SWR Aural Enhancer Bypass

[duff2]

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?



Thanks,
Duff2

[Lemoore-on]

Subscribed!

[aBoMoFo]

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..."]

[duff2]

For those who are interested, I have also posted this thread here:

http://music-electronics-forum.com/t18931/

No responses yet, but I'm still hopeful.

Cheers,
Duff2

[chadds]

Turn it all the way down?

[Bongolation]

"Flat frequency response" is much more an issue of remedying the tone stack on SWR amps, which are notoriously scooped, not the "Aural Enhancer."

[alexclaber]

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.

[duff2]

Here's how it's done folks (well everything except the push/pull addition that is).



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.

Cheers,
Duff2

[Fuzzbass]

Wow. Very cool!

[BigOldHarry]

Originally Posted by Bongolation

"Flat frequency response" is much more an issue of remedying the tone stack on SWR amps, which are notoriously scooped, not the "Aural Enhancer."

+1

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

[FuzzBoxVoodoo]

I have a SWR Grand Prix Pre that has this mod and I highly recommend it,the sound is more usable in a live setting.
It is good to see how it was done now.

[duff2]

Originally Posted by BigOldHarry

+1

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

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:



Cheers,
Duff2

[mhduffl]

Originally Posted by duff2

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:



Cheers,
Duff2

Hey duff2,

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

Thanks.

[aBoMoFo]

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 (http://www.musicpartsguru.com/closeu...=911&offset=10)

If you wanted one with a pull switch for defeat then this might be the fella for you.
http://www.musicpartsguru.com/closeu...=915&offset=10

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.

[dmusic148]

I am dying to do this mod to my old SM900. But how do I find the physical location of the two caps?

[Jim C]

Nice work Duff; just assumed that when the knob was turned down it was out of the circuit; await you report back regarding performance

[duff2]

Originally Posted by mhduffl

Hey duff2,

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

Thanks.

It would look the same as the black curve but it be located between the black and green curves. Soundwise, the volume would increase slightly and the top end will have more sparkle added to it.

Cheers,
Duff2

[mhduffl]

Originally Posted by duff2

It would look the same as the black curve but it be located between the black and green curves. Soundwise, the volume would increase slightly and the top end will have more sparkle added to it.

Cheers,
Duff2

+2..

Thank you so much Duff2....

Cheers,
Man-Ho

[jb63]

This completely addresses my only gripe with the SM400, that mid scoop right in the meat and potatoes frequencies. I'm thinking about doing this mod even though my SM has been sidelined in favor of an LMII.

[baddarryl]

I take it that this is applicable to the WorkingPro 400?