Pedja Rogic Buffer and component choice for PCB design

[justblair]

Hi all

Apologies if this is answered in another thread, I have searched but I cant find what I am looking for

I am planning a pcb for the Rogic buffer and have to make a decision on component purchase. I've sourced the Jfets etc, but I am unsure what to use for the 1uf capacitor,



Most will be familiar with this circuit.

I have in the parts box 30 of 1uf 250v philips MKT type caps, but I not so sure that these are the best. I have also looked at various 63v MKT, MKS

Resistor wise I am guessing that 1/4w carbons will be fine, although I have metal films in the right values.

I plan to use box type precision trimmers in the R2 position

I have bought the sk170bl, J310 and Irf530 in bulks of 50, And was planning on ordering the same number of PCB. I need 4 for my current amp, 12 for my next project and a few no doubt to ruin.

I may be able to post off spare boards to others if this is not a problem for Pedja. Not a profit thing obviously.

In a future project I plan an active filter. I am sure that i have read somewhere that a discrete buffer can be used instead of an opamp, is this the case? Linkwitz reilly is whats on my drawing board.

Regards

Blair


Thanks in advance

[sidiy]

Hello,
Pedja might answer your questions in person here: http://www.diyhifi.org/forums/ Just register there and make sure to read the forum rules (no group buys...and that sort of thing ) He also has a website...you need to do a search.

About making a batch of 50 pcb using the exact number of devices... I think you need more FETs and MOSFETs because some matching is required.

Good luck!

[Nordic]

I have even bult it with a 1uf film cap that comes in those little yellow boxes... nice high voltage unit... cheap as chips... still sounded wonderfull in there...

Pedja Rogic's J-fet buffer for dummies.

[Nuuk]

And was planning on ordering the same number of PCB. I need 4 for my current amp, 12 for my next project and a few no doubt to ruin.

Why so many? You only need one pair of buffers per amp!

I would use a polyprop for the 1uF cap and after you have set the correct voltage for J2, replace the (multiturn) trimmer with a resistor.

Yes you can build an active crossover using discrete buffers instead of opamps. But I would say that using this design for each stage of a crossover though is a bit OTT! You can find a much simpler version used in the active crossovers shown here .

[justblair]

Originally posted by Nuuk


Why so many? You only need one pair of buffers per amp!

I have mission 753 speakers, there are 5 drivers per speaker. I thought it would be overkill fun to build up to a power amp per driver. So thats 1 buffer per amp.

My current amp has four power sections in it. Feeding the biamp speaker terminals on the missions. I would use this to test the buffer design.

Originally posted by Nuuk
I would use a polyprop for the 1uF cap and after you have set the correct voltage for J2, replace the (multiturn) trimmer with a resistor.

Can you suggest a part number so that I can find similar? Are there any small ones that are good?

Originally posted by Nuuk
Yes you can build an active crossover using discrete buffers instead of opamps. But I would say that using this design for each stage of a crossover though is a bit OTT!

There comes an economy of scale when building lots of the buffers, It seems a shame to go for op amps in the crossover if it is not too expensive to use discrete..

@Nordic. I will post a piccie of what I have. see if its similar to what you used.

I aim to factor a couple of cap choices into the buffer.

[Nuuk]

I have mission 753 speakers, there are 5 drivers per speaker. I thought it would be overkill fun to build up to a power amp per driver. So thats 1 buffer per amp.

Yes, an amp per driver, but you can drive them all from the same buffer!

My current amp has four power sections in it. Feeding the biamp speaker terminals on the missions.

Yes,mine too but with just the single buffer feeding both.

Can you suggest a part number so that I can find similar? Are there any small ones that are good?

Farnell order code 1215552.

There comes an economy of scale when building lots of the buffers, It seems a shame to go for op amps in the crossover if it is not too expensive to use discrete..

I agree but what I am saying is there are simpler buffer stages than this one.

[Nuuk]

How's progress with the buffer(s) Blair?

[r!sc!]

Boban

[r!sc!]

Boban

[justblair]

Hi NUUK

I am honoured you remembered me.

I got caught up in a measurement mic project which I will be completing the casework for this week, and a new dog who has been taking up some time.

However I just recieved a large order from Rapid where I sourced IRF510's from so I now have the parts to build the buffer.

I still have to source the caps. I have numerous 1uf polyester caps in my parts bins but only 4u7 polyprops. The X2 types.

My plan in my design though is to allow for various cap sizes so that I can try it out with polyesters but change over to something more exotic for my final amp.

I was reading this thread just a couple of nights ago. One comment that I do wonder about is the need for matching mosfets. I found instructions on matching transistors from the same batch ie 2sk170's but I am unsure how that applies to the buffers design as there is only 1 of each type in the design.