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jFET phono preamp - boozhoundlabs
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Author:  alahti [ 20 Mar 2014, 12:50 ]
Post subject:  Re: jFET phono preamp - boozhoundlabs

Just want to say that if RIAA 20 Hz ideal response is needed then replace 28K resistor to 56K. From 30-100 Hz is difference then 0.4db and in 20 000 to 75 000 Hz is -0.2 db. Original chematics were used.

Author:  malinky [ 09 Jul 2015, 12:31 ]
Post subject:  Re: jFET phono preamp - boozhoundlabs

Hi Guys,
I know that this is a really old thread but i have recently completed the Boozehoundlabs phono preamp, and it is fantastic.
The only problem is that it is REALLY quiet!
When i say quiet i mean that i have to turn the amp nearly all the way up to `11` to get even a reasonable volume.
And even i know that this is not a good idea.
I read the modification kindly posted by `Ht performance` which suggested placing a 470uF electrolytic audio grade capacitor to R3.
So i go online and see that capacitors come in different voltages, now i know that this is a stupid question but what voltage capacitor would be required?
I know nothing about electronics so go easy on me.
If anyone can suggest a suitable component, or even provide a UK link to a ideal quality one on the `Bay` I would be very grateful.
Thank you so much.

Author:  mwhouston [ 09 Jul 2015, 17:51 ]
Post subject:  Re: jFET phono preamp - boozhoundlabs

The phono preamp have good gain and a high output. It sounds like there is something wrong with your build. The cap may not fix the output issues. Recheck components. You may have a fet in the wrong way.

Author:  malinky [ 11 Jul 2015, 00:52 ]
Post subject:  Re: jFET phono preamp - boozhoundlabs

mwhouston wrote:
The phono preamp have good gain and a high output. It sounds like there is something wrong with your build. The cap may not fix the output issues. Recheck components. You may have a fet in the wrong way.


Many thanks mwhouston, I will look into that.
But does anyone know the answer to my question about capacitor voltages, as i would like to try the modification anyway.
Thank you.

Author:  mwhouston [ 11 Jul 2015, 01:07 ]
Post subject:  Re: jFET phono preamp - boozhoundlabs

where is R3, what resistor is it?

Author:  malinky [ 12 Jul 2015, 11:58 ]
Post subject:  Re: jFET phono preamp - boozhoundlabs

Have not looked yet.
Just asking about the modification suggested by `Ht performance` a few pages back.
Cannot find my printed circuit diagram at the moment, so I will have to look on the `Boozehound` site.

Author:  malinky [ 13 Jul 2015, 08:33 ]
Post subject:  Re: jFET phono preamp - boozhoundlabs

mwhouston wrote:
The phono preamp have good gain and a high output. It sounds like there is something wrong with your build. The cap may not fix the output issues. Recheck components. You may have a fet in the wrong way.

Just checked and all FETS are in correctly.

Author:  HT Performance [ 13 Jul 2015, 09:25 ]
Post subject:  Re: jFET phono preamp - boozhoundlabs

malinky wrote:
Have not looked yet.
Just asking about the modification suggested by `Ht performance` a few pages back.
Cannot find my printed circuit diagram at the moment, so I will have to look on the `Boozehound` site.


Hi!

I also felt the need for a little more gain, to feed the oddwatt tube amplifier, because I am running the 6SL7 tube instead of the higher gain 12AX7.

By that time, I made several calculations and also performance tests measurements and the RIAA response is perfect.

You can use electrolytic capacitors starting from 25v.

I am very sure, that if your project is currently well wired like the schematic, you will be extremely happy with this simple modification.

Let us know your listening impressions! :)

Image


Cheers,

Miguel

Author:  malinky [ 13 Jul 2015, 09:57 ]
Post subject:  Re: jFET phono preamp - boozhoundlabs

HT Performance wrote:
malinky wrote:
Have not looked yet.
Just asking about the modification suggested by `Ht performance` a few pages back.
Cannot find my printed circuit diagram at the moment, so I will have to look on the `Boozehound` site.


Hi!

I also felt the need for a little more gain, to feed the oddwatt tube amplifier, because I am running the 6SL7 tube instead of the higher gain 12AX7.

By that time, I made several calculations and also performance tests measurements and the RIAA response is perfect.

You can use electrolytic capacitors starting from 25v.

I am very sure, that if your project is currently well wired like the schematic, you will be extremely happy with this simple modification.

Let us know your listening impressions! :)

Image


Cheers,

Miguel

Many thanks for your reply (help from Portugal and Australia, what a wonderful thing).
I will do the modification you have suggested, and I apologize for my lack of knowledge.

Author:  mwhouston [ 13 Jul 2015, 19:25 ]
Post subject:  Re: jFET phono preamp - boozhoundlabs

Now I see where the cap is to go. Yes should improve gain.

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