how would i go about getting about 6db of gain out of an opamp?

[PRR]

> how to do a trimless mu-amp

Put the higher Idss part on top. (Or is it vice-versa?)

> Op amps ... seem to be a little taboo among stompboxers around these parts...

What parts do you live in? Move!

Or do you mean this forum? Everybody has a different opinion. Objectively, simple (discrete) has "more interesting distortion". But when you need precision frequency-sawing, can't easily beat an opamp. And you find many plans using opamps in utility chores (buffers, mixers) supporting "flavor stages".

> tolerant to the variation in device characteristics, for instance. Op amps do seem to be

That's what they are for. Mathematical operations with precision far better than the +/-20% slop in tubes. If you need the simple operation "times 10", you can aim a tube for gain of 10, and actually get 8 to 12. Or you can work two tubes at Gv=30, total 1,000, then use 1% resistors to get gain of 10 +/-2%. Couple transistors gives gain over 10,000, few more give differential inputs and buffered outputs.....

[DougH]

Gain (db) = 20 Log Gain

I didn't see anyone mention that.

[Mac Walker]

Gain (db) = 20 Log Gain

I didn't see anyone mention that.

It's been a while, but...

gain = 10 log v1 squared/v2 squared = 20 log v1/v2, where v=peak to peak voltage

So for a gain of 6 db -

6 = 20 log v1/v2

therefore v1/v2 should be around 2:1

[sault]

In my audio programming I came across a relatively quick and dirty method of converting db to ratios... converting back isn't quite as easy, though!

db -> ratio  is   2 ^ ( db / 6 )
ratio -> db  is   6 * (log ratio) / (log 2)

It's a lot cheaper CPU-wise. At plus or minus 40 db it's about 1% inaccurate, at 60db about 10% inaccurate. Not bad. Plus, it's an easy way to approximate mentally... I can think "oh yeah, 6 db divided by 6 is 1, so db is therefore 2x".

[PRR]

10:1 Voltage is 20db exactly.

So "40db" must be 10*10= 100"1 ratio of voltage.

2:1 is actually 6.02db. So for "about 6db of gain" we can pencil "2:1", but if you extrapolate to say 40db you come out a little off AND it's easier to use 10=20db.

Other cheats:
10db is about 3 (3.162:1)
15db is about 5 or 6 (5.63)
60db is 1000:1 exact
3db is 1.414
1db is very close to 10% more (1.122)