Building a Wal....ish

[Daz39]

21 minutes ago, LukeFRC said:

Mate, even if not to your normal standards the stain was better than 99% of us could do - Its ok, you can make mistakes, you don't need to drive into oncoming traffic to distract us 

Yeah - attention seeker. "Don't look at me, I'm shy!"

 

 

[Andyjr1515]

51 minutes ago, LukeFRC said:

Mate, even if not to your normal standards the stain was better than 99% of us could do - Its ok, you can make mistakes, you don't need to drive into oncoming traffic to distract us 

Maybe the other driver was a Basschatter        Probably predicted the error (or any of the others I have done and am likely to do in the future) and thought, 'I'll stop this nonsense!!!' **

 

 

 

 

**or maybe he just fell asleep at the wheel....

 

 

[funkle]

Well, I was today years old when I heard about the Underhill Bass Preamp, which has switchable modules, including a low pass filter module. 

 

https://www.underhillbass.com/about-4

 

The filter module page is here - https://www.underhillbass.com/copy-of-pd1-dual-preamp-1

 

No experience with it, but may be of interest to others looking at different makes of filter preamps. 

 

EDIT - found a review. https://www.talkbass.com/threads/review-underhill-dual-filter-onboard-preamp.1564526/

Edited July 6, 2022 by funkle

[slowburnaz]

19 hours ago, funkle said:

Well, I was today years old when I heard about the Underhill Bass Preamp, which has switchable modules, including a low pass filter module. 

 

https://www.underhillbass.com/about-4

 

The filter module page is here - https://www.underhillbass.com/copy-of-pd1-dual-preamp-1

 

No experience with it, but may be of interest to others looking at different makes of filter preamps. 

 

EDIT - found a review. https://www.talkbass.com/threads/review-underhill-dual-filter-onboard-preamp.1564526/

 

Ooooh...  very cool!

[funkle]

I still plan to video the Lusithand preamp and get it on YouTube for your collective pleasure. Lots of personal stuff last few months which has gotten in the way. 
 

However I really want to also do a trial of @slowburnaz’s pickups with the John East Uni Pre system, to show what they sound like flat. I have one handy, just need to get to that as my next step after the Lusithand. 
 

The guy making the Wal clones (Octave Basses) comments on his FB page that he feels the Underhill preamp is similar in sound to the ACG EQ-01 and sounds good. 

[Andyjr1515]

Re-do of the stains on the neck has gone OK and thinned wipe-coats of varnish now being applied.  These things always photograph differently under different light conditions so here are a variety:

 

 

 

 

 

[Andyjr1515]

Well, it's the little things in life...  (roughly translated to, "Simple things please simple minds"   )

 

Remember the discussion about splitting the centre section or not?  Well maybe I can see now why Wal prefer to split-and-flip on theirs.  To a humble hobby-builder, this is very pleasing.  I'll probably start doing this as a norm:

 

[Passinwind]

On 02/07/2022 at 17:03, paul_5 said:

Low current drain and high fidelity is difficult to achieve!

Easier these days than ever before though, at least when the needed modern SMT parts are in stock. 😉

[TrevorR]

1 hour ago, Andyjr1515 said:

Well, it's the little things in life...  (roughly translated to, "Simple things please simple minds"   )

 

Remember the discussion about splitting the centre section or not?  Well maybe I can see now why Wal prefer to split-and-flip on theirs.  To a humble hobby-builder, this is very pleasing.  I'll probably start doing this as a norm:

 

That is very pleasing as you say!

[Andyjr1515]

Final gloss coat done on neck and back of headstock - this will now be left to harden fully before polishing - and flattened gloss coats finished on headstock front prior to @funkle's decal being applied, followed by a couple of final sealing coats.

 

 

Over the next couple of days I'll add the side and top dots and then finally  do the fretlevelling, etc..  Should be ready to ship off to @funkle the week after this one coming,

Edited July 17, 2022 by Andyjr1515

[Andyjr1515]

Top and side dots added:

 

 

Still have to do the fretwork - and have another go at a decal.  @funkle sent me a decal from Rothko and Frost... I followed the instructions but it still melted at the mist coat stage.  I've used Rob's decals (very similar type, but presumably different inks?) at guitardecals.co.uk successfully in the past so I'll order one from him (and, unlike Rothko and Frost, he always sends a spare which, with these modern gossamer-thin types, is important!).  Should be with me by the time I've finished the final fretwork.

 

 

[Kinkh]

Hello everyone!

I have been provided with the preamp photos by @funkle and been asked to share my findings here. it took a while due to various personal reasons, but here are the results.

From the photos provided I have drawn this schematic. I'm sure it is about 90% accurate. Some parts were hard to trace by just looking at photos, and some values are approximate. The opamp used here is a generic opamp, since the original is not produced any more. Also, due to the obsolete opamp, the schematic doesn't include 4 resistors used to set the quiescent current of the opamp. 

 

Wal MK2 Trace.pdf




What is interesting here is that the filters are tuned to different frequencies. The most interesting thing is how the Attack function is implemented. The signal from the Neck pickup is taken directly after the summing amp (which sums all the individual coil pairs), and put through a high-pass filter to leave only the high frequency content of that pickup. Then, that filtered signal is ADDED to the maim mix of the bridge and neck pickups after they have been filtered by their individual filter controls.

