Idea for the ultimate in T-series noise & hum elimination

[Wes]

I don't know why, but as of yesterday the hum in the T500 I've been working on has practically disappeared. I haven't really been targeting the hum, but I did recently cut out the wires going to the cassette. I also did "Skill 1" of the keyboardpartner mods, removing 5 capacitors. The ground wire going to the Rhythm III unit has been disconnected during this work while I repeatedly removed/replaced the top, but yesterday I re-connected the ground and the hum went away.

Sounds like the R3 unit was either picking up or emitting RFI.

I hate it when the R3 units hum. I like the R2 units much better. They just bleep and bloop.

[wayshot]

Update regarding the hum/noise/crackle fight on my T:
Replaced two caps in the power supply (C616 and C617). Less overall hum, but still the same "extra hum" when reverb is selected. I also replaced another transistor (Q853) on the recovery/non-vib board, making the faint crackling disappear. I replaced Q854 and Q855 earlier, this reduced the crackling significantly but it didn't disappear until now.

[Brendon Wright]

Update regarding the hum/noise/crackle fight on my T:
Replaced two caps in the power supply (C616 and C617). Less overall hum, but still the same "extra hum" when reverb is selected. I also replaced another transistor (Q853) on the recovery/non-vib board, making the faint crackling disappear. I replaced Q854 and Q855 earlier, this reduced the crackling significantly but it didn't disappear until now.

Good man!

Could the hum be the cables or tank picking up RF?

[RogerRabbit]

I've used a variable Q notch filter to remove hum from old things I have recorded, similar to this sort of thing http://www.radio-electronics.com/inf...tch_filter.php

[Papus]

I've used a variable Q notch filter to remove hum from old things I have recorded, similar to this sort of thing http://www.radio-electronics.com/inf...tch_filter.php

Excellent article, thanks.
I use a very tight notch filter in Apple Logic to remove hum from my Leslie 122. I always end up notching the following (I'm in 50Hz Land)

100
150
250
350
5,000 (not sure where this originates but it seems to be accentuated by the horn sweep)

As you can see, they're all the first series of harmonics of 50Hz. Strangely, 50Hz itself is not a problem....?????

[enor]

The NS-2 gate will remain closed unless a signal is present on the pre-swell line out. The gate then opens, allowing the post-swell line out to pass signal via the NS-2's send-return loop.
By using the pre-swell line out as the trigger for the gate, the position of the swell pedal has no bearing on whether the gate opens or closes. This means that if your post-swell signal is near or below the noise floor, the gate will still function correctly even when the swell pedal is so low that an ordinary simple gate would not be able to differentiate between noise and actual low-volume organ signal.

A bit like putting a piece of electrical tape over the "check engine" light in your car, when the catalytic converter fails. :)

[Wes]

. Strangely, 50Hz itself is not a problem....?????

Suggests to me your issue is with power rectification buzz as opposed to magnetic field from the power transformer.

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. Strangely, 50Hz itself is not a problem....?????

Suggests to me your issue is with power rectification buzz as opposed to magnetic field from the power transformer.

[Papus]

Suggests to me your issue is with power rectification buzz as opposed to magnetic field from the power transformer.

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Suggests to me your issue is with power rectification buzz as opposed to magnetic field from the power transformer.

Ah, eureka!
Would this be resolved by new caps, or valve(s)?
My 122 is still running its original valves. I drive it very hard, Jon Lord style

[Wes]

New capacitors immediately after the full-wave bridge rectifier (four diodes).

Full-wave rectification of AC produces a "buzz" whose fundamental is twice that of the AC line frequency, and contains many harmonics above that. Half-wave rectification includes the fundamental in the buzz. Noise from transformer EMF should be basically a sine wave at the fundamental.

Wes

[Papus]

OK I finally got around to procuring a Boss NS-2 to test my theory.
The result is outstanding. 100% elimination of noise & hum when no notes are played. The full dynamic range of the organ is preserved, from minimum swell with the volume soft tab engaged, all the way to full swell with no soft tab.
I had to experiment quite a lot with the placement of some external attenuators (simple voltage dividers using resistors) and transformer isolators in order to level-match to the guitar pedals and eliminate ground loops.
I started off by using the Tone Cab output (Pin 24 on the power amp board) but there was a consistent radio station bleed regardless of the placement of transformer isolators throughout the signal chain (these seemed to induce a lot of radio station bleeding for some reason, although they work perfectly on my guitar rig. Go figure).
In the end I obtained the clearest sound by using the T202's headphone output into a 30dB attenuator, with no transformer isolator.
My signal path is thus:

T202 pre-amp output (Pin 3 on recovery board) feeds into Boss NS-2 "Input" - this acts as the gate trigger. The pre-amp Pin 3 output remains connected to wherever it goes next in the T202, I'm just tapping into it to obtain a clean pre-swell trigger.
The T202 headphone output feeds into a 30dB attenuator which feeds into the Boss NS-2 "Return". This causes the NS-2's gate to act upon the T202's final output, but the gate is triggered directly by the recovery amp's output for clarity no matter what the position of the swell pedal.
The Boss NS-2 "Output" feeds into a few guitar pedals for modulation and delay before hitting my Leslie 122RV's custom inbuilt 1/4" guitar-level preamp.

