Traynor TS-50b

[irfrench]

Hello all.

I have decided to go ahead and give this (bass) preamp a go as I believe the need for a bit of grit is approaching soon.  I have looked around for advice/analysis as much as possible but I'm still new to the more in depth side of electronics and was hoping for some help.

I have attached the full schematic below for reference.

I have created a single sided board layout (with only a few jumpers) which I am pretty happy with:

I have a couple/few questions so if anyone can help I'd be really grateful. 


1. I have never been sure of pot wiring, but as I'm using board mounted pots I was hoping that they'd be right (first time?  :-[).  Do these look right?  Sorry to ask...

The original schematic does not show pot pin numbers - so I have done them like so with the intention of clockwise being 'more' (I'm confident about the volume one  : so I've only shown the others):

2. The boost switch looks to just be a connection to ground (switched via jack socket if pedal is inserted).  Have I totally misread that section!?

3.  The next part is the one where I guess I'll have to do some trial and error, but if anyone can steer me in the right direction I'm all ears!  -  Transistor substitutes...

I cannot seem to find a 'normal' source for the original 2n5425, I have assumed a standard 2n5457 would be fine here?

The MPSA18 can still be had but as an option would the 2n5088 be suitable?

The most intriguing part of the circuit is the 'ladder' of PNP transistors at the end, to my untrained eye it looks like the signal is split and this is where compression/clipping occurs.  I'm hoping to be able to get some MPS8598/8599s but if that proves unfruitful - again would a simple 2n5087 be suitable?

Once I've got it all working OK I'll be sure to share the project as it seems to be a desirable way to get a gritty bass sound.

I'm sorry there are so many questions.

Ian.

 

[PRR]

Any N-type JFET, though higher Vth is better.

If leads are very short (all inside a pedal), replace the JFET with a mechanical switch.

The 6-pack splits lows, highs, and mids and distorts them separate. Any PNP Silicon part.

The emitter follower before that is any non-sucky NPN.

> board mounted pots I was hoping that they'd be right

Image is small. Pots marked 1 2 3 instead of Gain Mid Treb etc. Too much work to check.

Gain Mid and Bass are 2-terminal. Put nearly-touching solder pads between pot legs. Blob solder across two pads. If the control turns backward, knock that solder off, blob the other pads, make a note for future build.

 

[irfrench]

PRR,

Thanks for the advice and the reassurance to just go ahead and give it a go! 

I'll post developments as/when they happen.

Ian.

 

[irfrench]

So I decided to get my feet wet on this.  And I figure in for a penny - in for a pound.  So I thought I'd try to get my head around LTSpice...

I have a working model -

I exported a 'tweaked' version from Eagle (replacing all the components with LTSpice friendly versions) and then respecifying everything so LTSpice knew what it was actually intended to be! - anyway, I have had some success but the Opamp still doesn't appear to be behaving as it should - giving only one level of gain.

The gain control appears to do nothing in the model and I need to re-try the Boost functionality.  I am not sure if this is an LTSpice component error or if I am doing something wrong here?


As the JFET is only acting as a switch am I correct in supposing that the physical switch could simply replace the Source and Drain connections?

Ian.

 

[irfrench]

Still goin',

I had chance to etch a board and stuff it over the Christmas break (I was kindly gifted a digital soldering station - so what better excuse to get stuck in?  ;D).  I want to correct a slight snag with the cap near the Middle pot but other than that the layout was actually quite nice to work with.

As it needed a +/- supply I broke out the 51x PSU using an extender card and powered it from that:

I intend to play around with transistors so they're all socketed.  Initially I had a 2n3904 in the emitter follower Q as I had it to hand - I've since tried a BC550C in there (180degree rotated) and it sounded a heap load better.  I'm going to try out subs in the various positions to see if they sound better (to my ears anyway  ;D) or not.

I did a quick and inelegant test on the pad and boost sections by shorting the to switch pads with a screwdriver and can confirm that they - and therefore the 2n5457 sub - are OK.

Once I've had chance to play and substitute the transistors a little I'll report back.


Ian.

 

[irfrench]

Quick update:

Only had a short time with this - but so far I like it!  It definitely is a Character Preamp for bass, and absolutely benefits from running it through a poweramp & speaker.

In the absence of noise tolerance I recorded the line out signal and ran it through a quick speaker sim in my DAW:

https://soundcloud.com/minoian/traynor-ts50b

I apologise for the inspiration-less bass line and the hurried recording thereof.

This was recorded with a J-bass, no pad and no boost.  The emitter follower was a BC550C and the PNP Q's in the 'ladder' section are MPS2907A. 

I'm thinking I may just go all out and spend the 54p on an MPSA18 as originally spec'd to see if it makes a difference.

Big spender. 


Ian.

 

[clintrubber]

Nice thread, wanting to breadboard this preamp for while - seeing your PCB triggers me again. 


Bye

 

[suadevices]

Nice thread irfrench!

Did you finished this project? I am working on it too and damn I love the tone!

 

[klem]

anyone know what's the input impedance of the TS-50B?