API 312 Thread!

Shop deals on ebay
Advertise with us
shop deals on amazon
GroupDIY Audio Forum

Help Support GroupDIY Audio Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
Hey everyone,

I'm building a pair of these and the BOM i'm using suggests using this selector switch:

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=71BDF30-01PAJS-ND

However, i cannot find any stocked anywhere. Does anyone know of a source or a replacement for this switch?

Thanks!
 
http://www.grayhill.com/wherebuy/where-to-buy.html

Grayhill sells directly to customers and through local sales representatives and distributors.                   

Grayhill                                                                                                                                                       

561 Hillgrove Avenue
LaGrange, IL 60525-5997
ph: 708.354.1040
fax: 708.354.2820

They are very nice and will help you.

GARY
 
You will find that hardly any place stocks Grayhill shorting switches (part# ending with S)
while the non shorting version of the same switch can often be had (part# ending with N)

Most folks, unlike us audio geeks, don't use switches for gain control (which alway need
the shorting type).. They just use cheeeeep old pots.

I've have received custom ordered Grayhill switches in 7 to 10 days in the past.

GARY
 
Hey Gary,

how is the grayhill-direct pricing compared to distribution channels? Do you have to buy large quantities?

thanks!
 
Stupid question time:  What's the consensus on voltage for an API style preamp with a 2520?  I'm running mine at 16vdc, but I heard today from someone I trust that it should be 24vdc.  That seems high to me.
 
b3groover said:
What's the consensus on voltage for an API style preamp with a 2520?  I'm running mine at 16vdc, but I heard today from someone I trust that it should be 24vdc.  That seems high to me.
Click to expand...

Whoever told you that seems high to me. just kidding  ;) The api 500 series racks run at +/-16v. I run 2520s at +/-15v because they are in my console and those are the rails that were already there. Also, I left out the diodes on the power rails, so mine are getting about the same voltage they would get with the diodes installed and +/-16v rails. Anyhow... +/-16v is great, +/-24v may gain you more headroom, but i'm not totally sure it's safe and that probably depends on the 2520 your using (i.e. burdij, api, sca, avedis, fabio, peter purpose, etc...) and the components it uses... but there is plenty of more in-depth information about it on the forum.
-Best, Ben
 
I wouldn't do it. Well, maybe on fourth of July. Original spec sheet says:

+- 12 to +-20

http://www.waltzingbear.com/Schematics/API/API_2520.htm

Maybe they've changed something in recent years, but I think I remember a thread when someone smoked their 2520 with too much voltage. Anyway, better safe than sorry, unless you have one around that you don't mind destroying for educational purposes.
 
Alright noob here with some 312 problems.

I'm building two channels of these right now. Here's the situation: Basically, i'm getting a hiss/buzz and no signal passing. I'm not really sure what's going on... it happens at different gain settings at random different levels. That is... its not just at high gain settings. It's happening in both channels. I do, however, get signal output when i insert the signal at the input transformer (i.e. after the relay...). It doesn't seem like the relay would cause a buzz like that.

If anyone has any ideas, i would greatly appreciate it.

By the way, i'm using peter purpose opamps (@ 16v) and cinemag trafos. Dunno if it's relevant/helpful, but the opamps were getting pretty warm to the touch.

Thanks!
 
hi,
without knowing what your input circuit is (you have not mentioned if it is going through some type of utilities circuit - relay based pad, polarity and PP) it would be difficult to guess what might be the problem area(s). 

if you are getting clean signal (and the rest of the pre works - i.e. gain adjust) when you inject the signal at the input transformer primaries, why don't you just inject the signal from the XLR input all the way through the audio path up until the input transformer primaries and see where audio appears.  i would think that it is most likely the component that the audio appears after.  simply put...circuit tracing 101. ;)  but you may have already done this, if so please disregard my post.
regards,
grant
 
Hey thanks, Grant.

I have been doing a little tracing and trying to figure it out and asking questions as well. Come to find out, i needed to bridge a couple pins of the i/p transformer, which i was unaware of.

So now it seems to be working great for all but the highest and lowest few gain settings. At which point there's alot of hiss/buzz and i think i heard some RF pickup too. Any ideas from here?

Thanks again!
 
hiss/buzz, both? 
are you sure it's not oscillation (lowest and highest gain settings makes me wonder)?  is there a ticking or motorboating sound with the noise?

if you still get RFI on the input even with the chassis cover on, you might want to try adding some ferrite beads to the leads on the hot and cold of the XLR connector.  i usually just use any small round ones and slip them over the leads coming off of the pin 2 and 3 solder cups. or you could use the ones with leads. seems to help.  purest may cringe at this idea though.

i think the 2520 DOAs are susceptible to some interference, but it's always been hum from the PSU transformer if anything in my experience.  i doubt its the noise problems you are having.

-grant

 
Yeah it seems to be both sometimes. A little 'motorboating' sometimes. It very well may be oscillation. I'm not sure what it sounds like tho haha. And i don't have a scope here with me so i can't really check. Should i try messing with the bypass caps to try and tame the oscillation?

I'm not really sure what else to do hah!

Thanks again for the help.
 
hi guitarguy,
it would be easiest to see if the signal is oscillating with a scope of course, but if you are hearing a putt...putt...putt... or a tic...tic...tic... it probably is oscillation.

raising the value of the compensation cap (i think that is what it is referred to as - can't remember).  i may be thinking of the melcor DOA (a 120pF - 220pF cap between the -IN and +OUT DOA pins?  search for oscillation on DOA cures), but you might try it to see if it works.  just use some alligator clips.  maybe go up in value if it doesn't cure the oscillation, but if you need to go beyond 470pF there might be something else.

are you adjusting your gain with a pot or a switch (i've used both a switch on my Reliquia 312 and 22K rev. log pots on my other units and only my switch had slight problems with oscillation on the highest setting).

also, if it is oscillation, make sure that all your audio runs are shielded cable with the shield grounded at only one side and keep the runs as short as possible - this might help.

regards,
grant


 
Guitarguy, make sure your preamps are star-grounded at one point, and make sure they are well shielded.

You could increase the value of the feedback cap, but this is a bit of a bodge and will reduce bandwidth. Also, depending on what transformers you areusing, you may want to fit a zoebel network to reduce transformer ringing (I had this cause oscillation before).
 
roddy is right.  increasing the feedback capacitor (that's what it's called - thanks roddy!) will limit your bandwidth.  i'd try using short runs of shielded audio cable first and see if that helps.
regards,
grant
 
Hey guys thanks.

I am using a selector switch for the gain. Also, the only cable runs are for the power... i'm using bicyclerecordings layout which has pcb mount xlr's. So i don't think there's much of a problem from there.

I haven't been paying too much attention to grounding, so i will make sure i have a solid ground scheme first and see what happens.
 
I'm just about to finish my fisrt two channels using a cinamag CMOQ-2 as an output trafo. I read a couple of times, that the color coding should correspond to the one on fabios board - has that been verified? I compared the schematic to the trafo-datasheet and it seems like the socend primary winding is used in comination with a secondary winding on the output side - does that make sense? I'm quite new when it comes to tranformers, so I'm wondering how the circuit works...

Thanks!
Christoph
 

Similar threads

frob
312 collected info, is this right?
Replies
1
Views
1K
soundguy
S
T
Calrec 1061 Filter Simulation - help needed.
Replies
7
Views
6K
TomWaterman
T

Latest posts

Back
Top