Replacing VTB1 Opamp?

I'd imagine the DAV guys would know a lot about the layout of ultra cheapo mic pres like Behringer and Studio Projects. Seeing as how they've basically been reverse-engineering them, putting them in cool-looking boxes and slapping a DAV logo on them.

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chessrock said:
I'd imagine the DAV guys would know a lot about the layout of ultra cheapo mic pres like Behringer and Studio Projects. Seeing as how they've basically been reverse-engineering them, putting them in cool-looking boxes and slapping a DAV logo on them.

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wow, if this isn't actually true, is that libel?:confused::eek:
 
Hi,
I recently finished my first Green Pre. It sounds very nice. I have tried it with 5532 and opa2132. I recorded with both setups, and cross-listened. Both sounds nice and clear. I find it very hard to really hear the difference though. Would a OPA 2604 be worth trying in the Green Pre? Do you know how to test for distortion etc? Are there any softwares for this?
I have two OPA2604 in my ART Tube MP (I replaced the TL072's). It sound really nice now.

Best regards

Sunyata
 
Thanks!
Interesting software! I tried it quickly. How do you know what results depend on the soundcard and what on the mic-pre? Is it possible to calibrate for the soundcard?

Sunyata
 
sunyata said:
Thanks!
Interesting software! I tried it quickly. How do you know what results depend on the soundcard and what on the mic-pre? Is it possible to calibrate for the soundcard?

Sunyata
Click to expand...
Obviously if you use software then you're always going to be relying on your converters to get a signal out to whatever it is you're testing. I'm just a hobbyist and if it sounds good I'm not too bothered, I just use RMAA for a sanity check and to make sure nothing's really out of whack.

If you want good accuracy then get yourself a hardware signal generator and a scope.
 
Hi,
here's a short sound-clip. Acoustic -> ADK a51 -> Green Pre -> Soundcard -> Cubase (reverb plugin):

 
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sunyata said:
Thanks!
Interesting software! I tried it quickly. How do you know what results depend on the soundcard and what on the mic-pre? Is it possible to calibrate for the soundcard?

Sunyata
Click to expand...

You can test a converter for noise and distortion the same way you test a preamp. But you should be able to rely on your converter's specs. You can also use your PC & soundcard as a signal generator to test a preamp. A straightforward way to calibrate that is to loop the output straight back to the input and measure.

When you are testing a preamp, you are mainly concerned with distortion and noise specs. Preamp noise is measured as equivalent input noise (EIN), which is output noise less gain. You can measure the amount of gain with your converter (comparing to the converter loop). A good preamp would have lower EIN than many converters can manage, but if you add a minimal amount of gain (say 20 to 30dB), then the output noise of the preamp should exceed the input noise of your converter, and can thus be easily measured. The standard measurement for noise uses a 150 ohm resistor connected to the preamp input, and then the thermal noise of the resistor is subtracted. The resistor's noise is very low, so you can probably safely ignore that step in your noise analysis.

Distortion is much simpler, just use a multimeter to calibrate the output level of the converter's test signal (1VRMS would be a standard) and send that to your preamp. If the preamp has too much minimum gain (which you measured above), it could be too hot of an input signal, so attenuate the converter output until the preamp doesn't clip. Then you know what maximum input level of the preamp is. Typically this would be stated at 1% THD, which is below clipping--but how much below depends on the preamp. So just use test signals at various amplitudes until you have a full understanding of its distortion behavior.

Also you will see distortion figures as THD at a given input level, typically a nominal level, say -50dBV or so. A reasonable preamp should maintain low THD until the input signal gets near the maximum input.

You can measure frequency response with white noise. It shouldn't be any trouble at all for a preamp to test flat 20Hz-20kHz.

Then there are other test signals you can try; looking for intermodulation distortion using a combined 18.5kHz and 19kHz signal is one that I like. You can also try to model various transient signals.

I think you will find that the differences between different quality opamps are hard to measure in a real-world swap situation, and even more elusive to hear, especially if the ultimate performance is dominated by the surrounding components.
 
