RMI-FC100, a single stage audio power amplifier

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#921
Sheldon,

Thanks for pointing me to that thread. The SymAsym is interesting, especially if it has boards available.

However, this amp is still my preference! So what you are saying is that I won't be able to get the boards for this amp! ??? :bawling:

Yes I understand that it is not easy with perfboard so perhaps I shouldn't attempt that. A good amp is a good amp, whether it is used for the tweeter or not. I guess most amps behave well at low / mid frequencies. It is hard to find an amp that sounds smooth, accurate, transparent without much noise, sharp edges or brightness in the treble. I think this amp will do extremely well.

Regards,
Bill
 
#922
This is a brilliant amp, a brilliant creation, with tremendous amount of efforts and top talent behind it.

If there are no PCBs, no kits available, then ordinary DIYers won't be able to benefit from it, a degeneration of the spirit of the DIY community. This amp has been brought to a death as far as DIY is concerned for most DIYers, except for those who have advanced skills and experiences to learn from it.

The more brilliant the amplifier is, the more shameful this fact is.
 
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#923
Bill,

This is, I agree, a brilliantly conceived amp. But as a rule, the better the product, the worse the marketing.

You can get the patterns for the pcb - I think Sheldon has them in fact - and then have proto pcbs built at ourpcb.com in China for around $US110 including shipping to Oz.

The Symasym was designed by Michael Bittner, a very clever young software engineer. He and Mihai Rauta have both given selflessly of their time here. Strongly recommended.

Hugh
 
#924
I pointed out the symasym thread, partly because it incorporates some of Mihai's design input, uses more readily available parts, can use a single output pair and partly because there is some group buy activity on boards. Search the forums, if you are interested in that.

But if you really want to build this amp, then go for it. I bought the boards as part of an earlier group buy. Maybe someone has an extra pair. If not, the files for the boards are in the first few pages of the thread. You can have them made by Hugh's source. Were I to use it as a tweeter amp, I'd be tempted to mount the six output transistors, but leave out the base stopper and emitter resistor for Q2/25/4/27. That way you can still use the diodes for bias but only use the output from a single pair. Later, if you need the full power, just add the base and emitter resistors (assuming adequate heat sinking).

Search through the tread for parts too. I think someone mentioned getting some parts and matching them (pooge, maybe?). There are group buys on the forum for the input jfet's. I have extra's of matched BC parts and. I also have extra's of the 2sa/2sc, and the jfet's but no real tight matches of either.

Sheldon
 
#925
Thanks, Hugh and Sheldon.

I think at this stage I would need to do a bit of studies and see if I could obtain all the parts and match them, etc.

I don't know much about power amps but have built 5 power amplifiers from kits and have just realised some of the major mistakes I made. When I looked at the PCB design of this amp it seemed to me it would solve all the problems I previously had. So I trust that both the circuit and PCB are so well engineered, before I even have to time to read through the historical evolution of this marvellous piece of design.

Regards,
Bill
 
#926
Hi Bill,

This amp and his PCB is 100% stable and functional.
Unfortunately, or not 🙂 ?, I do not earn my bread from electronics design and so I do not have more time to invest in this thread. From my point of view this is a complete and finished project.
Subjectively, for me and some friends of mine, this amplifier sound very good and actually drive my expensive pair of speakers very well and accurate.
I agree with Hugh that marketing is worse for good products but this is not a commercial design and so there is no marketing behind 😉
If you have questions uncovered by this thread I would gladly help you, but first I'll humbly encourage you to make an effort and read it all. There is no free lunch 😉
DYI is first of all a lots of fun and an enjoyable activity. The path is more enjoyable then the goal, at least for me 😀

Have fun,
Mihai
 
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#929
Joshua_1963 said:
did anybody try to modify thje design to use 2SC5200/2SA1943 ?
CAn anybody tell the experience or share the design. How to integrate or design the mentioned Vbe multiplier.
Click to expand...

I'm no expert, so I would seek confirmation for what I say. That said, I think you can replace the diode string with a typical VBE multiplier. Here's the version on the Symasym (which I have built): http://www.diyaudio.com/forums/atta...signed-michael-bittner-our-mikeb-symasym4.gif

If you look closely, you can see that you just replace the diode string, with a transistor and voltage divider. The rest of the circuit is very much the same. The only difference is that the FC100 uses a 15pf cap divider to the ground leg, while the Symasym uses 330pf caps paralleled with 47k resistors. If I were to try it, I would just replace the diode string with the Bd135 and it's resistive divider, and leave everything else as is. Of course, the VBE multiplier transistor must be located on the heatsink with the output transistors. Good approach is to fasten it directly on top of one of the outputs.

Sheldon
 
#940
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