Author Topic: can this FET preamp work on 9V?  (Read 2166 times)

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Offline ELS122Topic starter

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can this FET preamp work on 9V?
« on: October 24, 2019, 01:25:03 am »
so I found this schematic for a fantastic sounding FET preamp and I want to power it from a 9 volt.
can this be done whit changing some resistors of different FETs?
 

Offline 001

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Re: can this FET preamp work on 9V?
« Reply #1 on: October 24, 2019, 02:04:36 pm »
I see russian or greek (?) letters here
Old russian  components are  exotic so it is reason to avoid  this schematic
 

Offline ELS122Topic starter

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Re: can this FET preamp work on 9V?
« Reply #2 on: October 24, 2019, 02:13:45 pm »
I live in a place where it rains vintage soviet electronics!
the transistors are KP303A and KP303G idk any substitute for them tho
 

Offline 001

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Re: can this FET preamp work on 9V?
« Reply #3 on: October 24, 2019, 02:19:01 pm »
I live in a place where it rains vintage soviet electronics!

Why not to connect old local EEs?  :-//
 

Offline ELS122Topic starter

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Re: can this FET preamp work on 9V?
« Reply #4 on: October 24, 2019, 02:30:59 pm »
Why not to connect old local EEs?  :-//

wHaT?  :wtf:
i've been looking for 5 minutes on google 'what is a local EE' and just came up whit whine  :palm:
 

Offline 001

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Re: can this FET preamp work on 9V?
« Reply #5 on: October 24, 2019, 03:24:02 pm »

wHaT?  :wtf:
i've been looking for 5 minutes on google 'what is a local EE' and just came up whit whine  :palm:

EE is for electrical engineer  :-DD And You at eevblog now...
 

Offline SiliconWizard

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Re: can this FET preamp work on 9V?
« Reply #6 on: October 24, 2019, 03:29:44 pm »
 
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Offline schmitt trigger

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Re: can this FET preamp work on 9V?
« Reply #7 on: October 24, 2019, 03:50:11 pm »
I see several totem pole connected JFETs.
Additionally, without the JFET datasheet, it is impossible to determine the required Vgs biasing, but most certainly will be several volts.

With the minimum information provided, I would say it would be difficult to bias it correctly with only a 9v supply.

Do you want to power it up from batteries for portability? Why not use a boost converter? There many available at Ebay for a couple of Euros.
I know, they are noisy.....but you can always add lots of post filtering.

Now, if a boost converter is not an option, why not use a pair of A23 batteries? A little thicker than an AA, but 12 volts.
 
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Online Kleinstein

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Re: can this FET preamp work on 9V?
« Reply #8 on: October 24, 2019, 04:25:04 pm »
I don't see a real need for a high supply voltage. It may need different (lower threshold) JFETs for low voltage.  I would suggest a simulation in something like LTSPICE. With suitable FETs it could even run at 3 V or so.  The DC level could also depends on the FET matching. The circuit is 3 stages that could be looked at separately, and the 1 st 2 stages are the same type. The output stage is just a source follower with current sink and thus relatively non critical.

The amplifier works without direct feedback. So the sound could be a little tube like with well measurable distortion.
 
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Offline ELS122Topic starter

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Re: can this FET preamp work on 9V?
« Reply #9 on: October 24, 2019, 05:06:34 pm »
ok I'll try that.
 

Offline ELS122Topic starter

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Re: can this FET preamp work on 9V?
« Reply #10 on: October 24, 2019, 05:08:25 pm »
Why not to connect old local EEs?  :-//
that sentence didn't make sense in my books.
connect old engineers??  :-DD
 

Offline ELS122Topic starter

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Re: can this FET preamp work on 9V?
« Reply #11 on: October 24, 2019, 05:15:16 pm »
Have you taken a look here: https://www.diystompboxes.com/smfforum/index.php?topic=83787.0
wow I forgot about that tread, I've seen it before just forgot about it!
 

Offline SiliconWizard

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Re: can this FET preamp work on 9V?
« Reply #12 on: October 24, 2019, 05:50:55 pm »
I guess you could replace the JEFTs with the more common J201, especially if you want it to work properly at lower voltages. You will probably have to adjust many of the resistors' values though.
LTSpice has a model for it, so you can start simulating a bit before building the preamp.
 


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