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How do those Spring Reverbs work in guitar amps?

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  How do those Spring Reverbs work in guitar amps? oldschool@tubes.com - 2017-03-18 19:12 -0500
    Re: How do those Spring Reverbs work in guitar amps? rickman <gnuarm@gmail.com> - 2017-03-18 20:47 -0400
      Re: How do those Spring Reverbs work in guitar amps? Phil Allison <pallison49@gmail.com> - 2017-03-18 18:11 -0700
    Re: How do those Spring Reverbs work in guitar amps? Phil Allison <pallison49@gmail.com> - 2017-03-18 18:08 -0700
      Re: How do those Spring Reverbs work in guitar amps? Don Kuenz <g@crcomp.net> - 2017-03-19 05:08 +0000
        Re: How do those Spring Reverbs work in guitar amps? Phil Allison <pallison49@gmail.com> - 2017-03-18 22:38 -0700
          Re: How do those Spring Reverbs work in guitar amps? jurb6006@gmail.com - 2017-03-19 02:46 -0700
            Re: How do those Spring Reverbs work in guitar amps? Phil Allison <pallison49@gmail.com> - 2017-03-19 04:25 -0700
              Re: How do those Spring Reverbs work in guitar amps? jurb6006@gmail.com - 2017-03-19 06:01 -0700
              Re: How do those Spring Reverbs work in guitar amps? jurb6006@gmail.com - 2017-03-19 07:46 -0700
        Re: How do those Spring Reverbs work in guitar amps? "Dave M" <dgminala@mediacombb.net> - 2017-03-19 22:49 -0500
          Re: How do those Spring Reverbs work in guitar amps? Phil Allison <pallison49@gmail.com> - 2017-03-19 22:31 -0700
            Re: How do those Spring Reverbs work in guitar amps? "Michael A. Terrell" <mike.terrell@earthlink.net> - 2017-03-23 19:01 -0400
              Re: How do those Spring Reverbs work in guitar amps? Phil Allison <pallison49@gmail.com> - 2017-03-23 16:24 -0700
                Re: How do those Spring Reverbs work in guitar amps? "dcaster@krl.org" <dcaster@krl.org> - 2017-03-23 16:37 -0700
                  Re: How do those Spring Reverbs work in guitar amps? Phil Allison <pallison49@gmail.com> - 2017-03-23 17:46 -0700
                    Re: How do those Spring Reverbs work in guitar amps? "dcaster@krl.org" <dcaster@krl.org> - 2017-03-23 18:05 -0700
                      Re: How do those Spring Reverbs work in guitar amps? "Michael A. Terrell" <mike.terrell@earthlink.net> - 2017-03-25 03:18 -0400
                Re: How do those Spring Reverbs work in guitar amps? "Michael A. Terrell" <mike.terrell@earthlink.net> - 2017-03-25 03:16 -0400
            Re: How do those Spring Reverbs work in guitar amps? Jasen Betts <jasen@xnet.co.nz> - 2017-03-26 19:36 +0000
          Re: How do those Spring Reverbs work in guitar amps? oldschool@tubes.com - 2017-03-20 14:04 -0500
            Re: How do those Spring Reverbs work in guitar amps? Don Kuenz <g@crcomp.net> - 2017-03-21 17:22 +0000
          Re: How do those Spring Reverbs work in guitar amps? Don Kuenz <g@crcomp.net> - 2017-03-20 19:27 +0000
      Re: How do those Spring Reverbs work in guitar amps? George Herold <gherold@teachspin.com> - 2017-03-20 12:24 -0700
        Re: How do those Spring Reverbs work in guitar amps? Clifford Heath <no.spam@please.net> - 2017-03-21 09:14 +1100
          Re: How do those Spring Reverbs work in guitar amps? George Herold <gherold@teachspin.com> - 2017-03-20 17:04 -0700
            Re: How do those Spring Reverbs work in guitar amps? "dcaster@krl.org" <dcaster@krl.org> - 2017-03-20 20:06 -0700
              Re: How do those Spring Reverbs work in guitar amps? jurb6006@gmail.com - 2017-03-21 00:18 -0700
              Re: How do those Spring Reverbs work in guitar amps? George Herold <gherold@teachspin.com> - 2017-03-21 05:55 -0700
                Re: How do those Spring Reverbs work in guitar amps? "dcaster@krl.org" <dcaster@krl.org> - 2017-03-21 06:46 -0700
        Re: How do those Spring Reverbs work in guitar amps? Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-03-21 03:15 -0400
    Re: How do those Spring Reverbs work in guitar amps? bitrex <bitrex@de.lete.earthlink.net> - 2017-03-19 22:25 -0400
      Re: How do those Spring Reverbs work in guitar amps? Phil Allison <pallison49@gmail.com> - 2017-03-19 19:52 -0700
        Re: How do those Spring Reverbs work in guitar amps? bitrex <bitrex@de.lete.earthlink.net> - 2017-03-19 23:14 -0400
          Re: How do those Spring Reverbs work in guitar amps? bitrex <bitrex@de.lete.earthlink.net> - 2017-03-19 23:14 -0400
          Re: How do those Spring Reverbs work in guitar amps? Phil Allison <pallison49@gmail.com> - 2017-03-19 20:32 -0700
            Re: How do those Spring Reverbs work in guitar amps? bitrex <bitrex@de.lete.earthlink.net> - 2017-03-20 00:01 -0400
              Re: How do those Spring Reverbs work in guitar amps? Phil Allison <pallison49@gmail.com> - 2017-03-19 22:32 -0700
            Re: How do those Spring Reverbs work in guitar amps? jurb6006@gmail.com - 2017-03-20 03:52 -0700
            Re: How do those Spring Reverbs work in guitar amps? bitrex <bitrex@de.lete.earthlink.net> - 2017-03-20 15:18 -0400
              Re: How do those Spring Reverbs work in guitar amps? Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2017-03-20 21:28 +0200
                Re: How do those Spring Reverbs work in guitar amps? bitrex <bitrex@de.lete.earthlink.net> - 2017-03-20 16:26 -0400

