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Old 1st September 2004, 02:45 PM   #1
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Default simple input stage for amp?

I am looking to build a voltage gain stage for a mosfet power follower.

gain of around 10-15.

low distortion...

thinking JFETS, BJTs, tubes?

ideas?

Thanks!
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Old 1st September 2004, 08:55 PM   #2
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Default Re: simple input stage for amp?

Quote:
Originally posted by AudioGeek
I am looking to build a voltage gain stage for a mosfet power follower.

gain of around 10-15.

low distortion...

thinking JFETS, BJTs, tubes?

ideas?
How 'bout... (here's your cue, Jam) transformers?

What will be driving the input stage? If it can drive a 1.5k load and has an output impedance of around 150 ohms or less, and depending on the input circuitry of the MOSFET power follower, it may be possible to get your voltage gain with nothing more than a transformer.

Oh, and depending on what sort of input levels you expect to be driving the transformer with.

se
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Old 1st September 2004, 09:00 PM   #3
jam is offline jam  United States
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Steve,

You are back...............I knew you could not stay away!

Here is one for you....
Attached Images
File Type: gif 13k7atb.gif (22.9 KB, 271 views)
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Old 1st September 2004, 09:23 PM   #4
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Quote:
Originally posted by jam
You are back...............I knew you could not stay away!
Me too. It's like trying to quit smoking.

Quote:
Here is one for you....
Ooooo! Let me go get some Jergins and some Kleenex!

se
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Old 1st September 2004, 10:07 PM   #5
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Quote:
Originally posted by jam
Steve,

You are back...............I knew you could not stay away!

Here is one for you....

Is this an audio transformer?? I like the fact that it is shielded. I am designing an amp that has a transformer input where the seconary drives the base of my first differential transistor. I like the sound and also the DC stability. Obviously the shielded transformer would be better in shielding RF and other noise. Where can I find one of these?????
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Old 2nd September 2004, 02:43 AM   #6
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Quote:
Originally posted by cunningham
Is this an audio transformer?? I like the fact that it is shielded. I am designing an amp that has a transformer input where the seconary drives the base of my first differential transistor. I like the sound and also the DC stability. Obviously the shielded transformer would be better in shielding RF and other noise. Where can I find one of these?????
You can find that one at Jensen Transformers. That particular model is a 1:5 step-up transformer designed for microphone preamps.

For a 1:1 input transformer, their JT-11P-1 or their JT-11P1-4 would be more suitable.

Also, CineMag makes high quality transformers (same level of quality as the Jensens as far as I've been able to tell) for significantly less.

se
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Old 2nd September 2004, 03:40 PM   #7
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Default pre-buffer?

If I used say a ZVP3310 p channel connected to a +30, -30 supply.

run as another source follower and cap couple with 4.7uf to gate of output mosfet.

if i did this... could I use a 1:5 or 1:10 input transformer?

and how would I connect the input circuitry?

The ZVP3310 is just "self biased" with a 1K resistor from source to +30v

The drain is connected to -30v.

how do I connect the gate of the input mosfet to secondary of transformer? how do i load the transformer?
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Old 2nd September 2004, 08:43 PM   #8
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Default Re: pre-buffer?

Quote:
Originally posted by AudioGeek
If I used say a ZVP3310 p channel connected to a +30, -30 supply.

run as another source follower and cap couple with 4.7uf to gate of output mosfet.

if i did this... could I use a 1:5 or 1:10 input transformer?

and how would I connect the input circuitry?

The ZVP3310 is just "self biased" with a 1K resistor from source to +30v

The drain is connected to -30v.

how do I connect the gate of the input mosfet to secondary of transformer? how do i load the transformer?
Before getting to all that, what component will be driving the input of the tranformer? A preamp I presume? If so, do you know what its output impedance is?

These microphone transformers were designed to be fed from a 150 ohm source impedance (or less). If you'll be driving the transformers with some high source impedance preamp such as a tube preamp, then the transformers may not be a good option.

se
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Old 3rd September 2004, 03:04 PM   #9
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Default how about this?

how about a tube driving either a CF or an IT connected to the gate of the mosfet?

OR.... a u-follower with a SS mosfet as load connected as source follower connected to gate of output mosfet?

similar to an alan kimmel gain stage connected to the source follower???

that should be low enough input impedance on the gate for HF use?

thoughts?

use a ECC99 with a IRF712 or something cap coupled (10uf oils) to gate of IRFP240n running at 30vdc and 4A.
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Old 3rd September 2004, 09:54 PM   #10
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Default Re: how about this?

Quote:
Originally posted by AudioGeek
how about a tube driving either a CF or an IT connected to the gate of the mosfet?

OR.... a u-follower with a SS mosfet as load connected as source follower connected to gate of output mosfet?

similar to an alan kimmel gain stage connected to the source follower???

that should be low enough input impedance on the gate for HF use?

thoughts?

use a ECC99 with a IRF712 or something cap coupled (10uf oils) to gate of IRFP240n running at 30vdc and 4A.
Well, as you can see, there are any number of possible solutions. Which one will give you the best result will be difficult for anyone to say. If you've the time, why not experiment yourself with a few different options?

se
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