FS-50B Build Diary - Famed Traynor bass preamp in pedal form from Aion FX

[Bassybert]

As I mentioned in the DIY Effects thread, I've recently purchased an Aion FS-50B kit from Musikding - The kit is based on the pretty awesome sounding amp used by players like Bob Weston from Shellac and David Wm Sims from The Jesus Lizard. It's a 50watt solid state amp from the late 70s/early 80s I believe, and has a pretty big following in alternative music, especially for recording. The Tronographic Rusty Box pedal is based on the same amp and used to great effect by Adam Devonshire in the Bristolian behemoth that is Idles. Think snarly, mid heavy growl but thick and chunky and you're in the right ballpark.

 

It took couple of weeks for the kit to arrive from Germany, and when it did arrive it was sans enclosure - I had a card in the box saying it was on backorder. A bit annoying seeing as I had to chase the guys from Musikding up to see if the kit had been posted (They say allow up to 7 working days for the kit to be marked as shipped but I didn't hear anything for 8 days so dropped them an email which seemed to get the ball rolling). Hopefully it won't be long before the enclosure arrives 🤞

 

Kit looks decent, all quality parts with the PCB being a really nice matte finish, all components organised into bags and the hookup wire has been recut and part stripped so it should be easy to hookup once I get the enclosure.

 

1. Ready to rock and roll! I printed the instructions out from the pdf, everything is really comprehensive.

 

 

2. The PCB comes with a perforated link that you can snap apart if needed, hopefully I'll be able to keep it all in one piece within the enclosure and just run the jumper wires for power and signal to the main part to the power/switch part.

 

 

3. All nicely organised - FYI all pots have plastic covers which helps avoid any accidental grounding to the soldered side of the PCB

 

 

4. I always start adding parts from smallest to largest, so it's resistors up first!

 

 

5. Even though all values are labelled, I still double check them with a multimeter just to be sure as I've been caught out with this in the past. Thankfully these were all spot on.

 

 

6. It also helps my brain if I check the values off the list when I've soldered them in. I tend to solder 3-5 parts at the same time but depends - If there's loads of the same value I'll do all of them together.

 

 

7. Working through them all...

 

 

 

8. With added inductors (These look like larger resistors in the bottom left) and diodes - only 3 small ones in this circuit.

 

 

9. Capacitor time! Again working from smallest to largest, I tend to add ceramic/film caps first then electrolytics at the end

 

 

 

10. Once they're in, it's time for transistors and ICs. I pretty much always socket transistors and always socket the ICs - It's a lot easier to swap them at a later date if needed but more importantly they're really sensitive to heat and it can be easy to cook a transistor. So sockets in first. I also added the big ass power supply chip (TEC 2-0923) in the bottom left of the smaller board. Never used on of these before, but it's a one stop shop for converting 9V DC to 15V DC.

 

 

11. All ready for the trannies!

 

 

12. That's the board pretty much as far as I can go without the enclosure - I tend to add the pots and switches to the enclosure and then add the PCB to that before soldering all in place, it makes it much easier than soldering them to the board then finding out they're misaligned!

 

 

Edited November 19 by Bassybert

[Bassybert]

If anyone's eagle-eyed enough to see that C18 is missing, that's intentional and part of the design. The extra cap is there if you want the TS-60B version as that was the only difference between to 50 and 60 apparently.

 

Now it's just a case of waiting for the enclosure...

 

 

[rwillett]

Thanks for this. Is this just a pre amp or will it evolve into an amp stage as well?

 

Rob

[Bassybert]

11 minutes ago, rwillett said:

Thanks for this. Is this just a pre amp or will it evolve into an amp stage as well?

 

Rob

Hi Rob, it’s just the preamp. I was planning to use it the same way I use my Sansamp by running it into the effects return of an amp. 

[rwillett]

Got you. Thx

[LukeFRC]

9 hours ago, Bassybert said:

The PCB comes with a perforated link that you can snap apart if needed, hopefully I'll be able to keep it all in one piece within the enclosure and just run the jumper wires for power and signal to the main part to the power/switch part.

Snap it off - the two parts sit at different levels - one set by the pots and the other by the 3pdt

[bloke_zero]

Thanks - loving your calm and organised approach! I'm thinking of buying the full IVP kit from them - I have the PCB but haven't got round to sourcing the components yet (what happened to my life!?) - getting the enclosure drilled will help too.

 

How're you planning to do the labelling?