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#452760

On Sun, 19 Mar 2017 22:49:52 -0500, "Dave M" <dgminala@mediacombb.net>
wrote:

>>
>> This site seems like a good source of information:
>>
>> https://www.amplifiedparts.com/tech-corner/spring-reverb-tanks-explained-and-compared
>>

That is exactly the info I was looking for. The PDF file includes
pictures too, and is very useful. Thanks for the link.

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#452906

oldschool@tubes.com wrote:
> On Sun, 19 Mar 2017 22:49:52 -0500, "Dave M" <dgminala@mediacombb.net>
> wrote:
>
>>>
>>> This site seems like a good source of information:
>>>
>>> https://www.amplifiedparts.com/tech-corner/spring-reverb-tanks-explained-and-compared
>>>
>
> That is exactly the info I was looking for. The PDF file includes
> pictures too, and is very useful. Thanks for the link.
>

You're welcome.

AmplifiedParts personnel kindly sent me Document 126-00005, which was
written in 1978. It appears that only the two spring variety of tank was
manufactured at that time. Document 126-00005 is now available at:
http://crcomp.net/electronic/reverb/accutronics_document_126-00005.pdf
Here's what it says about the mechanical physics of the tank:

        Accutronics' electromechanical reverberation devices
    consist of input and output transducers and a set of transmission
    springs. These components are mounted on an aluminum channel,
    which  is  usually supported by four springs to an outer case
    or channel.
        Briefly, the device operates as follows: An electrical
    signal applied to the input transducer is translated by the
    magnetic circuit to a torsional force on two small cylindrical
    magnets. The magnets are mechanically coupled to a pair of
    transmission springs and the torsional motion is propagated
    slowly along the spring path. At the output, a replica of the
    original input signal is produced by the action of magnets
    again coupled to the transmission springs. The signal has now
    been delayed by some period, determined by the diameter, wire
    gauge, and length of the transmission springs. Additionally,
    most of the torsional energy is reflected back to the input
    transducer. The result is a multitude of reflections each
    smaller in amplitude than the last. The delay time of each
    additional reflection is 2T since the torsional motion must
    travel the spring path twice to reach the output transducer.

