inline gain ?

[hobbycore]

Hello, I need to make some sort of inline gain device to increase the level of a drum trigger before hitting the sampling device. I'm not terribly brilliant with electornics, but I think i can figure out something this simple with guidance.

I figure I need about 8db to get the sensitivity in optimal range, but the sampler is tunable so something in that range is usable.

How do I go about this?

edit: I should mention that audio quality doesn't really matter much since this is a trigger signal.

[nclayton]

A really simple way would be to use this:

http://www.edcorusa.com/products/transf ... k-15k.html

If you wired the primary just to the center tap you'd have about 2.5K:15K and pretty darn close to the gain you want without having to worry about powering or really building anything more than a box.

There are lots of options for active circuits. how do you want to power it? Battery or AC?

[hobbycore]

Well, here is where I demonstrate my absolute ignorance of electronics...

I was hoping for a passive way to do so. Quite simply, the trigger signal is too soft for this particular sampler so I need it louder.

I currently just throw it through my mixer, but that's not the most elegant solution live. I am trying to keep the kit as small as possible (a set of pads and a laptop).

It appears that transformer would work well, any other options?

[apropos of nothing]

Well, here is where I demonstrate my absolute ignorance of electronics...

I was hoping for a passive way to do so. Quite simply, the trigger signal is too soft for this particular sampler so I need it louder.

I currently just throw it through my mixer, but that's not the most elegant solution live. I am trying to keep the kit as small as possible (a set of pads and a laptop).

It appears that transformer would work well, any other options?

Lord have mercy do I wish there were passive amplifiers. Unfortunately, no pain, no gain. ...As it were.

[nclayton]

It appears that transformer would work well, any other options?

Ditto the last post, if you want passive a transformer is basically the only way, but it's a good way, and those edcors aren't too expensive.

I say basically, because theoretically you could passively multiply the voltage using diodes since you're only concerned about level and not passing a listenable signal. But if you're already dealing with a low level signal the diode voltage drops would probably be a problem. I don't think it's probably worth experimenting with.

Ned

[Andy Peters]

It appears that transformer would work well, any other options?

Ditto the last post, if you want passive a transformer is basically the only way, but it's a good way, and those edcors aren't too expensive.

I say basically, because theoretically you could passively multiply the voltage using diodes since you're only concerned about level and not passing a listenable signal. But if you're already dealing with a low level signal the diode voltage drops would probably be a problem. I don't think it's probably worth experimenting with.

HUH? This is NOT an application for a voltage multiplier.

-a

[hobbycore]

How do I figure the "gain" I'd be getting by using the transformer?

[FiveFish]

If the transformer has a 1:2 ratio, then it's 6dB gain.
1:3 ratio .. = 9dB
1:4 ratio = 12db
1:8 ratio = 18dB

[emrr]

How do I figure the "gain" I'd be getting by using the transformer?

There's a basic formula you'll find if you search the innertube. I don't keep it in my head, or have it in front of me ATM. Theoretical gain will also be affected by transformer loss (-1/2db with Edcor) and load impedance. If you put the 15K secondary into something like a 5K input, you'd probably have additional loading losses, though they may be minor.



Voltage multiplier; hmm. Only have 2 sec to think about this, but seems interesting. Losses maybe too great, but as stated, listenable signal not an issue, only louder signal with some remaining AC component. Probably. Worth a try for shits and giggles. I can't say definitively it won't work.


Cheap step up transformer easier on the DIY.

[brianroth]

If you know the *turns* ratio, that is also the (approx) voltage step up/down ratio. IOW, a transformer with a 1:2 turns ratio will step up the voltage by 2x. (The "approx" allows a bit of wiggle room for insertion loss that a "real world" transformer has).

To convert from voltage ratio to dB, you take the common logarithm of that number then multiply the result by 20. That's a no-brainer to do with a cheap $10 "scientific" calculator. Examples, as punched into the cheapo TI-30Xa I keep in my briefcase:

1. Assuming the transformer has a 1:2 turns ratio (hence, output = 2x input), I punch in the digit "2" (which is the turns and/or voltage ratio) then punch the "LOG" key, then the digits "20", and the result is 6.020599913 <G> dB. Call it 6 dB!

2. Assume a mic transformer with a 1:10 turns ratio (and hence a 10x voltage step-up), I punch in the digits "10", punch the "LOG" key, then the digits "20" and I end up with 20 dB.

Now, if you don't know the turns ratio, but instead the spec sheet talks about primary and secondary impedances (more on that subject in a moment), there is an extra step you have to make. Example:

1. Transfo spec sheet says "primary impedance 600 Ohms, secondary 10,000 Ohms". Divide 10,000 by 600 and you come up with an impedance ratio of 16.66666.... Next, punch the "square root" key on the calculator to get the turns ratio of 4.08. THEN punch that number into the formula I mentioned above: 4.08 (punch LOG key) then multiply by 20. That answer will be approx 12.22 dB.

Finally, a transformer does NOT have an "inherent impedance". In my last example using a spec sheet, the manufacturer was saying that "if you connect a 10,000 Ohm load across the secondary, then 600 Ohms will be "reflected" back to the primary."

More info here:

http://www.jensentransformers.com/an/Au ... hapter.pdf

Bri

[hobbycore]

Thank you brian, that was clear and helpful.

[nclayton]

HUH? This is NOT an application for a voltage multiplier.

-a

Did somebody say it was?

But in GENERAL, in addition to a transformer, there's at least one other way to passively amplify a signal and that's with a diode multiplier. It will be acceptable if 1) you're only interested in the peak level being amplified and don't need any other information out of the signal and 2) you have enough signal to overcome the diode drops to the point you get worthwhile amplification.

#1 applies in his case.

I don't know the actual trigger level or the driving level, so can't judge whether #2 applies, but I'm guessing it does not, and so it's not a good fit. With ideal diodes or a much bigger signal, though, it would probably work great for him and actually be the best solution. With Ge diodes it MIGHT actually work. Si...not likely.

Like a transformer it swaps voltage for current so you need a lower impedance source and a higher impedance load.

I don't think it's worth his time or effort to mess with when a $10 transformer is guaranteed to do the job OK.

just trying not to lie.

[nclayton]

How do I figure the "gain" I'd be getting by using the transformer?

If you wired that transformer the way I suggested you'd be getting about 7.8 dB of gain minus any insertion loss.

I think Brian and others covered most everything, but I think one thing that was left out was impedance ratio vs turns ratio.

If you know a transformer's suggested impedances at each coil, you find the ratio of them and take the square root to get the turns ratio. So here's how you get from A to B with the transformer I suggested.

That's a 10K to 15K transformer.

15,000/10,000 = 1.5 (impedance ratio)

The square root of 1.5 is 1.225 (turns ratio)

If you wire just to the center tap the primary will have 1/2 the number of turns as it would have otherwise, so the turns ratio doubles to 2.45.

So you get voltage step up of 2.45

20*log(2.45) = 7.78

So the gain is 7.78 dB


Now working backwards, since you know that the impedance ratio is equal to the turns ratio squared and the turns ratio is (with the center tap wired) 2.45, then the new impedance ratio must be

2.45^2 = 6

So the primary impedance is 1/6 of the secondary impedance. If the secondary impedance is 15k ohms, then the primary is 2.5K ohms.