OK.  So I think I'll go for the BUF634T.  This seems to perform better than the DIP8 package and allows the use of a heaksink.

  Quote:   I need to make a decision on the buffer to use.  I've done a lot of reading (perhaps too much) but seem unable to arrive at a decision.   If I go for the HA3-5002, this amp will, in terms of the schematic, be essentially a clone of the PPA V1 (Tangent doesn't sell these...

Quote: I've read elsewhere that a 5kHz wave is also recommended....especially for tube amplifiers.  Is there a reason for this?

I may have found the answer for this one for myself   I noticed on amb's site that he provides oscilloscope analysis for his amps.  When using square waves, he uses a 1 kHz, 10kHz and 100kHz square wave.  So, if my maths is right (and it often isn't)....     kHz    Time on (uS) ...

Finally managed to get into the LTSpice forum on yahoo and posed some questions around modelling my circuit and I've had a couple of replies.  While I don't doubt the expertise of these guys I am concerned that some of their suggested values for modelling the circuit are a little conservative...

Thanks, id.....er Prog Rock Man ;-)  I'm making progress but a lot slower than I would like.   Good to keep in touch.

Looking forward to the pictures of the build...

Thanks for your reply jcx.   I intend to use a DIP8 socket, so could switch to use a SOIC package using an adapter in the future.   I'd like to go with the separate buffer bacause, as you say, they are easy for beginners to produce something which sounds good.   As far as the...

  Thanks for your comments jcx     I'd like to stick to DIP8 and was considering the AD843.      Do they sound any good? I haven't come across too many designs using the LT1210.   PPL clearly rates the HA3-5002 very highly, esp with the AD8610. Presumably Tangent supports...

Quote:   Yeah...it's ugly ;-)  

Quote: Thanks Avro_Arrow.

Quote: From reading the various datasheets/application notes I don't think it's necessary to place resistors after or before the BUF634.  However, I'm happy to be educated.   C2/C4.  Agree.  But isn't 2200u a bit excessive?  I was thinking more along the lines of 100-200u.

  Quote:   Yes, it's the latter. I'm using LTSPice to produce the schematic and and do a bit of modelling as well. I know that there's better ways of representing a pot in LTSPice but fortunately, my efforts to join the Yahoo forum have failed so far. I sent off my email request but have...

Quote: Well, I was hoping to produce a single board which could be used for however many channels you wanted eg 2 for passive grounding, 3 for active grounding and 4 for balanced.  That was the aim.....but it would mean a lot of extra wiring e.g. for the pot. 

This is the design so far.      It's getting more complex than I would have liked and is likely to cost more than I expected.  Anyone spot any silly mistakes?    I think the design has a little way to go yet.  Clearly, I still need to consider the power circuit and I may have to...