Thank you,

--
Don Kuenz KB7RPU

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#452769

Dave M <dgminala@mediacombb.net> wrote:
>
>>> ** The long springs transmit torsional waves, twisting back and
>>> forward so must be driven the  same way. Tiny tube magnets are made
>>> to twist by the drive coil assembly while at the far end a near
>>> identical transducer converts the twisting back to an electrical
>>> signal.
>>>
>>> The drive assembly is a kind of motor that makes the magnet rotate on
>>> its axis about +/- 30degrees. A torsional wave travels fairly slowly
>>> down a spring, making for long reverb times.
>>>
>>> A major benefit of this method is that external vibrations do not
>>> induce torsional waves in the springs but only lateral ones and so
>>> are largely rejected by the pick up assembly.
>>>
>>> AFAIK the idea was patented by Hammond in the late 50s - then made
>>> famous by Fender in the 60s guitar amps.
>>>
>>> BYI  I agree, it is not easy to find the above info on the net since
>>> the Accutronics site disappeared.
>>
>> Your followup just now made me aware of that a company named
>> Accutronics used to exist. There's a couple of spring reverbs in my
>> bone pile. The metal tanks are stamped with "ACCUTRONICS GENEVA,
>> ILL." The tanks originally came from PAIA as part of a kit:
>>
>>    http://www.paia.com/proddetail.asp?prod=6740K
>>    http://www.paia.com/ProdArticles/hotspuse.htm
>>
>> This site seems like a good source of information:
>>
>> https://www.amplifiedparts.com/tech-corner/spring-reverb-tanks-explained-and-compared
>>
>> Thank you,
>
> Accutronics is now known as Accu-Bell Sound Inc.
> http://www.accutronicsreverb.com/
> There's a link at the top of the home page "How Reverb Works", which
> describes the operation of a spring reverb and why it sounds like it does.
>
> I still have a few reverb tanks stored from the days of building my own
> guitar amps.  Fun stuff! It's really spooky how the length and number of
> springs affect the sound you get from them.

Accu-Bell "hides" their website behind Adobe flash. Fortunately, "How
Reverb Works" also appears at other more "open" websites:

    http://www.tubeampdoctor.com/en/shop_Reverb_Cans_Effects/

"How Reverb Works" contains a spring reverb history mini-history. Here's
an excerpt:

        The use of coiled springs to delay audio signals was
    originated by early telecommunications engineers to simulate
    the effects of long-distance telephone lines. While the
    prolonged sequence of echoes was undesirable for their purposes,
    it seemed most useful to an inventor named Laurens Hammond,
    who promptly appropriated the concept for use with the keyboard
    instrument which bears his name.

The www.amplifiedparts.com link in my first followup points to "Spring
Reverb Tanks Explained and Compared" by Kurt Prange. Prange's tutorial
references:

    Scott, J. L. - Chief Engineer; Accutronics document 126-00005

That Accutronics document may explain the gadget's wave physics in
greater detail. In light of the telecommunications history mentioned at
your link, Bell Labs documentation also seems like a good prospect to
discover the more mechanical principles of operation.

Thank you,

--
Don Kuenz KB7RPU

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#452765

On Saturday, March 18, 2017 at 9:08:19 PM UTC-4, Phil Allison wrote:
> olds...@tubes.com wrote:
> >
> > The Spring Reverbs inside guitar amps have always fascinated me, and I
> > took them one step further by connecting one to my stereo years ago, and
> > the sound was really cool! 
> > 
> > So, yea, I know the basic operation. According to one web article, there
> > is a transducer at one end of a spring and a pickup on the other end.
> > This caused the spring to vibrate and create the reverb effect. One
> > group from the 1960s and 70s that really used them was the Ventures. (I
> > have to mention that I love that groups music). Often when they play,
> > you can actually hear them springs. 
> > 
> > I've taken them inside guitar amps and bnaged them, and they really can
> > make a clatter.
> > 
> > But what I am not finding is exactly what or how does this transducer
> > work. Is it similar to a speaker coil? Or what goes on inside there?
> > 
> > And the pickup, is that similar to a microphone, or what? 
> > 
> > There seems to be nothing that actually details the workings inside of
> > them on the web. So, I thought I'd ask on here.
> >
> 
> ** The long springs transmit torsional waves, twisting back and forward so must be driven the same way. Tiny tube magnets are made to twist by the drive coil assembly while at the far end a near identical transducer converts the twisting back to an electrical signal. 
> 
> The drive assembly is a kind of motor that makes the magnet rotate on its axis about +/- 30degrees. A torsional wave travels fairly slowly down a spring, making for long reverb times. 
> 
> A major benefit of this method is that external vibrations do not induce torsional waves in the springs but only lateral ones and so are largely rejected by the pick up assembly. 
> 
> AFAIK the idea was patented by Hammond in the late 50s - then made famous by Fender in the 60s guitar amps. 
> 
> BYI  I agree, it is not easy to find the above info on the net since the Accutronics site disappeared.
> 
> 
> 
> ....  Phil