Wow!
that's plenty of information. Thanks! Now I will be busy for a while.

Btw, The last few months I have updated some of my budget gear with new opamps:

-Alesis AI3: OPA 2134 instead of 4560 JRC. Tried one input-channel sofar. Much clearer now. Planning to upgrade one more input plus two outputs

-Samson S-amp (really cheap headphone amp): opa2134 istd of jrc4580. BIG difference!! Those 4580 really distort. Maybe there are better options for headamps?

-ART Tube MP. OPA 2604 istd of TL072. Plus new JJ-12ax7-tube. Real warm and nice now. Well it doesn't match the Green Pre though.

-Yamaha CDC-635. I replaced the 2068JRC output ops with opa2134. Now it can handle heavy low transients from my "Bohren - Black earth" CD

I'm planning to replace three 4560 in my DBX MC6 compressor. I haven't seen the schemo yet, so it will be a blind trial. Any schematics out there? I have looked around w/o luck.

It's inspiring to be able to upgrade my machinepark with just a few bucks.

Regards

Sunyata
 
I wouldn't think OPA2134 is the best headphone amp. 4580 manages a bit more output current at 50mA vs 35mA for 2134. Even so, for a serious headphone out you'd want to be able to drive 40 ohm cans fairly hard, I would think. 1VRMS would be peak current of 35mA.

I haven't done a can amp myself so I don't have recommendations . . .
 
I see what you mean, still the 2134 sounds so much better. The head amp has four channels, so I was able to cross-listen, and hear the difference. Which is so obvious. From now on, i don't want anything to do with those cheap op's anymore...
 
warble2 said:
Isn't it more fun to just record than just tinker around with budget gear to make it sound better?

I just put some $$$ down, got some good gear, and have been blasting away at recording. I didn't spend tons...kept it modest. A pre I've been using and have been happy with is my True Systems P-Solo. Sold my VTB-1's off and won't look back.

OK, modding might be fun - I've thought about doing some, but man, just get to recording...would you. :)
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This is my kinda dude that is speaking my kinda language. But DO upgrade your GAP-pre73 with Carnhill's. THAT is well worth it and very easy.
 
dickiefunk said:
I'm thinking of trying to mod my VTB1 by replacing the Opamp. It currently has a 4580 Opamp and am thinking of replacing it with a OPA 2134 or Burr Brown INA163. Which would you recommend as being the best Opamp for upgrading from the 4580 and is there anything else worth replacing on it?
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I changed it using a guide I found.

"2 TI NE5532 for the JRC4580s
1 LM833N for the JRC2114
1 LM353N for the JRC2082"

Great improvement! The sound is warmer and clearer at the same time and has different characteristics. Just better. And it works without doing anything with caps and the power and feedback loops.

The desoldering was a b*tch. Finally I just cut the legs off and took one leg out at a time, heating it with the soldering iron at probably too high temperatures. Great little investment. To bad I didn't have a better tube at hand.
 
Joni0001984 said:
I changed it using a guide I found.

"2 TI NE5532 for the JRC4580s
1 LM833N for the JRC2114
1 LM353N for the JRC2082"

Great improvement! The sound is warmer and clearer at the same time and has different characteristics. Just better. And it works without doing anything with caps and the power and feedback loops.

The desoldering was a b*tch. Finally I just cut the legs off and took one leg out at a time, heating it with the soldering iron at probably too high temperatures. Great little investment. To bad I didn't have a better tube at hand.
Click to expand...

Hmm very interesting! I'm wondering how this compares to my current DMP3?
 
chessrock said:
I can't really answer that question without knowing more about the design, but for the most part, these are all technically interchangeable, and it would be a matter of dropping them in and seeing how they behave ... but since SP recommended the opa2134, I would imagine that one would be a safer choice at the input.

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I saw Alan Hyatt post the same thing on here somewhere. It's really hard to find because he posts so often.
 
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