Anyone using SCA pres with a MHLabs 2882?

[niccolo]

Hi,
I'm using a rack of n72, a12 and j99 into an MH 2882DSP card and I get some strange distortion - that does not look like clipping but more like HF spikes - when AD is at circa -9dBFS, especially when using my j99's. This does not seem to happen when using other (cheaper) converters. I remember reading on the MH mailing list that some preamps could have resonances in the region above 20kHz, and, due to the 2882's very high analog bandwidth, this could cause the distortion..
I would like to know if any other forum members are using my converter-pres setup and what is their experience, after all it could well be my card having problems..

thank in advance

niccolo' gallio

[niccolo]

...mm, guess Metric Halo 2882 are not very popular among SCA users...

[tpryan]

The J99 is flat to well beyond 20K, but there are no peaks or resonances in the response curve. Do you notice the symptom at all gain settings, or only a few? Are the spikes accompanied by increased noise or distortion?

[niccolo]

Hi Tim and thanks for the reply.
It's kind of strange..
the spikes occur at most any gain setting, with any kind of mike and are strongly dependent on level.
Let me clarify this: spikes occur at loud parts in the performance, but at such levels which should be well handled by the pre's, infact when they happen the converters (with the analog input stage set to accept +4 signals) read circa -9 dBFS (for what I hear DA stage should clip before the unpadded pres). The resulting waveform in not clipped, but is full of "spikes", i.e the waveform gets really rough.
What I'd like to do now is to measure the output voltage from the pres when such symptoms happen and then report..
could that help?

thanks a lot

niccolo' gallio

[tpryan]

Do you have a signal generator? A synth that makes a constant sine wave will work.

[niccolo]

Yes I can output any waveform from my computer.
Would you be so kind to suggest a troubleshooting method?

thanks a lot.

niccolo' gallio

[tpryan]

Run a sine wave into the module at about -40dBu. Increase the gain until you see the symptom and record the output level. Decrease gain one step and increase level of input signal until you see the symptom again. Repeat for every gain step. Let us know what you find.

[Jeff]

Hi, new SCA user here. I'm experiencing something similar to the original post and was wondering if this had been resolved and if so in what fashion?

I have 3 J99 and 2 N72 pres: the N72's in the fist two slots next to the PSU and the J99's in slots 4-6. The N72's work great and sound amazing. The J99's sound great also, except on occasion with the J99's I get sudden spikes of noise, seemingly during louder or more aggressive versions of a track. If I'm running the pre hot, it might clip the converters, if I'm running it moderate, it won't. Doesn't seem to care what kind of mic I use, but seems to happen more on tube and condenser mics.

As suggested, I ran a sine wave from the DAW oscillator without issue at all gain stages with the exception that it would get a smaller spike when clicking the gain knob up to to the next level.

Any suggestions?

[niccolo]

Are you using my same converters?

[Jeff]

Yes, Metric Halo 2882.

[Jeff]

Turns out this is an MH issue. with the input on the 2882 set to +4 there is a tendency for the analog portion of the 2882 o overload. Set to -10 resolves the issue by forcing the external pre gain to be set lower.

[tpryan]

Interesting. Did MH verify this?

[niccolo]

Interesting indeed!
So you say that putting the input sensitivity to -10 allows you to get hotter digital levels? Not that I need to get nore than -12dBFS but I used to get nasty distortion circa @ -6 dBFS with an input sens of +4, does using -10 solve the problem?
Is this experienced by other 2882 users? Are you subscribed to MH's mail digest?
Thanks a lot for you suggeestion, I'll try it out tonite during the rehearsal of a gig I'm going to record..

niccolo

[Jeff]

Interesting. Did MH verify this?

https://www.mhsecure.com/faq/index.php? ... %20preamps

This link from the FAQ section of the MH site details the behavior, although it applies to unbalanced connection. MH, via BJ on the list serve and MH on a support ticket, said setting the MH Console to -10 should resolve the issue and if it didn't, then it would have been their contention there was a problem with the preamp. From support:

"If the input was set to -10 and the spikes still persist, other than the possibility of some high frequency oscillation, we would suspect that there could be a problem with the preamp, or that perhaps the output is not balanced."

They suggested some further testing using an oscilloscope, which I unfortunately do not have access to, but since setting inputs to -10, I've not had an issue. Well, other then not having a lot of gain to work with in some situations.

I also conferred with a few 2882 end users in town. They all reported having the same issue (albeit with different external preamps) and suggested the same course - set the MH Console input to -10.

[Jeff]

Interesting indeed!
So you say that putting the input sensitivity to -10 allows you to get hotter digital levels? Not that I need to get nore than -12dBFS but I used to get nasty distortion circa @ -6 dBFS with an input sens of +4, does using -10 solve the problem?
Is this experienced by other 2882 users? Are you subscribed to MH's mail digest?
Thanks a lot for you suggeestion, I'll try it out tonite during the rehearsal of a gig I'm going to record..

niccolo

Well, they certainly are hotter. If you read the link to the FAQ in the previous post, setting the input to -10 has something to do with the analog stage clipping before the converters do and -10

"will move the analog breakover point to be higher than the digital clip point and will give you reliable metering. "

The rest of your post was addressed in my last one, I think. I don't think it's a real problem with other 2882 users unless they are using pres that run a bit hotter then the average pre. I don;t have any issues with the N72's or A12's at +4. But for shits and giggles I run everything now at -10. It's just one last thing to try to keep straight.

BTW, running the J99's into my ULN via the inserts I have not had a problem.