I have also made a SPICE simulation of the circuit to better show what is happening here. Due to the transistors and opamp being obsolete, I replased them with generic ones, and put a normal summing stage at the input.
When trying to build this circuit, the transistors can be omitted if a modern low noise opamp is used. This kind of stage was used in back in the day when low noise opamps were not readily available, and a simple transistor differential amp could make up for that by being added in front of the opamp.
A logical question remains: do the outdated components contribute to the sound characteristic of this preamp? Maybe, maybe not. The opamp has limited bandwidth, and the overall stages might produce some distortion. As there is no definitive datasheet info on these parameters, it's up for debate and experimentation to answer that question.

Anyways, here are the graphs from the simulations.
Pickup_01 is neck, and Pickup_02 is bridge.

 

 

Now the Attack gives off some strange results depending on how you set the Attack trim pot inside. So here are a few results. 









That's about all I can think of that's worth mentioning at this time. IF you guys have any more questions, feel free to ask

Cheers!

 

Edited July 30, 2022 by Kinkh

[PaulThePlug]

^ Album cover artwork right there...

[PaulThePlug]

Is the pre going external box for proto compare and contrast and easier build n mock-up and mod?

[funkle]

It’s fascinating. I guess the only way to know for sure is to build a ‘modern’ version of the circuit and see if it sounds similar. 
 

Perhaps though, @mhoss32or Nuno from Lusithand have basically done this already. Or the Underhill chap. With their own twists. 
 

I am interested to see that that circuit is apparently relatively even in the low end and low mids until you sweep the filter down there. 
 

That largely leaves the pickups, the neck, or the body, or a mix thereof, as the source for the low mid boost that Wals seem to enjoy.  
 

The neck should be ready soon…

[Andyjr1515]

1 hour ago, funkle said:

The neck should be ready soon…

Indeed...we're on the final knockings

 

[funkle]

2 hours ago, PaulThePlug said:

Is the pre going external box for proto compare and contrast and easier build n mock-up and mod?

@Kinkh has threatened to build a pre based on the schematic but not sure if it will be in an external box, as this would negate the ‘per pickup’ filtering that would happen. 

Edited July 30, 2022 by funkle

[Kinkh]

1 hour ago, funkle said:

 

I am interested to see that that circuit is apparently relatively even in the low end and low mids until you sweep the filter down there. 
 

That largely leaves the pickups, the neck, or the body, or a mix thereof, as the source for the low mid boost that Wals seem to enjoy.  
 

 

Might not be the method by which you can tell what component comes from where, but it could help when comparing two different instruments.... If you could record a note plucked from each string (from each of the coil pairs) directly from the pickup, and then plot a spectrogram ("3D" plot, with frequency, time, and intensity). Assuming the multi coil pickup is "transparent" in that it can pass all the frequencies produced by the vibrating string, you would get an actual idea of what sound is being produced by the bass itself (strings, neck, material, all those factors). Then start comparing that info with other known basses. And this is where a LOT of testing would need to be done...
You would probably need to fit the original Wal pickup into other basses for testing consistency.

One other interesting example would be to fit a random "known" pickup into the Wal, record a spectrogram, then record a spectrogram from another bass with that same pickup. Then compare the differences, and start guessing where they come from.

This would be a big project, and pure physics related at that. But it might give some interesting insight if done properly. 
Just a food for thought... 😇

[Kinkh]

3 minutes ago, funkle said:

@Kinkh has threatened to build a pre based on the schematic but not sure if it will be in an external box, as this would negate the ‘per pickup’ filtering that would happen. 

I like the word threatened

At one point, I'm going to try this schematic and build something of it. But be warned, I'm interested in copying these graphs, so I probably won't copy the schematic 100%. I'm just going to use it as a starting point. I have done a filter based preamp based on this particular filter topology, but not this exact implementation, and with some different ideas. So far it worked nice
But when I start working on this, I'll start from there and use this as a guide, as I hate copying other people's work 😇

[Kiwi]

7 minutes ago, Kinkh said:

I like the word threatened

At one point, I'm going to try this schematic and build something of it. But be warned, I'm interested in copying these graphs, so I probably won't copy the schematic 100%. I'm just going to use it as a starting point. I have done a filter based preamp based on this particular filter topology, but not this exact implementation, and with some different ideas. So far it worked nice
But when I start working on this, I'll start from there and use this as a guide, as I hate copying other people's work 😇

Just make it growl. 

[3below]

Frequency plots are really informative (remind self, must get a life other than physics/electronics).  It will be interesting to hear the results of taking a J or P bass (as a starting point), and applying the plot boosts/cuts using a free VST graphic equaliser e.g. the Moss Equalizer,  a 265 band FFT equalizer.  

Edited July 30, 2022 by 3below

[Kinkh]

I remember that there was a way to take a .wav file as an input in LTSpice, pass it through the circuit, and record the output as a .wav.
I may have done that once more than 10 years ago, so I currently have no clue how to do that anymore... But, it might be the "best" way to see how something sounds when passed through one of these circuits.

Edited July 30, 2022 by Kinkh

[3below]

Useful link,  https://vmascagn.web.cern.ch/LABO_2020/LTspice_and_wav_files.html.

[Kinkh]

Yep, now I remember how it was done.

All that remains are two things: some samples to try out on, and time to do it

[NickA]

brilliant work kinkh.  I'd had an idea to do it for years but never had the patience.  I'm really suprised that the pick attack is derived from the neck pickup; I'd always assumed it was from the sum of both or maybe from the breidge (which is the default in the ACT=EQ-01).  It makes sense as the only way to get a good slap sound out of a Wal is to blend in more neck than bridge pup - evidently that is wher the "twant" comes from.

 

One thing to remember is that the impedance of the pickups themselves is also part of the circuit; those RC circuits on the inputs will likely interact with the pickup inductance.

 

PS A good (free) circuit simulator is Microcap - easy to put *.wav files into circuits as inputs.