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Author Topic: CA-UGLY pre as attenuator???  (Read 4428 times)

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Offline yates7592

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CA-UGLY pre as attenuator???
« on: May 18, 2012, 09:24:05 AM »
I have a Church Audio UGLY preamp and understand the gain dials as follows:

Full gain - fully clockwise at about 4/5 o' clock = +20dB
Neutral - about 11 o'clock = +/-0dB
Min gain - fully anticlockwise at about 7/8 o' clock = -ve gain = attenuator??

Is the minimum gain setting at around 7-8 o'clock actually also +/-0dB, or is it really attenuating the signal. If so, does anybody know by how much?

Another question, I routinely set the gain knobs at 2 o'clock believing this gives me about +10dB gain - is this correct?

Offline Gutbucket

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Re: CA-UGLY pre as attenuator???
« Reply #1 on: May 18, 2012, 12:08:20 PM »
Paging Chris Church, please pickup the white courtesy telephone.

Chris can answer definitively, but I'll try and help.  My UGLY preamps are about 5 years old, not sure if the new ones are the same.  If you need attenuation, it's probably better to use external attenuators or attenuation cables between the UGLY and the recorder.. or better still, substitute a simple battery box for the preamp and use the attenuators.

UGLY gain range:
Fully counter clockwise mutes the input.
Fully clockwise is ~+20dB.

The adjustment isn't linear at the bottom of the range.  Most of the adjustment range favors the gain region between about +5 to +20dB. It gets tricky to match channel gains accurately below that with very small adjustments of the pots. Unity gain is possible, with a setting rather close to the counterclockwise position.

There are several ways to determine what the gain actually is.  Here's one simple method- send a steady state test signal like a sine wave output from a signal generator, test CD, soundcard, etc. into your recorder's input. I use an inexpensive Berhinger cable tester box. Put the recorder in rec/pause and note the level on it's meters.  Then insert the UGLY between the signal source and the recorder and again note the level on the meter.  The gain of the Ugly is the difference between those two readings.  Adjust the gain pots while watching the meters to set whatever setting you want.

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Offline yates7592

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Re: CA-UGLY pre as attenuator???
« Reply #2 on: May 18, 2012, 12:18:44 PM »
Thanks for that advice. So I just did that and found (for my UGLY at least):

Maximum = +20.4dB
3:00 = +20.1dB
2:00 = +19.3dB
1:00 = +17.7dB
12:00 = +14.9dB
11:00 = +12.4dB
10:00 = +9.9dB
9:00 = +0.2dB
8:00 = -51dB (!)
7:00 = off

So I was totally wrong thinking that my 2:00 setting was giving me +10dB gain, more like double! Anyway, no problem, because it has worked absolutely fine every time with very low sensitvity mics. I was also wrong to think that 11:00 was the neutral point. In fact it is about 9:00 (on mine at least). You are entirely correct that the relationaship is very non-linear with a gradual reduction in gain from 4:00 to 10:00, then quite sharp beyond that.

Offline Church-Audio

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Re: CA-UGLY pre as attenuator???
« Reply #3 on: May 18, 2012, 12:41:23 PM »
Thanks for that advice. So I just did that and found (for my UGLY at least):

Maximum = +20.4dB
3:00 = +20.1dB
2:00 = +19.3dB
1:00 = +17.7dB
12:00 = +14.9dB
11:00 = +12.4dB
10:00 = +9.9dB
9:00 = +0.2dB
8:00 = -51dB (!)
7:00 = off

So I was totally wrong thinking that my 2:00 setting was giving me +10dB gain, more like double! Anyway, no problem, because it has worked absolutely fine every time with very low sensitvity mics. I was also wrong to think that 11:00 was the neutral point. In fact it is about 9:00 (on mine at least). You are entirely correct that the relationaship is very non-linear with a gradual reduction in gain from 4:00 to 10:00, then quite sharp beyond that.

Thanks for doing that.. I know I should have done that at some point in time lol.. If I could find an audio taper pot that would change the scale. I will see if I can find one although I dont think one exists.

Chris
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Offline Gutbucket

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Re: CA-UGLY pre as attenuator???
« Reply #4 on: May 18, 2012, 01:57:32 PM »
Hey Chris, here's an idea which would help us significantly (regardless of whether or not you can source that ultra-elusive miniature audio taper pot)-

Could you parallel a resistor with the gain pot so that when turned fully counter-clockwise it dead ends at a zero gain setting instead of muting completely? That would make the available gain range to 0 - 20dB

I realize that increases your parts count by a couple resistors.  But for the end user it would make for a much more flexible device.

Why?

