Benson Preamp  [traced]

General documentation, gut shot, schematic links, ongoing circuit tracing, deep thoughts ... all about boutique stompboxes.

Re: Benson Preamp

Postby Nocentelli » 18 Aug 2019, 15:15

knottypine wrote:Could I use 2N5457 in lieu of J201?


May be worth trying


knottypine wrote:How about BS170 MOSfet?


Probably won't work
brownwhopping wrote:How can I learn by reading threads an making circuits, when some day I can see a lawsuit or somebody beat me in the face for that?
User avatar
Nocentelli
Tube Twister
 
Posts: 2118
Joined: 09 Apr 2009, 08:06
Location: Leeds, UK
Has thanked: 894 times
Have thanks: 855 times

Re: Benson Preamp

Postby temol » 18 Aug 2019, 20:10

Here's some Ltspice simulation screenshots.
Comparison between J201 and 2N5457. Drain resistor values adjusted to get the same voltages as with J201.

Frequency response
benson1.jpg


Output sine.
benson2.jpg
benson3.jpg


Sine at drain of Q1. 2N5457 in green.
benson4.jpg


Sine at drain of Q2. 2N5457 in green.
benson5.jpg


Sine at drain of Q3. 2N5457 in green.
benson6.jpg


T.
You do not have the required permissions to view the files attached to this post.
User avatar
temol
Solder Soldier
 
Posts: 154
Joined: 25 Feb 2017, 21:58
Has thanked: 13 times
Have thanks: 134 times

Re: Benson Preamp

Postby Manfred » 19 Aug 2019, 08:55

I tried to adapt the circuit values in order to get the same stage gains using the 2n5457 Fets.
The adaption of the drain and source resistors is only possible when the supply voltage is 18 Volts.
Manfred
Diode Debunker
 
Posts: 913
Joined: 05 Apr 2009, 00:42
Has thanked: 1040 times
Have thanks: 624 times

Re: Benson Preamp

Postby temol » 19 Aug 2019, 15:51

It may be cheaper to use charge pump than buy MMBFJ201 transistors :)

T.
User avatar
temol
Solder Soldier
 
Posts: 154
Joined: 25 Feb 2017, 21:58
Has thanked: 13 times
Have thanks: 134 times

Re: Benson Preamp  [traced]

Postby Manfred » 19 Aug 2019, 18:19

BensonPreampWamplerOutputCircuitry.jpg

I renamed the components of the Wampler Output circuit.

I made these Layouts according the componet names in the schematics.
BensonPreampLayout.JPG

BensonPreampLayoutComponets.pdf

BensonPreampLayoutSolderSide.pdf

BensonPreampLayoutSolderSideMirrored.pdf

BensonPreampWamplerOutputCircuitryLayout.JPG

BensonPreampLayoutWamplerModComponets.pdf

BensonPreampLayoutWamplerModSolderSide.pdf

BensonPreampLayoutWamplerModSolderSideMirrored.pdf

SprintLayout6 file contains both versions:
BensonPreamp.zip
You do not have the required permissions to view the files attached to this post.

For this message the author Manfred has received thanks: 2
atalas (20 Aug 2019, 05:26), Nocentelli (24 Aug 2019, 11:12)
Manfred
Diode Debunker
 
Posts: 913
Joined: 05 Apr 2009, 00:42
Has thanked: 1040 times
Have thanks: 624 times

Re: Benson Preamp

Postby knottypine » 20 Aug 2019, 05:04

Because I am a bit impatient I went ahead and wired one up with what I had so buckle up...

I didn’t have a:

250pf so I used a 300pf

470pf so I used a 680pf

J201 so I used 2N5457 (Q2 & Q3 biased at 4V)

2M so I used a 1M for the bass pot

What I’ve observed is....

Decent output volume

Very subtle (if any) Bass response

Treble control seems to work in reverse (fully clockwise the sound is “dampened”, moving it counter-clockwise “brightens” the sound)

Drive is pretty distorted even on the lowest settings / starts to squeal past 12 o’clock

I have on order the correct values/replacements so I will implement and report back.

