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DIY Stompboxes => Building your own stompbox => Topic started by: skiraly017 on March 08, 2007, 06:09:48 PM

Title: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: skiraly017 on March 08, 2007, 06:09:48 PM
There's something about a Fender brownface vibrato that is unreal. My Carr Rambler has a tube driven trem but it's not the same. Is there a pedal out there that captures the Fender sound? What if you subsituted the tube with a JFET as done in a couple of projects? I know RG just posted about using JFETS in Fender amps to free up a tube. Could this be done or am I thinking too far outside the box?
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: markm on March 08, 2007, 06:36:21 PM
I always thought of the EA Trem reminding me of the brownface trem.
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: skiraly017 on March 08, 2007, 06:47:31 PM
I always thought of the EA Trem reminding me of the brownface trem.


I have to disagree. I built the EA Trem and have gone back to it several times just to be sure and that "feel" is just not there. FWIW, my basis for comparison is a '61 or '62 brownface Fender Pro. I'm very close to buying the amp just for the vibrato. It's evil, sexy, magical and swampy all at the same time.
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: markm on March 08, 2007, 06:54:09 PM
Well, I have to say it's been a VERY long time since I've been even near a brownface amp that I'm basing my opinion on bad memory!  :icon_lol:
Buy it if ya can.....Real Nice amps those are!  :icon_cool:
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: Ace on March 08, 2007, 06:59:44 PM
I haven't tried one, but the "Swamp Thing" was supposed to have that "Brown face" sound.
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: markm on March 08, 2007, 07:04:46 PM
I haven't tried one, but the "Swamp Thing" was supposed to have that "Brown face" sound.

Is that a Homebrew stomper?
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: Dragonfly on March 08, 2007, 07:12:08 PM
The vibrato in the brown face pro I used to have always sounded like a tremolo that had some slight "univibe-like" or "phaser=-ike" qualities going on "behind" it. At least thats *my* recollection of it.


AC
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: Eb7+9 on March 09, 2007, 05:22:33 AM
I got the Fender Champ-Trem emulated with jFET's but I had to run the circuit at 18volts and use the Vibe style oscillator for getting good range ... haven't tried this signal path yet ...
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: KB on March 09, 2007, 05:34:14 AM
Look at Fender schematics with the 6G code

6G4 or 6Ga "Brown Super"
6G5 or 6G5a "Brown pro"
these two are my favorites. 

I have thought of trying to build a "Brown Super" just for the "Harmonic vibrato" as fender described it.  There was some discussion on Ampage way back when, about what made these amps sound different.  I cannot really remember what was posted and cannot find my notes now.  I seem to remember that they were a

The vibrato used two tubes (3 in the Ga models) and is a very complex design.  Other fender amps from this period used different methods like directly varying the bias, or the now common optosolator.

These amps sound very distinctive... I remember trying 6Ga Super in London eight or nine years ago the vibrato / trem is different from all the pedal type trems I have heard.  I have to agree with skiraly017 it is a very sexy sound... very addictive... especially at slow speed. 

Kevin
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: Sir H C on March 09, 2007, 08:41:48 AM
Those fenders tremolo the low frequencies the opposite polarity of the high frequencies.  So your low notes are out of sync with the highs after the trem.  A really cool complex effect.  I guess you should be able to do it with transistors as that stage is not supposed to be adding distortion and the like.  Also unlike the blackface/silverface amps the trem does not use LDRs, it is all varying the gain on the amplifying stages.
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: Serge on March 09, 2007, 09:41:38 AM
In the layouts gallery there is a schematic for the Blues Pearl Teja trem.  I thought that was supposed to do the Brownface vibe/trem thing
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: stm on March 09, 2007, 09:56:16 AM
Those fenders tremolo the low frequencies the opposite polarity of the high frequencies.  So your low notes are out of sync with the highs after the trem.  A really cool complex effect.  I guess you should be able to do it with transistors as that stage is not supposed to be adding distortion and the like.  Also unlike the blackface/silverface amps the trem does not use LDRs, it is all varying the gain on the amplifying stages.

This is very interesting information, Sir HC.
Where/how did you learn this?  I took a look at the suggested amp schems and it is not trivial to understand what's going on there!
Also, that description could fit in a 2-stage univibe, where a broad notch is swept either attenuating the lows or highs depending on which part of the sweep you are in.
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: tcobretti on March 09, 2007, 09:58:21 AM
So, is the part of the schem below that is outlined in red the entire vibrato part of the amp?


