Cheap Nice and Funky Amek 2500 preamps

[saint gillis]

First of all here's the schematic :
http://sub-continental.com/diy/amek/amek_sch.jpg

 

[saint gillis]

I don't understand the ICs voltage charts, are they the voltages at the corresponding pins without the ICs on the sockets?

 

[ip_dalie]

First of all here's the schematic :
http://sub-continental.com/diy/amek/amek_sch.jpg

Thank you for the Schematic.
I'll try to learn how its work 

Ipin

 

[ip_dalie]

I don't understand the ICs voltage charts, are they the voltages at the corresponding pins without the ICs on the sockets?

Yer, on the sockets without all the ICs on, maybe I have to more into your schematic first to find out what happened. I just wonder how its happened? 
Sorry for the questions  ;D 
Thank you Saint Gillis

Ipin

 

[L´Andratté]

Saint gillis, just noticed the caps on the input are not back to back like they ought to be

ipindalieson
standard approach: inject a signal (could be sine wave) and trace it (with an oscilloscope) along the signalpath, where does it vanish? Is it present at the input, the output of the tl072´s, at the output of 5534, etc.
That gives an idea where to look---
Also you need to check the soldering at least thrice
That´s how it is, always a stupid mistake or a couple that needs to be found!

 

[moamps]

There is no need to have two electrolytic capacitor in series at input. Amek used it most probably because they used caps rated to 40V only. One 10uF/63V would be enough. Or you can try to use MKP 4u7/63V instead.
C12 is backwards in redrawn schematic, also why it is 220uF? Could someone calculate -3dB point when it is loaded with 10k pot?
@ipindalieson
Put in the socket only 072 and measure DC voltages on it and report back. Measuring voltages on sockets without ICs do not say too much.

 

[ip_dalie]

Saint gillis, just noticed the caps on the input are not back to back like they ought to be

ipindalieson
standard approach: inject a signal (could be sine wave) and trace it (with an oscilloscope) along the signalpath, where does it vanish? Is it present at the input, the output of the tl072´s, at the output of 5534, etc.
That gives an idea where to look---
Also you need to check the soldering at least thrice
That´s how it is, always a stupid mistake or a couple that needs to be found!

Thank you L´Andratté 

 

[ip_dalie]

There is no need to have two electrolytic capacitor in series at input. Amek used it most probably because they used caps rated to 40V only. One 10uF/63V would be enough. Or you can try to use MKP 4u7/63V instead.
C12 is backwards in redrawn schematic, also why it is 220uF? Could someone calculate -3dB point when it is loaded with 10k pot?
@ipindalieson
Put in the socket only 072 and measure DC voltages on it and report back. Measuring voltages on sockets without ICs do not say too much.

Thank you moamps 

 

[saint gillis]

There is no need to have two electrolytic capacitor in series at input. Amek used it most probably because they used caps rated to 40V only. One 10uF/63V would be enough. Or you can try to use MKP 4u7/63V instead.

This is exact! I didn't thought about that when I made the boards, it's not a problem though..

C12 is backwards in redrawn schematic, also why it is 220uF? Could someone calculate -3dB point when it is loaded with 10k pot?

That's right, it looks like a mistake, or maybe I've measured the polarities on my first board and found the output of the IC slightly positive, I don't recall. In fact with the 10K pot anything between 47µ and 220µ will give a decent low pass filtering and phase shift...

 

[12afael]

it seem that the gain cap needs to be low ESR.  I´m not being very scientific but I have seen low voltage, non polarized and many in parallel in that position.

Would be great to hear an explanation why.

 

[chilidawg]

Your version is a bit of an overkill with the additional output gain trim and the extra expensive differential output driver IC.

I have built almost a hundred channels for myself and my friends since I came across the schematic on Jakob's website a very long time ago. It's a very nice sounding mic preamp, cost only a few dollars (buy BC560C/2SA970GR in bulk quantity, then hFE matched them 10 pcs for one channel) and also very easy to troubleshoot/repair.

What I had done back then was to replace the 1KC pot with a 12 position MBB rotary switch with calculated resistor values that follows the reverse log (or for simplicity, a linear) pattern to cover the wide 60dB input gain range.

