PRIMOVA - GKFX-11 Subsonic Filter Project

Started by CodeSmart, July 18, 2014, 02:26:45 PM

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CodeSmart

I have just sent my first ever surface mount board to prototype production. It's my version of a Subsonic filter. The board is pretty small 40x90 mm and hosts two GK jacks (GK IN & GK OUT). The board also has a connector for a motherboard in case I manage to make an improved GKMX switcher one day.

Anyhow, I have one test pilot but also would like to have second opinion by someone fellow geek technically interested. Unfortunately I don't own a piezo guitar myself  :(

Is there anyone out there considering himself/herself suitable who will help me test the filter board/compare tracking? It's 100% free. I pay shipping etc. You keep the board and the GK cable I provide. You probably own one or two piezo guitars and unmodified GR-55/VG-99 and know their ins and outs regarding tracking.

Show your interest by emailing me at sound@primova.se

I hope to get the board ready (if I didn't screw up the design completely) in a couple of weeks.
But I got more gear than I need...and I like it!

Elantric

#1
Check your inbox

CodeSmart

Quote from: Elantric on July 18, 2014, 02:36:58 PM
Check your inbox

Thanks.
It looks you've found me a test pilot.
No more candidates required at this time.
But I got more gear than I need...and I like it!

CodeSmart

Well, so this is the plan...if the stuff works.
No extra, no bells and whistles, just a GK subsonic, rumble removing filter in a small box.

There's a small 2x10 socket on the board to access the Hex in, Hex out, +7V, -7V and GND.
Could be good for testing or to piggyback it onto another board..

But I got more gear than I need...and I like it!

drbill

Looks like exactly what I begged RMC to make instead of yet another internal solution for the GR-55. What are you thinking about pricing?
GP-10, KPA
BM i2.13p, '76 Les Paul Deluxe w/GK-3, MiM RRS, Ibanez RG420GK, Charvel strat copy w/GK-2a, FTP

Elantric


thebrushwithin

Are you going to make a yellow one?  :)

CodeSmart

#7
Quote from: drbill on July 19, 2014, 10:16:33 AM
What are you thinking about pricing?

Components are dirt cheap but I need to build a couple to see the working hours. I have no clue about the demand/volume so I assume there will only be a few handmade/hand soldered units.

My current guess abt. $100-$150

Quote from: thebrushwithin on July 19, 2014, 10:36:04 AM
Are you going to make a yellow one?  :)

Yellow is a nice color. We'll see  8)
But I got more gear than I need...and I like it!

CodeSmart

So far so good. Got the boards today. The look fine ;D
But where are my components... :(
Please Mr UPS man, hurry up!!!

But I got more gear than I need...and I like it!

CodeSmart

Ha-ha, got the Components yesterday ;D

You have to be careful when you cough or sneeze. These guys are seriously tiny.
Actually is was fun hand-soldering them. First time for me. Some practice and it went faster than expected.



These are the first prototype boards. Two of them will be sent away to my test pilots.
Did basic testing with an iPad as signal generator and a AC Voltmeter.
Filters appear to do their job now, but question is... Is it good enough  :o

Took some hours to figure it out why some of the filters behaved weird.
Turned out that a few of the capacitors were not within spec.  :P
Luckily my brand new voltmeter measures capacitance, otherwise I would have been completely lost.

But I got more gear than I need...and I like it!

CodeSmart

Today I meet my old friend who's been a professional car painter 40+ years and gave him nine enclosures to paint in GP-10 yellow in case this filter actually works.

I destroyed the 10'th enclosure in the drilling machine.

Almost lost a thumb as the box slipped and started to rotate. I need to be more careful, I guess the left thumb is pretty useful when playing.... 8)
But I got more gear than I need...and I like it!

gumbo

I can hear the groans from Mrs CS from here.......   

...ignore them and keep soldering.... ;)

Peter
Read slower!!!   ....I'm typing as fast as I can...

CodeSmart

Quote from: gumbo on August 04, 2014, 03:02:37 AM
...ignore them and keep soldering.... ;)
Peter
Yeah,yeah, I'm always been a pain doing things without hesitation. Mama told me long time ago.

