i need at least 30 db gain as a buffer...what do i do?

[casey]

I'd be really happy if someone else could try the RG Adjusticator and give some report, I've 3 of them and it's amazing!

I used 5532 opamp.
It has enough boost for using it as "nice" practice amp with my 4x12 marshall cab, I was scared when I first tried it as an amp.

Regards
Kleber AG

where is the schematic for this?  it sounds interesting...

[puretube]

it's quieter than the TL062/72/82 stuff.

sorry to interfere, here;
the TL0x stuff goes s.th. like this:
TL06X = lo current consumption;
TL07X = lo noise;
TL08X = normal;

[gez]

5532...beautiful sounding amp, quiet...but a little high on the juice compared to many amps (well, the ones I use), plus a little tight when it comes to headroom (2V short of each rail if my memory serves me well...which would be a first!).

[David]

Casey:

Did you try running the guitar through the preamp first, and then adding EQ to the result?  I've tried a Blue Tube in the past, and it seemed like it had a pretty even, flat response to me...

[R.G.]

Casey,

Just curious - how did you come to needing at least 30db of gain?

[puretube]

R.G.: http://www.lrbaggs.com/html/products/pickups_ibeam.shtml
(click "features" : it says 20 to 25 dB, and I guess casey wants some xtra
dB for making up equalizing losses)

[casey]

Casey,

Just curious - how did you come to needing at least 30db of gain?

hey r.g. - i am needing 30 db of gain due to an eq that i am
building out of a book that says that the preamp to run it,
has to be at least 30 db to make up for losses to at least
run unity....  it's a schem. of a guitar eq.....  this book as
alot of guitar circuits ive never seen.  one of them is
a tube vibrato that looks fairly simple.....

i was looking at the preamp by bob blick.....i figured that would
be a good start....so then i was just going to blend the two into
one circuit......  plus..... the presonus tube pre is being pushed about
half way to make up for the 10 M (i think) from the passive i-beam.

[casey]

R.G.: http://www.lrbaggs.com/html/products/pickups_ibeam.shtml
(click "features" : it says 20 to 25 dB, and I guess casey wants some xtra
dB for making up equalizing losses)

yup

[RDV]

Casey:

If you use the simple little circuit I posted with a 100k trimpot in the FB loop, I believe that you can dial in the amount of gain you're wanting. It's just based on R.G.'s 'Adjusticator'(which would also work). I would use a dual OA and use the 1st half as a simple buffer to drive the EQ, and then my little circuit at the end as a volume recovery.

But that's just me.  :wink:  

RDV

[casey]

yup, i think that would be the most graceful way to do it....

i think ill give that a try.....

thanks rdv

Casey:

If you use the simple little circuit I posted with a 100k trimpot in the FB loop, I believe that you can dial in the amount of gain you're wanting. It's just based on R.G.'s 'Adjusticator'(which would also work). I would use a dual OA and use the 1st half as a simple buffer to drive the EQ, and then my little circuit at the end as a volume recovery.

But that's just me.  :wink:  

RDV

[puretube]

the presonus pre only got an input-impedance of 1M (good for normal magnetic pickups),
i.m.h.o.  not enuff for piezo, what I suspect the i-beam to be...

this is the hi-Z pre I suggested:


you can use other opamps, and probby need some caps in front and after, if you convert it to single power supply.
Somebody else will help with that. (gez?  :wink: )

ps: I`m not too sure about the Z-in calculation, but should be roughly so...

[casey]

the presonus pre only got an input-impedance of 1M (good for normal magnetic pickups),
i.m.h.o.  not enuff for piezo, what I suspect the i-beam to be...

this is the hi-Z pre I suggested:


you can use other opamps, and probby need some caps in front and after, if you convert it to single power supply.
Somebody else will help with that. (gez?  :wink: )

ps: I`m not too sure about the Z-in calculation, but should be roughly so...

wow, thanks pure tube.....  
your the best!!!  

ill let you know how it goes....

[puretube]

ahh, borrowed the schem from "Horowitz & Hill"
(Art of Electronics)  

[Mark Hammer]

A common strategy with creating big output voice mic preamps is to cascade several gain stages.  Remember that gain is multiplicative.  So, two stages, each with a gain of 10x, yields a gain of 100x.

One of the advantages of this, which generally means diddley squat for electric instruments but much more for acoustic ones, is that slew rate is less of an issue.  When the amount of voltage swing needed is distributed across several devices, no single device has to swing farther than it is capable of.  As well, higher gain from a single stage will often mean a higher value resistor *somewhere*, and that can mean more thermal noise.  In the case of Ton's suggested OP-41 circuit, this seems not to be an issue, though.

[casey]

A common strategy with creating big output voice mic preamps is to cascade several gain stages.  Remember that gain is multiplicative.  So, two stages, each with a gain of 10x, yields a gain of 100x.

One of the advantages of this, which generally means diddley squat for electric instruments but much more for acoustic ones, is that slew rate is less of an issue.  When the amount of voltage swing needed is distributed across several devices, no single device has to swing farther than it is capable of.  As well, higher gain from a single stage will often mean a higher value resistor *somewhere*, and that can mean more thermal noise.  In the case of Ton's suggested OP-41 circuit, this seems not to be an issue, though.

dumb question:

what is a op-41 and where do i find it?
also, where does the voltage come in on this circuit?  same as others?

[Mark Hammer]

(not so) dumb question:

what is a op-41 and where do i find it?
also, where does the voltage come in on this circuit?  same as others?

Though it is not one I am familiar with, I am assuming the OP-41 to be another in Analog Devices line of high quality op-amps.  I tried searching for it at Analog Devices website (http://search1.analog.com/searchProxy.asp) but it didn't show up.  If you have the time, you canm try seeing if it is here (http://www.analog.com/Analog_Root/sitePage/mainSectionResource/0,2131,level4%253D%25252D1%2526Language%253DEnglish%2526level1%253D150%2526level2%253D%25252D1%2526level3%253D%25252D1%2526resourceWebLawID%253D13,00.html) in their complete listing.

If the OP-41 is a single op-amp, the chances are 99.999% that it will have the same pinout as a 741 or TL071, which means V+ will go to pin 7 and V- to pin 4.

[casey]

very cool.... thanks.  

i appreciate everyone's help here..... ya'll have been very helpful.  

[puretube]

don`t think an OP41 is "neccessary";
guess you get good results with some NE55xx,
or any FET-input opamp;

have tried the circuit with 1/4 LM324, single supply: works
(however did I not measure any impedances or noise issues...)

[Kleber AG]

Casey
Sorry, I'm too late, but if you still have not found the Adjusticator, it's at the RG site:

http://www.geofex.com/circuits/Adjusticator.gif

Kleber AG

[casey]

Casey
Sorry, I'm too late, but if you still have not found the Adjusticator, it's at the RG site:

http://www.geofex.com/circuits/Adjusticator.gif

Kleber AG

that's cool.....i think i can use this on another project as well....
so it's not too late....  thank you kleber...