Prototyping a 100W CFB amp... - Page 2

sam9 · 27th November 2003, 05:18 AM

I know I'll sound ignorant, but what in the world are ALL those caps for?! I know what caps are for in an amp - but that just seems like an awful lot relative the remainder of the component count.

OliverD · 27th November 2003, 09:41 AM

Input, driver and output stage have separate supplies. This is needed, as the PSRR of a CFB input stage is horrible. Additionally, the opamp for the DC servo has its own +/- 15V supply. I first experimented with capacitance multipliers, but I found a simple R-C low pass works best. That's why I have so many caps. And component count is not that low for a 100W mono board. Including output devices, last time I counted I got 27 transistors

Compare that to an Aleph!

BTW, I'll be building three stereo amplifiers of this type together with a friend who'll be making a carbon fiber case

sam9 · 27th November 2003, 08:56 PM

Well, that makes sense. Interesting way to go about things. I would be interested to see the schematic if you get a chance to post it. Or can it be seen at another URL?

Also please post updates as you progress.

OliverD · 27th November 2003, 09:46 PM

Please understand that I cannot post the schematics as I received them under the condition of not posting them in the public. I already moved away from the original a bit (the PCB layout is mine) and probably will change some more things after experimenting, but I gave my promise about that.

I guess most of you can figure out the circuit from the principle schematic below (taken from Accuphase P-370 product literature). Another very similar design is the Elektor Giant 2000 (or whatever it was called in the English issue).

I will update the thread with new pictures when work progresses, and I intend the focus to be more on the mechanical part of the project. There are some interesting things to come

Blitz · 4th March 2004, 08:41 PM

Any news ?

OliverD · 7th March 2004, 08:53 PM

Blitz, just a short update. From an electronic point of view, there was no progress in the project since my last post, as I was very busy. However, I will have some spare time in March and April and I hope to finish this project. I do have a prototype case and heatsinks now.

Next week I'll rework the PCB. I was not happy with the grounding scheme although I didn't have any issues (when running only one channel from a bench PSU, that is). Also, I was not happy with some of the signal tracks. It seems to be a good idea to make a preliminary PCB and have a look at it some weeks later. Sometimes you see some very obvious way of improving things after a pause. With the prototype case at hand, it turned out the PCB can grow a bit bigger which makes life easier.

Stay tuned for some updates (and pictures) this month.

A fully discrete CFB balanced-in / balanced-out preamp will follow

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27th November 2003, 05:18 AM	#11
sam9 diyAudio Member Join Date: Jun 2002 Location: Left Coast	I know I'll sound ignorant, but what in the world are ALL those caps for?! I know what caps are for in an amp - but that just seems like an awful lot relative the remainder of the component count.

27th November 2003, 09:41 AM	#12
OliverD diyAudio Member Join Date: Nov 2002 Location: Germany	Input, driver and output stage have separate supplies. This is needed, as the PSRR of a CFB input stage is horrible. Additionally, the opamp for the DC servo has its own +/- 15V supply. I first experimented with capacitance multipliers, but I found a simple R-C low pass works best. That's why I have so many caps. And component count is not that low for a 100W mono board. Including output devices, last time I counted I got 27 transistors Compare that to an Aleph! BTW, I'll be building three stereo amplifiers of this type together with a friend who'll be making a carbon fiber case

27th November 2003, 08:56 PM	#13
sam9 diyAudio Member Join Date: Jun 2002 Location: Left Coast	Well, that makes sense. Interesting way to go about things. I would be interested to see the schematic if you get a chance to post it. Or can it be seen at another URL? Also please post updates as you progress.

4th March 2004, 08:41 PM	#15
Blitz diyAudio Member Join Date: Nov 2002 Location: Cologne, Germany	Any news ?

7th March 2004, 08:53 PM	#16
OliverD diyAudio Member Join Date: Nov 2002 Location: Germany	Blitz, just a short update. From an electronic point of view, there was no progress in the project since my last post, as I was very busy. However, I will have some spare time in March and April and I hope to finish this project. I do have a prototype case and heatsinks now. Next week I'll rework the PCB. I was not happy with the grounding scheme although I didn't have any issues (when running only one channel from a bench PSU, that is). Also, I was not happy with some of the signal tracks. It seems to be a good idea to make a preliminary PCB and have a look at it some weeks later. Sometimes you see some very obvious way of improving things after a pause. With the prototype case at hand, it turned out the PCB can grow a bit bigger which makes life easier. Stay tuned for some updates (and pictures) this month. A fully discrete CFB balanced-in / balanced-out preamp will follow

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