If out at a gig and the pre-selected gain level turns out to be too high, the user could then simply turn both pots fully counter clockwise (without looking) for a zero gain setting without fear of muting the signal.  As it is the risk of making such an adjustment is either a wild channel imbalance or muting one or both channels, so it’s better to not to touch it at all.
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Offline Church-Audio

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Re: CA-UGLY pre as attenuator???
« Reply #5 on: May 23, 2012, 06:33:56 PM »
Hey Chris, here's an idea which would help us significantly (regardless of whether or not you can source that ultra-elusive miniature audio taper pot)-

Could you parallel a resistor with the gain pot so that when turned fully counter-clockwise it dead ends at a zero gain setting instead of muting completely? That would make the available gain range to 0 - 20dB

I realize that increases your parts count by a couple resistors.  But for the end user it would make for a much more flexible device.

Why?

If out at a gig and the pre-selected gain level turns out to be too high, the user could then simply turn both pots fully counter clockwise (without looking) for a zero gain setting without fear of muting the signal.  As it is the risk of making such an adjustment is either a wild channel imbalance or muting one or both channels, so it’s better to not to touch it at all.

Thats a great idea.. I have never thought about it. I have many customers that "set and forget" that preamp because the headroom is so high on it. That you really can run it at 90% all the time and just reduce gain on the recording device with out fear of overload because most mics will be around -30 db at 114 db or so. So adding +20 db gives you gobs of head room still for your recorders input. thats the way I designed this preamp to not use the gain controls so much but to just set it and leave it and the two gain pots make matching up your mics much more easier. These pots are not designed for constant tweaking. They have a life of 20000 or so rotations. So I suggest customers leave this preamp set to a preset gain and leave it alone turn it off and turn it on use it to match your mics ( my mics dont require this ) but dumpster Dpa and other mics that are "claimed" to be matched but almost never are.

Chris
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Offline Gutbucket

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Re: CA-UGLY pre as attenuator???
« Reply #6 on: May 24, 2012, 11:55:14 AM »
Confirming the answer to the original question- YES, you can attenuate (not just theoretically, but practically) I just re-measured both of my UGLYs night before last, figuring I had them set somewhere around unity, and realized that I currently have the gain set to ~ -5dB on all channels.  They are attenuating.


Chris, I do really like having the ability to balance individual channel gains and leave them safe from accidental adjustment, in 'set and forget' mode.  That's especially valuable for my applications in closely matching four channels between two UGLYs.
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Offline Gutbucket

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Re: CA-UGLY pre as attenuator???
« Reply #7 on: May 24, 2012, 12:46:42 PM »
In addition to that 'set & forget' channel balancing and basic gain setting for a particular set of mics, there is a separate issue of needing to adjust overall gain for various SPL recording situations with gross gain adjustments.  As you mention, that adjustment can often be made by adjusting the recorder’s input gain (within its adjustment limits and/or the limits of acceptable noise at one end and overload distortion at the other). 

Unfortunately, the range of usable gain adjustment on some recorders is pretty limited.  The line-input of the Tascam DR2d is limited to about a 5dB total useful adjustment range.  So without re-adjusting the UGLYs, my gross gain adjustment for different styles of music is limited to 5db using that recorder.

I try to keep the same UGLY gain setting for almost everything I record with this rig, both to retain my set channel balances and avoid wear on the pots. So to avoid overloading the Tascam’s inputs I’ve reduced the gain on the UGLYs.  Now that I’ve re-measured it, I know now the gain is -5dB, or about 10dB less than my previous setting of +5dB).

I set gain levels so that the loudest, close-proximity clapping peaks at about -2dBFS on the recorder. That works OK since I don’t usually record super loud material and also don’t hear a noise problem when increasing the level of the recording later for quiet material without loud nearby clapping, even though it was recorded at a level far lower than I’d otherwise prefer. 

I thought about this again recently because I just made some ambient nature recordings which really could have used additional gain, but didn’t want to re-adjust the UGLYs.


Here’s my question for you Chris:

How much headroom is there in the UGLYs?  I’m using DPA 4060s which have a relatively high sensitivity of 20 mV/Pa as you know. What if I set the base gain of the UGLYs high enough to accommodate those quiet nature recordings (set-and-forget) and then used external attenuators of several values between the UGLY and recorder to accommodate higher SPL material?  I could choose between, say, three attenuation values. Would I reach unacceptable distortion levels in the UGLY that way for the loud stuff?   Lets assume I kept the gain on the UGLYs near +20dB and then selected between using no attenuation, -10dB, -20dB or -30dB depending on the highest expected SPL level. 

That would give me a range of adjustment wide enough to accommodate anything I wanted to record by inserting the appropriate attenuator, and I wouldn’t need to adjust gain on the UGLYs.
« Last Edit: May 24, 2012, 11:13:00 PM by Gutbucket »
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Offline Gutbucket

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Re: CA-UGLY pre as attenuator???
« Reply #8 on: May 24, 2012, 01:08:06 PM »
Does this help?

