312 Replica project

Hi all,

I've been picking away at this 312 replica for quite a while, and I can't wait to hear it. I haven't had as much time to concentrate on it as I'd like because there's that unfortunate thing called working...

This is based on the scans in the 312 meta, Sowter input transformers and Tommytones' output transformers. I don't think a high-quality preamp project could get much simpler than this. That's a pair of NOS 2520s that have been lying around my house for years.













This is a pair of 22k reverse-log 24-step attenuators from a Marchand Electronics kit. They'll do custom values and tapers. Nice folks. And, of course, my namesakes.



I'm going to use Peter Purpose's relay and switchboards, and SSLTech's psu design. It's truly a Lab project. Now I just have to write a good song...


:guinness: :sam:

looks nice. how did you print the traces? looks pretty homemade.

know of any places to get 2520's other than canabalizing or ebay'ing?

It's totally homemade - press 'n peel. For something this simple with big traces it's very good. I'm afraid I don't know of anyplace to get 2520s except API. John Hardy 990s are excellent, Fred Forssell's opamps are excellent, I hear JLM Audio's are excellent. Somewhere in a thread I don't remember the name of, someone pointed out that the choice of transformers is more likely to characterize the sound than anything else. I expect you could do very well with any of those.

:thumb:

Nice! Your in for a treat!
:guinness:

Dan Alexander wanted $75 ea last time I asked about 2520´s.

Also, check the Seventhcircle new 2520 clone, and the Avedis one also (forgot the number).

Or...

DIY a melcor 1731 or even a 2520. Not hard at all.

The last sounds the best option for me.

I think the Avedis is the 1122. IIRC they were $75 when I last spoke to him.

Correct, it's 1122, I paid them $75... Can't wait to try them, I'm waiting for the output trafos from Tom.
I want to build also the melcor and the 2.5.2.0 and do some comparisons but didn't find the plans/schems for the latter as I've not been around here for some times, can anyone point me to them?
Thanks,
Frank

FrankSL,
you mean this? sorry if its wrong. just saw it on Dan Alexander's site:
http://www.danalexanderaudio.com/ApiInfo/api2520_02.jpg

Nice one Seth... :thumb:

Nice Seth! I´m also in love with API right now.

I did some boards for 2*5*2*0...


original layout and parts


original layout, substitution parts


original layout, different one with mixed parts.


Didn´t test them yet.

If someone want I can post a ready-to-transfer PDF with the layouts...

cheers!
Fabio

Fabio.... you tease..!!

Seth,
I'm slightly worried about the 48V grunt of Keith's supply for running the relays. Check with him to see if all is OK.

peter

Ay, Ay AY......!!!

Don't be Staaaartin' mate! Seth, you can probably run 24V relays from the unregulated inputs to the regulators on my PSU, there certainly shouldn't be any real need to use 48V for the relay coils. -Using unregulated DC will keep the regs themselves cooler also. :grin:

Top work Seth, Nice going Fabio! -This is all starting to look very nice indeed!

Keith

This is a pair of 22k reverse-log 24-step attenuators from a Marchand Electronics kit.

Click to expand...

Hi Seth,

Nice project and, ooooh, I love those attenuators!!!
I am waiting on my toes for Fabio's *2*5*2*0* boards too.

Tamas

Fabio,
It would be great if you could post that pdfs, schematics also if possible (for parts numbers, etc), many thanks...

Asm, I'm looking for opamp schematics and eventually layouts, thanks anyway,

Frank

Ok some folks are asking for the PDFs. Since there´s 3 type of 25yaknow and 1 Melcor, I´m thinking about 5 files, 1 for each opamp arranged on pannels and 1 with all of them, let´s say 2 of each, depending on the size of the panel. :?:

Since I dunno the size of the baords you guys buy , I´d like you to tell me
a good pannel size. Maybe eurocard size (160x100mm) will do for everyone?

Oh, I need to know also how much space between the baords is good to you to separate them...

lemme know.

cheers!
Fabio

I think eurocards are ok, I would also include a page with only one layout in case someone (no, not me... :grin: ) wants to make only one piece as a trial...
Frank

Thanks guys. This is a great thread - it'll be good to see all this stuff up and running. I'm going leaf-peeping this weekend - volts will not be in my vocabulary. I'll check out the relay voltages when I get back.

So Keith, you're saying use the unregulated but filtered 25 or so volts coming off the 18V transformer to power 24V relays? Will the over voltage be a problem or should I lower it to 24V with resistors?

:thumb: :guinness:

Seth,

They'll usually work fine, but if you have any doubts, stick a small resistor in series with each relay coil. You might have to try a couple of values to see how much is about right.



Keith

I'm still in doubt about the R4 and the C5.

1. what's the value of R4 and what type of C5 ?
2. Are they needed ?