I am very excited at the potential of this circuit and I appreciate this forum and everyone involved.

Cheers!
Last edited by knottypine on 20 Aug 2019, 05:30, edited 2 times in total.
knottypine
 
Posts: 6
Joined: 12 May 2012, 16:02
Has thanked: 0 time
Have thanks: 0 time

Re: Benson Preamp

Postby atalas » 20 Aug 2019, 05:27

temol wrote:It may be cheaper to use charge pump than buy MMBFJ201 transistors :)

T.


More importantly, it may make other, more readily available JFETS viable.
atalas
 
Posts: 35
Joined: 24 Jul 2019, 22:22
Has thanked: 7 times
Have thanks: 22 times

Re: Benson Preamp

Postby Manfred » 22 Aug 2019, 08:39

I tried different drain and source resistors at supply voltages greater than 9 Volts.
It is at least 30 Volts requiererd to achieve the stage gain and the clipping behaviour using the 2N5457 Jfet.
Manfred
Diode Debunker
 
Posts: 913
Joined: 05 Apr 2009, 00:42
Has thanked: 1040 times
Have thanks: 624 times

Re: Benson Preamp

Postby knottypine » 04 Sep 2019, 02:24

Checking in!

Switched Bass from 1M to 2M

Just replaced the 2N5457’s with J201’s

Q3 & Q2 are biased at 4v

Q1 measured at 6v

Also I had to rearrange the legs on the on the J201 to DSG (not DGS) to get Output. So I am not sure if the pin out on the strip board layout is correct

Overall more usable gain and more noticeable bass.
knottypine
 
Posts: 6
Joined: 12 May 2012, 16:02
Has thanked: 0 time
Have thanks: 0 time

Re: Benson Preamp

Postby FlyingWild » 04 Sep 2019, 08:44

Hi Knttypine,

Does it still squeal when the drive is turned up beyond 12 O'clock?

Pedal PCB has leg 3 of the treble pot connected to the 22nF cap, 2 to ground and 1 not connected, is this how you had yours wired up?
FlyingWild
 
Posts: 12
Joined: 28 Oct 2018, 22:01
Has thanked: 3 times
Have thanks: 1 time

Re: Benson Preamp

Postby modman » 04 Sep 2019, 10:45

Manfred wrote:I tried to adapt the circuit values in order to get the same stage gains using the 2n5457 Fets.
The adaption of the drain and source resistors is only possible when the supply voltage is 18 Volts.


We are back home!
Image
http://runoffgroove.com/sd.html

However, modding it to Wampler Plexithingie should not be the subject of this thread.
Also, whatever the builder says, don't believe him until you seen traces and values.

For this message the author modman has received thanks:
alexradium (13 Sep 2019, 08:02)
User avatar
modman
a d m i n
 
Posts: 4341
Joined: 19 Jun 2007, 17:57
Has thanked: 3267 times
Have thanks: 608 times

Re: Benson Preamp

Postby knottypine » 05 Sep 2019, 02:48

FlyingWild wrote:Hi Knttypine,

Does it still squeal when the drive is turned up beyond 12 O'clock?

Pedal PCB has leg 3 of the treble pot connected to the 22nF cap, 2 to ground and 1 not connected, is this how you had yours wired up?



I got it to stop squealing once I used the right value on the 250pf and 470pf caps.

Kinda curious why my bass and treble boost when the knobs are CCW
knottypine
 
Posts: 6
Joined: 12 May 2012, 16:02
Has thanked: 0 time
Have thanks: 0 time

Re: Benson Preamp

Postby atalas » 05 Sep 2019, 09:53

knottypine wrote:Kinda curious why my bass and treble boost when the knobs are CCW


Reverse your lug 1 and 3 connections on your pot, and the jumpers if you installed them.

modman wrote:
Manfred wrote:I tried to adapt the circuit values in order to get the same stage gains using the 2n5457 Fets.
The adaption of the drain and source resistors is only possible when the supply voltage is 18 Volts.


