Behringer ADA8000 modifications..

[thedug]

All I did was replace the the opamps with mc33079s (in & out)

Yeah, the existing schematic uses a pad to knock down the voltage then sends it throught he preamp, even after the pad, the mic pre couldn't be turned up past 9 oclock, so I was just curious if there would be issues with bypassing the mic pre without some sort of pad.

d./

 

[mike_relay]

I was looking at the specs of these various opamps, but I guess I'm not sure what I am looking for. What qualities of the MC3079 are better than TL074 for audio?

Also, I was talking to one of the engineers here and he was of the opinion that these quad packages are not very good. We actually used the 3079 in an air pressure probe and ended up going to a dual.

I'd appreciate if anybody has some deeper insight into this.

 

[gyraf]

Hi Mike,

What qualities of the MC3079 are better than TL074 for audio?

Much, much lower distortion - and higher GBP. And lower noise.

Re the quad/dual pakages, we need the quad ones for PCB compatibility. And I've never had any 33079's misbehaving compared to duals..?

Jakob E.

 

[juniorhifikit]

Any progress on the signal path upgrade, or bypassing the pre-amps?

(Also, a big thank you for the SSL compressor project!)

 

[Flatpicker]

Since everyone's trying to bypass the pres on this thing, has anyone tried the ULTRAMATCH PRO SRC2496? It looks like a new dual A/D/A converter for only $130 at Musician's Friend. Not as much bang for the buck since it's only 2 channels, but if something like replacing op amps gets it even close to the higher-end A/D/As, it'd be well worth it. (Sorry if this was already mentioned. I've read through this thread at various times, but can't remember if it was.)

 

[Rochey]

tut tut, it's a sample rate converter ... not an ADC DAC :grin:

In which case, chuck out the ADI crap that's probably inside and put one of the TI SRC419X SRC's in.

I'll let you guys look up the stats - the difference being, if I tell you the stats you think "just another sales guy" wheras if one of you discovers it - it's "wayhey!" :wink:

Behringer probably went for the cheapest sample rate converter possible. The odds are it takes an i2S in and chucks out an i2S. Therefor, you could hook an SRC419x device in quite easily. In fact, it's pin for pin with the AD1895 and the AD1896.

Ahhhh... pitch over.

 

[mcs]

[quote author="gyraf"]Re the quad/dual pakages, we need the quad ones for PCB compatibility. And I've never had any 33079's misbehaving compared to duals..?[/quote]
I think the 33079 op. amps. are similar to the LM833. How about the LM837 quad?

Best regards,

Mikkel C. Simonsen

 

[Flatpicker]

[quote author="Rochey"]tut tut, it's a sample rate converter ... not an ADC DAC :grin:...[/quote]Quote from the Behringer site: "Ultra High-Resolution 24-Bit/96 kHz A/D-D/A & Sample Rate Converter".
Here's a link: http://www.behringer.com/SRC2496/index.cfm?lang=ENG
I bet you're thinking of the ULTRAMATCH SRC2000 which is described as a "Ultra-Linear Sample Rate/Format Converter and Jitter Remover"? :wink:

 

[Flatpicker]

I just realized that the ULTRAMATCH PRO SRC2496?s converters are 24-bit/96 kHz where as the ADA8000?s converters are only 24-bit/48 kHz. So, looks like it?s better for A/D and D/A purposes.

 

[Rochey]

doh - my bad...

sorry.

 

[dpaton]

[quote author="thedug"]Yeah, the existing schematic uses a pad to knock down the voltage then sends it throught he preamp, even after the pad, the mic pre couldn't be turned up past 9 oclock.[/quote]
It sounds to me like there's too much gain somewhere, or perhaps not enough bias? Perhaps the fix is to change the gain structure? If the mic pre clips that easily, I'd immediately suspect a mis-biased diff pair or a clipping stage. I've only given it a cursory glance, and it looks to me like the stages are all OK, but their relative matching is off. has anyone checked the internal gain structure? I didn't see it anywhere else in the thread... Anyone have Hfe numbers for the transistor pairs used? To me, it doesn't look like a circuit that needs to be thrown away...just tweaked a little.

thedug...how'd the listening tets go?

-dave

 

[mike_relay]

I replaced one of the opamps with a mc33079, and I wanted to AB them against the same source. If I wanted to use a condenser mic and use a splitter, but what would I do about phantom power? Turn it on for both channels?

Thanks,
Mike

 

[tony dB]

i assume you can safely swith on both channels.
48V will stay 48V no matter howmany times you parallel feed it.
Since 2 mikes "eat" 48V it should be fine.

Cheers,

Tony

PS if you try this and you see smoke coming out of the unit,
i was wrong :green: , just joking!

 

[wiz1der]

[quote author="Flatpicker"]I just realized that the ULTRAMATCH PRO SRC2496?s converters are 24-bit/96 kHz where as the ADA8000?s converters are only 24-bit/48 kHz. So, looks like it?s better for A/D and D/A purposes.[/quote]

This sounds like the ticket. A clean ADC that rivals say, a Mytec Stereo96 for about 1/8th the cost? wow.....

 

[synthi]

Does the B unit rival with the Mytec actually??? Did you comapred both units?

Synthi

 

[Flatpicker]

[quote author="wiz1der"]This sounds like the ticket...[/quote]Check out Mariks thread for a hint about what I'm going to do when I can afford one and a couple of transformers. I have no idea as to how good it will sound, but it's not a very expensive gamble. If it sucks, you could always sell the b'ger and use the transformers for something else.
http://www.groupdiy.com/index.php?topic=3019&highlight=alesis

 

[mike_relay]

I have been unable to get my hands on a XLR Y splitter, but I did some tests on the modded channels of my ADA8000. The only thing I have changed is the TL074 to the MC3079.

I recorded my girlfriend singing into an MXL2001, and I noticed a lot more sibilance in the MC3079 channels than in the umodded channel. I'm not ready to say that is true for sure, because they were two different takes. Once I get the splitter I will try again.

The other thing I did was run the THD measurement in audioTester ( this program was crashing on my computer about every 2 minutes or so.. anybody have a better suggestion of something else I could use?) and the MC3079 performed better. I will post some samples and some graphs when I get a chance. If anybody has ideas about tests I could run, I'd be interested.

Thanks, mike

 

[Rossi]

Take a look at the Rightmark Audio Analyzer http://audio.rightmark.org/

It's free, and it's a really cool program. There are two test modes: normal for soundcards (also for audio equipment) and "acoustics" for room measurements. If you can't turn on all test categories, you're in acoustics mode. Go to test options and disable acoustics mode testing. Now you can enable all tests. It took me a few days before I figured that out, because there's almost no documentation. Another tip: If you wanna test one channel only (as for instance in a comparison of two mono channels) connect the left channel only. You can't hit "done", but it will still do the tests when you hit "cancel".

In the case of the ADA8000 you can do a loop-through test. Connect the output to the input with an analog cable; mute all other channels so only this one channel is active for recording on your soundcard. The meter should read about -1 dB. Hit "done" or "cancel," and there you go. Testing takes less than a minute. The RMAA can create a HTML test report - which you can post here :wink:

 

[gyraf]

AudioTester.. this program was crashing on my computer about every 2 minutes or so..

Did you buy the licenced version? The Demo version runs for only two minutes at a time, and then needs restarting. It's really a good program!

Jakob E.

 

[tony dB]

Expensive? only had a brief look there and didn't read all the details...