Add Gain to Country Hick

thought this old circuit was not working as it only had a gain of 1,

come to remember that is normal, meant to transform impedance down from guitar pickup,

seems a shame to waste power and transistors,

is there an easy mod to get maybe a x 10 gain out of this?

thanks!

CJ not without a circuit change.
That is a nice follower circuit.

The schematic shows a source follower with a constant current source in the source leg and the added JFET current boost from  the top NPN. Note R8 and the Vbe drop of the "top" NPN and the somewhat constant current in the JFET.

I am thinking about what R9 is for.
S and D are drawn backwards however,  IIRC a 2n5457 is symmetrical maybe the schematic is drawn this way to mislead a little.

It is a simple follower... to add gain means changing the design.

The output buffer may also be drawn incorrectly. More likely the two diodes are between the two bases with resistor to ground.

JR

Look at the schematic in the following link note the follower setup
http://www.coutant.org/sonyc37fet/c38b.pdf
also look at AKG schematics

The diodes are in the right place for a constant current section in the source leg.

Is the schematic a trace of the DI if so has it been confirmed to be correct?

we built it and it works, but you have to turn up the gain so much on the mic pre that you get more noise than using a simple passive 8:1 transformer for impedance conversion,

thanks for the help you guys!

i have never built the Bo hansen DI so we are excited to give that a shot! 

Removing or shorting r1?

Gus said:

Look at the schematic in the following link note the follower setup
http://www.coutant.org/sonyc37fet/c38b.pdf
also look at AKG schematics

The diodes are in the right place for a constant current section in the source leg.

Is the schematic a trace of the DI if so has it been confirmed to be correct?

Click to expand...

yup my bad a current source loaded emitter follower.

JR

CJ said:

we built it and it works, but you have to turn up the gain so much on the mic pre that you get more noise than using a simple passive 8:1 transformer for impedance conversion,

Click to expand...

Sounds odd though, it should be louder with a 2.5:1 stepdown and healthy out-Z?

Just to rule it out S1 is not somehow internally closed or something? (sorry )


PS: can you frankenstein it into a Hamptone? With improved buffer-
PPS: I don´t understand that odd feedback as well R8/R9

we left that spk circuit out,

maybe it's this cheap yamaha mixer i am using, gonna plug it into an API and see what happens,..

CJ

Something might be wrong with the build as posted before you should have a good output

post voltages at the transistor legs this should help, noise can be flux and dirt by the gate and gate resistor.

5v333 said:

Removing or shorting r1?

Click to expand...

Oh sorry... ignore my post. thought r3 was much lower in value...

made a sim without R9

JFET source  NPN base about 10.2VDC

Output about 9.56VDC

constant current about 1.38mA

JFET has about .247mA    (without R9, Vbe of Q3 / 2.7k = JFET current)

1.38mA - .247mA = mA for the "top" NPN

CJ clean the input area well, diodes 2.5meg, 10meg, 2.7K, gate

CJ
I drew up two DIs with gain. Without the output transformer one has about X10 and the other about X5.7.
They have an extra fun adjustment in the circuits.

Twin-X seems to be gone so what is a good way to post images?

Thanks Gus! i will give that a shot,  i just upload attachments jpg, png,pdf...

we get unity gain out of this thing before UTC 1.58:1 OPT (from RCA solid state preamp)

output looks clean now after we changed the FET to 5457, had J202 in there before,  we will try it again,

left off gate protection diodes, can not see blowing this up with an acoustic guitar pickup,

here are the voltages>

Also interested in the drawing!

ok we rebuilt this on a better circuit board and used the right Fet and it sounds awesome now!  12 volt supply, stripped down model ,

it now beats out the passive DI xfmr by adding a bit more of a compressed sound,  and there is not much extra noise,

100 mv in = about 70 mv out at 1 k hz

using a film cap for the output, batteries will last a long time with the low current draw of this circuit,

The clamp diodes are there to protect against static hits or hot signal voltage at input. Probably added after failures.

JR

i figure that input cap will guard against most of the rough stuff,