The end result is 100% noise elimination, whilst retaining the quietest output from the organ even when the signal level is below the noise floor of the headphone output!
I'd call this a major win.

I actually have a proper effects loop at Pin 3 of the recovery amp, but in this instance I'm only using the Send to obtain a trigger. There's no Return connected, so the Pin 3 Send output simply shunts straight back to wherever it goes next. I can easily connect guitar effects within the Pin 3 effects loop if needed.

I'll post samples as soon as possible.

:-)

[Papus]

As promised, here are audio samples of the Boss NS-2.
In the tracks labeled "Dry" the Boss NS-2 is bypassed so you can hear the self-noise of the T202. I included a small sample of full volume T202 noise at the start of each track.
The full dynamic range of the T202 is demonstrated, from minimum swell with soft tab engaged, all the way to maximum swell with no soft tab.
There is no processing on the recordings other than a soft limiter on the stereo buss. There are no noise gates on the amps - a small amount of amp hiss/Leslie mechanical noise is audible, but it is of such a low volume that it will not be audible in a mix or in a live situation.
My T202 has Lower Manual bass foldback, no pedals are played in these samples.
Glorious all-valve distortion throughout, no surprise as I was raised on Jon Lord & Uriah Heep. If distortion is not your thing then these samples are probably not your cup of tea :-)
The delay is courtesy of a Korg A5 guitar multi-effect pedal.

Marshall 2061x half-stack is mic'd with an Oktava MK52 ribbon mic slightly off-axis. It is permanently mic'd for my guitar, and the tone suited the T202 nicely.
Leslie 122 is mic'd with a pair of Sennheiser e609's on the horn in 90 degree configuration centered on the axis of rotation, approximately 50mm away from the rear opening of the horn compartment. Horn has diffusers intact. Bass rotor is mic'd with a Beyer Dynamic boundary microphone approximately 50mm away from the rear opening, with a Proel pop/wind filter in front of it.

A reminder: I'm not actually a keyboard player, this is not a talent demo :-)

https://www.dropbox.com/sh/auq2v666s...egqDkDtZa?dl=0

[enor]

It does seem to "eat up" the keyclick on the first note played after a complete silence though, which is a bummer... but only to be expected since any gate needs some time to trigger and the click is such a quick transient. Other than that - nice results!

[Brendon Wright]

My apologies for not commenting sooner, Papus!

The NS2 (nothing to do with National Security?) does a great job on your recordings. It's a keeper.

However, may I throw a boomerang amongst the Pidgin, just to max the mitaphor...

Your T is remarkably quiet even on the dry recordings.

There's not any dirty great hum and the shimmering skirl of tone generator bleed is something I've been in love with since I first saw Star Trek (the original series).
That right there's the "music of the spheres," the twinkle of a clear night sky. The sound of alien planets with minimal set dressing.
Damn, it's fine!
It's also the chaotic sound of ROCK n Roll I reckon, as is hum and 60Hz buzz, though I could do without the latter two.

My own hum has been well solved by the way, but that's another story involving a miswired modification and some toroidal transformer titivation.

[Papus]

My apologies for not commenting sooner, Papus!

The NS2 (nothing to do with National Security?) does a great job on your recordings. It's a keeper.

However, may I throw a boomerang amongst the Pidgin, just to max the mitaphor...

Your T is remarkably quiet even on the dry recordings.

There's not any dirty great hum and the shimmering skirl of tone generator bleed is something I've been in love with since I first saw Star Trek (the original series).
That right there's the "music of the spheres," the twinkle of a clear night sky. The sound of alien planets with minimal set dressing.
Damn, it's fine!
It's also the chaotic sound of ROCK n Roll I reckon, as is hum and 60Hz buzz, though I could do without the latter two.

My own hum has been well solved by the way, but that's another story involving a miswired modification and some toroidal transformer titivation.

Thanks for the appraisal, you're too kind.
I'm not convinced about the relative quiet of my T202..... listen again to the first track "Marshall 2061x (Dry)" between 0:05 and 0:11. The self-noise sounds rather strong to me, that's with the swell pedal floored and the soft tab disengaged.
Also listen to the first 5 seconds of "Leslie 122 (Boss NS-2) before the NS-2 is engaged.
If that's quiet then I wouldn't want to know how bad a noisy T can be!

I'd like to bring out a bit more key click and leakage. I've removed all of the miller filter caps on the UM and LM boards. Are there any easily removed filter caps on the recovery board?

[Brendon Wright]

Ah yes!
The beginning of the Marshall (Dry) one does have a lot more noise, not just TG bleed but hum and noise like a single coil pickup on heavy distortion.
It's cleaner through your 122.

( cue the horrible noise on my own T some years back: even more not-so-good)

Having a noise gate will save a lot of that ghastly hum witch-hunting.

Recently I rebuilt the power supply with a new, enclosed chassis and a toroid transformer. I removed all of the redundant power supply wires now that the beat box, internal leslie and accompaniment board are gone, also removed ground-wire double-ups.
There was a LOT of wire in a pile when I was done, and the hum and noise has gone too. A lot of it will be in my notes but it'll need editing to find the good stuff.

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I'll look into the filter thing, there were quite a few but I'll need to find what they were.