Talk about soldering Mr Peter  ;D
I have a bag of components, leftovers/residue, with you in mind, that will build a 99% GKMX-42 on the PCB board you stowed or dug away somewhere in your yard, muttering: where's my freaking tiiiiiiime!!! Do you want them? They are free. I won't be building anymore of those wire mount components units. I'm happy to give them to you amigo.
Just let me know and I'll slip them in an envelope.
Best
Robert
But I got more gear than I need...and I like it!

CodeSmart

Test pilot #1 is using a Godin Multiac Nylon string and a GR-55.
Here's his first feedback (Google-translated from Swedish to maintain wording):

"Hi Robert!

I think the filter is promising! Following a spin around among GR-55'an presets and changed the filter / no filter,
I feel a little tentatively, that the filter provides better stability to the sounds. It is perhaps a little difficult to try
explain with words, but a few expressions such as "more definition" and "clarity" describes one of my first
impression. Of course the different PCM instruments require different guitar expressions,
but still it feels way more "safe" and controlled with the filter than before."


But I got more gear than I need...and I like it!

Elantric

#14
The big deal tests which the sub EQ filter is designed to address  are:

* GR-300 COSM  lower noise when  palm muting at bridge.

* Improved GTR - MIDI tracking and ghost note immunity control.

* Improved GTR -PCM tracking and ghost note immunity control

CodeSmart

Ok, I'll tell him to listen for that.
Thanks.
But I got more gear than I need...and I like it!

CodeSmart

Still awating the parcel for test pilot #2 to arrive. US customs is really sluggish this time.

Meanwhile I got nine enclosures painted in a GP-10 "similar" RAL colour. Unfortunately the Pantone color that Elantric kindly provided could not be ordered by my painting guy, had to be a RAL code instead. However I'm afraid it got more light yellow than GP-10. I'll know better by Monday when I pick up my brand new GP-10  ;D

Black screen print is the next step...

If the filter doesn't work as planned I either have to make a better filter or throw away the enclosures and give up the idea.
(...but I won't give up without a fight).


But I got more gear than I need...and I like it!

CodeSmart

Quote from: thebrushwithin on July 19, 2014, 10:36:04 AM
Are you going to make a yellow one?  :)

Thebrushwithin, thanks to you I hope you can see now the thing is yellow alright. Two-component hi-grade truck/car paint. It will remain yellow long after we're ten foot under. The screen print will also be two-component. Lasts forever. The color and print is expensive. I see EHX is using digital prints on a unpainted Alu box. Will investigate further down that path. I'm not sure 20-30$ extra cost for premium painting/printing is rewarded whatever the box does.

I also painted my very last 8 pcs of guitar switchers GKMX-41 in this strange color.
Photos will be posted in the GKMX-42 thread when they are printed and assembled.
But I got more gear than I need...and I like it!

billbax

#18
Hi CodeSmart,

Nice looking and well designed board there. 

Why are you using SMD's in your designs?  SMD's are normally used by electronics manufacturers for convenience and automated pcb component placement.  I'm guessing you chose SMD's in order to make the pcb as small as possible.  You already know, a through-hole component would have given you access to a vast range of hi-end audio audiophile components, plus you wouldn't have the pain with soldering SMD's. Last Q...what dual op-amps did you choose for your hi-pass filter board?

Sorry mate just thinking aloud...an audiophile's SMD component choice has puzzled me all day ???

Thanks, Bill

CodeSmart

Low noise TL074 quad op amp.
If you have a better choice let me know.
Is choice of op-amp really audible?

Yes everything is size related (I tell my wife it's not ;) )

SMD:
- Smaller size
- Cheaper boards
- Less lead required
- Possibility for automated production
- Cheaper freight
(IMHO more benefits than drawbacks)

Mixing wired and SMD is possible, keeping
op amps wired but there's also a pin out issue...
But I got more gear than I need...and I like it!

billbax

#20
Hi CodeSmart,

QuoteLow noise TL074 quad op amp.
If you have a better choice let me know.
Is choice of op-amp really audible?

Op-amp choice is quite a topic. Some hi-end audiophile manufacturers seem to take delight in advertising hi-specification op-amps in their designs.  TL074 op-amp is around 30 years old, although in your case it simply does the job. A few years back I swapped out 15 NE5532 op-amps in a soundcard with AD8066. I couldn't believe the mod added another zero to a THD figure of 0.08%, to something like 0.004%.

