AD815 preamp PCB group buy thread

[nickcase]

Carl - what's the dimension of the pcb?

[hacker]

It's 2.84" x 2.17", or 72x55mm in new money.

[Uzinusa]

pm sent re group buy. cheers, andy

[nickcase]

Cheers Carl.

Everyone paid up yet?

I've got a plan for where the first board is going to go now

[hacker]

Not everyone, still waiting to hear from 3 people and have assurances of pending payments from 3 more. After that, it'll be all systems go

I'm looking forward to doing a Starfish vs AD815 celebrity deathmatch!

[nickcase]

Starfish vs AD815 celebrity deathmatch!

Exactly what I was thinking!

A fully Wima'd, Traco'd, NERT'd, regulated Starfish will take some beating - where's my BFG Nuke kit ... ?

[hacker]

Originally Posted by nickcase

Exactly what I was thinking!

A fully Wima'd, Traco'd, NERT'd, regulated Starfish will take some beating

Damn right it will! I've been thinking about it, and in each channel of a fish-based system the signal goes through 4 coupling caps. Add in another 2 per channel from a CD player (DAC and output coupling), plus another in the power amp input and that makes for 7 coupling caps per channel!!

With the AD815 you can null the DC offset and reduce that count to 3 per channel which has got to have some great benefits. Much like the Starfish, it's also regulated and in many builds I'll bet people go for SRs or TeddyRegs instead of stock LM317/LM337 monolithics.

I suppose if you really wanted to, you could also do NERT tricks with the AD815. Like the Starfish, the AD815 has proper star earthing and very, very tight layout with components. I'm not for a minute suggesting that the layout is as good as the one Jiiim came up with (he spent a _lot_ of time making sure that the layout was optimised carefully), but the AD815 amp itself only has 5 components plus the opamp in the extremely short signal path.

All of this makes things very interesting indeed and the only thing I know for sure is that people who have both Starfishes and AD815 amps will have a pair of stonkingly good preamplifiers.

I've got a suspicion that the Starfish's bandwidth-limiting design (the HF roll-off) will make it a bit of a winner with Naim power amps that don't like a lot of HF. The AD815 isn't filtered at all, although it does have quite amazing PSRR at higher frequencies.

[neiljadman]

Originally Posted by nickcase

...Traco'd, NERT'd, regulated Starfish will take some beating

It may have already been done, I'm currently using an ESP +/-15v power supply and it's at least as good (better IMHO) as the Traco/NERT - more rhythm and firmer bass - same airy trebles.

I'm also in the throws of building a Sigma 22 supply - see Aidan's postings in the Starfish thread!

It's still going to be an interesting comp though!

Neil

[nickcase]

Very interesting Neil - I must check back into the Starfish thread

[new naim boy]

Originally Posted by neiljadman

I may have already been done, I'm currently using an ESP +/-15v power supply and it's at least as good (better IMHO) as the Traco/NERT - more rhythm and firmer bass - same airy trebles.

I'm also in the throws of building a Sigma 22 supply - see Aidan's postings in the Starfish thread!

It's still going to be an interesting comp though!

Neil

Yeah the sigma 22 powers my Starfish and my dodgy looking AD815 very well. I've now built three of these Amb power supplies. One supplies 5V to a SB3, which makes a huge difference to the stock PSU.

[jamadlavy]

Carl, you have PM, e-mails don't seem to get through

Eric

[new naim boy]

I changed two 100nf ceramic layer caps (which were placed about an inch from the chip) for two 100nf Vishay MKTs which are soldered right on the legs of the chip. The difference is quite amazing. There is now a lot more bass. The sound is simply superb.

Just thought I'd wet your apetites.

[hacker]

I meant to ask about that... what are peoples opinions on dielectrics for the 100nf SMD decoupling caps that are located a couple of mm from the opamp on the PCB? At the moment they're specced as C0G ceramics, but polyester films are available for the same price.

Anyone care to offer informed opinion? The caps are C1 and C3 in this picture:

[nickcase]

C1 & C3 look as close as you are going to get them really unless you nudge them both outwards a mm or two so that the tracks from U1 run vertically, might save a mm of track.

You really wanted to know about cap choice - totally unscientifically I'd prefer polyester film as they look nicer

[PigletsDad]

I would choose the one with lowest ESL; both will have low enough ESR that the resonance will be pretty lightly damped, so you want the inductance as small as possible, so it goes to the highest frequency.