Building a home stereo amplifier

[bobsmith1492]

Howdy,

I'm looking to build a basic black-box amplifier - RCA left and right in, power in, and two speaker outputs. I have the circuitry all set and am working on ordering parts (transformer is ordered, woot!). It should do >60W per channel (REAL power) into an 8 ohm load and I'm putting differential inputs on to make it quiet. My intent is to run the output from my computer to it and I have a nice 24-bit sound card so everything should sound gooood.

Anyway, I need to figure out what to do for a box and heatsinks. What I've done in the past was use CPU heat sinks and I just may do the same if there are any of proper dimensions and big enough.

For the box I am at a loss right now. I'd like it to look decent, maybe black, smooth wood or wood grain. I suppose metal would work but I'd rather not.

Any thoughts on where to find such things or overall suggestions?

Thanks!


PS: I have built this amp before and it sounded amazing even though it was just on perfboard. This time I'm doing it right and getting PCBs. This is the amp I'm working from and this was my previous effort.

 

[CycloWizard]

You might want to post this in the A/V forum or even the cases and cooling forum if you want a retail solution. Most of what the people here will recommend is something custom-made since we're dorks. I don't even know who made the enclosures that I used since they were just available in a storage room.

 

[bobsmith1492]

Hey I'm not adverse to custom-made provided the right materials are there. I don't want a plywood box!!

 

[Modelworks]

One thing I noticed on the schematic is that it appears the ac power ground and the signal ground are the same.
Thats generally not a good idea.

Your running it through a transformer so that makes the amplifier isolated from ground, which is great for an amp, no chance of ground loops. But if you attach the ac ground to it, your throwing out that isolation.

I usually like to build the amp so that the pc board ground is isolated from the case.


This is someone that makes lots of cases.
http://www.hammondmfg.com/index.htm

If you find what you want just contact digikey or mouser to get the case.

 

[bobsmith1492]

Yeah, that's why I have a differential op amp on the input - any ground potential noise is canceled by the CMRR of the amp which is very high.

Hm, they have a pretty good selection but seem too industrial somehow...

Whew, I'm finding all kinds of cool cases now!

I think I found my case. Black body with a gold faceplate.

 

[Analog]

A couple of notes from someone who has designed and built amplifiers for 20+ years.

* Use a toroidal power transformer - superior noise and transient response.

* Get the power supply circuits off your perf board and place them as far away as the front end as possible.

* Shield the front end with a ground plane if possible

* Use shielded microphone cables for all inputs.

* Use RF beads on the power supply rails at the main amp.

* Rod's amp doesn't have any output protection, so I'd advise doing some rudimentary output protection.

* A Zobel network on the output would also be advised.

* This is a classical Negative feedback amplifier with DC blocking (look at the feedback network). It will be sensitive to temperature and thermal runaway due to the class AB output stage. You may want to look at Rod's MOSFET amps, especially the one that uses the lateral MOSFETs for better temperature control.

* here is a free PDF of a book on guitar amps, and has some good information on what I've talked about:
http://www.thatraymond.com/dow...teemu_kyttala_v1.0.pdf
HTH

 

[bobsmith1492]

Thank you Analog:

- Check on the toroid (toroids.com, from Maryland!)
- Bridge rectifier is off-board, filter caps are onboard though - it's going to be a long board though, with power supply on the left, input stage on the far right, and power transistors in the middle
- Ground planes for sure
- Shielded cables too, going to be as short as possible (<3-4 inches most likely)
- I have a couple of massive choke coils; I'll put one on the mains transformer input at least
- The amp has an RC load on the output (0.1uF->10ohms); it's on the main schematic
- I'll put as big of heatsinks as possible on it; also, I built one of these already and ran it for a long time and it barely even got warm

I would like to add at least short-circuit protection but I'm not sure how to go about it...

Thanks for the PDF; I'm reading it now at work.

 

[Oyeve]

You can always go with a fan for cooling, especially if using class A or even class AB. I once built a class AB amp, 100w mono. Put in a fan in the compressed board chassis I made. made a huge dif in heat and did not add any real noise.

 

[Howard]

You're better off asking on diyaudio.com