Stage Center Rever - Microphonic sound

[petemoore]

 Â Here's one that has two "B"s in the part #,
 4AB3C1B
 The codes also have two 'B's one represents the ohmage, the other represents the tank orientation [horizontal, vertical etc.], and I haven't yet sorted the four B codes.
 This one has 3 springs : 9AB3C1B
 I suppose the extra spring makes more depth.

[Dror3332]

I don`t believe, that simply swapping IC`s in that schem
will "de-microphonicate" the sound...

Read carefully all what Mark wrote
It has two sections:
1.  How to lose this low and annoying freq.
2. And how to adjust the OpAmp to the reverb input tank.

[Mark Hammer]

I don`t believe, that simply swapping IC`s in that schem will "de-microphonicate" the sound...

Well, as always, you're right.  My suggestion of changing the op-amp was largely prompted by the observation that Anderton never specified what pan to use with the circuit, and some of the pans that people get their hands on are probably unsuited to that circuit, and vice versa.

The challenge is, to my mind, really more one of assuring that the springs can be driven in as efficient a manner as possible so that gain in both the drive and recovery stage can be kept to a blessed minimum.  Particularly with all the wires running here and there in reverb units, the possibilities for stray signals, and leaving things cranked because you need to, creates an opportunity for squeals of different types to emerge.  As well, poor drive of the reverb pan can diminish high end, resulting in a perceived need to turn the reverb up.

We both know there are many, many ways to provide the appropriate current drive for a low-impedance input on a reverb pan.  Many of them, however, would require a different sort of circuit than the SCR one Dror is attempting.  A chip change may not be the penultimate reverb driver, but it may improve the performance of that particular circuit with his particular reverb pan in a direction that reduces the risk of weird or undesirable noises coming out of it.

I think it's time for me to scan and post that old ETI reverb project article with the built-in limiter. 

[puretube]

well, err, Peter surely knew, why he posted that link in reply #11...

and though it`s not explicitely explained amongst those circuits,

there are indepth teachings available about how (and: why ) to get along with
the inherit shortcomings of the various spring-units...

the key thing is not the sheer amount of deliverable current (you could e.g. use an LM386 for that...)
but: constant current;

i.e.:
including the current flowing thru the coils (which varies with frequency-dependant coil impedance), inside a feedback loop.

of course, there have been patents on this topic in the 40`s/50`s or 60`s... 

[Dror3332]

Hi All,

After twicking a little the GGG original circuit with what Mark wrote in reply 6 ( Thanks Mark ) It's sound better to my taste but still very limited. I want to suggest something that maybe someone will post an idea how we can do it.

The better way I think is to have the ability to EQ the RETURN of the effect in the circuit. The source will stay pure of course.
Maybe one way to do it is to be able to connect a Boss GE7 ( or other ) only to EQ the effect not  the source.

Thanks
Dror

[Dror3332]

Hi All,

After twicking a little the GGG original circuit with what Mark wrote in reply 6 ( Thanks Mark ) It's sound better to my taste but still very limited. I want to suggest something that maybe someone will post an idea how we can do it.

The better way I think is to have the ability to EQ the RETURN of the effect in the circuit. The source will stay pure of course.
Maybe one way to do it is to be able to connect a Boss GE7 ( or other ) only to EQ the effect not  the source.

Thanks
Dror

Any Ideas? 

[Mark Hammer]

This is precisely what some of the higher end rackmount spring reverbs have done.  Things like the Orban and comparable units.  Keep in mind that since the spring itself is not going to do a fabulous job transmitting treble, most of the post-spring EQing you'll do will be getting rid of annoying resonances.  Here, a semi-parametric midrange (i.e., tunable resonant frequency and cut/boost), and a variable highpass, may be just about all you really need.

[jimbeaux]

Even though Craig Anderton didn't mention what Accutronics Reverb Tank to use with the SCR (in the Guitar Player Column)  - the one that came with the SCR kit (by Godbout Electronics) was model #1FB2B1D.

It's still sold today by PAIA Electronics. Also used for the "Hot Springs" Reverb kit.

-Jimbeaux

[Dror3332]

This is precisely what some of the higher end rackmount spring reverbs have done.  Things like the Orban and comparable units.  Keep in mind that since the spring itself is not going to do a fabulous job transmitting treble, most of the post-spring EQing you'll do will be getting rid of annoying resonances.  Here, a semi-parametric midrange (i.e., tunable resonant frequency and cut/boost), and a variable highpass, may be just about all you really need.

This is all I'm asking for. "Getting rid of annoying resonances".
Can you please give me some direction where can I find this kind of post spring EQ or its circuit, and how can I integrate it correctly? 
Thanks

[Mark Hammer]

Easy.  Take a look at some of the documents on parametric EQ over at RG Keen's site ( http://www.geofex.com ).  They will show you how to  make a simple cut/boost EQ section with tunable centre frequency.  This can easily be inserted between the recovery gain stage (the one immediately after thereverb pan) and the mixer stage.  You would stick the reverb level pot AFTER the EQ section.  The variable highpass can be an active unit or it can simply be a dual-ganged pot and a pair of caps.  First take a look at the parametric sections at GEOFEX and ask questions on that stuff.  We'll tackle the other stuff later.

I have to head home now, but you might want to do a search for an Orban Reverb unit schematic while you,re waiting to re-establish contact.  There might be some ideas in there.

[Mark Hammer]

Home now, and I should have looked before I leaped.  I have a schem for the Orban 111B Spring Reverb, and boy is it butt-ugly!!

I can tell you the following, though:

1) It uses op-amps throughout, and has a FET-based limiter before the driver stage to keep the springs from sproinging.

2) It has a high gain recovery stage after the springs, as expected, and feeds THAT through a midscoop/notch filter similar to what you see on the Univox Superfuzz.  I can't make out all the component values so I can't tell you how broad/shallow it is and where it is centred, but it's clearly a midscoop (that's one blow against the evil resonance empire).

3) After the midscoop comes an attenuator to set reverb level.

4) From the reverb level control it heads into a gain recovery stage (x10) and frmo there into an EQ section. much of which is shown as a box labelled EQ MODULE).

5) The EQ section has a fully parametric midrange, providing control over centre frequency, bandwidth, and boost cut.  It also has a bass shelving EQ (cut/boost, like your stereo).  That's it.

Seems to me you can easily stick the midscoop of some type just ahead of the Dwell control on the GGG schem.  You can do like Orban and stick a single parametric section after the Dwell control.  That only needs a dual op-amp, if you follow the model shown in:  http://www.geofex.com/Article_Folders/EQs/paramet.htm  The output of that stage can go directly to the 4k7 mixing resistor into the last op-amp stage of the SCR.  You can either keep or scrap the .01 treble-cut cap to ground.  AS for bass control, that can be either a parametric section, or you can simply use a switch to select between alternatives to the .22uf cap after the recovery stage.

[Dror3332]

ohhh this is complicated 

but I'll try to find my way thru this.
I'll start with sticking the parametric EQ inside.

Thanks again Mark