Solid State Amps...Interested In Learning More

[keithb7]

Hi folks. I am a bit of a hobby-ist amp nut. I have built 3 tube amps, first one was a kit, then I got a little more creative and sourced my own parts and did a few mods on two more I built. I hate to just assemble parts from instructions, so I read lots and learned a ton before I started my first amp build. I enjoyed what I learned and wanted to carry on. I have serviced my own amps since, and am continuously learning. I have 4 tube amps, 3 which are vintage, that I have maintained, and they are running top notch it seems. I am out of things to tinker with and learn, so I placed an ad locally to repair amps if anyone was in need. I would prefer to work on non-PCB tube amps, but am willing to take on others, in the hopes of learning more and satisfying my desire to work on amps. It turns out I have 2 guys who want me to look at their "scratchy" solid state amps. I have never worked on a solid state amp, and I told them so. I explained to them my history as I did here to you, but they would still like me to poke around in their amps. I expect many SS amp parts are going to share similarities with tube amps. Wires, caps, resistors, diodes, bridge rectifiers, pots, switches ect. I can take a look around. Maybe it won't be so easy and I'll have to try and trouble shoot. I don't have the amps yet in my shop, but I started doing some research. Some of my initial concerns are: Are there others here on this fine forum willing to help out a fairly inexperienced hobbyist? If I start a thread and post some q's, I may need some assistance. Also, do I need to drain any caps like the electrolytic caps on a tube amp that store electricity? When a SS amp is unplugged, can it still shock me? If so, I'll start a simple thread with photos and a schematic and take it one step at a time. Thanks for reading, and possibly responding. - Keith

[The Dude]

You'll find plenty of threads here about solid state amps. If someone can help, they usually will, so ask away. SS amps do not generally have voltage levels as high as tube amps, but yes, they can be equally dangerous. Many SS amps have caps in the thousands of microfarads- not something you generally see in tube amps. They can store voltages for a very long time, so never assume caps are discharged- even after being left off for days. Poking around without discharging caps can not only be dangerous, but can cause circuit damage if your probe slips, so it's always a good idea to discharge those buggers.

[nsubulysses]

http://www.jeanpierrepoulin.com/PDF/transistor.pdf

If you really want to get into the nitty gritty give this book a look.

People on this forum are extremely helpful so I'm sure you will get some assistance and also if you just search and peruse through old threads there is a ton of info available as well

[keithb7]

Great link to some reading. I'll be reading up for weeks! Thanks, Keith

[Mick Bailey]

Also, do I need to drain any caps like the electrolytic caps on a tube amp that store electricity? When a SS amp is unplugged, can it still shock me? If so, I'll start a simple thread with photos and a schematic and take it one step at a time. Thanks for reading, and possibly responding. - Keith

SS amps can provide a few nasty surprises;

As already noted, the main PSU filter caps are larger in value than in tube amps, by a good margin. The voltage can be on the high side as well, depending on the output power. Add into this that you've generally got a +/- supply, so consider the rail-to-rail voltage and the instantaneous energy that can be discharged. Not only can you get shocked, but a short with a probe can cause a lot of damage to components and PCB tracks. Im working on an amp right now that has 220v rail-to-rail.

One of the features of most SS amps is the PSU caps generally drain fairly quickly when the amp is switched off, though it's always best to check. In a fault situation you can't always be certain. Additionally, if the PSU can be separated from any circuit load, then it's important to discharge the caps before reconnecting it. If not you risk blowing some part of the circuit. Especially true if you're working on a Marshall Mode 4 or similar. When you re-mate a PSU connection you don't know for certain if the - rail will make contact before the + rail, or vice-versa.

[spsimmons]

Keith- I've found this forum to be frequented by some of the smartest, most knowledgeable, and most generous people I've encountered in cyberspace.

[Silvertone Jockey]

http://www.jeanpierrepoulin.com/PDF/transistor.pdf

If you really want to get into the nitty gritty give this book a look.

People on this forum are extremely helpful so I'm sure you will get some assistance and also if you just search and peruse through old threads there is a ton of info available as well

The people who post here in my experience do not have restraint when it comes to helping anyone who wants to learn that can follow directions. Seriously you won't find more knowledgeable posters who love to freely share their experience and more importantly their TIME with those in need of help on the net. Others probably exist but I have not encountered them. This forum is a model that all forums and their members should emulate. Worry not OP you will get all the help you need in a timely manner here, you are in the right place