Category 5

Different Op-Amps for different sounds (discrete type)
« on: August 05, 2004, 12:55:44 AM »
Please forgive me for jumping right in.  I am new here and a bit of a novice in this realm.  I am glad to have found all of you to learn from!  Hopefully this time next year I'll be helping other noobs get started.

In the mean time, I have decided to build a pair of Seventh Circle A12 mic pres.  The kits look very simple based on my intermediate soldering and electronics skills, and I think they'll make a great first project.

I have experimented with my P r e s o n u s MP20 by replacing the input trannys with the Jensen parts (originals were generic) and also replacing the 5534 chips (Phillips type which I understand are the best) with Burr Browns and Ad797s.  I found the Jensen/AD797 combo to be the best sounding and have left it at that.

Now I am doing the A12 and want to substitite a real 2520/990 type op-amp for the included chip based dughterboard.

My first choice would be a real 2520.  I could buy some A-P-I line cards from a local electronics guy and sacrifice them for the op-amps (and save the trannys for a future project).

How would you describe the difference in sound between the various generations of 2520?

My other choices would be Millennia's M99, The Forssell 992, the John Hardy 990, the Avedis (Brent Averill), or even the OSA (are these available?).

What kind of differences in sound can I expect?  I know your opinions are subjective and will be very general, but as of right now I have NOTHING to go on.

My only 2 preamps currently are the modified P r e s o n u s MP20 (which is actually quite nice) and a new G-r-e-a-t River MP-2NV.  I am just looking for new flavors, and thought it was a great opportunity to get my feet wet with a real full kit.

I believe the kit uses a Cinemag CMMI-8-PCA input tranny and a Profile output tranny that are said to sound very close to the original API parts.  Since the power to the op-amp is variable from +/- 15v to +/- 35v I can use any of the above op-amps without problems.  What should i try?

Thanks!  I hope to eventually become a contributor to your community.  Until then, please offer any help you can and thanks in advance!

Shane


Kev

Different Op-Amps for different sounds (discrete type)
« Reply #1 on: August 05, 2004, 03:31:12 AM »
This kit will probably slot neatly in between the PreSonus and the Great River ... with any of the gain blocks you choose.

Use what ever you can get .. including a JLM99v.
Be sure to double check your rail voltages before you plug it in and experiment you heart away.

Then let us know what you discover.

You could always try one of the gain block PCBs talked about here at the LAB.

Melcor 1731 ... thanks Pete C

A very well known unit ...
one option with original parts
and one option with substitute parts .... thanks Fabio

I'm sure someone else was working on a new unit - a FET gain block and PCB ... Frank , Thomas ??
Kev
DIY Factory

Category 5

Different Op-Amps for different sounds (discrete type)
« Reply #2 on: August 05, 2004, 09:26:11 AM »
Quote from: "Kev"

A very well known unit ...
one option with original parts
and one option with substitute parts .... thanks Fabio

I'm sure someone else was working on a new unit - a FET gain block and PCB ... Frank , Thomas ??


Where can I find information on these, especially the option with original parts?  I am definitely too new at this to make my own PCB, but if they are available with some pictures, maybe even a good parts list (dare I hope for some type of instructions) I would love to try some!

What do you do about the epoxy?  Is it needed only for securing circuit design, or is it essential for effeicient heat dissipation of the components?

Shane

dale116dot7

Different Op-Amps for different sounds (discrete type)
« Reply #3 on: August 05, 2004, 09:37:03 AM »
Thermal matching between the two input devices is critical, so the epoxy helps there. Unfortunately, it also increases thermal transfer between the output and input devices (which you don't want). That's why there's a LM394 matched pair on the Jensen JE990. If you're using that part, I'd skip the epoxy for now.

Bauman

Different Op-Amps for different sounds (discrete type)
« Reply #4 on: August 05, 2004, 09:46:37 AM »
Don't forget Peter P. here Kev, great partner on this matter...  :sam:  :sam:  :sam:

Soon we'll  have some 2520 impressions all around.

cheers!
Fabio
cheers!
Fabio
_____________________
www.thediypill.com/store

Category 5

Different Op-Amps for different sounds (discrete type)
« Reply #5 on: August 09, 2004, 07:19:53 AM »
How would you go about potting the modules once they are done?  Is there someplace that the epoxy can be gotten "pre made" or is it something you hve to ccok up yourself.  i assume it is important if it helps to dissipate heat from the mounted components.

Shane


 

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