Mic Pre Gain Steps

[ruffrecords]

It kinda does look better in the third version you showed , but Id take the version with the extra gain positions in the lower range anyday , I often find with my tube mics that I need less than 30db gain on loud signals, I often use line input for mics on high level sources too ,upping the input impedance means less load on the transformer and slightly cleaner performance at high levels .

There is a 20dB pad that will extend the range down to 10dB gain. There is also a line input.

Cheers

Ian

 

[Tubetec]

Its only my personal point of view ,but Id generally go with function over form ,I guess its no problem in any case to make both sets of stencils available ,and allow the maker to choose to stop down the switch at 10 or 12 clicks .Im thinking there would be a slight penalty on the lower ranges in terms of noise by having to engage the 20db pad .

 

[abbey road d enfer]

Like this?

Exactly.

 

[abbey road d enfer]

Im thinking there would be a slight penalty on the lower ranges in terms of noise by having to engage the 20db pad .

There is almost always a "slight noise penalty" when it comes to signals in the -30dBu vicinity, unless using a preamp specifically optimized for that range. Most solid-state mic pres exhibit an EIN that rises when gain decreases. That is due to the topology of the NFB loop. Vacuum tubes preamps also have a weak spot in the -30dBu region for different reasons. Most use a two-stage topology that does not lend them to overall gains inferior to about 30dB, so tend to loose headroom there.
It seems not many designers are interested in that aspect, although it's the most frequent area for modern music  that uses close-micing a lot. Clearly, it is much easier to advertize about 70+dB gain than boasting about behaviour at 30dB gain.
Returning to the noise penalty, it must be taken with enough salt; typically, even if the noise factor degraded by 30dB (which is a lot) the actual S/N ratio would still be respectable at 70+dB.

P.S: I've developed some time ago a preamp that's optimized for close-micing of loud sources  (drums, electric gtr, Leslie, percs), that I and a number of friends/colleagues have in daily use, but being SS is irrelevant to this thread. 

 

[5v333]

I dont no if i dreamt about it, saw it on scope in a jlm  preamp or read about it, but i think the s/n sweet spot is often around 20db gain in a mic pre.

That is my sweet spot when working however.

There are times when a more difficult mic is brought to the show. A ribbon or re20 for ex. Perhaps as very distant room mic aswell. More gain and alot more gain is usefull then.

And then theres the people who likes to see if theres some harmonics to be found when going to eleven.

 

[ruffrecords]

Its only my personal point of view ,but Id generally go with function over form ,I guess its no problem in any case to make both sets of stencils available ,and allow the maker to choose to stop down the switch at 10 or 12 clicks .Im thinking there would be a slight penalty on the lower ranges in terms of noise by having to engage the 20db pad .

The extra 2 clicks to lower the gain to 23.3dB cold still be there but just not marked on the dial.

There will be a  noise penalty using the pad but there is a 20dB gain in headroom.  How much extra noise  depends on the topology.  At lower gains there tends to be more problems maintaining headroom which is very much the case with this design. Short of the added complexity of switching out the first stage completely for lower gains (like the Neve 1073 does) a pad is the simplest option.

Cheers

Ian

 

[ruffrecords]

I dont no if i dreamt about it, saw it on scope in a jlm  preamp or read about it, but i think the s/n sweet spot is often around 20db gain in a mic pre.

This depends on the output noise in the mic pre. At high gains, input noise predominates. For example, at 60dB gain, the noise from a 150 ohm input ( about -130dBu) is amplified by 60dB and comes out the pre at about -70dB. At 40dB gain, the amplified input noise drops to -90dB. At this point, the noise from the output stages tends to dominate. If you reduce he gain to 20dB, the amplified input noise will only be -110dBu but the output noise, which might be -90dBu in a good design, means the -110dBu figure is not attained. This means in most mic pres, the noise tend to reduce as the gain is reduce until a point, often around 40dB or so, where the noise flattens out. Once you get beyond this point it makes little noise differnece if you reduce the gain or add a pad.

Cheers

Ian

 

[abbey road d enfer]

I dont no if i dreamt about it, saw it on scope in a jlm  preamp or read about it, but i think the s/n sweet spot is often around 20db gain in a mic pre.

Not really. 20 dB is the lower limit of adequate operation for most mic pres; for lower gain optimization, there is a need for a different topology, or a pad.

That is my sweet spot when working however.

That is not my experience, unless you are tracking at very low level (which is made possible if you record in a DAW, where the actual recording medium's S/N ratio allows it, although there is no benefit in doing so.
I've found that most of my signals are in the -30+/-5 range.

 

[5v333]

I've found that most of my signals are in the -30+/-5 range.

well we are probobly working very alike!

when i work with live sound (digital desks mostly) i set all channels to about 20db and just hope i dont have to even think about gain. theres so much to think about when mixing, esp when you have never worked with the band and you have 30-60min to find out how the game is to be playd. so i like to prepare alot so i can think about the music more instead. fiddling with gain takes time and focus.
then sometimes i turn up about 10-15db if something is really low in volume. other wise use a pad when meters are slammed which is mostly the case when using condensers for  toms for ex.

it will maintain a great amount for headroom booth in the pres and mixbuss = fantastic sound!

but ofcourse when tracking theres no mix buss to consider so we can gain alittle bit more.

 

[BluegrassDan]

I like the last version, Ian.

 

[ruffrecords]

I like the last version, Ian.

That seems to be the most popular choice. I will go with that unless I hear any strong opinions otherwise.

Thank you everyone for taking the time to respond.

Cheers

Ian

 

[Tubetec]

Many thanks also Ian and Abbey for the in depth explanation about noise in two stage pre's .