I also didn't change the output buffer (NE5534) after TL072, but simply add another 47R resistor to connect RING (TRS) or pin 3 (XLR) to the common ground for an impedance balanced output instead. However, if you insist on using NE5532, the 2nd opamp can be used to invert the signal for a differential output.

it seem that the gain cap needs to be low ESR.  I´m not being very scientific but I have seen low voltage, non polarized and many in parallel in that position.

Would be great to hear an explanation why.

Really? at the time I just used what I had in stock, a Chemicon SME (general purpose electrolytic) 2200uF/6.3V, and there was no problem whatsoever. Only for the recent ones that I built I used a low ESR Panasonic FC/FM because dude is so obsessed with them  ;D

 

[saint gillis]

Sure you can just make a simple impedance-balanced output with a single resistor!
Using a 2nd 5532 to make a balanced output is not a good idea, because if the negative pin of the xlr output is shorted to the ground you will get some horrible distortion.

 

[chilidawg]

Using a 2nd 5532 to make a balanced output is not a good idea, because if the negative pin of the xlr output is shorted to the ground you will get some horrible distortion.

Is that so? Then I guess it was silly for Jakob to do that with his GSSL output section either, not to mention a ton of other designers who also uses the same balanced circuit since the day it was invented.

And yes, I literally meant that as a sarcasm  :

 

[saint gillis]

Hahaha yes... that's how I understood what floating meant..

 

[ip_dalie]

First of all here's the schematic :
http://sub-continental.com/diy/amek/amek_sch.jpg

Finally it's finished. It was not working before because the ground pin on the PCB was not connected to the ground trace, silly me. Finally I found it!

Thank you Saint Gillis

Ipin

 

[saint gillis]

Cool !
Looks great

 

[geesara]

Hello there I like your premap and Amek m-2500 and I want to build one of these for my studio.

First I want to say I'm a noobie
1)My question is what is the difference of those 2 preamps ( Yours and amek one)?

2)What is the better one ?
Finding THAT ics are little bit difficult for me and I think building Amek one ( Gyraf schematic) is little bit easier for me.

3)If i'm building gyraf schematic Amek m2500 how do I add 48v phantom power ?

This is the link to the schematic.

https://gyraf.dk/schematics/Amek_2500_micamp.gif
4)I don't know how to read capacitor in thet schematic. What is the meaning of 10/40 ,
10/35, C12- 150p , 2200/6v3 ?

 

[nielsk]

Seems like a good use for a matched transistor array like the ones THAT makes... any reason why the balanced output can't be taken right off the TL072s? Looks like the 5534 is just making the output unbalanced to go on to the next stage. Other than that it is differential all the way through

 

[ip_dalie]

Hello there I like your premap and Amek m-2500 and I want to build one of these for my studio.

First I want to say I'm a noobie
1)My question is what is the difference of those 2 preamps ( Yours and amek one)?

2)What is the better one ?
Finding THAT ics are little bit difficult for me and I think building Amek one ( Gyraf schematic) is little bit easier for me.

3)If i'm building gyraf schematic Amek m2500 how do I add 48v phantom power ?

This is the link to the schematic.

https://gyraf.dk/schematics/Amek_2500_micamp.gif
4)I don't know how to read capacitor in thet schematic. What is the meaning of 10/40 ,
10/35, C12- 150p , 2200/6v3 ?

Hi Geesara.

I'm a noobie as well
1. I think its same design, I built them both, my Amek 2500's run balanced, and the Funky one's run unbalanced
2. They are the same IMHO, but I like the Funky's reaction to the signal, I don't know why haha
3. Try this Amek M2500 Build and Support Thread
4. 10uf (microfarad)/40v (volt) - 150p (picofarad)

Ipin

 

[geesara]

Hi Geesara.

I'm a noobie as well
1. I think its same design, I built them both, my Amek 2500's run balanced, and the Funky one's run unbalanced
2. They are the same IMHO, but I like the Funky's reaction to the signal, I don't know why haha
3. Try this Amek M2500 Build and Support Thread
4. 10uf (microfarad)/40v (volt) - 150p (picofarad)

Ipin

Thank you for replying.

Do you have the schematic for the black amek m 2500 that you built and posted.?