The 4060 has a sensitivity of 20 mV/Pa, and is spec'd at <1% distortion up to a 120dB SPL RMS sine.  It should produce a -6dBu output at 120dB SPL (according to the table here, I suck at audio math)

The 4060 is spec'd for a maximum SPL before clipping of 134dB, which should produce +8dBu.
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Offline Church-Audio

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Re: CA-UGLY pre as attenuator???
« Reply #9 on: May 24, 2012, 06:05:06 PM »
In addition to that 'set & forget' channel balancing and basic gain setting for a particular set of mics, there is a separate issue of needing to adjust overall gain for various SPL recording situations with gross gain adjustments.  As you mention, that adjustment can often be made by adjusting the recorder’s input gain (within its adjustment limits and/or the limits of acceptable noise at one end and overload distortion at the other). 

Unfortunately, the range of usable gain adjustment on some recorders is pretty limited.  The line-input of the Tascam DR2d is limited to about a 5dB total useful adjustment range.  So without re-adjusting the UGLYs, my gross gain adjustment for different styles of music is limited to 5db using that recorder.

I try to keep the same UGLY gain setting for almost everything I record with this rig, both to retain my set channel balances and avoid wear on the pots. So to avoid overloading the Tascam’s inputs I’ve reduced the gain on the UGLYs.  Now that I’ve re-measured it, I know now the gain is -5dB, or about 10dB less than my previous setting of +5dB).

I set gain levels so that the loudest, close-proximity clapping peaks at about -2dBFS on the recorder. That works OK since I don’t usually record super loud material and also don’t hear a noise problem when increasing the level of the recording later for quiet material without loud nearby clapping, even though it was recorded at a level far lower than I’d otherwise prefer. 

I thought about this again recently because I just made some ambient nature recordings which really could have used additional gain, but didn’t want to re-adjust the UGLYs.


Here’s my question for you Chris:

How much headroom is there in the UGLYs?  I’m using DPA 4060s which have a relatively high sensitivity of 20 mV/Pa ask you know. What if I set the base gain of the UGLYs high enough to accommodate those quiet nature recordings (set-and-forget) and then used external attenuators of several values between the UGLY and recorder to accommodate higher SPL material?  I could choose between, say, three attenuation values. Would I reach unacceptable distortion levels in the UGLY that way for the loud stuff?   Lets assume I kept the gain on the UGLYs near +20dB and then selected between using no attenuation, -10dB, -20dB or -30dB depending on the highest expected SPL level. 

That would give me a range of adjustment wide enough to accommodate anything I wanted to record by inserting the appropriate attenuator, and I wouldn’t need to adjust gain on the UGLYs.


You will have no issue what so ever with using them for nature recordings. Run them at 100% for live recording of loud sources I recommend no more than 90% not to avoid overloading the ugly but to prevent overload of your recording device.

They can handle a large input signal. Before overload.
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Offline Gutbucket

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Re: CA-UGLY pre as attenuator???
« Reply #10 on: May 25, 2012, 10:38:31 AM »
You will have no issue what so ever with using them for nature recordings. Run them at 100% for live recording of loud sources I recommend no more than 90% not to avoid overloading the ugly but to prevent overload of your recording device.

They can handle a large input signal. Before overload.

OK, sounds like that confirms the UGLY shouldn't overload or distort significantly with that hot of a mic input.  If so then padding their output sufficiently should keep the recorder from overloading even with loud sources. 

Currious, have you measured what VRMS or V Peak-Peak output it is capable of?  I'm using Maha 9.6V Imedions with them.
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Offline Church-Audio

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Re: CA-UGLY pre as attenuator???
« Reply #11 on: May 25, 2012, 01:13:45 PM »
You will have no issue what so ever with using them for nature recordings. Run them at 100% for live recording of loud sources I recommend no more than 90% not to avoid overloading the ugly but to prevent overload of your recording device.

They can handle a large input signal. Before overload.

OK, sounds like that confirms the UGLY shouldn't overload or distort significantly with that hot of a mic input.  If so then padding their output sufficiently should keep the recorder from overloading even with loud sources. 

Currious, have you measured what VRMS or V Peak-Peak output it is capable of?  I'm using Maha 9.6V Imedions with them.
I have 14 or so to build this coming week I will check it out.
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Offline Gutbucket

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Re: CA-UGLY pre as attenuator???
« Reply #12 on: May 25, 2012, 02:29:08 PM »
Thanks Chris, you're the best!

BTW, I may be about ready to order a couple more of these soon.  Can you make them with mini-XLR's in/out?  If a power switch is out of the question, I can just remove the battery to turn them on/off, which is what I often do now.
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Offline Church-Audio

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Re: CA-UGLY pre as attenuator???
« Reply #13 on: May 27, 2012, 11:46:17 AM »
Thanks Chris, you're the best!

BTW, I may be about ready to order a couple more of these soon.  Can you make them with mini-XLR's in/out?  If a power switch is out of the question, I can just remove the battery to turn them on/off, which is what I often do now.

I can do a break out to mini xlr from a single multipin but there is not enough room for locking connectors on the ugly.
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Offline Gutbucket

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Re: CA-UGLY pre as attenuator???
« Reply #14 on: May 27, 2012, 01:25:21 PM »
That can work, I'll get back to you on it.
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Better recording made easy - >>Improved PAS table<< | Made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<<

 

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