Mic Pre Gain Steps

In a mic pre with a stepped gain control, is anyone really bothered exactly what the step size it? Neve have them at 5dB, I did them at 3dB in the EZTubeMixer.

The reason I ask is I have just been doing the front panel for the new 7HP Classic mic pre in which I have used a 12 way rotary switch for coarse gain selection. Initially I was going to use 3dB steps but, when you lay out the panel you really only need to place an actual value on the panel every 90 degrees. If you do this with 3dB steps you get values on the panel of 60, 51,42 and 33 and they look really odd to my eye. It occurred to me if I made the steps 3.33 dB then every quarter would be 10dB so I could label the panel 60, 50, 40 and 30. I tried it on the panel layout and it does look a lot better. Will anyone really care that the two steps between each labelled gain is 3.33dB??

Cheers

Ian

3.33dB sounds like a good value to me. It's still small enough to finely adjust, but it's not so small that it becomes a volume knob. Seems sensible to me.

3.33dB gets my vote

emrr said:

3.33dB gets my vote

Click to expand...

+1

I have a commercial pre with no number markings at all,  just lines.  24 position,  I don't even know the step size,  never bothered me.  The important thing is just something logical where it is easy to write down the settings for future use.

Is the full range 30-60 dB? Is there a +/-  trim as well?

john12ax7 said:

I have a commercial pre with no number markings at all,  just lines.  24 position,  I don't even know the step size,  never bothered me.  The important thing is just something logical where it is easy to write down the settings for future use.

Is the full range 30-60 dB? Is there a +/-  trim as well?

Click to expand...

There's a 20dB switched pad as well so the full range is 10dB to 60dB. There is no trim other than the channel fader.

Cheers

Ian

Worth remembering a lorlin 12 way doesnt rotate 360 degrees ,I guess it would take 13 clicks to go full circle ,so the indexing comes out at 27.69 degrees  per click ,do double check this in any case .
The 3.33 db steps and a marking every 10db definately looks more logical to my minds eye .

ruffrecords said:

It occurred to me if I made the steps 3.33 dB then every quarter would be 10dB so I could label the panel 60, 50, 40 and 30. I tried it on the panel layout and it does look a lot better.

Click to expand...

A clever and elegant solution!  Gets my vote and I might just use that idea myself in the future 

ruffrecords said:

Initially I was going to use 3dB steps but, when you lay out the panel you really only need to place an actual value on the panel every 90 degrees. If you do this with 3dB steps you get values on the panel of 60, 51,42 and 33 and they look really odd to my eye.

Click to expand...

If using 3dB steps I would label every 6dB: 60, 54, 48, 42, 36, 30

I would determine the step size with the min and max gain you want divided by the number of steps - seems a little strange to chose the switch and the step size first.

dmp said:

I would determine the step size with the min and max gain you want divided by the number of steps - seems a little strange to chose the switch and the step size first.

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That is what I did. That's how I came up with 12 x 3dB steps. It was only when I drew the front panel I realised it didn't look so good.

Cheers

Ian

Tubetec said:

Worth remembering a lorlin 12 way doesnt rotate 360 degrees ,I guess it would take 13 clicks to go full circle ,so the indexing comes out at 27.69 degrees  per click ,do double check this in any case .
The 3.33 db steps and a marking every 10db definately looks more logical to my minds eye .

Click to expand...

Lorlins rotate 330 degrees in 30 degree steps. Position 1 is 0 degrees, 2 is 30, 3 is 60, 4 is 90, 5 is 120, 6 is 150, 7 is 180, 8 is 220, 9 is 240, 10 is 270, 11 is 300 and 12 is 330.

Glad you like the 3.33dB steps.

Cheers

Ian

Hi Ian

I have turned to switches intead of pots in my builds and I have thought about this "problem" as well. I found out that I might want to change or alter the circuit at some point and it would be very impractical to get a new front panel at the same time so I decided to "write" -dB for every step... like -3dB, -6dB etc.

I try to chose steps that includes the whole gain range... like if I have 66dB of gain in a preamp I make the switch a 11 step 6dB... I have another swith for fine adjustment as well.

And thanks for the tip about the 220µF caps...

Best regards

/John

ruffrecords said:

I did them at 3dB in the EZTubeMixer.  if I made the steps 3.33 dB then every quarter would be 10dB

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The gain on a classic mic amp is only accurate to within about 0.5dB of the silkscreen label anyway. Nobody is going to care about .33 of a dB.

merlin said:

The gain on a classic mic amp is only accurate to within about 0.5dB of the silkscreen label anyway. Nobody is going to care about .33 of a dB.

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Good point.

CHeers

Ian

Big fan of 3.33...huge!

Gustav

ruffrecords said:

Lorlins rotate 330 degrees in 30 degree steps. Position 1 is 0 degrees, 2 is 30, 3 is 60, 4 is 90, 5 is 120, 6 is 150, 7 is 180, 8 is 220, 9 is 240, 10 is 270, 11 is 300 and 12 is 330.

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We used to have brain teasers at school with fences, the number of posts and number of panels, and the exception when the fence is closed.... I believe there's the same in the UK.

abbey road d enfer said:

We used to have brain teasers at school with fences, the number of posts and number of panels, and the exception when the fence is closed.... I believe there's the same in the UK.

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We have the same right now trying to decide how many Portuguese Laurel plants to buy to fill the border along our back fence. The ones we have chosen need to be planted 60cm apart. Do you just divide the fence length by 60cm and add one? or do you subtract one? or neither?

Cheers

Ian

ruffrecords said:

We have the same right now trying to decide how many Portuguese Laurel plants to buy to fill the border along our back fence. The ones we have chosen need to be planted 60cm apart. Do you just divide the fence length by 60cm and add one? or do you subtract one? or neither?

Cheers

Ian

Click to expand...

Several possible answers:
C) they can be planted 30cm from the final post (or wall), then you do L/60cm, because actual required clearance is 30cm either side
B) you really want them 60cm away from the final posts, then you substract one
C) there is no final posts on either side, you need to add one

abbey road d enfer said:

Several possible answers:
C) they can be planted 30cm from the final post (or wall), then you do L/60cm, because actual required clearance is 30cm either side
B) you really want them 60cm away from the final posts, then you substract one
C) there is no final posts on either side, you need to add one

Click to expand...

Exactly. We will probably go for the first option because we have fences at either end and we want the long term growth to be (relatively) even. Not easy to explain to my better half.

Cheers

ian

ruffrecords said:

Not easy to explain to my better half.

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I've found that making a nice drawing (particularly if the colours of the plants are nicely rendered) helps a lot