Cool!  This is mostly unrelated, but with the right choice of mass and moment of 
inertia you can make a Wilberforce Pendulum, where the torsional mode is almost the 
same frequency as the vibrational mode, and you can get them to couple.  
https://www.youtube.com/watch?v=S42lLTlnfZc
We made these with slinkys and 1 foot rulers (with pennies taped on the ends).  

George H.

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#452786

On 21/03/17 06:24, George Herold wrote:
> ...with the right choice of mass and moment of
> inertia you can make a Wilberforce Pendulum, where the torsional mode is almost the
> same frequency as the vibrational mode, and you can get them to couple.
> https://www.youtube.com/watch?v=S42lLTlnfZc
> We made these with slinkys and 1 foot rulers (with pennies taped on the ends).

Sweet! I want to make one :)

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#452805

On Monday, March 20, 2017 at 6:14:49 PM UTC-4, Clifford Heath wrote:
> On 21/03/17 06:24, George Herold wrote:
> > ...with the right choice of mass and moment of
> > inertia you can make a Wilberforce Pendulum, where the torsional mode is almost the
> > same frequency as the vibrational mode, and you can get them to couple.
> > https://www.youtube.com/watch?v=S42lLTlnfZc
> > We made these with slinkys and 1 foot rulers (with pennies taped on the ends).
> 
> Sweet! I want to make one :)

Right, the slinky is not as good, lower Q. 

You can't make a Wilbur reverb, (just dreaming) unless you were 
willing to hang one of the magnets.  Maybe if you hung some weight
in the middle you could couple vibration into angle.. 
maybe not at the middle. (some harmonic sweet spot?)  

I never knew (some) reverb was by the torsional motion of springs. 
I want one of those.... I wouldn't mind a slightly broken one 
if it had most of the parts.  

George H.  

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#452842

On Monday, March 20, 2017 at 8:05:04 PM UTC-4, George Herold wrote:


> I never knew (some) reverb was by the torsional motion of springs. 
> I want one of those.... I wouldn't mind a slightly broken one 
> if it had most of the parts.  
> 
> George H.

Not the same thing, but you might look at the PT2399 ic.  

                                          Dan

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#452862

On Monday, March 20, 2017 at 10:06:25 PM UTC-5, dca...@krl.org wrote:
> On Monday, March 20, 2017 at 8:05:04 PM UTC-4, George Herold wrote:
> 
> 
> > I never knew (some) reverb was by the torsional motion of springs. 
> > I want one of those.... I wouldn't mind a slightly broken one 
> > if it had most of the parts.  
> > 
> > George H.
> 
> Not the same thing, but you might look at the PT2399 ic.  
> 
>                                           Dan

Not the same thing might be the understatement of the year. To use that IC for an actual reverb, not just echo, you have to do quite a bit. 

First of all you have to take the clock speed up quite a bit, and then you have to figure out a feedback circuit with just a hair under unity gain. The circuit is not likely to be very stable and that might be why they don't do it. 

If you want that IC to sound like a spring reverb the parameters are on the edge to get the sustain. It would be easy to kick the thing into oscillation. All it takes is one little slight error in design and the right input and the thing will probably howl. 

I am not sure a PT2399 will clock fast enough to emulate a spring reverb no matter what. And the design, as far as I know about that chip, would probably be more trouble than it is worth. Using two of them might help, but only if they can clock fast enough. If not you are fucked. 

