fet boy

[skipwave]

Fabio's BOM on the first page of this thread: http://www.thediypill.phx.com.br/forumfiles/FETboyMICPRE_bom.xls

Bias 100k's are trimmers. There's no supplier info, but I picked up everything needed from the local RadioShack. You might be able to source all of it locally.

 

[ruairioflaherty]

Thanks Skipwave,

I have that list and have been slowly picking through what I need using online vendors. We don't have anything like radioshack in Ireland I'm afraid. I'm sure I'll be back with more questions,

thanks,
Ruairi

 

[skipwave]

Sorry that wasn't any help. Maybe someone here has spares they can ship you as a "kit." Post in the Black Market with a subject like "WTB - FETBoy parts."

 

[matta]

Hey Ruairi,

I assume that in in Ireland you have access to RS Components and Farnell? I don't have the parts numbers on hand, but if you are keen to build it I don't mind helping you find the right parts number to build your FETboys.

Drop me an e-mail at matt(@)matt-allison(dot)com (remove the brackets and the word dot and replace it with .) and I can try and hlep you out.

Cheers

Matt

 

[Kev]

[quote author="ruairioflaherty"]Hi Kev ... is the link to the parts list meant to be functional or is it not live?
.... /fetboy/DIYF_parts_lists_old.xls
[/quote] mmmm
:roll:
doesn't seem to work
I'll look into it

 

[ruairioflaherty]

Skipwave,
no worries. I'll persevere and pop in here with questions - I think I'll learn more that way.


Matt,
thanks a bunch for your offer. You are correct that I have access to RS and Farnell (have used RS previously). I will try to find the parts myself during this week and maybe contact you with my inevitable questions a little later. BTW your page on Kev's site is great.
Any rough idea what the parts for a 2ch fetboy will cost (sans PSU)? I have sold a Millennia Origin to fund my DIY adventures and want to make it stretch as far as I can.

Kev,
no worries on the link and thanks for hosting Matt's page and for your site in general.

It's 3am again and my mac says I've been online for 6 hours :shock:



cheers,
Ruairi

 

[skipwave]

Matt,

What sort of sockets did you use for the JFETs? The TO-220 type?

I can't find any intended for TO-92 packages. Digikey has them for TO-5 and TO-220. I've never seen a TO-5, but the TO-220 should work fine. Socketing seems like such a great idea for testing in circuit. Thanks for the suggestion!

EDIT: Searching is a good thing when you do it. :green:
http://www.groupdiy.com/index.php?topic=1625

 

[matta]

Matt,

What sort of sockets did you use for the JFETs? The TO-220 type?

I can't find any intended for TO-92 packages. Digikey has them for TO-5 and TO-220. I've never seen a TO-5, but the TO-220 should work fine. Socketing seems like such a great idea for testing in circuit. Thanks for the suggestion.

Hey Skipwave,

I used TO-92 in mine, I don't see why TO-220 shouldn't work. Yeah socketing is VERY much needed to find the best JFET's I went through quite a few to find the right ones.

Cheers

Matt

 

[fum]

anybody have problems with their fetboys bustin into HF oscillation at higher gain?

Just getting one up and going on the bench, and it done be oscillating

ju

 

[chrissugar]

The fet amp modules have very high input impedance so if the layout of the pre is not optimal, the signal from the out can reach the input and you have oscillation. Be carefull with the layout and use screened cables.

chrissugar

 

[fum]

thanks for that chris,

will check it out.

Regards

ju

 

[matta]

Fum,

Another thing to mention, you need to have the OEP can as well, the transformer picks up all kind of crap if you don't, and could be aiding your oscillation. Also as Chris says, use screened wires in and out.

Cheers

Matt

 

[matta]

Hey Fum,

Since I'm not sure what you are listening to I decided to make a clip to compare it to yours.

This sample is with the gain cranked full, no PAD, with a SM57. At first there is ambient silence, like the slight whirl of my PC with the sound of passing traffic and then I talk into the mic, with a normal talking voice about an inch from the mic, then silence again.

Does this sound the same as yours? I'm not really sure what I should be listening for? Both channels respond the same way.

http://www.ashtonaudio.com/goodies/fetboy/FETboy_Full_Gain.wav (1.6MB)

Cheers

Matt

 

[fum]

Hey Matt,

will check it out.

I also didn't order the (not so optional) shield cans, but have a pile of mu-metal I picked up, so fashioned a box to put them in (if you've ever taken apart a lundahl transformer, it gives you a good concept for how to fashion these.

And I did watch on the scope as all the crap went significantly down.

Unfortunately, it didn't do anything for the oscillation. As to what I'm hearing, I'm not hearing yet. I'm watching this on a scope. Gain get's to certain point, amp goes apesh*t =)

Regards

ju

 

[Bauman]

Ju, if you dont need that much gain, just remove C1 and it will sound cleaner and will not oscillate. :thumb:

And yea, get that can, it is not optional :green:

cheers!
Fabio

 

[skipwave]

[quote author="fum"] Gain get's to certain point, amp goes apesh*t =)[/quote]

Hey Fum,

I had the exact same issue. Did you pull C1 to reduce the gain?

Here's mine: http://www.groupdiy.com/index.php?topic=17030

Normally I would just yank that cap and see if that does it, but my box is so tight it will be chore.

Thanks!

Brian

 

[skipwave]

Bump-ity-bump. Doesn't anybody care? :wink:

 

[skipwave]

I put a big 22k carbon comp resistor between the wiper of the pot and the gate of the second gain stage. No more oscillation. Sounds sweet! :green:

 

[BR]

Hey guys,

I populated two of these boards and tried to do the bias calibration and here is what I got:

Board 1 - When powered it up, I smoked R5 and I think Q4 was smoking too. I don't know what I did wrong.

Board 2 - No smoke, but I measured 8.4V between both legs of R5 and no matter the amount of trimming I did, it wouldn't change. I have a feeling I'm doing it wrong..

Could any one shine a lite on this for me??
thanks
Gil

 

[skipwave]

I didn't use the fet boy boards, but in following thread the pitfalls of this design are discussed in detail:
http://groupdiy.com/index.php?topic=1504

Most likely, you have transistors for the CCS that have too high beta. In my first gain stage I used 2N4401 and I had to add an additional 40k in series with the 100k trimmer to get it to bias correctly. I should have just found some transistors that had a more appropriate beta, between 100-150. My second stage I used MPSA06 and that biased properly at close to 50k in the trimmer. In both stages, I paralleled these transistors and they are running pleasantly warm, not hot.