'59 Bassman amp sim schematic corrected !!

[MartyMart]

http://aronnelson.com/gallery/Martys-layouts-and-photos/BassBoy59V1_1?full=1

Mike spotted an error with the original drawing, the first 100k from the feedback path was
on the wrong side of the Q1 22n drain cap and this caused bias problems.

It's now corrected !

Marty.

[George Giblet]

Marty that doesn't make sense to me.

There are two 100k's connected together on the original bassman 59.  These are not feedback resistors, they are 100k plate resistors for the two input (first) stages that go a +V rail.   There is another 100k resistor which is the plate resistor for the second stage which connects to the same (+V) point.  The grid of the cathode follower (the third stage) is DC coupled to the output of the second stage.  There's actually no feedback in the preamp.  I suppose the confusion is that the three plate resistors connect to point X which is a power rail.

The correspondance between your circuit and the original is:

V1A =  Q1
V1B  not present
V2A  = Q2
V2B  = Q3
not present  = Q4    (sort of power amp)

[MartyMart]

George, yes "feedback" was totally the wrong term !
I've used the "normal" channel from my '59 original bassman schem, there are two plate
resistors ( 100k's ) the lower one would feed the "bright" channel .. BUT there's a node
between both which connects to the plate of V2B and V2A via another 100k, also V2B's
grid ( Gate on the fet )
This is where my "odd" looking dual 100k connection comes from, this makes perfect sense
to me, when you ignore the bright input section.
There are a couple of things to "make" the fet version work, like the 50k trim at Q3 to help bias
that up and the speaker sim type roll off at the end etc.
When first built ( without the schem error BTW ) it was compared with a friends original amp
and was VERY close .... enough for him to ask me to make one for him !!

MM.

[George Giblet]

That's where it doesn't make sense to me!

The way I see it is the bright and normal signals are mixed after the bright and normal volume controls by the two 270k resistors (and before V2A).  The two 100k's on V1A and V1B are just plate resistors and there is no mixing at their junction.

The other thing is on the Sim you have got the source resistors (the pots) *and* the 100k's where as the original circuit *only* has the 100k's.

[MartyMart]

I see what you mean, all I need is drain (plate) trimmers and a direct link from
V2A's drain to V2B's gate  !!   
That makes sense now, though when biased up it DOES work well !

Thanks for clearing that little mess up !

[George Giblet]

> That makes sense now, though when biased up it DOES work well !

I suppose if you adjust the bias pots it compensates for any evils.

Perhaps it could sound better as is, hard to tell with this stuff.  What then - haha!

[mydementia]

Here's a corrected layout/pcb. 

About 1" x 2"

[grolschie]

What does it sound like? Any clips yet? 

[MartyMart]

http://aronnelson.com/userfiles/59Bassboyclean.mp3

http://aronnelson.com/userfiles/59Bassboyfull.mp3

http://aronnelson.com/userfiles/59%20pushed%20TS9.mp3

Sounds like this

MM.

[grolschie]

Hi there. Thanks for posting those! 

What other Fender amps have been modeled with JFETs beside this and the Fender Princeton (Professor)? Anyone done a deluxe reverb or something?

[alderbody]

Anyone done a deluxe reverb or something?

Although it's got nothing to do with a DR circuit, the peppermill is said to be sounding like a cranked Deluxe.

I love the sound of mine, despite the fact that i never played a real DR... So i cannot really double that opinion.

[gcme93]

Anybody still got this schematic kicking around? Bit of a long shot I know!

Thanks, if not sorry for bringing this thread back out!

[MartyMart]

In my Gallery, old link was dead !!

http://www.aronnelson.com/gallery/main.php/v/Martys-layouts-and-photos/BassBoy59V1_1.jpg.html?g2_imageViewsIndex=1

Cheers,

Marty.

[gcme93]

Thank you very much! it'll be the soul of my tiny giant build hopefully (or I may try it before a normal car audio amplifier) as a cheap low powered bluesy practice amp.

Great to have resources like yours around Marty

[MartyMart]

No worries, I really like it, also sounds great being driven by a TS9 or similar :-)

EQ would have been great but I prefer a simple "one / two knobber" that sounds good and has a balanced tone.

You could add something like the SWTC or Muff tone control if you were so inclined.

Marty.