[rwillett]

2 hours ago, LukeFRC said:

Snap it off - the two parts sit at different levels - one set by the pots and the other by the 3pdt

That's the sort of useful information that makes such a difference. [ Update: Just reread this and it sounds like I'm being sarcastic. I'm not.  ]

 

Rob

Edited November 19 by rwillett

[bremen]

I mentioned in Bert's original thread that, having looked at the schematic, I couldn't fathom how the mid control was anything other than a bass cut.

Here's the relevant section:

 

With the mid control anticlockwise, C7, C8, R9 and the subsequent circuitry form a high pass filter. Turning it clockwise progressively bypasses this, so bass is restored.

 

Now here's the "CL" circuit from the Ampeg SVP-CL (essentially a mid-cut "scoop")

 

C18, R33 and C17 are the HPF here. But parallel to that we have R37, C16 and R36, a low pass filter.

 

I think that by adding a circuit like R37, C16 and R36 (but with different values  (the following stage of the Ampeg has a high input impedance) across the middle pot in the Traynor-a-like, the mid control would become a variable 'scoop' rather than a bass cut.

 

Or, as Neepheid might say: a meringue?

 

 

 

[Bassybert]

1 hour ago, bloke_zero said:

Thanks - loving your calm and organised approach! I'm thinking of buying the full IVP kit from them - I have the PCB but haven't got round to sourcing the components yet (what happened to my life!?) - getting the enclosure drilled will help too.

 

How're you planning to do the labelling?

Thanks mate, I find it quite a relaxing thing to do 😊

I was planning to use some of my children's Posca pens to decorate the enclosure, will probably prime it first and then come up with something a bit creative. It's quite easy to get an old school ZVEX kind of vibe with the pens.

Edited November 19 by Bassybert

[LukeFRC]

I want to try posca pens, I've done paint then transfer paper, vinyl stickers and more recently metal stamping. 

Also want to try proper UV printing

[LukeFRC]

sorry this is OT  and not the DIY thread!

[Bassybert]

35 minutes ago, LukeFRC said:

I want to try posca pens, I've done paint then transfer paper, vinyl stickers and more recently metal stamping. 

Also want to try proper UV printing

 

I really like the style of the punched letters 😊

[LukeFRC]

53 minutes ago, Bassybert said:

 

I really like the style of the punched letters 😊

So do I - my day job is graphic design so while I could get quite a decent finish on things with stickers/uv it’s quite nice to not stare a screens 

[Bassybert]

52 minutes ago, LukeFRC said:

So do I - my day job is graphic design so while I could get quite a decent finish on things with stickers/uv it’s quite nice to not stare a screens 

Ha, I know exactly what you mean, I used to be a graphic designer and got into web development around 2005/6 which then morphed into data analysis around 5 years ago.

 

8 or more hours a day looking at a screen full of code means I'm craving hands on/organic stuff!!

[Bassybert]

9 hours ago, bremen said:

I mentioned in Bert's original thread that, having looked at the schematic, I couldn't fathom how the mid control was anything other than a bass cut.

Here's the relevant section:

 

With the mid control anticlockwise, C7, C8, R9 and the subsequent circuitry form a high pass filter. Turning it clockwise progressively bypasses this, so bass is restored.

 

Now here's the "CL" circuit from the Ampeg SVP-CL (essentially a mid-cut "scoop")

 

C18, R33 and C17 are the HPF here. But parallel to that we have R37, C16 and R36, a low pass filter.

 

I think that by adding a circuit like R37, C16 and R36 (but with different values  (the following stage of the Ampeg has a high input impedance) across the middle pot in the Traynor-a-like, the mid control would become a variable 'scoop' rather than a bass cut.

 

Or, as Neepheid might say: a meringue?

 

 

 

 

Having looked at a couple of different sources it seems the mid control is acting as a filter...

I found this (From Talkbass) by searching on the big G...
 

Quote

 

TS50B arrangement is simplistic: Mid-range control is a passive "notch-T" filter, which introduces a mid-range notch similar to that of the tonestack. The control can -cut only- and its turnover frequency slides in interaction with the dial. As tonestack's source impedance, it will alter overall frequency response some. Tonestack, however, will not be loaded excessively by the 1M input resistor of the following emitter follower.

 

 

Aion's own instructions gives the following info...

 

• Mid is a variable bridged-T filter allowing the mids to be scooped or boosted.
• Treble and Bass form a 2-band amp-style tone stack.

[bremen]

As shown though, it's not a notch-T filter. It's a 1st order high pass.

 

I suspect the kit you have is based on a schematic that's missed a few bits. Easily done.

 

Anyway. Build it, see if the mid control does as it should, if not we can look at what might be missing.