Microphone Preamp

[richardash1981]

Question: what should I look at for a no-frills, "transparent" microphone preamp to go in front of a Roland UA-101 audio interface?At the moment I can only find three candidates:

1. IMG Stageline MPA-202 (small, cheap, but very probably no better than the internal preamps)
2. ART USB Dual Pre (not necessarily any better, and I didn't want a USB interface)
3. Something broadcast, like a SBS Solutions Mic-IT second hand off ebay. Seems like the right spec (see below), but I don't really know what to look for.

Context: I do a reasonable amount of recording events that I either play in or do sound for, mainly so the performers can hear afterwards what it was like out in the audience. For the last 15 years this has been done with a stereo crossed pair mic into a Korg D1200 hard disk portastudio (44.1kHz, 24-bit), using the internal mic preamps (which are not at all bad). This is rather a pain having to export the audio, then upload to PC over a USB 1 port. So I'm trying to migrate to recording onto a laptop. I have a Roland/Edirol UA-101 USB interface, which makes very nice 24-bit recordings. But it only has two mic preamps (not four) and they aren't very good - they have significantly less gain than the Korg, and are noisier.I have made recordings using a Behringer XENYX 802 mixer as pre-amp, into the line-only fixed gain channels of the UA-101. I'm pleased with the results but:

1. It's a fairly awkward form factor to carry about with damaging
2. There are lots of controls to mess up the recording with (EQ, channel pan + gain, main mix gain ...)
3. I'd like something with a much shorter audio path (there are no direct outs, and no insert points to do instead)
4. I'm a bit worried that the pots are starting to get old/worn/dirty and are a source of crackles (I've had it over 10 years).

Because I'm trying to capture the live sound, I'm not interested in adding any form of distortion or compression to the sound (plus this kit will run unattended so have to look after itself). So valves, opto-widgets, "warm" sound (indeed any named preamp sounds) and variable transformer saturation are all out.

Rationally, I want a box which:

• takes two (maybe four) XLR microphone inputs
• Produces two analogue outputs at +4dBu line level
• Has gain controls (but separate controls and stepped switches would be fine)
• Has phantom power
• Nothing else!

Unfortunately the market seems to be made up of products which are one of:

• 8-way devices with ADCs and ADAT out (which I have nothing to receive)
• Very simple, not very good quality boxes based on basic op-amps
• A massive range of named sound preamps intended for studio recording, and intentionally modifying the sound.

Hence the very short list above, and a feeling that I am missing something?

[James Remo]

What about simplifying your setup by buying a Presonus AudioBox USB 96 and ditching the UA-101?

[paulears]

What’s the problem with the Roland mic inputs? Cascading another preamp won’t make it any better, but the Roland gets quite good reviews for its input? Is yours noisy or something?

[richardash1981]

What about simplifying your setup by buying a Presonus AudioBox USB 96 and ditching the UA-101?

 

Good question. As far as I can see it won't do 4 channels of recording simultaneously, which is what I often do (two from microphone, two from PA system either analogue line level, or SPDIF from mixer digital out). I'm also not clear if it works under Linux (what my laptop runs) or not - the UA-101 was bough substantially because it was known to work. I'd want to keep the UA-101 it for doing 10-channel recording (from inserts on Soundcraft EPM12) anyway.

What's the problem with the Roland mic inputs? Cascading another preamp won't make it any better, but the Roland gets quite good reviews for its input? Is yours noisy or something?

With the Sony electret connected, I have to put the trim controls all the way to maximum, and still can't get full scale on the ADCs. It's pretty noisy run like this. By comparison with the same mic, the Behringer trim is one tick sort of full, other controls to 0dB and plenty of level, with much lower noise. I've been running the Behringer into channels 3 and 4 of the interface, which have no pre-amp at all (just fixed +4dBu sensitivity for full scale).

[James Remo]

It's discontinued but the bigger PreSonus Audiobox 1818vsl sounds like it would fit the bill, and initial bit of googling suggests it works with linux out of the box. There is one on the popular auction site for £250 https://www.ebay.co.uk/itm/PreSonus-Audiobox-1818vsl/323901546382?hash=item4b6a095f8e:g:qroAAOSwJVxdbAlG Edited November 16, 2019 by James Remo

[paulears]

The Sony electret? Condensers are normally quite sensitive. I’ve got a presonus FireWire interface and a tascam for multiple inputs and a two channel lexicon and there’s very little difference between their sensitivity and none of them are very noisy although their gain settings vary wildly on the knob. On yours what kind of level can you get before the noise creeps up? Have you a different mic to swap to to get a comparison?

[richardash1981]

The Sony electret? Condensers are normally quite sensitive. I've got a presonus FireWire interface and a tascam for multiple inputs and a two channel lexicon and there's very little difference between their sensitivity and none of them are very noisy although their gain settings vary wildly on the knob. On yours what kind of level can you get before the noise creeps up? Have you a different mic to swap to to get a comparison?

The mic I am using is a Sony ECM-S959C (mid-side stereo mic with built-in matrix to produce left/right out). It's originally a video mic with 3.5mm output, but mine is ex-BBC (according to the seller) and came with twin XLR tails (I have added impedance balance resistors in the plugs). It runs of a 1.5V AA battery (apparently for ever!) no phantom power. I'm assuming that is partly responsible for the low output level. I'm pretty sure I bought it after a recommendation on here somewhere.

 

 

I have a pair of t.bone SC140 small diaphragm condensers which are phantom power and I could try as a comparison (been meaning to do so, but never had time to set both up for an actual event).

