H_A_M_P_T_O_N_E jfet amp modules

[clintrubber]

Thanks for the info. Just curious, are these 'utility/convenience'-changes or based on new thoughts ?

 

[matta]

Hey Chris,

I have often stumbled across this post (again) and am now most intrigued. I
have read all the pages and checked out the links, downloaded the Tape Op
article and seen your lovely Red Boxes in this post:

http://www.groupdiy.com/index.php?topic=4737

Now...

How did you put this all together? From what I see in the Tape Op article
you use 2 of these Jfet Gain block to make a Pre, with some additional parts
(i.e trano?s, pots, resistors etc).

You have be gracious enough to share you gain block board but how do these
translate into you Red Box pres (the 1U rack looks cool for a simple, no
frills pre)? Did you make a main board and ?plug? in your gain modules for
the pres, or wired point to point?

I?d be interested in seeing a pre board if you did do one as these look like
a great little project to throw oneself into.

Cheers

Matt

 

[chrissugar]

Yes Matt, I use a double sided main board, with the jfet amp modules installed with Millmax type pins like the 990 opamps. Double sided, but the upper side mostly as ground plane.
I will take some shots and post pics from the inside of the preamp.

chrissugar

 

[edanderson]

peter-

the on semi 2n5457 having a lower hFE means that the overall gain of the block is more reasonable. the output bias set resistor going up means less current which means less heat for the output devices. scott claims that for a 600 ohm load, the new value still provides enough current. why he changed the mps-a14 to the ztx603 i don't know.

ed

 

[mfdu]

i've been hunting for this thread for a while - i remembered being very impressed.

i just got my shinybox ribbon mic, and am looking for around 20dB gain prior to my console preamp.

ideally, the gain unit would run off 48V phantom, and not pass any through to the ribbon mic.

these look so juicy i was wondering if you thought they could give me what i'm after?

i have downloaded the hamptone document you link to but haven't had time to get into it yet.

suggestions or comments or pcb's would be greatly appreciated.

chris.

 

[seanjean3000]

Hi all,

just going to casually necro-bump a very old thread, don't mind me...

So I'm looking at building a couple of Hamptone JFP preamps and came across this thread, complete with some layouts graciously (and conveniently) provided by Chris Sugar. But I'm staring at this and scratching my head--it looks like on the layout (on page 1) that the 2nd and 3rd / MPSA14 and ZTX653 transistors have their emitters tied together, whereas in the TapeOp schematic it appears the MPSA14 emitter goes to the ZTX653 collector.

Am I totally missing something? Maybe it's too late and I need to rest my eyes, but I've been looking at this a while. It seems hard to believe that it's wrong since it looks like Chris made a small army.  Any thoughts would be appreciated!

Here's the TapeOp article / schematic, for reference: https://i1.wp.com/wiki.diyrecordingequipment.com/wp-content/uploads/2011/02/hamptone_fet_scan.jpg

Sean

 

[L´Andratté]

You´re right. But you can just turn the ztx-part around...

 

[MRK_LAB]

You´re right. But you can just turn the ztx-part around...

Sorry , can you explain better , i've the same Sean's doubt.

 

[MRK_LAB]

it looks like on the layout (on page 1) that the 2nd and 3rd / MPSA14 and ZTX653 transistors have their emitters tied together,
Sean

Ok , found the solution !
That scheme is wrong , the ztx653 must be drawn upside down.
As you (and me too) can see in this detail , the ztx653 is reversed.

 

[L´Andratté]

Yeah but you can use the layout by flipping the transistoraround before soldering...

 

[dario84]

Before I answer all the questions here are the pictures for the solder and components side:

and you can download [right click and SAVE TARGET AS] from here the high resolution BMP to make the PCB:
http://www.geocities.com/chrissugar7/CMS-LAB-JFET-AMP-SOLDER.bmp

Sorry Fabio but I have no gerber files, I made the project with a freeware software, then captured it with a freeware printscreen capturing software. I know, it is a bit hardcore but all my small boards are made this way. :grin:

I have to say that I was surprised that DaArry's board is 80 percent like mine. My idea was to make it more like a plugin amp module like the 990 type opamps but in a diferent footprint.
Why do I need all these modules? Good question. I played with this circuit for long enough time and explored it and I can say that I was even more impressed by this than my 10 channels of N_E_V_E preamps or the A_P_I types because it is so simple, it sounds great and is very versatile. From a very clean classA to a coloured distortion box it can do everything. I tried it with Lundahl1636, 1538 and OEP and it can sound beautifull.
A module like this has aproximately 26 to 29 dB gain depending on the fets and resistor values you use.
So why I need all these modules? I have over 120 ouputs from my synthesizers/samplers, many from the harddisk recorder and also many from the digital fx boxes. But that is not the complete answer. I try to design my new toys in dual topology like the Millenias designed by Fred. For example tube and jfet amp modules, or bipolar amp and jfet amp modules. Enough variations. Just think about compressors, limiters, equalisers and you will find that 60 is not too much. :grin:
By the way you could ask why have I built 40 Millenia type opamps, and all those NTP, QuadEight and melcor and the answer would be the same.
:grin:

chrissugar

hey there!

I know this is more than 15years old but do you maybe still have the hi resolution for this? if not do you know the size of the board?

would appriciate it veeeery much!
thanks in advance!

 

[Rob Flinn]

I haven't got the pcb layout but the 1st part of the  original document is attached.  2nd part to follow.

 

[Rob Flinn]

2nd part attached.

I built this up on a bread board at the time & you definitely need good heatsinks for this one.

 

[peterc]

I posted the PCB files in the Tech Docs thread

Beware the transitors run HOT. This is normal working temperature.

https://groupdiy.com/index.php?topic=52448.0