OPA4134 looks like a hi-end alternative for your filter board, and it's available in an SMD package.   
http://www.ti.com/product/opa2134

Anyway, I shall leave your topic alone.  Will pm you with any further thoughts.

All the best,

Bill

CodeSmart

#21
Quote from: billbax on August 17, 2014, 02:56:15 AM

OPA4134 looks like a hi-end alternative for your filter board, and it's available in an SMD package.   
http://www.ti.com/product/opa2134


Thanks Bill,
Appretiate your input.
OPA4134 is a much better OP-amp with THD=0.00008% compared to TL074 with 0.01%
Increase in price would be abt. $12 USD for each board. I'll give it a thought.
I guess there is something available in between these two as an compromise.

Actually found its possible to get a better price direct from Asia if buying a few. Probably use this op amp if everything else works out.
But I got more gear than I need...and I like it!

CodeSmart

#22
I have just got more positive feedback from Test Pilot #1
- Overall better playability using the filter with piezo guitar and violin
- Palm muting: The filter makes palm muting work better than without the filter.
- Ghost notes: Less PCM ghost notes occur using the filter.


The diagram shows the frequency response measured on one of the physical filter boards using a Sine tone generator and a AC volt meter.
Note:
- Any de-tuning discussed below relates only to detuning present at filter input (guitar detuning), not to be confused with de-tuning happening after the filter (i.e. Roland VG/GR unit).
- Guitar de-tune considerations apply to all Subsonic Filter vendors.

STR6 (Low E-string) Orange color bar show standard tuning (E2). Filter curve: Orange (leftmost).
Comment: At standard tuning there's no loss in magnitude.
However, If detuning to Drop-D (D2) a minor loss of 5% magnitude should be expected.
For Drop-C tuning (C2) the loss grows to 10%. Further guitar detuning below C2 should not be used when filter is in operation.

STR5 (A-string) Dark blue color bar show standard tuning (A2). Filter curve: Dark blue (leftmost), covered by orange curve.
Comment: At standard tuning there's no loss in magnitude. Same restriction as E string, should not detune below C2.

STR4 (D-string) Magenta color bar show standard tuning (D2). Filter curve: Magenta (mid curve).
Comment: Should not be detuned below F2#

STR3 (G-string) Green color bar show standard tuning (G3). Filter curve: Green (mid curve).
Comment: Should not be detuned below F2# (very unlikely tuning)

STR2 (B-string) Red color bar show standard tuning (B2). Filter curve: Red (rightmost curve).
Comment: No detuning problem should ever occur. The filter cut-off frequency is far below the fundamental frequency of the string.

STR1 (High E-string) Light Blue color bar show standard tuning (E4). Filter curve: Light blue/red (rightmost curve).
Comment: No detuning problem should ever occur. The filter cut-off frequency is far below the fundamental frequency of the string.
But I got more gear than I need...and I like it!

CodeSmart

The new Subsonic Filter / Tracking enhancer for Piezo pickups in reality. It sound great and it looks great.
Meet the new family:

The GKFX-11 High-pass filter removes rumble, improves tracking and enhances the sound. Shipped with a gold plated 1 meter GK Cable.







But I got more gear than I need...and I like it!

CodeSmart

#24
NOW FOR SALE: Totally 8 units available at $120 + shipping and comes with a 1-meter gold plated GK cable. Delivery time abt. 2 weeks (hand-built/carefully tested)

Just connect it into the GK signal chain and improve:
- PCM Tracking and ghost note immunity
- COSM Tracking and ghost note immunity
- Lower noise when Palm muting at bridge

Contact me at sound@primova.se.

Most noted effect on GR-55, VG-99 with Piezo guitars.

How it works? It contains carefully designed EQ filters eliminating low frequency content below:
100Hz (the two lightest two strings)
75Hz (mid strings) and
50 Hz (the two thickest strings)

Circuitry self-powered by GK cable.
Note: If you are planning getting one of my 10 units GKPX-14 Parallel box in a few weeks, they will have an option with an internally mounted filter board. So there will be a GKPX-14 and GKPX-14F (F=Filter). So with GKPX-14F you don't need a separate GKFX-11 Subsonic Filter box. Just to clarify.



(Edited: There are now 8 left and the price is shown without shipping cost.)
But I got more gear than I need...and I like it!