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SWR Aural Enhancer Bypass

duff2

duff2

Guest
Dec 16, 2007
528
457
#1
Has anyone modified their older SWR amp to bypass the aural enhancer circuit and achieve a flat frequency repsonse?

Specifically, I'd like to replace the original aural enhancer knob with a pull pot on my SM-400 so that I can have access to the original and modified preamp voicings.

Is this possible? If it is, where should the switch be positioned in the circuit below?

SWRSM400Preamp.jpg


Thanks,
Duff2
 
#3
Good idea for a neat mod. Taking a quick look at that schematic, I don't see a quick and easy way to do it. One physical limitation to using the push/pull pot MIGHT be the actual space alloted for it within the casing of the 400.

If you get the mod done though I'd love to see it and hear your thoughts on the results.

[edit in the line talking about "push/pull pot WOULD be the..." I intended to say "push/pull pot MIGHT be the..."]
 
#7
With my old SWR GP the closest to flat response was with the aural enhancer off and everything flat apart from the lower mid semi-parametric EQ which had an 8dB boost at 250Hz. I also found the the aural enhancer did was just a simple boost for the first third of its rotation, after which it added yet more cut at 250Hz. If the SM400 is similar I'd try that first.
 
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#8
Here's how it's done folks (well everything except the push/pull addition that is).

swrmod.jpg


In text format:
1. remove the 0.1 uF capacitor
2. Use it to replace the 0.001 uF capacitor

This most awesome modification will apparently flatten the preamp voicing and leave the added gain available by turning up the aural enhancer knob intact.

Thanks to kringle77 and Walter Harley (of Cafe Walter headphone amp fame) for all their help in this matter.

I am planning on taking my amp to a tech later this week. I'll let you know how the mod turns out. :bassist:

Cheers,
Duff2
 
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#12
BigOldHarry said:
+1

And if you dial that "Aural Enhancer" all the way down, are you not removing it from the chain?
Click to expand...

Not exactly, the mid-scoop is present even with the aural enhancer set to zero (unlike the Enhance control on the Eden and Thunderfunk amps). Up to a 2 O'clock setting the SWR aural enhancer controls how much additional signal from your bass passes through the second half of the 12AX7 tube. This adds gain and extra high end harmonic coloration to your sound but does not change the preset EQ curve present when the control is in the off position. At settings beyond 2 O'clock there's no extra gain, but rather an additional mid scoop added around 200 Hz.

Graphically, here's what the aural enhancer control does on an SWR amp:

SWRauralenhancer.jpg


Cheers,
Duff2
 
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#13
duff2 said:
Not exactly, the mid-scoop is present even with the aural enhancer set to zero (unlike the Enhance control on the Eden and Thunderfunk amps). Up to a 2 O'clock setting the SWR aural enhancer controls how much additional signal from your bass passes through the second half of the 12AX7 tube. This adds gain and extra high end harmonic coloration to your sound but does not change the preset EQ curve present when the control is in the off position. At settings beyond 2 O'clock there's no extra gain, but rather an additional mid scoop added around 200 Hz.

Graphically, here's what the aural enhancer control does on an SWR amp:

SWRauralenhancer.jpg


Cheers,
Duff2
Click to expand...

Hey duff2,

Do you have any data for aural enhancer at lower setting , such as 8, 10 o'clock???

Thanks.
 
#14
Very cool! I'm anxiously awaiting the results and your thoughts. Looking at this mod and my mouth is watering.

I took a look through a few resources and it looks like the Aural Enhancer pot is a 50K for your SM400 (Link Removed)

If you wanted one with a pull switch for defeat then this might be the fella for you.
Link Removed

Now I can't be dead certain that this is the right pot but a quick call to the parts retailer would confirm the fact that the one with the switch is the same as the non switch version. (i.e. Log vs. Linear)

It also looks like SWR used 50K pots all over the place on their front panel controls. Those of you with "aural enhancers" in the 750X, 550X, Super Redhead, Black Beauty, Workingman Series, Cali Blonde, Strawberry Blonde, Studio 220, Bass 350, Silverado, Redhead, Baby Blue II, Basic Black, SM-900, SM-500, and Grand Prix units might be able to use this 50K w/ switch for the original 50K pot that your units came with.
 

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