs. You can buy one cheap on eBay (even better if it's broken), throw out the insides, and build YOUR preamp in the case. You get a nice case, nice matching knobs, and you might even get to reuse the power supply and input jacks (although they aren't that great). There is also a 'coolness factor' with the look and controls of some vintage equipment - even if the equipment itself wasn't that good. It's neat to have something that looks like a 'well-preserved old clunker', but performs like modern equipment when you turn it on. For example, I've seen some cool GainClone chip-amps built inside salvaged Dyna Stereo 120 or Stereo 80 cases.
Here are a few suggestions you should consider though:
1) Equipment varies widely in terms of 'reusability'. I would go as far as to say that you shouldn't consider this unless you are familiar with the piece involved. Generally things that were kits (Heathkit, Dyna, Eico) are easier to take apart and modify (since they were designed to be put together by normal human beings). Modern receivers are often the opposite - with steel punchout chassis, plastic jigsaw-puzzle parts, and controls that are board mounted (and so can't simply be attached to the front panel). Also, with the kit stuff, you can often find a construction manual online and see if you can get it apart BEFORE you bid on it (Dyna and Heathkit manuals are pretty easy to find online - try Google).
2) You MAY be able to reuse the power supply, but don't count on it. As you should know if you've gotten this far, requirements vary a lot between different units. It's not all that likely, for example, that YOUR new power amp design will need exactly the same voltage as the one that came in the cabinet. (Of course, you can turn this around by buying the carcass first, then designing something to go in it.) One common case in GainClone chip amps - they generally run at lower voltages than those used by big power amps. Also, the power supply that came with might be defective or poor anyway - so don't count on it. Kits are great here (like Heathkit or Dyna) because you can get the schematics - which include the power-supply schematics. Old preamps tend to have power supplies that aren't especially good; many modern designs prefer or benefit from better ones - so don't get carried away with reuse. Don't count on those original controls either - they may be in good shape, but they mak be noisy or even broken.
3) For things like preamps, old ones often have their in and out jacks in the form of cheap crimped RCA jacks mounted on that brown phenolic plastic - often riveted in. It's easy to drill out those rivets, screw in a nice piece of Lexan, and use nice gold-plated RCA jacks. You probably already know that nice gold plated RCA jacks and binding posts are available pretty cheap on eBay. Lexan IS better than Plexiglas or acrylic - because Lexan is VERY resistant to cracking (it actually scratches a bit easier, but won't crack while you're cutting it, and you can tap threads into it if they don't have to be too strong). Note that both Lexan and Plexi are very good insulators, but are NOT at all heat resistant. There are other fancier plastics that are heat resistant if that's needed.
4) Many old speakers come in very nice cabinets. This isn't such an eBay thing because cabinets tend to be heavy and cost a lot to ship - and because it's hard to tell really nice cabinetry from a photo. However, finding a nice pair of speakers at a garage sale or locally, with great cabinets but ripped drivers or some such, is a great way to get a nice set of cabinets cheap. Many old cabinets are real wood veneer or even solid wood. (There's not much you can do to help restore damaged plastic, but real wood veneer will often look like new if you apply a bit of linseed oil, let it soak in, then wipe it off. Real stains and water spots and rings usually won't go away entirely, but that dried-out, whitish look usually will.) Reusing the crossovers is unlikely (because they probably won't agree with your project, and because many commercial speakers have really cheesy crossovers), but possible as well. Some speakers will see a marked improvement if you replace the damaged (or just crappy) drivers with good ones - but don't count on that.
5) Keep in mind that most commercial speakers (and many DIY ones) are glued together, so you may not be able to remove panels to work on them. That means that you'll have to figure out how to modify cutouts and such with the panel in place (saber saw). You CAN cover holes or make adapter plates to install smaller drivers in bigger holes rather easily. Even plywood or masonite that is thinner than the cabinet is usually stiff enough to cover a small hole successfully. There are all sorts of fancy stuffing alternatives, but the pillow stuffing from the fabric store works well and is quite cheap. (Fiberglas works well, but is itchy to work with.) Also note that you CAN buy nice pre-finished DIY cabinets from places like PartsExpress - they aren't cheap but they are very nice and come with removable and replaceable front panels.
Well, hope I've given you a few ideas.
Have fun.
When building a DIY (do-it-yourself) project, a major part of the work is often the cabinetry and controls - which, for a preamp, may include a cabinet, knobs, and switches. Some of us, unfortunately, are 'woodworking challenged' or 'metalworking challenged'. I personally enjoy DESIGNING circuitry. I don't mind building or designing PCBs or doing point to point or prototype board wiring, but I really hate metalworking and woodworking (which is probably why I'm not very good at them). You've also probably noticed that those nice pre-fab cabinets (where you just have to drill a few holes and you're done) are rather expensive. They look great, and do allows folks like me to produce a nice looking finished product without too much pain, but sometimes they cost almost as much as a working piece of used equipment.