I heard of one thing that beats a spring reverb. Long time ago. About a recording studio that had a well dug accessible in the building, they dropped a mic down there and had a speaker somewhere. Now THAT'S a tank ! 

The spring job is the next best thing as far as I know, unless you go totally digital. Even then, some people do not like the sound of the digital, hell some even play records because they don't like CDs. But once everything is mixed down I have much doubt as to whether they will be able to tell. 

But the PT2399 is a cheap chip. I think all it is is a BBD with an oscillator. Nothing wrong with that, but it is NOT going to sound like a good reverb tank.

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#452880

On Monday, March 20, 2017 at 11:06:25 PM UTC-4, dca...@krl.org wrote:
> On Monday, March 20, 2017 at 8:05:04 PM UTC-4, George Herold wrote:
> 
> 
> > I never knew (some) reverb was by the torsional motion of springs. 
> > I want one of those.... I wouldn't mind a slightly broken one 
> > if it had most of the parts.  
> > 
> > George H.
> 
> Not the same thing, but you might look at the PT2399 ic.  
Oh, (thanks) I have very little interest in the reverb, but the physics of 
driving magnets on springs and picking up at the other end looks interesting.  

George H. 
> 
>                                           Dan

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#452883

On Tuesday, March 21, 2017 at 8:55:52 AM UTC-4, George Herold wrote:
 
> Oh, (thanks) I have very little interest in the reverb, but the physics of 
> driving magnets on springs and picking up at the other end looks interesting.  
> 
> George H. 
> > 


I programmed on a computer that used mercury as a delay line.  It had a trough that was about 5 feet long.  A transducer at one end to put sound into the mercury and anther transducer at the other end to pick up the sound.  The pulses were reshaped and retransmitted.  

                                           Dan

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#452861

On 03/20/2017 03:24 PM, George Herold wrote:
> On Saturday, March 18, 2017 at 9:08:19 PM UTC-4, Phil Allison wrote:
>> olds...@tubes.com wrote:
>>>
>>> The Spring Reverbs inside guitar amps have always fascinated me,
>>> and I took them one step further by connecting one to my stereo
>>> years ago, and the sound was really cool!
>>>
>>> So, yea, I know the basic operation. According to one web
>>> article, there is a transducer at one end of a spring and a
>>> pickup on the other end. This caused the spring to vibrate and
>>> create the reverb effect. One group from the 1960s and 70s that
>>> really used them was the Ventures. (I have to mention that I love
>>> that groups music). Often when they play, you can actually hear
>>> them springs.
>>>
>>> I've taken them inside guitar amps and bnaged them, and they
>>> really can make a clatter.
>>>
>>> But what I am not finding is exactly what or how does this
>>> transducer work. Is it similar to a speaker coil? Or what goes on
>>> inside there?
>>>
>>> And the pickup, is that similar to a microphone, or what?
>>>
>>> There seems to be nothing that actually details the workings
>>> inside of them on the web. So, I thought I'd ask on here.
>>>
>>
>> ** The long springs transmit torsional waves, twisting back and
>> forward so must be driven the same way. Tiny tube magnets are made
>> to twist by the drive coil assembly while at the far end a near
>> identical transducer converts the twisting back to an electrical
>> signal.
>>
>> The drive assembly is a kind of motor that makes the magnet rotate
>> on its axis about +/- 30degrees. A torsional wave travels fairly
>> slowly down a spring, making for long reverb times.
>>
>> A major benefit of this method is that external vibrations do not
>> induce torsional waves in the springs but only lateral ones and so
>> are largely rejected by the pick up assembly.
>>
>> AFAIK the idea was patented by Hammond in the late 50s - then made
>> famous by Fender in the 60s guitar amps.
>>
>> BYI  I agree, it is not easy to find the above info on the net
>> since the Accutronics site disappeared.
>>
>>
>>
>> ....  Phil
>
> Cool!  This is mostly unrelated, but with the right choice of mass
> and moment of inertia you can make a Wilberforce Pendulum, where the
> torsional mode is almost the same frequency as the vibrational mode,
> and you can get them to couple.
> https://www.youtube.com/watch?v=S42lLTlnfZc We made these with
> slinkys and 1 foot rulers (with pennies taped on the ends).
>
> George H.
>

Fun, thanks.

