RMI-FC100, a single stage audio power amplifier

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AndrewT

R.I.P.
Joined 2004
I like Roender's front end regulator. :)
Using 41V Zener, output is 42.7V cold and rises to 43.1V when warm (62V @ 32mA = 2W sink dissipation). About 8mA is lost to ground through the other components.
The LEDs allow just 950mV across R3 & R4. I'm going to drop these resistors from 27r to 22r.

I found the second jumper, eventually.
The two LEDs face in opposite directions. Take care.

Nice operation. When the LED is out the CCS is not up to full current. When it just lights the CCS is just operating at minimum voltage drop (~0.7Vdrop) and at full brightness the CCS is fully operational.
 
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pooge

Member
Joined 2003
Mihai,

I'm trying to understand your ground layout, especially the use of 10 ohm R25. This resistance separates the input grounds from star ground and the lag comp caps. Are you just trying to reference the signal ground to the preamp ground and break a loop from the preamp ground to the power amp supply?

Also, your lag comp caps are connected to the dirty ground of decoupling caps C10 and C11. I don't fully understand the operation of the lag caps in this circuit, but I would have presumed them to be directly coupled to input signal ground, and not share a dirty ground.
 
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pooge

Member
Joined 2003
Sheldon said:


Problem is, they have 3423-Y and 1360-O. I haven't found anyone with 1360-Y grade (or, for that matter, anyone with 3423-O grade).

Sheldon
Click to expand...


I bought these same items from them last year for another amp, and they were both Y grade. Did you ask them to check their stock?

I'll leave it up to Mihai to tell you if it really matters what grade they are.

I didn't find their prices to be that bad, especially for small quantities and a minimum order of $15. Plus, they carry a large inventory. However, they are not a Toshiba authorized distributor. In my order last year, I got some Toshibas that looked rather dubious and didn't measure well. I called them up and they looked at their stock, and noticed the same variance in appearance. They made no bones about it and sent me another set of that item that appeared like real Toshibas, and they measured well when I checked them.

I never got the feeling they were trying to cheat me, and they immediately made good on it, so I have no complaints with them. I guess they are subject to the same sleaze as everyone else, but I don't know why they couldn't have avoided the problem if they bought from an authorized distributor.
 
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Sheldon

Member
Joined 2003
pooge said:
I bought these same items from them last year for another amp, and they were both Y grade. Did you ask them to check their stock?

I'll leave it up to Mihai to tell you if it really matters what grade they are.
Click to expand...

Yes, I asked. I also asked an outfit called Audio Lab, which had them listed in stock. They had the Toshiba 2SC -Y, but the 2SA were a Chinese copy. Nice that they were upfront about it.

I'd guess that the O vs. Y is not the biggest issue (though higher gain is probably a good thing). But it's gonna be hard to find matches for complementary pairs.

Sheldon
 
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m2003br

Member
Joined 2004
Don't worry about toshibas grade. here is a hfe overlap between O and Y grades, more chances to get a matched pair. But, for who I know about Toshibas, probably both stay at an hfe of about 150.

Farnell have Sanyo's 2SA1209-2SC2911, good for this amp, I guess. only little higher Cob.

cheers,
Marcos
 
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pooge

Member
Joined 2003
I've got a suggestion for mounting C1, especially if you can only locate rather long ones. You can nestle it on top of and between the smaller ps caps, and silicon it to the inside top edges of the PS caps. It shouldn't stick out as high as the big PS caps, so it won't look that unnatural. The leads could be bent down to connect to the output transistor base resistor traces running parallel to the outside edges of the board, at the middle transistor base resistor.

This could provide some damping effect for those capacitors, be out of the way of the access holes on the board for the driver transistors, shorten the average discharge loop path and take that loop farther from the input stage.
 
roender

roender

Member
Joined 2006
pooge said:
Mihai,

I'm trying to understand your ground layout, especially the use of 10 ohm R25...
Are you just trying to reference the signal ground to the preamp ground and break a loop from the preamp ground to the power amp supply?
Click to expand...

Yes.
Doesn't meter where compensation caps are referred, to dirty or input GND
If you don't use an integrated DAC or preamp, is a good practice to put two 1n4148 antiparallel diodes in parallel with R25. Think what could happen when R25 is interrupted ;)
 
W

wai235

Member
Joined 2007
2SC3423/2SA1360

roender said:
At 2.5mA, A1360/C3423 ft is three time over MJE15034/15035 (ft 50Mhz).
Increasing CFP drivers current will not bring big improvements unless other slave transistors are used as a1306/c3298 (ft 100Mhz)
Click to expand...


Mihai,

Is it good to use Fairchild's KSC3503/KSA1381 (F-grade) http://www.fairchildsemi.com/ds/KS/KSC3503.pdf instead of 2SC3423/2SA1360?

It offers good result in simulation!

Wai
 
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pooge

Member
Joined 2003
Re: Front End PSU

barryblue said:
Hi

I have nearly finished the BOMs now but am struggling to find suitable caps for C13 & C14 on the Front End PSU.

They are specified as 100uF 50 volt low ESR but have a small profile and 2.5mm pitch.

Has anyone found a suitable solution?


Thanks
Click to expand...

That is actually a 3.5mm pitch, and Nichicon HE and Panasonic FM fit in those values. But now they've been changed to 10uf a day after I placed an order?

Edit: Whoops! That IS a 2.5mm pitch. I better get this amp done before my eyes get any older! This may as well have been a SMD board!


roender said:
Barry,

Maybe is my mistake ... those caps are not 100uF but 10uF

Cheers,
M
Click to expand...

What would happen if 100uf is used?
 
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