My suggestion is that it is often much easier to buy a vntage piece of equipment and reuse the case and controls. For example, the Dyna PAT-4 is a terrible preamp, but it has a reasonably decent cabinet, a nice aluminum faceplate, and really nice aluminum knobs. You can buy one cheap on eBay (even better if it's broken), throw out the insides, and build YOUR preamp in the case. You get a nice case, nice matching knobs, and you might even get to reuse the power supply and input jacks (although they aren't that great). There is also a 'coolness factor' with the look and controls of some vintage equipment - even if the equipment itself wasn't that good. It's neat to have something that looks like a 'well-preserved old clunker', but performs like modern equipment when you turn it on. For example, I've seen some cool GainClone chip-amps built inside salvaged Dyna Stereo 120 or Stereo 80 cases.
Here are a few suggestions you should consider though:
1) Equipment varies widely in terms of 'reusability'. I would go as far as to say that you shouldn't consider this unless you are familiar with the piece involved. Generally things that were kits (Heathkit, Dyna, Eico) are easier to take apart and modify (since they were designed to be put together by normal human beings). Modern receivers are often the opposite - with steel punchout chassis, plastic jigsaw-puzzle parts, and controls that are board mounted (and so can't simply be attached to the front panel). Also, with the kit stuff, you can often find a construction manual online and see if you can get it apart BEFORE you bid on it (Dyna and Heathkit manuals are pretty easy to find online - try Google).
2) You MAY be able to reuse the power supply, but don't count on it. As you should know if you've gotten this far, requirements vary a lot between different units. It's not all that likely, for example, that YOUR new power amp design will need exactly the same voltage as the one that came in the cabinet. (Of course, you can turn this around by buying the carcass first, then designing something to go in it.) One common case in GainClone chip amps - they generally run at lower voltages than those used by big power amps. Also, the power supply that came with might be defective or poor anyway - so don't count on it. Kits are great here (like Heathkit or Dyna) because you can get the schematics - which include the power-supply schematics. Old preamps tend to have power supplies that aren't especially good; many modern designs prefer or benefit from better ones - so don't get carried away with reuse. Don't count on those original controls either - they may be in good shape, but they mak be noisy or even broken.
3) For things like preamps, old ones often have their in and out jacks in the form of cheap crimped RCA jacks mounted on that brown phenolic plastic - often riveted in. It's easy to drill out those rivets, screw in a nice piece of Lexan, and use nice gold-plated RCA jacks. You probably already know that nice gold plated RCA jacks and binding posts are available pretty cheap on eBay. Lexan IS better than Plexiglas or acrylic - because Lexan is VERY resistant to cracking (it actually scratches a bit easier, but won't crack while you're cutting it, and you can tap threads into it if they don't have to be too strong). Note that both Lexan and Plexi are very good insulators, but are NOT at all heat resistant. There are other fancier plastics that are heat resistant if that's needed.
4) Many old speakers come in very nice cabinets. This isn't such an eBay thing because cabinets tend to be heavy and cost a lot to ship - and because it's hard to tell really nice cabinetry from a photo. However, finding a nice pair of speakers at a garage sale or locally, with great cabinets but ripped drivers or some such, is a great way to get a nice set of cabinets cheap. Many old cabinets are real wood veneer or even solid wood. (There's not much you can do to help restore damaged plastic, but real wood veneer will often look like new if you apply a bit of linseed oil, let it soak in, then wipe it off. Real stains and water spots and rings usually won't go away entirely, but that dried-out, whitish look usually will.) Reusing the crossovers is unlikely (because they probably won't agree with your project, and because many commercial speakers have really cheesy crossovers), but possible as well. Some speakers will see a marked improvement if you replace the damaged (or just crappy) drivers with good ones - but don't count on that.
5) Keep in mind that most commercial speakers (and many DIY ones) are glued together, so you may not be able to remove panels to work on them. That means that you'll have to figure out how to modify cutouts and such with the panel in place (saber saw). You CAN cover holes or make adapter plates to install smaller drivers in bigger holes rather easily. Even plywood or masonite that is thinner than the cabinet is usually stiff enough to cover a small hole successfully. There are all sorts of fancy stuffing alternatives, but the pillow stuffing from the fabric store works well and is quite cheap. (Fiberglas works well, but is itchy to work with.) Also note that you CAN buy nice pre-finished DIY cabinets from places like PartsExpress - they aren't cheap but they are very nice and come with removable and replaceable front panels.
Well, hope I've given you a few ideas.
Have fun.
Guide created: 07/11/09
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