Cheers

Phil Hobbs

-- 
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

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#452668

On 03/18/2017 08:12 PM, oldschool@tubes.com wrote:
> The Spring Reverbs inside guitar amps have always fascinated me, and I
> took them one step further by connecting one to my stereo years ago, and
> the sound was really cool!
>
> So, yea, I know the basic operation. According to one web article, there
> is a transducer at one end of a spring and a pickup on the other end.
> This caused the spring to vibrate and create the reverb effect. One
> group from the 1960s and 70s that really used them was the Ventures. (I
> have to mention that I love that groups music). Often when they play,
> you can actually hear them springs.
>
> I've taken them inside guitar amps and bnaged them, and they really can
> make a clatter.
>
> But what I am not finding is exactly what or how does this transducer
> work. Is it similar to a speaker coil? Or what goes on inside there?
>
> And the pickup, is that similar to a microphone, or what?
>
> There seems to be nothing that actually details the workings inside of
> them on the web. So, I thought I'd ask on here.
>

Take a look at the reverb unit schematic for the Roland Jazz Chorus:

<http://music-electronics-forum.com/attachments/34861d1437104328-screen-shot-2015-07-16-8.49.19-pm.png>

The spring is large in this one so the transducer is driven by a small 
power amplifier - you need to put a decent amount of energy into it to 
drive the acoustic waves.

More "refined" designs like this one have a current-sense resistor in 
the transducer ground leg and wrap the drive amplifier feedback loop 
around it to even out its nonlinear response.

The output signal is picked off by a regular op-amp amplifier in 
non-inverting configuration.

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#452671

 bitrex the bullshtiter wrote:

> 
> Take a look at the reverb unit schematic for the Roland Jazz Chorus:
> 

** The spring unit is made by OC Electronics, has a folded spring but otherwise is very similar in operation.

> <http://music-electronics-forum.com/attachments/34861d1437104328-screen-shot-2015-07-16-8.49.19-pm.png>
> 
> The spring is large in this one so the transducer is driven by a small 
> power amplifier - you need to put a decent amount of energy into it to 
> drive the acoustic waves.
> 
 
 ** Complete bollocks. 


> More "refined" designs like this one have a current-sense resistor in 
> the transducer ground leg and wrap the drive amplifier feedback loop 
> around it to even out its nonlinear response.
> 

** Cut the crap - it's just simple current drive. 

The input coil used has a nominal impedance of 8 ohms at 1kHz, much lower at 100Hz and much higher at 10kHz. 

Drive power requirement is around 10mW, some as other designs, but the low impedance means it cannot be driven fully by a single, regular op-amp. 

The reverb units in Roland amps and tape echos are easily driven into distortion  - needing a resistor of about 56 ohms in series to eliminate.

See pic of the inside of one.

https://upload.wikimedia.org/wikipedia/commons/4/48/Reverb-3.jpg


....  Phil 

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#452673

On 03/19/2017 10:52 PM, Phil Allison wrote:

> The input coil used has a nominal impedance of 8 ohms at 1kHz, much lower at 100Hz and much higher at 10kHz.
>
> Drive power requirement is around 10mW, some as other designs, but the low impedance means it cannot be driven fully by a single, regular op-amp.

That makes sense. How much average voltage would one expect to see 
between terminals 4 and 5 of the tank input prior to the unit distorting 
with a guitar signal?

The Bandit in this unit from a Q on sci.electronics.repair seems to be 
using a single 4558 section to drive the tank. Also with current feedback

<http://music-electronics-forum.com/attachments/34861d1437104328-screen-shot-2015-07-16-8.49.19-pm.png>

The collector of Q3 is connected to ground, while Q4 is going to what I 
guess is the negative supply. Interesting.

> The reverb units in Roland amps and tape echos are easily driven into distortion  - needing a resistor of about 56 ohms in series to eliminate.
>
> See pic of the inside of one.
>
> https://upload.wikimedia.org/wikipedia/commons/4/48/Reverb-3.jpg

BOY-YOY-YOY-YOY-YOYING...

