Guyatone's PS-021 Guitar Exciter/Compressor

[Mark Hammer]

Interesting.  But what the hell is an LA6324?

[digi2t]

I Googled it. http://www.onsemi.com/pub_link/Collateral/LA6324N-D.PDF

LM324 equivalent?

[PRR]

>> what the hell is an LA6324?
> LM324 equivalent?

I think so. Possibly a micron-exact copy of '324, though specs taken and quoted marginally differently. Note 32V max supply; IIRC the '324 can stand more, but not an issue in a 9V/18V world.

[Mark Hammer]

I Googled it. http://www.onsemi.com/pub_link/Collateral/LA6324N-D.PDF

LM324 equivalent?

Ha!  The power of subvocal speech and rotated images.  I looked at it rotated and thought "sixty-three twenty-four".  Had it been staring at me in the "right" orientation, I would have thought "Oh, another 324 with a 6 prefix".

The human mind is a perpetual barrel o' laughs.

[digi2t]

I Googled it. http://www.onsemi.com/pub_link/Collateral/LA6324N-D.PDF

LM324 equivalent?

Ha!  The power of subvocal speech and rotated images.  I looked at it rotated and thought "sixty-three twenty-four".  Had it been staring at me in the "right" orientation, I would have thought "Oh, another 324 with a 6 prefix".

The human mind is a perpetual barrel o' laughs.

.siht ekil etirw t'nod I gniht dooG

[Mark Hammer]

!erom eerga t'ndluoC   

[Tham]

The LA6324 is a quad op-amp originally made by Sanyo.

The LM324 is the equivalent.

http://www.hkinventory.com/p/d/LA6324.htm



Technically, the low power LM224 and LM2902 can also be used.

http://www.electroschematics.com/7143/lm2902-lm124-lm224-lm324-datasheet/

http://www.ti.com/product/LM224-N


The LM348 is even lower power, but with a minimum supply
voltage of 8 volts.

http://www.ti.com/product/LM348



Part of the design features would come from the LM3080N,
the transconductance amplifier which acts as the envelope shaper.

http://www.hkinventory.com/p/d/LM3080.htm


Equivalent for the LM3080N would be the dual LM13600/13700,
but with more pins.

http://www.hkinventory.com/p/d/LM13600.htm

[Tham]

The TL074. TL084 and TL£2074 are all quad op-amps
and should also be replacements for the LA6324.

http://www.ti.com/product/TL084

http://www.ti.com/product/tle2074/description

[PRR]

The '324 series has inputs that will go to V- (Gnd). Many other opamps wont.

[Tham]

A search of the LA6324 replacement  turns up the Renesas (Hitachi) HA17324.

http://www.allxref.com/search.htm?part=LA6324

https://www.digchip.com/datasheets/parts/datasheet/192/HA17324.php

[Tham]

As crossreferenced in the DigChip link above, the NEC μPC324
is also a replacement for the LA6234.

http://pdf.datasheetcatalog.com/datasheet2/1/02e1lrjrqha8tpeu5qr9f3jf23wy.pdf


You can get it from China. It's actually made in Malaysia.



Seems many of their suppliers there are willing to
send a single chip to you by small packet post.

https://www.aliexpress.com/item/UPC324C-UPC324-C324C-DIP-DIP-14-new-original-low-operational-amplifiers/1872256619.html

[Tham]

The LM3080N and replacement, CA3080E, have apparently
been discontinued by NS and Intersil.

Plenty of suppliers in China.



https://www.aliexpress.com/item/1PCS-LM3080N-LM3080-DIP8/32470241229.html

https://www.aliexpress.com/item/LM3080N-DIP8/32611758482.html



https://www.aliexpress.com/item/CA3080E-LM3080N-DIP8/32558270503.html

https://www.aliexpress.com/item/CA3080E-CA3080AE-LM3080N-DIP8/32454378401.html

https://www.aliexpress.com/item/NEW-OP-AMP-IC-DIP-8-CA3080E-CA3080EZ-CA3080/32705574595.html

[Tham]

@Digi2t

Oh, looks like you have made a video on your newly acquired exciter.

The sustainer/compressor part of the circuit would be built around the envelope shaper IC, the LM3080 transconductance amplifier.

[Tham]

I let this young Chinese guitarist, Benson, who was then with this local Malay band, Belantara, use the Guyatone exciter when they recorded their album, ''Infiniti'', way back in 1990.


I remember him saying that the PS-021 was used on the
last song on Side 2,  ''Jalan Pulang''.

I think he placed it after a Boss HM-2 Heavy Metal.

He had a vintage Fender with a DiMarzio PAF Pro bridge pickup.

He's the first on the right, white shirt and blue jacket.

The same song in HQ audio.

[Tham]

If I remember correctly, he said during the recording for the
above song, the ''Exciter'' control was at 9 to 10 o'clock, while
''Sustain'' was at 2 o'clock.

I can't remember what his ''Color'' setting was, but I think it
was more on the bassy side, about 10 o'clock, in order to
obtain the fatter, heavier sound in the solo.

His usual settings for the Boss HM-2 was Bass 3 o'clock,
Treble 2 o'clock, Distortion 3 o'clock.

[Tham]

The Guyatone exciter was used and popularized by Tomoyasu Hotei, the lead guitarist of the Japanese pop band, Boowy, in the 1980s.

