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Solid State Amplifiers => Amplifier Discussion => Topic started by: Jopyeweed on August 31, 2020, 01:48:54 PM

Title: Help with Crate CR112 Tonestack
Post by: Jopyeweed on August 31, 2020, 01:48:54 PM
Hello everyone,

I am wondering if anyone can help me with this tonestack.
I basically want to convert to a standard fender tonestack with the component values adjusted for SS. As I understand I can divide by 10 for the resistors eg. 250k for tube = 25 k for SS. Is that true? I read it somewhere and cannot find the original source now. What about the caps though... how does one convert the values for those?

I would like to load this tonestack into the Duncan tonestack calculator but it is not a perfect match in its layout. The .22 cap is located on a vertical line between the bass pot and the mid resistor, rather than on the horizontal lines, and there is only one cap instead of two. My limited knowledge doesn't know how to interpret this. How could I plug this into the fender format in the Duncan calculator so I can see the frequency response? As the calculator wants a cap on each horizontal line in the tonestack. Are both the Bass pot and "mid" resistor to ground below that sharing that .22 cap?

As I understand it the mids in this amp are active as they run back through the feedback loop in IC1. My idea was to just jumper the mid pot or introduce a fixed resistor to negate this active section...and then hook the leftover unused mid pot up for a passive mid at the bottom of the tone stack proper, for a more traditional mid section ala Fender. Attached is the full tone section of the schematic, as well as just the tonestack for reference.

Many thanks to anyone who would like to help

Title: Re: Help with Crate CR112 Tonestack
Post by: phatt on September 01, 2020, 08:01:38 AM
Hi Jopy,
Having messed with circuits for many years now I've found it's often a lot easier and cheaper to work outside an amp than inside.
My suggestion is build an external tone pedal.

Why you ask,,
Most amps are PCB and later ones tend to use fine traces and solder pads. It only takes one stuffed trace or pad lifted only to find you just wasted all the time making land fill. :'( :'( :'(

As you are wanting the Fender tone stack may I suggest you would be far better served building a PhAbbTone.
This will be more fender than a,, hum what were they called?
oh yeah fender. ;)

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Re altering tone stacks from Hiz To low Z.
Just divide the resistors x10 and multiply the Cap x10.
So a 250k becomes 25k and a 47nF becomes 470nF and it will work in similar manner but not always as it depends more on the circuit Z.
Has more to do with Circuit impedance (Z) and little to do with SS or Valves.
cheers, Phil
Title: Re: Help with Crate CR112 Tonestack
Post by: Jopyeweed on September 03, 2020, 09:24:09 AM
Thanks Phil,

I may try to build your pedal in the future. In case you didn't see it I want to thank you for your detailed reply to my previous post about this amp. I didn't respond until some time later so you might not have seen it.  :dbtu:

I still would like to be able to plug into this amp though and have it sound good straight away. I did put an eminence Swamp Thang speaker in it which does help but of course, doesn't really change the essential character of the tone. Maybe a Cannibas Rex would tame the harshness. Sigh, this amp...I've had better amps, a hot rod deluxe, a 66 bassman, both of which I was forced to sell in leaner times. This one stays with me because it has no resale value so... I keep finding myself playing through it again and again and hating it.  :grr

Thanks again,
Title: Re: Help with Crate CR112 Tonestack
Post by: Enzo on September 03, 2020, 12:07:51 PM
It is fun to try to tweak an amp for tone, but remember, no matter what you do to a hamburger, you will never make it taste like a lobster.
Title: Re: Help with Crate CR112 Tonestack
Post by: Jopyeweed on September 03, 2020, 04:25:55 PM
Thanks Enzo, now if I could only convince my spouse of this same logic. Try as she might to change me, I'm just a hamburger, I will never be...a lobster. :lmao:
Title: Re: Help with Crate CR112 Tonestack
Post by: phatt on September 09, 2020, 08:12:50 AM
Having found time,,,I just simulated the preamp up to C15 tone output,,
A couple of observations.
On Clean the bass response at the output of U1 starts with a hump at 2 hZ which is kinda silly.
But when drive is used the bass rolls off at a more sane 50~60hZ.
I can only assume this would create an obvious imbalance between clean and drive mode.
Maybe too much bass on clean and next to none on drive. In combination with the diodes D1,2&3 would likely be kinda harsh.

The mid control does little to create a mid cut at the classic 400hZ. so yeah proly not nice to play if you want a more fender tone. xP

I would first remove the diodes and use an OD pedal for dirt and just use the drive mode.
This will give the Amp a lot more clean headroom,, And leave the OD tricks for pedals which do a far better job.

If you need more bottom end up the value of C4.
As for the tone ,, you would have to rebuild it or I as mentioned easier to build an external tone pedal. 8|

Sorry  to say but if you try to turn your hamburger into a lobster you may only end up with a bad smell. ;)
Title: Re: Help with Crate CR112 Tonestack
Post by: Enzo on September 09, 2020, 01:38:53 PM
Hamburger claw meat just isn't that good to start with...