> ....  Phil
>

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#452674

On 03/19/2017 11:14 PM, bitrex wrote:
> On 03/19/2017 10:52 PM, Phil Allison wrote:
>
>> The input coil used has a nominal impedance of 8 ohms at 1kHz, much
>> lower at 100Hz and much higher at 10kHz.
>>
>> Drive power requirement is around 10mW, some as other designs, but the
>> low impedance means it cannot be driven fully by a single, regular
>> op-amp.
>
> That makes sense. How much average voltage would one expect to see
> between terminals 4 and 5 of the tank input prior to the unit distorting
> with a guitar signal?
>
> The Bandit in this unit from a Q on sci.electronics.repair seems to be
> using a single 4558 section to drive the tank. Also with current feedback
>
> <http://music-electronics-forum.com/attachments/34861d1437104328-screen-shot-2015-07-16-8.49.19-pm.png>
>
>
> The collector of Q3 is connected to ground, while Q4 is going to what I
> guess is the negative supply. Interesting.

In the Roland circuit that is

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#452677

bitrex wrote:

> On 03/19/2017 10:52 PM, Phil Allison wrote:
> 
> > The input coil used has a nominal impedance of 8 ohms at 1kHz, much lower at 100Hz and much higher at 10kHz.
> >
> > Drive power requirement is around 10mW, some as other designs, but the low impedance means it cannot be driven fully by a single, regular op-amp.
> 
> That makes sense. How much average voltage would one expect to see 
> between terminals 4 and 5 of the tank input prior to the unit distorting 
> with a guitar signal?
> 
  
  ** 500mV rms maybe. 

> The Bandit in this unit from a Q on sci.electronics.repair seems to be 
> using a single 4558 section to drive the tank. Also with current feedback
> 

 ** You posted the wrong schem.

Most PVs have nominal 600ohm reverb tanks that are comfortably drive by half a 4558. 



....  Phil 

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#452685

On 03/19/2017 11:32 PM, Phil Allison wrote:

>> The Bandit in this unit from a Q on sci.electronics.repair seems to be
>> using a single 4558 section to drive the tank. Also with current feedback
>>
>
>  ** You posted the wrong schem.
>
> Most PVs have nominal 600ohm reverb tanks that are comfortably drive by half a 4558.
>
>
>
> ....  Phil
>

<https://peavey.com/forum/download/file.php?id=14455>

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#452693

 bitrex wrote:
>
> >
> >  ** You posted the wrong schem.
> >
> > Most PVs have nominal 600ohm reverb tanks that are comfortably drive by half a 4558.
> >
> >
> 
> <https://peavey.com/forum/download/file.php?id=14455>


** Not available to me. 

 PV forum members only. 

 There are plenty of PV Bandit schems on Google Images.


....  Phil 

....  Phil 

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#452701

>"Most PVs have nominal 600ohm reverb tanks that are comfortably drive by half a 4558."

I saw one amp, don't remember the brand, but it used a 6V6 to drive the tank. Had its own output transformer to boot. 

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#452762

On 03/19/2017 11:32 PM, Phil Allison wrote:
> bitrex wrote:
>
>> On 03/19/2017 10:52 PM, Phil Allison wrote:
>>
>>> The input coil used has a nominal impedance of 8 ohms at 1kHz, much lower at 100Hz and much higher at 10kHz.
>>>
>>> Drive power requirement is around 10mW, some as other designs, but the low impedance means it cannot be driven fully by a single, regular op-amp.
>>
>> That makes sense. How much average voltage would one expect to see
>> between terminals 4 and 5 of the tank input prior to the unit distorting
>> with a guitar signal?
>>
>
>   ** 500mV rms maybe.

Any of them ever use push-pull to drive the transducer? That is to say, 
not push-pull in the way a regular complimentary output amplifier or 
op-amp is, but say a bridged configuration of two op-amps driven 
out-of-phase.

I had wanted to drive an inductive load with a varying impedance over 
frequency with a bridge configuration to put more power into it than 
what the supply could provide single-ended, but couldn't figure out the 
proper sense topology so both amps could provide current drive over the 
whole cycle.

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