That is why when you search for the Guyatone PS-021 on the
net, especially in those Japanese auction sites, you will see the
name "Boowy" listed along with the Japanese description of it.

[digi2t]

Kevin over at Aion has this (and the bass version) on the bench now. It might be out as diy pcb at some point.

[Tham]

Kevin over at Aion has this (and the bass version) on the bench now. It might be out as diy pcb at some point.

It's good to know that they are making a DIY PCB for it.

The PS-020 Bass Exciter's PCB and components looks virtually identical,
even the position of the preset variable resistor, so initially I thought it
was the same circuit in a different box.

Is the sound much different from that of the PS-021 Guitar Exciter ?

[aion]

I was finally able to finish the trace on the PS-021.

PNG: https://aionelectronics.com/schem/guyatone_ps-021.png
PDF: https://aionelectronics.com/schem/guyatone_ps-021.pdf

Let me know if anything looks wrong and I can double-check.

The compressor half is nearly part-for-part identical to a Dynacomp, with the exception of the Sustain knob (and yeah, I triple-checked the R10 resistor value: green-blue-yellow... that and the value of the Sustain knob itself are the only components that are different).

The exciter portion looks pretty familiar too:
http://experimentalistsanonymous.com/diy/Schematics/OOP%20Japanese%20Electronics%20Book/phase-exciter.gif

The bass version uses the same PCB, so I assume it's just a matter of swapping out a few capacitors here and there. As digi2t said, I've got the bass version as well, so I'll get that one cracked open before too long and post the changes for that version.

I'm planning on putting together a DIY PCB project for this which will probably be available shortly after the new year. But in the mean time, I thought I'd make the schematic available for anyone who wants to have a stab at putting one together on their own, or just studying it.

[Mark Hammer]

Putting both a couple of Boowy/Hotei videos and the schematic together, I get the sense that the unit is a kind of alternate approach to a bright compressed sound, different from compressors that include a wet/dry blend, but aiming for the same outcome.

The compressor portion seems like a ringer for the Dynacomp/Ross, and the output of it goes to a gain-recovery stage, followed by a Big Muff style tone control (Color) and buffered output.  The circuit is a bit simpler if one uses true bypass switching, rather than the FET switching shown.

What differentiates it is the inclusion of an exciter-type circuit to supplement the compressed signal.  IC2C provides 90 degrees of phase shift, beginning around 480hz. IC2D provides a 2-pole highpass filter, to isolate the higher-frequency content of the compressed signal.  IC2A provides a simple gain of just over 3x to make the HF content more evident.  IC3A provides a unity-gain phase-flipping stage, such that when the Exciter control pans between the outputs of IC2A and IC3A, it is either favouring the non-inverted or inverted version of the highpass signal, or allowing them to cancel each other out (middle position).  If a builder finds they would like to have more sizzle to their excitement, simply make R30 larger (e.g., 27k or 33k) or make R29 smaller (e.g., 8k2 or 6k8).

Unlike the Big Muff, whose lowpass and highpass sections form the tone control, with corner frequencies chosen to provide a midscoop, the lowpass (R36/C17) and highpass (C18/R37) sections in the PS-021 overlap, such that there is still a fair amount of treble at the full bass setting and still a fair amount of lower mids at the full treble setting.

What I think is fairly evident from the videos and the circuit diagram, as well as from my experience with exciters in general, is that the guitar itself has to have some HF content, and the amp has to be fairly bright, for what is distinctive about this pedal to stand out.  In other words, dull-sounding HBs or P90s are not going to realize any magic from this pedal.  In the absence of those factors, it becomes simply a Dynacomp with a tone control.  That's certainly not a bad thing - I imagine many a player would love to have a tone control on their Dynacomp/Ross/Keeley/Retrosonic compressor.  But what sets it apart is the ability to add the upper frequency content, to give more articulation.  And if you don't feed it what it needs to do that, you won't hear the difference.  Again, that is true of pretty much ALL exciter pedals; which I feel is largely responsible for them not selling very well, historically, despite enjoying considerable usage in studios.  Bottom line: they need a single-coil-equipped guitar.

In view of the considerable similarity to the Dynacomp, I draw your attention to R19, which sets gain-recovery time.  This is often replaced with a pot in series with a 10k resistor, and labelled "Attack".  Shortening the gain recovery time, combined with the exciter function, should bring one squarely into Nile Rogers territory...which isn't a terrible place to be.

Finally, I will draw a parallel here with the Woody acoustic simulator I whipped up a decade back.  Where the PS-021 uses a 2-pole highpass and boosts that, I used a 3-pole highpass, and boosted/clipped that output before blending back in with the straight signal.  I stole the idea from Jules Ryckebusch's Harmonic Sweetener, that had originally appeared in Electronic Musician.  Jules used 4 poles of highpass and LEDs for clipping, in contrast to my 3 poles and asymmetrical silicon-diode clipping.  He added an inverting unity-gain stage to bring everything into phase prior to blending.  Like the PS-021, I also use a single phase-shift stage, but where the PS-021 shifts phase for a smaller part of the spectrum, and does so ahead of the highpass and boost, I do it after everything (before the mix control), and set max phase-shift for 160hz and up.  No two ways about it, the Woody can be hissy, and could probably benefit from a built-in noise-gate.  BUt the basic principle of blending in addentuated high-end with a straight signal, can be a desirable thing.