aviel

looking for recommendations: preamp a perfboard - EDIT: FETBOY
« on: November 06, 2018, 09:30:11 AM »
Hey,
i just completed my DIY 500 lunchbox, equipped with a diyre cp5. looking to add another one to the the arsenal.
i am looking for something that i can build on my own (perfboard, since i am not int etching yet), do you have any recommendations? something "colored" can be nice.
« Last Edit: November 25, 2018, 06:07:32 AM by aviel »


Re: looking for recommendations: preamp a perfboard
« Reply #1 on: November 06, 2018, 03:32:24 PM »
My advice is the Hamptone JFET Preamp aka Fetboy. Easy to build,  tons of colour as micpre and DI for instruments.

aviel

Re: looking for recommendations: preamp a perfboard
« Reply #2 on: November 06, 2018, 05:28:22 PM »
Thanks! Will have a look on this forum i assume there should be plenty of info? Did you build one?

Re: looking for recommendations: preamp a perfboard
« Reply #3 on: November 06, 2018, 05:47:17 PM »
Yes, you will find everything you need here in the forum and yes, I have build some of them.

aviel

Re: looking for recommendations: preamp a perfboard
« Reply #4 on: November 08, 2018, 06:48:15 PM »
Another thing is, i would like to use it with my current psu in the lunchbox. I have +-16, i assume i could convert it to a dual rail supply, what do you think?

Re: looking for recommendations: preamp a perfboard
« Reply #5 on: November 08, 2018, 10:02:02 PM »
You do not need a dual rail psu for the fetboy, it will work with a  16V single rail supply. 24V would be better though.  You asking for colour, the low voltage will give you more of them. 8)

Just build it up, only a few components a needed. You can start without the transformer, just use it as a DI box, then you can extend it with a cheap 1:5 to 1:10 input transformer and you will get everything you want.

It is a perfect project to build it up on perfboard, the result could be great in my opinion. The only challenge is to work with FETs, the need a lot of adjusting or selecting.

Have fun!
« Last Edit: November 09, 2018, 01:51:12 AM by rock soderstrom »

aviel

Re: looking for recommendations: preamp a perfboard
« Reply #6 on: November 09, 2018, 02:31:40 AM »
Awesome!
one thing though,
must of the links are offline, do you have some on your side that you might share? pictures/diagram/sound samples/ anything?

Thanks! ;D

Re: looking for recommendations: preamp a perfboard
« Reply #7 on: November 09, 2018, 04:42:20 AM »
Awesome!
one thing though,
must of the links are offline, do you have some on your side that you might share? pictures/diagram/sound samples/ anything?

Thanks! ;D

I know it is a bit PIA but it is all there. Check the several threads here in the forum, you will find a lot of useable infomation.

aviel

Re: looking for recommendations: preamp a perfboard
« Reply #8 on: November 13, 2018, 01:15:51 AM »
got it,
i am still thinking if i should i convert it to dual rail supply. +-16.
what psu did you use? just a regulated wallwart?

Re: looking for recommendations: preamp a perfboard
« Reply #9 on: November 13, 2018, 05:19:50 AM »
I have done it with a LM317 based PSU and it works with a unregulated wallwart, aswell. Null problemo! There is no need to convert it to a bipolar PSU, but its DIY you can do it that way if you want to.


aviel

Re: looking for recommendations: preamp a perfboard
« Reply #10 on: November 13, 2018, 06:14:41 AM »
the only reason i wanted to convert is to use it with the PSU i already have, which is +-16v for diyre CP5 preamp. i am assuming that 16V  supply only will reduce the headroom drastically.

Re: looking for recommendations: preamp a perfboard
« Reply #11 on: November 13, 2018, 08:10:23 AM »
AFAIK, +-16V = 32V with a floating earth. You can use that or regulate it down to 24V with a LM7824 or LM317. I have never done this before, but it should work, right?

I would start with a test setup based on the +16V rail, just to see if the headroom is sufficient for your application. My bass DI operates with 18V and I really like it.

aviel

Re: looking for recommendations: preamp a perfboard
« Reply #12 on: November 13, 2018, 08:19:02 AM »
Im not sure about converting it, the PSU earth is grounded to the chasis and to the wall, so i wouldn't say it is floating. the audio grnd is also grounded to the chasis, i am not sure if it iwll work.

Re: looking for recommendations: preamp a perfboard
« Reply #13 on: November 13, 2018, 08:30:40 AM »
My idea was to isolate the ground of the fetboy from chasis and PSU ground so that the Fetboy is floating. But I am not sure if it works.

Again: "I would start with a test setup based on the +16V rail, just to see if the headroom is sufficient for your application. My bass DI operates with 18V and I really like it."  ;)

aviel

Re: looking for recommendations: preamp a perfboard
« Reply #14 on: November 13, 2018, 09:03:30 AM »
yes, i will definitely try it first with 16 Vdc. will also add a input transfomer for mic input

aviel

Re: looking for recommendations: preamp a perfboard
« Reply #15 on: November 21, 2018, 05:28:16 PM »
rock soderstorm, what jfet did you use in your build?


aviel

Re: looking for recommendations: preamp a perfboard
« Reply #17 on: November 22, 2018, 03:44:53 AM »
what about the BD139? did you use darlington pair as in Fabio's schematic? is it critical to get that hfe of 20.000?
there was some discussion regarding if you should match and bias them, but seems that the links are offline

Re: looking for recommendations: preamp a perfboard
« Reply #18 on: November 22, 2018, 05:08:20 AM »
I use always the MPSA14/ZTX653 version, they are cheap and easy to source. In my opinion it is critical to bias the FETs into the right position (~B+/2). You can do that with trimmers. I prefer to select my 2N5457s for the the right one. I got a little selfbuild testing device for that. The disadvantage of this method is, you need a lot of FETs, because their parameters are all over the place.

Another advice: I have made my source capacitors switchable, so I can control THD, gain and the overall sound of the preamp. Very useful in my opinion. Some have used potis for that, for me the three switching positions are enough. Choose the size of the caps according to your taste.
« Last Edit: November 22, 2018, 07:39:27 AM by rock soderstrom »

aviel

Re: looking for recommendations: preamp a perfboard
« Reply #19 on: November 22, 2018, 06:03:30 AM »
will a DMM that measure  hfe be enough for selecting the fets?

i have ~6x 2N5457 and ~20x J201, hopefully i can use J201 instead. do you select the 5457s according to hfe? or Voltage?


 

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