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Preamp Tone: No Tone Stack


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3/20/2004 6:34 PM
Jack Koochin
Preamp Tone: No Tone Stack
Hi gang,  
I was doing some mod or other on my preamp some time ago, and recalled that several high-end stereo preamp/amp manufacturers don't even offer tone controls on their gear. This is on the basis of the "less is more" approach... that tone controls cause phase shifts, uneven attenuation and otherwise affect the pure signal coming from the source.  
 
So, I thought what the heck and bypassed the tone stack from the preamp (although I don't recall now how I loaded the stage) and the thing just sounded like shit! Very middy, muddy, and untoneful to my ears. Back in went the stack.  
 
I recalled this recently, thinking of messing with it again someday, and thought I'd bounce it off you more seasoned, knowledgeable types.... I don't get why this happened. At the time, I expected a full-bandwidth, relatively flat frequency response, purest tone I ever heard, and what I got was mud. Any ideas?  
Thanks,  
Jack
 
3/20/2004 7:43 PM
ted m
Good points, my best stereo preamp ever was dual mono, with no tone controls.  
 
I used to own this amp, still wish I did:  
 
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3712673448&category=10171  
 
Tone is in the fingers, not in how many tone robbing dials you can spew on the chassis ... ;)
 
3/20/2004 10:21 PM
Richie

It depends on the amp your useing it in..  
And you can kinda voice the amp with no tone control..the tone control bypass is a great mod on a fender. I usually put it in the normal channel,since most don't use it. And use the bright switch as the swith to kick in the bypass..So it can be in or out.  
But if you use the tone bypass..your coupling caps from the preamp,and into the PI will shape most of how it sounds. I wouldn't use anything bigger than a .022 off the preamp.. but you can try anything from a .0047 .01 to .022  
And you can also just move the cap for the brightness..or off the switch,on to the volume pot..  
Richie
 
3/21/2004 5:41 AM
Jack Koochin

Well, you sure couldn't get confused about your amplifier settings with that Maxon!  
Richie,  
I guess I'll have to put in the tone bypass on the Fender.... never use the bright switch anyhow.  
Jack
 
3/21/2004 6:49 AM
Steve A.

Jack:  
 
    I believe that the typical BF tone stack cuts the signal ~20dB so it is possible that you were overloading the following stage. Was this a Fender-style or Marshall-style tone stack that you were experimenting with?  
 
    Like Richie said, you replace the tone stack with a small coupling cap to fine-tune the signal going to the next stage (or Volume control in a BF/SF amp). If the signal is still too hot you might want to bleed off some of it to ground through a resistor.  
 
    The newer *umble amps use a Tone Stack Defeat Boost which basically uses the treble cap as the coupling cap. The simple way to do that is to disconnect the jumper wire from the treble pot to the bass pot. If you want to get more complicated you can also cut the connection from the mid pot (or resistor) to ground. BTW the early Mesa Boogie amps had a boost switch which interrupted the ground connection from the the mid pot to ground. For a less intense boost put a 56k to 82k resistor across the switch terminals so that in the boosted position there is still some continuity between the tone stack and ground; another advantage is that you still have some control over the tone when adjusting the bass and mid controls.  
 
Steve Ahola
 
3/21/2004 8:19 PM
Jack Koochin

Some great points and ideas there, Steve.  
I guess I should've re-tried this first instead of relying on hazy memory... and then asked you the question, but thought someone might have had a similar experience....  
 
IIRC, I just removed the standard Fender tone stack after the first stage, and ran thru a coupling cap to a volume pot, and on to the next stage. Without any overdrive happening, the tone changed lots, to a muddy sound. I was surprised how much the stack improved the tone, and at the time didn't get why.  
Thanks for your ideas,  
Jack
 
3/21/2004 8:56 PM
jaysg
About 10 years ago, a pal of mine was running a company called PS systems, which later became Ebtech. The idea came from a '67 1987. They showed me that you could do pretty much anything with the TMB knobs while chunking chords and riffing with wild abandon, and there was no audible difference. I pointed out to them that tweaking the Presence did have an effect.  
 
They built a 50W Plexi amp with no tone controls that sounded great. They took it up to LA and showed to some retailers and studio guys. It was so upsetting to the retailers that they gave up on the idea.  
 
I believe the tweed Bassman architecture is more likely to work this way than BF.
 

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