[paulears]

I'd definitely try the T-Bones before you move away from your Roland. It's been a long time now but I had a similar Sony mic in the early 80s and it had quite a high output. The low battery voltage impacts a little on the available dynamic range but it was matched pretty well to the unbalanced mic inputs on cassette recorders at that time.

[richardash1981]

I'd definitely try the T-Bones before you move away from your Roland. It's been a long time now but I had a similar Sony mic in the early 80s and it had quite a high output. The low battery voltage impacts a little on the available dynamic range but it was matched pretty well to the unbalanced mic inputs on cassette recorders at that time.

 

Well that was interesting. I had a go with both microphones and the two preamp paths last night. All the files are in Google Drive here. Audio files are as recorded (no editing at all), in my small bedroom with me talking to the mics head-on at arm's length. This isn't particularly representative of real signals but was what I could do easily!

• sony_lowgains.aiff: Sony ECM-S959C microphone (90 degree mode)
  Left -> UA-101 input 1
  Right -> Behringer Xenyx 802 -> UA-101 input 4
  Behringer gains as per last gig (worship band), Trim 1 spot back, channel 0dB,
  main 1 notch back.
  Adjusted UA-101 input 1 trim to get similar PPM levels. Maybe 1 spot below full
• sony_lowgains2.aiff: As above but microphone further away from Behringer PSU to get the hum level down, same configuration as first test put back.
  Seems to have worked.
• sony_highgains.aiff: Sony ECM-S959C microphone (90 degree mode)
  Left -> UA-101 input 1
  Right -> Behringer Xenyx 802 -> UA-101 input 4
  Behringer master control up to +1.5 notches others unchanged
  UA-101 input 1 trim to maximum setting
• tbone_highgains.aiff: Thomann t.bone SC 140 microphones
  Mic 1 -> UA-101 input 1, phantom power on
  Mic 2 -> Behringer Xenyx 802, phantom power on -> UA-101 input 4
  Same gain settings as previous
• tbone_highgains2.aiff: Thomann t.bone SC 140 microphones
  Mic 1 -> Pulse PH-PSU -> UA-101 input 1, phantom power off
  Mic 2 -> Behringer Xenyx 802, phantom power on -> UA-101 input 4
  Pulse PH-PSU is a little single-channel phantom power box with an 18V AC wall wart + stepup.
• tbone_lowgains2.aiff: Thomann t.bone SC 140 microphones
  Mic 1 -> Pulse PH-PSU -> UA-101 input 1, phantom power off
  Mic 2 -> Behringer Xenyx 802, phantom power on -> UA-101 input 4
  Gains in low gain positions as sony_lowgains2.aiff above, but same phantom power arrangements

A few things came out:

• The Beringher channel has substantially more gain available than the internal pre-amp. I could have lifted the pre-amp route substantially more to get a nearer full scale recording using the Sony, and none of the controls are maxed out.
• The t.bone mics are ~ 15dB louder than the Sony, so I am making the pre-amps work pretty hard using the Sony microphone compared to typical uses (as I also have the mics in far field not close mic'ed).
• The phantom power supply in the UA-101 is noisy! Not the way you might expect at high frequencies, but a massive amount of a pulsed waveform at 7.6Hz! This drives the metering crazy but is not audible. Hence using the external supply (but I've only got one channel).
  https://drive.google...cX_JXNCDjbeWPLT
• It's hard to judge white noise pickup over the rather obvious 50Hz (+ harmonics) hum picked up - I think this is due to all the equipment and mains leads / transformers being in a pile close together, not power on the floor and audio on a table, because I don't remember it being a problem before. Although all the kit is double insulated I did have an earth connection made to a spare jack on the UA-101.

I'm not sure where this leaves me - with microphones which might do better, but another reason not to go direct to the UA-101 inputs!

 

[paulears]

That's a little concerning for an interface that isn't at the cheap end of the spectrum. I wonder if it's genuinely faulty, because I've not heard any internet comments on these problems and usually people shout loud and clear. A shame the Sony is a little deaf - bit it sounds problematic as a distant pickup mic, doesn't it?

[richardash1981]

That's a little concerning for an interface that isn't at the cheap end of the spectrum. I wonder if it's genuinely faulty, because I've not heard any internet comments on these problems and usually people shout loud and clear. A shame the Sony is a little deaf - bit it sounds problematic as a distant pickup mic, doesn't it?

 

It may be - I bought the UA-101 second hand and probably haven't tried to use Phantom power on it until now. I am unconvinced that it's supposed to do this. FWIW with the phantom power on, but no cable in, the input is quiet. So it could be that the mic draws more / less / unbalanced? current which upsets whatever step-up device is used to turn 9V DC (from the mains adaptor) into 48V DC for the phantom power.

The odd thing is that with a preamp that copes (maybe higher input impedance > less loading > more signal?) the results are pretty good - I'll dig out something recorded on the Korg D1200 as an example. I think the Zin is close to 10k on that though, because the line and mic inputs are the same electronics.

[richardash1981]

I got as far as carrying out one more experiment before Christmas intervened - I took the pair of T.bone condensers, the Behringer mixer and the sound card to the next gig I was driving the worship band PA for, instead of the Sony mic. This confirmed the sensitivity difference - I had to wind the channel trim controls down 2/3 of the way with the T.bone mics on, from the back of the hall. So I take it as proven that (for some reason) the Sony mic is producing a very low output level. Unfortunately I don't know how to get it apart so am limited what investigation can be done at that end.

Shortly afterwards, the external PSU for the Behringer 802 mixer went pop (see new thread) which has put a stop to trying anything else at the moment.