RMI-FC100, a single stage audio power amplifier

ClassA power prediction

Vre=20mV.
Ire =0.02/Re
Re=0r1 Ire=200mA
Re=0r15 Ire=133mA
Re=0r22 Ire=91mA
Three output devices in parallel pass three times the quiescent current.
Maximum ClassA current ~twice the quiescent current.
Max IclassA; 1.2Apk for 0r1, 0.8Apk for 0r15, 0.54Apk for 0r22

The Max ClassA power is I^2*Rload/2
5.7W into 8r0, 0r1
2.5W into 8r0, 0r15
1.1W into 8r0, 0r22.
These Max ClassA powers are halved when driving 4r0.

If you set up with Vre=17mV then the Max ClassA is reduced appropriately (~72%).
 
I use 600mW 1% metal film resistors and they fit 0.3inch (7.62mm) pitch.
They seem to be a standard size here in Europe. Body size varies 6.0 to 6.5mm long and 2.3 to 2.6mm diameter depending on manufacturer.
Available from Truohm, BC components and Philips in the Rapid catalogue.
 
regulated PSU heatsink grounding

The four pads at the heatsink locations need to be connected to Gnd.
These pads will short to Gnd if screws are used to locate the heatsinks.

But if heatsink pegs/dowels are used then ensure that each peg does connect through the anodising of the heatsink.

I might be tempted to hardwire the four component connections back to the Gnd.
 
AndrewT said:
I use 600mW 1% metal film resistors and they fit 0.3inch (7.62mm) pitch.
They seem to be a standard size here in Europe. Body size varies 6.0 to 6.5mm long and 2.3 to 2.6mm diameter depending on manufacturer.
Available from Truohm, BC components and Philips in the Rapid catalogue.


Wow. Most of the 1/4 watt resistors I see are that size. I guess I'll be standing all the resistors up.
 
Thanks for the offer. Appreciate it, but I can get them OK. You've done enough to provide this amp for us.

For anyone in North America looking for a transformer for the input stage, I am making inquiries for R-core transformers. Unfortunately, suppliers are closed for the holidays, and can't be contacted. I have no idea what they will cost, but perhaps a group purchase would make it doable. But the only other supplier of stock transformers I found for the input stage PS so far is a Plitron toroid, and they aren't cheap either.
 
Guys,

This is not a cheap amp ... nor the sound :D
My grand total for this amplifier is over 1500 Eur, including the DAC (integrated in the same enclosure), but i must admit that I used a lot of butique parts and two big R-core transformers and a small one for the DAC.
This price doesn't contain R&D costs :(

Happy New Year!
Mihai
 
Roender,

It appears you've replaced all the capacitors in the middle of the board in post 353 vs. the ones in the original BOM and the picture in post 99.

You only mentioned the change to C1 as being an improvement. How did the change to the others affect anything, if any? What parts did you use in the changes?

Did you change any in the power supply board?
 
pooge said:
Roender,

It appears you've replaced all the capacitors in the middle of the board in post 353 vs. the ones in the original BOM and the picture in post 99.

You only mentioned the change to C1 as being an improvement. How did the change to the others affect anything, if any? What parts did you use in the changes?

Did you change any in the power supply board?

Keep the recommended changes, only C1 plus some small series resistor. I did a lot of experiments in order to find a lucky cap combination ... so I've spend a lot of money almost for nothing and I succeed to destroy a some boards by desoldering and resoldering components .
The only caps, besides C1, which might probably worth to be changed are in power supply (MUSE KG)