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AD815 preamp build thread

laverda said:
ron

I'm not using any coupling caps on my bugged 815 at the mo....but have implimanted the nulling circuit......

I'm going to try the PFM without the nulling, the power amp input cap should block off any mVdc its only about 50mv IIRC.

Graham
Click to expand...

What are you using for your pot/source, and how are you protecting that from the DC offset?
 
Graham,

I really am going to have to buy one of those attenuator boards...next month!

I suppose that the layout is something like this (me being dumb with impedence and all things electronic).

source -> pot/attenuator -> AD815 -> Amp

Thanks.
 
chiily said:
Graham,

I really am going to have to buy one of those attenuator boards...next month!

source -> pot/attenuator -> AD815 -> Amp

Thanks.
Click to expand...

Thats all I use.......the nice bit is that the attenuator's 'resistance' does not change with gain, unlike a wiper type pot.....;)

Graham
 
Hi everyone

Does anybody have any nice pictures of the KIT 3 that they could share....I would like to see what it should look like.

Can't post photo's of 'my effort' at the moment...computer does not show digi camera connected :confused: (PFM question on photo thread)

regards

geordie
 
Yes please from me too. In particular, what goes in R13 and R14? I think it must be the two spare 100ks I have left over which are down as R11 and R12 in the "don't use" BOM. But I'm not thats sure.

And another thanks to everybody involved in putting this group buy together - much appreciated and fun to put together so far. Struggled a bit on R5 and R10, but fingers crossed.
 
My thanks for Neil and Carl for putting this together.

Thought I'd show off my SMD soldering skills. This is a kit3 but without the local regulators being installed, well only the resistors. I'm going to try a couple of ALWSRs and then the local regulation.

DSCF2546.jpg


Better focus, but flash.

DSCF2543.jpg


DSCF2547.jpg
 
chiily said:
My thanks for Neil and Carl for putting this together.

Thought I'd show off my SMD soldering skills. This is a kit3 but without the local regulators being installed, well only the resistors. I'm going to try a couple of ALWSRs and then the local regulation.

DSCF2546.jpg


Better focus, but flash.

DSCF2543.jpg


DSCF2547.jpg
Click to expand...

Nice work indeed but a note of caution........you should solder all the legs of the AD815 chip to the PCB, thats how the heat generated by the chip gets shuntted away (via the copper plain) on the PCB.

Graham
 
Ah, maybe it's not clear in the picture, but all the legs have caught the pads. It does look like they have missed. There is a very small pool of solder around each leg...not that I've powered the board up yet. I may be proved wrong!
 
andrewhockley said:
Yes please from me too. In particular, what goes in R13 and R14? I think it must be the two spare 100ks I have left over which are down as R11 and R12 in the "don't use" BOM. But I'm not thats sure.
Click to expand...

You've got it exactly right, the 100K resistors are for R13 and R14 when using output coupling caps. Kits 1 & 4 don't have these.

Nice work everyone, you've certainly been quick off the mark! I'm so glad that we've got at least one report of a working (and decent-sounding) amplifier :D
 
chiily said:
Ah, maybe it's not clear in the picture, but all the legs have caught the pads. It does look like they have missed. There is a very small pool of solder around each leg...not that I've powered the board up yet. I may be proved wrong!
Click to expand...
Nice work but some pins have not much tin.
 
Quick update on how the PFM AD815 sounds ......:)..:)..:D

(KIT2 format (4.7 Caps to knock off the DC)) using ALW sregs at +-15vDC.

Concerns about heat are unfounded, runs warm at this voltage (not much cooler at +-12vDC if at all.) but is ok after two days burn in.

Sounds fantastic..........there's just a tad more midrange texture/detail (a good thing) and more weight in the lower registers, compaired to the bugged version I've been listening too for the past two years.

This is only slight but detectable and an improvement.

Looking forward to some tweeking.......

Graham
 
I was wondering if a 56uf Oscon SP or a 100uf Rubycon ZA would worth trying instead of that 68uf decoupling cap.

I was also thinking about trying a 100nf polypropylene instead of the polyester on the output of the regulator (only applies to people using the on board regs)
 
hacker said:
That's great news! Are you using input and output coupling caps, or just one or t'other?
Click to expand...

At this stage .........


is using both input and output 4.7uf caps supplied............so there should be improvments as we replace the input caps with the nulling and further gains removing the output caps having the power amp input cap to do do its work there.

Graham
 
fatmarley said:
I was wondering if a 56uf Oscon SP or a 100uf Rubycon ZA would worth trying instead of that 68uf decoupling cap.

QUOTE]

There are 100uf ZA's in my bugged 815 which work very well IMO. Always worth trying something differant though (just in case) I never bothered trying others cos it was so good.

Graham
Click to expand...
 
I used two 33uf tants in parallel in my bugged version which also sounded very good. I will definately be trying them again in the new amp.

I also want to try 0.1 MKTs soldered right on the legs of the chip instead of the SMDs. I originaly had 0.1 ceramic layers which were about an inch from the chip. The MKTs placed on the chip itself were an obvious improvement.
 
I remember in the huge thread on the other forum that Carlos said caps less than 68uF were fine, but anything bigger ruined the sound. YMMV.
 
Nothing to report on mine yet, soon as I get a pot I'll give it a try
Coupling caps I used are 3.3uf input and 10uf output, the 620R resistor in the feedback is a minimelf.
If the nulling works well the caps can easily be removed and linked out
DSCF0476.jpg
 
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