[fallout]

Well.. Might as well get it started!  :grin:  Here's the table of resistor values for a 24 position rotary switch. I was told you can skip ever other value if you want to use a 12 step switch. Here it is:

1 47k
2 36k
3 27k
4 22k
5 18k
6 15k
7 12k  
8 9k1
9 8k2
10 6k8
11 5k6
12 4k7
13 3k9
14 3k3
15 2k7
16 2k4
17 2k
18 1k6
19 1k5
20 1k2
21 1k1
22 910R
23 750R

Also, here's Bo Hansen's website that includes his DI mod for the API312 circuit as well as some other nice circuits!

http://w1.316.telia.com/~u31617586/

Keep 'em flowing!

-Jay

P.S. Does anyone have the info that was on the old archives that had inofrmation about putting a pot after the output transformer for an output control?

[Plexibreath]

That doesn't look right,  I thought the total value of the switch was supposed to be 25K.

On a related note,  is there a source for a good, right angle, PC mount 24 position, make-before-break, switch?  I haven't found any.  otherwise, what's the highest position count switch that's PC mount right angle?

Kelley

[fallout]

I mentioned on the old forum that it didnt look right, but I was told it WAS right, so.....  :cool:  Anyone have any insight on this?

-Jay

[jrmintz]

The 312s use 22K reverse log attenuators/pots, the 325s use 47k reverse log attenuator/pots.

[fallout]

Thanks for clearing that up Seth!

-Jay

[Plexibreath]

So I was confused in 2 ways, the 47K was for the 325, but I was thinking of a switch that would more resemble a pot with a wiper, where each click added another value in a long chain ending up with the total value of 25K.  But in this case, the switch is selecting a single resistor at a time, less resistors for the signal to flow through, but would you want a break-before-make or a make-before-break switch?  I would think the later.
Kelley

[gyraf]

Here's a good stepped-pot calculator:

http://www.quadesl.com/attenuator.html

Jakob E.

[fallout]

Thanks Jakob! That's a cool calculator! Is there any way to figure out a re.v log scale with that? I'm assuming the 3 tier option would be for a regular log scale? Thanks!

-Jay

[gyraf]

For a rev.log, you simply mount the resistors in the opposite order..

[Plexibreath]

How much attenuation is needed?  I understand of the 60db the 312 is capable of, a fair amout is acomplished by the 1:10 input transformer and 1:2 output transformer, how much is left that the opamp is actually doing?  I guess what I'm really trying to ask is with that step-up calculator, what number do I need to plug in for the Attenuation value?
Kelley

[gyraf]

1:10 equals 20dB

[jrmintz]

I could be wrong, but isn't the input transformer on a 312 1:8?

[Bauman]

At full gain you'll have Av= 1+20k/200 = 100, which is 40dB. Plus 20dB from the input transformer and 6dB from the output one.

"Sound is in the iron", right TK?

cheers!
Fabio

[Plexibreath]

I could be wrong, but isn't the input transformer on a 312 1:8?

I understand originaly they were 1:8, but I've been told 1:10 sounds punchier.  The Cinemag that everyone is talking about is 1:10.
Kelley

[Plexibreath]

At full gain you'll have Av= 1+20k/200 = 100, which is 40dB. Plus 20dB from the input transformer and 6dB from the output one.

"Sound is in the iron", right TK?

cheers!
Fabio

So the opamp is giving 40db, the transformers 26db, that means 66db, that's 6db more than I had heard the 312 puts out.
Kelley

[soundguy]

the 2622 was 150:10K

dave

[andre tchmil]

Hi,
have a question about the small caps for the 312 clone.
Is this ok for the220pF
http://international1.farnell.com/Search/search4-frame.jhtml?_DARGS=%2Fcommon%2Fprodsearchform_inone_dutch.jhtml

and for the 1000pf.
http://international1.farnell.com/Search/search4-frame.jhtml?_DARGS=%2Fcommon%2Fprodsearchform_inone_dutch.jhtml

Are these types ok to use?And is 1000pF the same as 1.0 Nf

[fallout]

Those links dont open up a specific product page..

-Jay

[andre tchmil]

ah ok:
Ordercode:747-099 and 746-990 and the 1000pf = 748-353 but it is valued as 1.0 nf !!!!

[Bauman]

Ok, this question is for those that are using the APIs on studio...

During a test on a friend's studio, I've notice some limitation on headroom of my API stuffed with Melcor opamp. I've seen that people used to have a pad on input (Brent Averill included), which I don't used to have on my micpres. PSU on my case is +/- 15V.

So do you think going +/-20V will be enough to prevent that limitation or I really need a pad on the API micpre? :?  Maybe 2520 opamp can handle more at input?

thanks a bunch for any clue.

cheers!
Fabio

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