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Solid State Amplifiers => Amplifier Discussion => Topic started by: Jopyeweed on January 05, 2020, 01:11:09 PM

Title: Crate CR112 tone stack
Post by: Jopyeweed on January 05, 2020, 01:11:09 PM
Hello all. I have a Crate Cr112 that I have been entertaining modding in the tone stack section. Overall the clean tone is sort of lower mid focused, I think. To get the sound I want I have to set the treble around 5-6, mids completely off or just a tiny bit. Bass around 3. I'm losing a ton of volume this way but it gets unpleasantly punchy anywhere north of that. My ideal clean sound is Jerry Garcia like, which is basically a twin reverb. I know, buy a twin reverb. Not an option unfortunately. The bright switch adds alot of character and the amp seems to come to life with it on but it is wayyy to harsh sounding. Sounds like a mid boost fat switch more than a bright switch.
Maybe just an efficient speaker like the swamp thang to counteract the volume loss and possibly audio taper pots would do the trick?

I once had an oxford speaker from a late sixties bassman cab that made the bright cap more usable.
Schematic and manual is here. Many thanks for your time if you want to look at it. The tone stack doesnt seem to really match anything in the duncan tone stack generator.
Title: Re: Crate CR112 tone stack
Post by: Enzo on January 05, 2020, 06:12:44 PM
Frankly I would experiment with speakers before going into the circuits.  Nothing will have more effect on tone.  A brighter speaker might be for you.

With the existing speaker, try this experiment.  Cut a piece of ply or just use heavy cardboard, cut to cover the open rear of the amp.  Not sealed up, just mostly covered.  How does that change sound to you?  If wrong direction, get rid of it.  If it seems to help, think of ways to more permanently cover the rear some.
Title: Re: Crate CR112 tone stack
Post by: Jazz P Bass on January 05, 2020, 09:33:05 PM
The 'Bright' capacitor C41 is 680 pf.
You could try a lower value, like 220pf.
Title: Re: Crate CR112 tone stack
Post by: Jopyeweed on January 06, 2020, 12:08:37 AM
Thanks for the replies!
 To Enzo:
I will try to close the back a bit and see what that does. I never considered that. The amp has a Eminence designed fender speaker that probably came out of a deluxe reverb or a hot rod deluxe. I believe it is supposed to be a version of their legend model speaker. Overall the amp has always had kind of limited dynamics and a harsh, piercing mid range. Bass and treble are sort of weak. Not enough of either, although I'm using less bass these days anyway. I am going to get a long decay reverb tank at some point too as a big part of the sound I like I am starting to think comes from the frequencies the reverb accentuates and sustains. I am getting very close now that I am setting the dials the way I mentioned, but loosing alot of volume in trade. From what I can tell from the manual the tone stack is boost only and that all happens around 3-4 on each pot. Unfortunately to get the necessary DB's it seems you need to dime everything and that is not a balanced tone for me. Maybe a more efficient speaker will render those boosts more pleasantly.

To jazz p bass:
Will lowering that bright cap shift the brightness upward frequency wise for more presence and sparkle?

Many thanks!
Title: Re: Crate CR112 tone stack
Post by: Jopyeweed on January 08, 2020, 11:19:18 AM
Would anyone be willing to tell me what kind of tone stack is in this amp? It doesn't really correspond well to any of the paradigms it seems. Is it just a modified Fender/vox/marshall? Active or passive? I'm trying to learn about electronics by modifying pedals and studying schematics. I'm in no hurry to hack into my amp unless absolutely necessary for safety reasons. I want to stay in the 9v world as much as possible. But I enjoy studying and thinking about it, reading tutorials and things online, etc. Apologies for the download requirement on the manual/schematic above, I couldn't figure out a way to do it otherwise on mobile.
Thanks again.
Title: Re: Crate CR112 tone stack
Post by: Jopyeweed on January 08, 2020, 04:38:16 PM
Disregard my last post, I realize thats probably kind of alot to explain.
Title: Re: Crate CR112 tone stack
Post by: phatt on January 10, 2020, 07:33:11 AM
Hi Jopy, Your amp circuit is an oddball and I doubt it will ever be ideal.
The Treb & Bass are Passive while Mid is Active, (mid similar to TS9 tone control).
I've just done a quick simulation of the preamp and it looks like it might be a design hickup. :loco
Sims are not perfect but handy for giving clues as to what might be wrong. 8|

The first thing I noticed is p2 (Level) is not grounded in clean mode causing a wacky tone curve and your bass starts with a 5dB hump at 5hZ,,, WTF? no guitar amp will work well with a response curve that low. :duh
That might explain why you have to back off the bass so much.
In clean mode p1&p2 are not in circuit but if I ground p2 while in clean mode then IC1 works in a normal manner, bass rolls off at ~100hz. Though you would then need to lower the value of C3. try 50pF.

The best I can make out is p2 needs to be grounded all the time otherwise IC1 works more like a notch boost at 5hZ.  :crazy2:

I've noted the area of schematic in question, see pic. maybe check that on the pcb as schematics are not always correct.
Of course when the OD is engaged the response curve is closer to what I would consider a normal curve. but then the diodes conduct and you might have more diode fizz to deal with.
It's complicated to explain as there would be a lot to do to make it work the way you want.
Hope that helps, Phil.
Title: Re: Crate CR112 tone stack
Post by: Jopyeweed on January 30, 2020, 01:16:00 PM
Hey Phil, I dont know if you'll see this but I just wanted for the record to thank you for your reply and efforts to help. I tried some more recently with the amp to see if the tone stack responded differently while in the OD channel. It seemed about the same but as I recall you said you would need to lower C3 in order to notice any effect anyway. I haven't opened it up to see if its grounded despite what the schematic says. As I keep playing through it I think I am getting a good enough sound and a speaker upgrade will probably make the most difference. I should probably relax and try that when I can afford it, and let it be what it is. Many thanks again!