Amplifier using 2SC3856/2SA1492

[jackand08]

Hi everyone,
Just wondering whether anyone has seen a design for an amp using 2SA1492/2SC3856. The reason is that I have about 10 of each lying around and would like to do something with them.

At first, I was thinking about constructing one of Rod Elliot's subwoofer amplifiers using the original transistors specified but thought that the danger and cost involved would be a bit too high for my liking. I was wondering though, for future reference, would a 50-0-50V transformer be able to power the amplifier properly?

Then I thought about trying Rod's Project 03 using these transistors (they seem suitably rated) instead of the 2N3055/TIP2955 combination mentioned. This is a bit more like it and is ideal for a test amp for me.

Thanks in advance.
Jack

[jaycee]

50-0-50 AC would give you 70V DC when rectified and filtered. You would need a massive, probably air cooled heatsink to build a P68 of that power.

Rod's P3A is a revised design. Your Sanken's should work just fine in this circuit. The only thing is that the particular design of the P3A is layout-sensitive, so you might run into trouble making your own circuitboards for this amp. The SymAsym amp (search this forum) is also a good design that will work well.

[jackand08]

Thanks alot jaycee.
I'll have a look round and see what I can find. I might buy the boards for the Project 3A amp or I might try to design my own. Also, which version of the SymAsym amp should I use with those transistors.
Thanks
Jack

[sakis]

if you have enough transistors you may as well clone a yamaha amplifier .... that is almost a pro amp that has all the features and protections and pcb wise will not be that hard to clone

if you want i can provide a schematic

[jackand08]

Funnily enough, sakis, that's where the transistors came from in the first place! I acquired the amp from my local church as it was not working and they no longer needed it. If I remember rightly, it was a P1600 with a fried driver circuit and input stages (I think). Somehow though, it hadn't blown up the output transistors. Since I got it free, it was too costly to repair and I would have no use for it, so I scrapped it for parts. I could've bought the service manual but yamaha wanted something like £18 for it and when I asked about the price for replacement parts, well, it was going to be expensive.

I saved the transformer and heatsink from there so I could use them if I was to clone the amp. Just wondering, do you have a schematic for the P1600 amplifier because I wouldn't mind cloning it.

Thanks
Jack

[sakis]

hmmm no sorry i havend got the schematic of this one ... but trully i think you ve done the wrong thing repairing amps like that is probably 10 minutes of work and damages created are in the level of a few resistors ...

that was a pitty i think

[jackand08]

As I said though, I got the amp for free and didn't have the space to keep it so I thought I might as well strip it for parts. I saved pretty much everything from it, now it's all just waiting to be used . Besides, because I didn't bother buying the service manual (where I could've sourced my own parts cheaper), yamaha were going to charge me a bomb for all of the different components needed to fix the amp (3 or 4 broken emitter resistors, a completely toasted driver and input stage and some burnt traces on the PCB that may or may not have worked).

I think I might just stick to jaycee's recommendations and just build a P3A or SymAsym with those transistors. I don't want anything complicated though because it will only be something put together for a bit of practice and to get some use out of my homemade UV box .

[jaycee]

I'd build the original SymAsym design. The others are quite complex and call for some fancy parts - particularly FETs that are not easy to get.

SymAsym5 - Project

The schematic shows MJL3281/1302 but the Sankens should work. You may need to reduce the 22pF feedback compensation cap to 3p3 or eliminate it altogether. Pavel Macura's page on it is worth a read

symasym

edit: look at this link instead - http://www.lf-pro.net/mbittner/Sym5_...ymasym5_3.html

[sakis]

P3a will be also very happy with thuis type of semis .... did a version with original YAmaha replacement sets and worked like a charm

[jaycee]

Agreed. The only reason I am hesitant to recommend the P3A, is the CFP output stage. This is OK if you have the PCB design experience, or just buy Rod's PCB's, but can make all sorts of trouble if you try and design your own. The Symasym has a tested PCB design that is freely available, and also a much more stable EF output stage.