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Old 28th March 2011, 03:58 AM   #1
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Default Modding my Old Mixer

Hey guys,

I am new to this board and somewhat to modding (not engineering though.)

Now, I found this old and crappy Samson MDR10 mixer and an idea sparked in my head. I want to switch the 4580 JRC op-amps to NE5532s and thatís not a problem. What iíd like to do is mod the EQ to sound and perform better. What modifications could I do to enhance an EQ section?
Iím painting the chassis and pretty much redoing this small console.

Thanks,

Louis
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Old 28th March 2011, 06:10 PM   #2
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Without knowing what exactly is inside it is hard to tell you what to improve. The usual suspects are power supplies, potentiometers, switches, connectors.
Replacing op amps with others is usually only useful, if you adapt the surrounding circuit accordingly.

What is it exactly that annoys you about the sound?
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Old 28th March 2011, 06:37 PM   #3
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If you want to experiment with opamps perhaps fit sockets and try the NE5532 and also some less obvious ones such as TL072 (really) and if you like those then try something like the OPA2604. The LM4562 is the successor to the NE5532.
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Old 28th March 2011, 08:30 PM   #4
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I did that to my fostex 450 mixer and it sounded great!

It was quite a job,it was.

I had to first clip the old chips out ,then yank each pin out and clean each hole seperately inorder to not destroy the board.
And then I installed sockets for all 32 (aprox) of them.

Tedious but it was well worth the effort as it was marginaly worth recording with stock.

I tried both the TL072 and NE5532.
The NE5532 would not work properly in the filter sections as they turned into oscillators for some reason,but they worked fine in the line sections.

So I just stuck with the TL072 throughout the board and the sound was transparent and had no noise.

Seriousley,It rivaled my mackie 32-8 in an a/b comparison.

I just read on a pro recording forum that the OPA2604 was the best to date for audio,but,I personaly don't have any experience with that opamp yet.

I hope this helps you. jer
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Old 28th March 2011, 08:46 PM   #5
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What exactly are you wanting to do to the filters?
As their center frequencies are where they should be musicaly.
Except that the midrange could be shifted up a bit IMHO.
That could probably be done with a simple resistor change.
Do you have the scematic? jer
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Old 28th March 2011, 09:18 PM   #6
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Thanks guys,

I don’t have the schematics yet, but i’ve taken it apart and studied it. I’m trying to learn as much as I can of the board for now, so thanks. I might go with the OPA2604 or the NE5532. I’m used to recording and mixing on Neves and SSLs, so when I found this old mixer I decided to give it a new engine if you get what I mean.
It’s a small project, just 10 channels, so it shouldn’t be too hard.

So what you guys are saying is that if just by replacing the op-amps, the whole board would sound that much better? EQs, Filters, Inputs, etc?
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Old 28th March 2011, 10:13 PM   #7
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Quote:
Originally Posted by lrichner View Post
Thanks guys,

I donít have the schematics yet, but iíve taken it apart and studied it. Iím trying to learn as much as I can of the board for now, so thanks. I might go with the OPA2604 or the NE5532. Iím used to recording and mixing on Neves and SSLs, so when I found this old mixer I decided to give it a new engine if you get what I mean.
Itís a small project, just 10 channels, so it shouldnít be too hard.

So what you guys are saying is that if just by replacing the op-amps, the whole board would sound that much better? EQs, Filters, Inputs, etc?
LM4562 Input Preamp
TL072 Filter section
LM4562 Output Stages

5532 might not work in preamp and will oscillate in the filter section.

Change any electrolytic capacitors to film types where possible, but absolutely replace the input pair at each mic preamp.
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Old 28th March 2011, 10:57 PM   #8
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Oh yes very much so.

Very good advice on the caps.

In my a/b comparison the one thing that didn't let it top the mackie was a very slight lack of punch on the low end with precussive instruments but it was only noticeable because of the comparison test.

Otherwise it was perfect.

And my guess is that it was due to the caps.

But I didn't get a chance to try different ones and I don't have that board anymore. jer
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Old 28th March 2011, 11:11 PM   #9
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Old mixers usually have scratchy pots, so that would be my first point of attack.
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Old 29th March 2011, 06:19 AM   #10
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Also, if there are a lot of opamps remember that the current requirements add up so check the data sheets and make sure it all falls within the supply capability.

Twenty 4558's will run happily from a 78L12 79L12 supply, twenty NE5532's will not.

The OPA2604 is a personal favourite, particularly in CD player output stages or I/V conversion from a DAC.
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