We are back home!
[ Image ]
http://runoffgroove.com/sd.html

However, modding it to Wampler Plexithingie should not be the subject of this thread.
Also, whatever the builder says, don't believe him until you seen traces and values.


We actually started with traces, and eventually got measured values. Benson only came in a made a few small clarifications at the end.
The schematic I last posted should be accurate.
But you're not wrong, and as I stated earlier, nothing revolutionary in this pedal.
atalas
 
Posts: 35
Joined: 24 Jul 2019, 22:22
Has thanked: 7 times
Have thanks: 22 times

Re: Benson Preamp

Postby knottypine » 07 Sep 2019, 03:39

Reverse your lug 1 and 3 connections on your pot, and the jumpers if you installed them.


- I did exactly this and the sweep functions as it should. Thank you.
knottypine
 
Posts: 6
Joined: 12 May 2012, 16:02
Has thanked: 0 time
Have thanks: 0 time

Re: Benson Preamp

Postby knottypine » 07 Sep 2019, 03:43

Is there a suggested voltage for Q1?

Pedal sounds pretty nice in front of my Music Man with Bass, Mid, and Treble set to 5
knottypine
 
Posts: 6
Joined: 12 May 2012, 16:02
Has thanked: 0 time
Have thanks: 0 time

Re: Benson Preamp

Postby atalas » 07 Sep 2019, 07:21

knottypine wrote:Is there a suggested voltage for Q1?

Pedal sounds pretty nice in front of my Music Man with Bass, Mid, and Treble set to 5


~5V, or if you have a bunch of J201, set the source resistance to 12K and swap JFETs until you get one sit at 5V at the source. This will achieve a closer sonic result than just changing the source resistance to achieve 5V for whatever JFET is in there now.
atalas
 
Posts: 35
Joined: 24 Jul 2019, 22:22
Has thanked: 7 times
Have thanks: 22 times

Re: Benson Preamp

Postby Sm4sh » 13 Sep 2019, 19:36

Hey !
@Bugg, I'm little confused here.
Why did you use a dual gang pot for the bass on your layout ?
https://www.pedalpcb.com/product/sobpreamp/
Sm4sh
 
Posts: 8
Joined: 07 May 2015, 10:03
Has thanked: 7 times
Have thanks: 2 times

Re: Benson Preamp

Postby plush » 13 Sep 2019, 19:56

Sm4sh wrote:Hey !
@Bugg, I'm little confused here.
Why did you use a dual gang pot for the bass on your layout ?
https://www.pedalpcb.com/product/sobpreamp/


1M dual pots are way easier to get, than single 2M.
When stacked, dual 1M emulates single 2M.

For this message the author plush has received thanks: 2
bugg (14 Sep 2019, 23:50), Sm4sh (13 Sep 2019, 20:03)
User avatar
plush
Resistor Ronker
 
Posts: 287
Joined: 08 Dec 2015, 10:29
Has thanked: 28 times
Have thanks: 73 times

Re: Benson Preamp

Postby Sm4sh » 13 Sep 2019, 20:05

plush wrote:
Sm4sh wrote:Hey !
@Bugg, I'm little confused here.
Why did you use a dual gang pot for the bass on your layout ?
https://www.pedalpcb.com/product/sobpreamp/


1M dual pots are way easier to get, than single 2M.
When stacked, dual 1M emulates single 2M.



Right!!! :slap:

Thank you! :thumbsup

For this message the author Sm4sh has received thanks:
bugg (14 Sep 2019, 23:51)
Sm4sh
 
Posts: 8
Joined: 07 May 2015, 10:03
Has thanked: 7 times
Have thanks: 2 times

Re: Benson Preamp

Postby andy-h-h » 16 Sep 2019, 09:22

Any suggestions as to what capacitors should be used to get the same response using a 1M pot instead of 2M or a dual 1M? :hmmm:

Thanks.
andy-h-h
 
Posts: 29
Joined: 22 Jul 2017, 04:54
Has thanked: 7 times
Have thanks: 5 times

PreviousNext

Return to Boutique Stompboxes dissected...

Who is online

Users browsing this forum: lechuuu_123, MJC and 8 guests