Mid cut mod on Guyatone PS-024 clone ?

[eh la bas ma]

Hello,

This circuit was built recently, i played with it for a few weeks :



https://dirtboxlayouts.blogspot.com/2021/10/guyatone-ps-024-distortion-h.html?sc=1686983892582#c1306353081879733681


schematics : https://drive.google.com/file/d/1Vs2NACcV8-uVlz0vmkIlmWbyJIM-HoQm/view

I wonder if there is some part(s) I can try to change in this circuit, in order to decrease the mids presence ?

I often have to turn Low mids, Mids and High mids controls fully CCW, to get some precision in the signal, and even then I still want to use an other EQ circuit to cut the mids around 800Hz.

EQ is built around this IC, supposed to cut or boost 10 db on the selected frequencies, if i understood correctly :

https://html.alldatasheet.com/html-pdf/140262/MITSUBISHI/M5226P/4229/7/M5226P.html

I hope I could get more useful range of most EQ controls, if i could turn the mids down...

Every observations and suggestions are welcome !

[garcho]

Could increasing the values of the high and low pots help? Or something to retain more of the signal you want instead of turn mids down more, since you can't.

What's Q3 doing? Just curious.

[eh la bas ma]

Could increasing the values of the high and low pots help?

Thanks for your reply !

I don't think so, I usually set Low and High controls somewhere around the middle of their rotation. They both have enough range, I think.

I guess it won't be as simple as putting one or two resistors on a toggleswitch... I will probably have to make some adjustments on the amplifier, or with an other EQ, to fine-tune the mids with this circuit.

[garcho]

I guess what I should have said is it might be easier to try to "boost" (or lose less) low and high without boosting mid, which is the same difference as cutting mid, depending on headroom. How much are you willing to modify or add to the circuitry?

[antonis]

What's Q3 doing?

It's a BJT based gyrator and it's (or should be) part of M5226P..

[eh la bas ma]

I guess what I should have said is it might be easier to try to “boost” (or lose less) low and high without boosting mid, which is the same difference as cutting mid, depending on headroom. How much are you willing to modify or add to the circuitry?

I understand. Even with Bass and Highs set on high values, i still use an other EQ to shape the mids, at least on low gain settings. The mid frequencies bump tends to disappear when the gain pot reaches 3/4 of its rotation. Lots of compression and high frequencies appear, flattening the signal.

I was discussing recently a similar modification on the Blues Driver. It has a tonestack with fixed values and can be easily modified.

I was hoping that something like that could also be applied to this circuit. I thought that there is always some tone-shaping going on in every circuits, even before the Tone control or the EQ section ?

Not sure how far i am ready to go, a big mod could be very interesting. On the other hand, i guess using an extra EQ after the PS-024 isn't really the end of the world...  (Edit : although, the earth shooked two days ago here in France, wich never happens. Let's hope it wasn't related...)

But i am curious to know what modification could be considered to cut the mids. If it doesn't seem possible now, i will probably try it later.

Edit 2 : M5226P can cut or boost 10 db on some frequencies. Does it mean that the EQ is in flat position with every controls at noon ? Is it the "true" sound of the PS-024, when all 5 bands are set at the middle of rotation ?

The PS-024 isn't doing exactly what the M5226P datasheet mentions as a typical application exemple, so i'm a little confused.

[garcho]

Sadly, "tone shaping", especially when you're talking about band-stop filters (e.g. cutting mid-range), isn't always just a swap-a-value capacitor change. The fact that said circuitry uses an IC for the EQ-ing doesn't help. Usually, the point of those ICs is to have as little external circuitry as possible. Because of that, much will be fixed and harder to adjust without adding completely new circuitry.
Basically, the only external components that are available to you outside of the IC, that can change the filters inside the IC, are the two capacitors along the pathway from the wiper of each pot to the IC. That's not a lot of wiggle room. Changing those values and ratios might achieve what you're after, but I doubt it.

M5226P can cut or boost 10 db on some frequencies. Does it mean that the EQ is in flat position with every controls at noon ? Is it the "true" sound of the PS-024, when all 5 bands are set at the middle of rotation ?

Yes, which is a great feature to have. If the circuit isn't behaving as you expect, maybe you accidentally wired the pots to the board incorrectly?

It's a BJT based gyrator and it's (or should be) part of M5226P.

Makes sense now that I've actually looked at the datasheet ( ), but apparently from the vero board layout, it's external to the IC. Thanks for clearing it up though, I can only pick out IC gyrators, transistors are exotic to me. The other day, a quick glance at Boss switching and I thought it might have been an envelope follower 

[eh la bas ma]

Sadly, "tone shaping", especially when you're talking about band-stop filters (e.g. cutting mid-range), isn't always just a swap-a-value capacitor change. The fact that said circuitry uses an IC for the EQ-ing doesn't help. Usually, the point of those ICs is to have as little external circuitry as possible. Because of that, much will be fixed and harder to adjust without adding completely new circuitry.
Basically, the only external components that are available to you outside of the IC, that can change the filters inside the IC, are the two capacitors along the pathway from the wiper of each pot to the IC. That's not a lot of wiggle room. Changing those values and ratios might achieve what you're after, but I doubt it.

I understand cutting some mids won't be easy on this build. I might as well give up on modifications, and build something else if the PS-024's tone doesn't suit me.

M5226P can cut or boost 10 db on some frequencies. Does it mean that the EQ is in flat position with every controls at noon ? Is it the "true" sound of the PS-024, when all 5 bands are set at the middle of rotation ?

Yes, which is a great feature to have. If the circuit isn't behaving as you expect, maybe you accidentally wired the pots to the board incorrectly?

Here is the build report including a sound demo :

https://www.diystompboxes.com/smfforum/index.php?topic=36392.msg1265905#msg1265905

I don't think there's something obviously wrong with my build. It didn't work the first time, so i triple checked everything until i found the issues. Please tell me if something looks or sounds suspicious.