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SWR Aural Enhancer Bypass

#61
12bass said:
Missed this thread until now.... always cool to read about hardware mods.

When set flat, the Eden WT preamp is flatter than the (stock) SWR curves shown here. However, there's a considerable roll-off of high frequencies above 12 kHz, which might explain why you're wishing for more upper harmonics. I've modded mine so that it goes all the way up to 20 kHz, and it sounds considerably more open now.
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now that's a mod you should post here as well! maybe we need an amplifier modifications thread in the FAQ sticky (note to self)

now come on who will answer my questions on the last page??:D
 
#62
IvanMike said:
sorry for the billion questions. as a russ allee preamp i'm wondering if this modification ended up making your swr sound a lot more like an AMP or Eden or thunderfunk. Even without a graph or scope i've always known the swr units had a 200 Hz cut by ear.
Click to expand...

I have also previously owned a Thunderfunk TFB420 and I presently own an Eden WT-400. The mod does not make the SWR sound like either of these amps. Even after the mod, the SWR retains that harmonic coloration that the amps are known for, especially with the aural enhancer cranked up.

Cheers,
Duff2
 
#63
Went ahead and did this mod to my old Redhead and as expected it does change the sound of the amp in a direction I like. Lots more beef and heft. My bass and my daughter's keyboard sound much more natural now.

Hope to experiment a bit with cap values and report back.
 
#64
I've read through all these posts and got facinated, this simple little mod seems to be SO worth doing. I own a Bass 350, and my idea is to do it with a DPDT switch so its possible to switch back and forth to the "standard/original" vs. "modded" settings. One might call it "shape" vs. "flat" switch...
So I opened the amp and found the two capasitors, but there's a "problem"...
The second (original) capasitor that's supposed to be 0,001uF has a got a stamped label that reads 1000/100!?
Take a look at the attached picture. It's the blue capasitor.
Question : Is that 1000/100 reading supposed to mean 1000pF/100V or 1000uF/100V (u = micro). I suppose it's 1000pF, otherwise I've got a different value on that blue capasitor than anyone else here... :)
 
#66
IvanMike said:
really odd question - can this mod be done with a switch on the unit to toggle between "classic" SWR voicing and the flatter response? I can see how the mod would be cool but i would miss the option of having the original voicing available.
Click to expand...

Yes it can with a simple 2 pole switch and an additional 100n cap. one pole switches the original 100N cap out while pole 2 switches a second 100N cap in across the 1n cap.

Paul
 
#67
BassmanPaul said:
Yes it can with a simple 2 pole switch and an additional 100n cap. one pole switches the original 100N cap out while pole 2 switches a second 100N cap in across the 1n cap.

Paul
Click to expand...

The only thing I'd add to that is that it's best to use shielded wire (shield connected to ground). If you notice most of the other cabling in the 350 (and others, I assume), it's shielded. I had made some mods (AE bypass) using non-shielded wire and got a horrific 60hz hum. Rewired with shielded wire and it's dead quiet again.

I've got more mods to add, but may need a 3-way switch for that.

My old schematics for my studio 220 gave me a lot of inspiration to finish my EE degree instead of dropping out to play music. I'll always have a place in my heart for *modified* SWR gear for that reason...
 
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#70
12bass said:
1000 pF = 1 nF = 0.001 μF

It's 1000 pF. 1000 μF would be a much larger electrolytic.
Click to expand...

Well that's what I thought too, I just had to get it "confirmed" :)

I did the mod by using a DPDT switch so the moded sound can easily be compared to the "original", and it does make it a bit more "heftier". Not as much as I expected, but noticable.
I also did a simple trick to lessen the terrible noise from the fan, it used to sound like a powerplant in there when the fan kicked up revs... so I lowered the voltage from 24V to 15V by connecting a voltage regulator (7815) between the poweramp and the fan. Quite an approvement, and the fan still moves enough air to keep things "cool" enough...
 
#72
duff2 said:
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
Click to expand...

Wow, that graph looks so flat and perfect it kind of makes me think that perhaps they stumbled upon the "SWR sound" by accidentally mixing up the caps. Does anyone know what the AE knob now does to the frequency response?
 
#73
FYI, you can get a 50k linear, DPDT Push/Pull pot for $2.65 at Small Bear:

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I'm still not sure if you need an audio or linear taper on it... the schemo doesn't seem to say. You can also buy the caps you'd need from there. It's a good little online store that I've used in the past.
 
#76
Stompin Tom said:
FYI, you can get a 50k linear, DPDT Push/Pull pot for $2.65 at Small Bear:

Invalid Link Removed

I'm still not sure if you need an audio or linear taper on it... the schemo doesn't seem to say. You can also buy the caps you'd need from there. It's a good little online store that I've used in the past.
Click to expand...

After some inspecting last night, it appears as if it's a linear pot... a 50k B.

FYI, mod accomplished, but sooner or later I'll bother to get a push/pull pot to switch between swr and flat.
 

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