API 553 PCB

[Strawtles]

Hello, can anyone help me to find the PCB design of the original API 553 eq module?

 

[gar381]

Maybe this will help!

This is the Datatronix copy machine shot of an unstuffed one.

Have fun!!

 

[gar381]

And this...

 

[Strawtles]

Thank you!!!
Is it possible you have a clear schematic?
In the one I have found there are some components incomprehensible

 

[gar381]

Checks Jeff CAPI site....

http://www.classicapi.com/catalog/images/reference_docs/API-553-schematic.pdf

Best copy I have seen.

Any questions on unreadable part values I can help you.

Best

GARY

BTW... Build yourself a CAPI 553f.  It;s better than the orginal

 

[Strawtles]

Thank you Gary
This schematic is better than mine, but still there are some value I am not too sure:
R9= 1.3k?
C5= 500uF 6v?
C6= 47uF 10v?
C9?= 5uF 6v? (the one after R1)

Do you know if it is possible to change the mid frequency control to 3Khz?

P.S.
I have considered the possibility to build the 553F but I'd prefer to try the original and simpler one

 

[gar381]

Thank you Gary
This schematic is better than mine, but still there are some value I am not too sure:
R9= 1.3k?  YES
C5= 500uF 6v?  YES..but use 560uf / 16v
C6= 47uF 10v?  Yes but use 47uf/16v
C9?= 5uF 6v? (the one after R1) Yes but use 47uf/16v.. less cap values to order

Do you know if it is possible to change the mid frequency control to 3Khz? YES.. change the value of C8
use a freq calulator      http://circuitcalculator.com/lcfilter.htm  (approx .028uf)

P.S.
I have considered the possibility to build the 553F but I'd prefer to try the original and simpler one
This is a 553 with some VERY useful filters added.

 

[Strawtles]

Thanks a lot Gary!

Do you think I can use a 10k:10k (Lundahl LL1540) transformer for balanced input?

What do you think about the Lundahl LL1539 as output transformer (I have a couple of these transformers at home)?

Finally, can you suggest to me some good inductors?

 

[Fablab]

Some years ago I realized an API 312 clone using the Lundahl LL1539 and it sounds good, but I can't confirm if it works in this project too

 

[jensenmann]

Lundahl cores have higher nickel content than the API output tranny. This will give you less distortion at lower levels. You can see it in these graphs: Nickel has a more linear range than iron.

 

[Strawtles]

It sounds as Lundahl is better ... but the ratio is different
API 2503 = 1:3
Lundahl LL1539 = 2:1+1; (1:1)

 

[Fablab]

In my API 312 clone I have configured the LL1539 in this way:

Wired pins 2,4,5 to +P
Wired pins 1,3,6 to -p

Pin 8 to +S
Pin 12 to -S

Join pin 7 and 11

 

[Fablab]

Gary is it possible that in the PCB design there are some missing parts?
Comparing the PCB with the unstuffed PCB photo it seems that the PCB is missing of the R13, C3 and R3 joining place and the C5, R11 connections to the transformer input
Anyway, I am interested to realize a couple of these circuits too

 

[Strawtles]

Thank you for the help Fablab 

 

[gar381]

Gary is it possible that in the PCB design there are some missing parts?
Comparing the PCB with the unstuffed PCB photo it seems that the PCB is missing of the R13, C3 and R3 joining place and the C5, R11 connections to the transformer input
Anyway, I am interested to realize a couple of these circuits too

Hi Fablab

These attachments are of real Datatronix PCBs that I scaned myself about 6 years ago.
I stuffed them and used peterc's 5003 Inductors. They sound GREAT.   In the next few days
I'll pull one out of the rack and see if I can answer your "missing" questions.  I stuffed
these guys years ago and can't remember if there were any  problems/mods that I had to do to
make them work.

Best

GARY

 

[Fablab]

Thank you very much Gary. Your help will be very useful for the realization of these equalizers

 

[Strawtles]

Thank you Gary!

 

[Walrus]

Picture of one of our 553's...

 

[Walrus]

Other side.

Note, R13 has been lifted on ours to remove the function of Gain Trim.

 

[mitsos]

Is everyone able to download these files?  For me they all seem to stop halfway. 

Edit: ok weird, it works on my phone (android) but not laptop (mac).