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AD815 preamp build thread

Shouldn't the pot be 20k? That's what i'm going to use in mine.

My boards completed. Just need to put it in the case and wire it up.

Does anyone know what would be a safe, maximum, DC offset?
 
I believe the max value of the pot should be 20k. Apparently 10k - 20k is specified, and the higher the impedance then the higher the dc offeset.
 
Superb work ron - every joint looks perfect.

Anyone got a spare AD815 chip they are willing to exchange/sell? I can't get building yet :(
 
Hi Everyone,

First, a big thanks to Carl and Nick for making this project possible for me. And of course to Carlos FM for his work on the original concept.

I've stuffed my board, but need to sort out the power supply. I think I'll end up using the +-30VDC one from my Pass D1 IV Stage project for the time being. I wonder if it'll drive headphones???

AD815a.jpg




Cheers

Jon
 
Hmmm, Nick, I was hoping to mail you out a spare AD815 as I was sure I had one. Unfortunately I can't find any of them at all after the last house move & they're not available as samples from the analog website anymore, shame.

Sorry,

J
 
I notice the regs are set to output about 18 and a half volts +/-, bit high IMO so I'm going to change the 3k3 to a bit lower
 
I went with Carlos' design as much as I could, but I agree 18V is a bit high. For those who'd feel more comfortable using the AD815 datasheet recommended voltages, swapping the 2 3k3 resistors for 2k67 resistors will give +/-15V.
 
ron said:
Ignore me Carl, just me being over cautious :D
Click to expand...

I think your right ron. I run mine at 15v with a large copper sink and that gets warm to the touch, so the area on the PFM board will be warmer (not sure how one guages this warmth though.)
 
I put a large chipset cooler od an old mobo on my chip, thats gets pretty warm. You guys want to think about heatsinking other than just the designated pcb tracks.

phil
 
I use ALW sregs they work very well with this chip at + - 12vdc, but I'm not sure about Teddy Regs. (I'm commited to SR's.) I would think a pair of Teddy's would do nicelly though.

I know many here love them, so one of these nice chaps will be along in a short while and promote / explain. Come on chaps.

Graham
 
I have been listening to this preamp every night this week. :)

I don't know whether it's just psychological but it seems to improve each night. :D
 
laverda said:
Is about as 'lean' as one can get (sregs are required).
2405104109_60fb86a706.jpg

Power up and bench test tomorrow
Click to expand...

Nice work Graham, but you'll need caps or links in C6 and C8 to get any sound out of it ;)

It just so happens I've got a couple of preconfigured +/-15V ALWSRs upstairs that I'll be using with mine... whenever I get a chance to build it. Work and life just seem to get in the way of hobbies :D

Edit: I've just noticed you're using links instead of output coupling caps. In this case, Carlos omitted the pull-down resistors (R13 and R14 on the PCB) from his diagram:

cfmad815preampcomplete_rev1.jpg


I'm not sure what, if any, difference will be made...
 
I just need a vol pot and then it can be tested.
Going to use the standard onboard regulation for now, if it all works I might then add ALW's
 
Thanks Graham, last one I lashed up point to point used ALW's for the convenience, these pcb's are nice and compact

I now have the regs set at +/-15v

You going to use coupling caps with yours and without the nulling circuit?
 
ron said:
You going to use with yours and without the nulling circuit?
Click to expand...

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
 
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