Preamp Gain Problem

[PetRawks]

Hello,

The chain is 2 KM184's drum overheads to Great River MP2 to 888/24 to PT Mix. For some reason, even with the gain on the preamps only up to about 12, the A/D is clipping. The drummer isn't playing loudly and the mics are 5 feet above the kit.

I don't understand why it's clipping the converters. Is the output of the KM184's extremely hot or something? Please help.

Thanks in advance!

[CO2]

Hello Pet:

This may be a combination of things.

First, unlike the original KM84, the KM184 has no -10 db pad. Although you say your drummer is not playing loudly and the position of the mikes is five feet, there is a possibility you may be overdriving the 184's.

Secondly, although I do not own a Great River MP-2 (and it looks mighty impressive), I would say the combination of the position of the impedance switch (which selects between 300 and 1200 ohms) coupled with the position of the Output Level control may have a lot to do with your problem.

Since the KM184's are fairly "hot" compared to the old KM84's, you will probably find yourself needing to attenuate your gain stages significantly.

Best Regards

[Mark Haliday]

Maybe your 888 is internally set for -10 dbV line level operation ?
If that is the case you may have a problem matching this with a preamp output probably calibrated for +4dbu. If you have a output gain on your preamp, then its fine.
If not, you will have to cheat and lower the Mic input gain, but at the expense of quality.

Or in the end you may have to change the 888 operating level.

[PetRawks]

Originally posted by CO2:

Although you say your drummer is not playing loudly and the position of the mikes is five feet, there is a possibility you may be overdriving the 184's.

<font size="2" face="Verdana, Arial">That's almost plausible, except I have been in other studios where KM184's were used as drum overheads at about 5' above the kit, and each time, the drummer was palying FAR louder than what I had in my studio the other day. No part of their signal chain was overloaded. Also, 184's can take a HELLUVA lot of level.

Originally posted by CO2:
Secondly, although I do not own a Great River MP-2 (and it looks mighty impressive), I would say the combination of the position of the impedance switch (which selects between 300 and 1200 ohms) coupled with the position of the Output Level control may have a lot to do with your problem.

<font size="2" face="Verdana, Arial">I doubt it. There is no impedance switch on the GR, and there is is no output level control. Are you thinking of another preamp? Also, impedance has nothing to do with level. It can affect clarity of tone, but not level.

For now the solution I'm using is to patch my cleanest compressor (RNC) and use it's output level to attenuate the signal going to the A/D. While this isn't an ideal solution, it works until I find out what's happening.

If anybody has some idea as to why the output of the preamp is clipping the A/D even with the preamp gain turned all the way down please tell me!

[PetRawks]

[quote]Originally posted by PetRawks:

Originally posted by Mark Haliday:
[qb]Maybe your 888 is internally set for -10 dbV line level operation ?
If that is the case you may have a problem matching this with a preamp output probably calibrated for +4dbu.

<font size="2" face="Verdana, Arial">If the 888 was set at a -10 operating level and receiving a +4 signal from the preamp, the difference would be -6 QUIETER. Would it not? Anyway, the 888 is set for +4 as is the preamp.

Originally posted by Mark Haliday:
If you have a output gain on your preamp, then its fine.
If not, you will have to cheat and lower the Mic input gain, but at the expense of quality.

<font size="2" face="Verdana, Arial">There is no output gain control on the preamp, and even with the mic input gain turned all the down, the A/D clips. The quality of the signal before clipping doesn't sound compromised at all, however. Some drum hits get through without clipping, but they are close to it. Those hits sound fine.

I'll get a chance today to run the 184's through different two channel pre's and I'll smack some drums out in the live room. This way I can determine whether the GR is the culprit or further process of elimination is required.

Thanks guys! I'll keep trying.

[CCash]

If the 888 was set at a -10 operating level and receiving a +4 signal from the preamp, the difference would be -6 QUIETER. Would it not?

<font size="2" face="Verdana, Arial">No, the preamp's output would be 14dB hotter than the nominal input to the 888 (or, 14dB hotter than what the 888 expects to see).

You're probably thinking of what happens when sending an unbalanced signal into a balanced input, in which case you'll usually lose 6dB.

Also, impedance can affect level. It's just not usually a big problem with modern gear until you start multing sources.

[CO2]

Hello again:

I was looking at the Great River MP-2NV, which apparently is not the same as your MP-2. MY FAULT!

You probably need to start at the head of the signal path and work through it.

Try another set of mics with the Great River to see if the distortion disappears.

If the distortion remains, try a different preamp and so on...

The main thing is to isolate the offender in your current chain by substitution. Once you do, you can take steps to correct problem.

Best Regards

[CO2]

Hello again:

I was looking at the Great River MP-2NV, which apparently is not the same as your MP-2. MY FAULT!

You probably need to start at the head of the signal path and work through it.

Try another set of mics with the Great River to see if the distortion disappears.

If the distortion remains, try a different preamp and so on...

The main thing is to isolate the offender in your current chain, by substitution. Ultimately, you should be able to isolate the offender.

Once you do, you can take steps to correct problem.

Best Regards

[Studio Dweller]

My first guess would've been that the 888 is internally set to -10, but since that's not the case, have you checked the calibration (input trim pots) of your 888?

[Mark Haliday]

test this :

try inputing a -10 dBV analog line source (consumer cd player, tuner, DAT etc) directly into your 888.
I assume you have a proper cable for going from a unbalanced to a balanced connection

- If the level in PT seems decent, then your 888 has inputs set for -10 dbV

- If on the contrary the input level is very very low and there is nothing you can do with the trim pots, then your 888 is set for +4dBu.

BTW the operating level of the 888 can be set differently for ins and outs I think (haven't checked on the manual though...)

hope it helps