(http://aronnelson.com/gallery/albums/TCobrettis-Stuff/Fender_pro6g5.gif)
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: skiraly017 on March 09, 2007, 10:30:45 AM
In the layouts gallery there is a schematic for the Blues Pearl Teja trem.  I thought that was supposed to do the Brownface vibe/trem thing

Nope. That's a slighly modified EA Trem.
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: stm on March 09, 2007, 10:44:45 AM
I found the following description:

"The Brown/Blond amps also introduced an effect sometimes known as 'harmonic vibrato,' a phase-shifting tremolo system that required two and one half 12AX7/7025 tubes but had a sweet swirl that has been imitated but not improved on in 40 years. Much of this tremolo's character results from the fact that it separates the low and high frequencies and applies the tremolo effect to each separately and out of phase."

Here: http://www.infoweb.co.nz/fender-amplifier-history (http://www.infoweb.co.nz/fender-amplifier-history)

P.D.  Here is more on the same subject: http://www.fenderforum.com/forum.html?topic_number=327608
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: R.G. on March 09, 2007, 11:24:16 AM
The subject vibrato does a split of bass and treble. The split is with a simple one-cap, one-resistor filter, so the bass and treble sides overlap a lot. In addition, each side of the filter has a phase shift associated with it, an inescapable part of a filter.

Each side is then amplitude modulated by modifying the bias on a section of a 12AX7. This introduces little distortion because the both the plate voltages and the input compliance voltages on the 12AX7 are so high. The two sides are then amplified and inverted in the 12AX7 sections, giving another 180 degree phase shift, and added back together in a resistive summer.

The addition of varying amounts of the bass/treble split with the phase shifts of the one-time-constant filter splitter produces phase interference and reinforcements, like a phaser, but not as extensive. The frequencies and depths of cancellation/reinforcement move around as the amplitudes change, again somewhat like a phaser but not as focussed.

The design probably started as a way to make the control voltages cancel. The control voltages are out of phase for high and low frequencies, and the bleedthrough would tend to cancel in the resistive adder. I suspect that they tried this and found out it sounded good as well as cancelling bleedthough.

A quick and dirty way to do this would be to set up the following:

Input buffer feeds an inverter and a single pole RC filter.
Inverter feeds the other sex filter (high vs low pass)
The high and low pass filters are mixed into the summing node of an inverting opamp.
The input mixing resistors are in series with a JET, of the typical P90 types.
An LFO with an inverted output feeds the gates of the JFETs.

Setting up the JFETs is about the same as the JFETs on a P90. The only difference is the inverted LFO feeding one of them.

I suspect that this gets 90% of the sound of the original, maybe even close enough not to need the other 10%.
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: Steben on March 09, 2007, 12:06:03 PM

....Each side is then amplitude modulated by modifying the bias on a section of a 12AX7.....


...An LFO with an inverted output feeds the gates of the JFETs....
Setting up the JFETs is about the same as the JFETs on a P90. The only difference is the inverted LFO feeding one of them.
I suspect that this gets 90% of the sound of the original, maybe even close enough not to need the other 10%.

Actually you can use bias modulation in FET's in the fetzer way almost going to the zero bias end, it is, however a little more tricky, since you have to detect Vgs,Idss,...
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: stm on March 09, 2007, 12:13:08 PM
......
A quick and dirty way to do this would be to set up the following:

Input buffer feeds an inverter and a single pole RC filter.
Inverter feeds the other sex filter (high vs low pass)
The high and low pass filters are mixed into the summing node of an inverting opamp.
The input mixing resistors are in series with a JET, of the typical P90 types.
An LFO with an inverted output feeds the gates of the JFETs.
......

RG, I looked in more detail at the 6G5, 6G14, 6G15 shcems available at the FIS, and don't see any phase inversion between the lowpass and highpass filters.  Apparently the extra inverter you mention wouldn't be needed, or if installed would produce a different effect from what we have.

Also, now I understand why such circuit is considered to be "richer" or "fuller" sounding in comparison to an LDR vibrato/tremolo; the operation of the gain varying stages is inherently nonlinear and adds odd-ordered harmonics.

Actually you can use bias modulation in FET's in the fetzer way almost going to the zero bias end, it is, however a little more tricky, since you have to detect Vgs,Idss,...

Steben, yes, now I understand the principle of operation and can clearly "see" how to extend this technique to the Fetzer Valve, and in general, a JFET amp stage.  Of course is highly recommended to fine tune the circuit to the particular Vp and Idss of the JFETs in use, and also a good idea to use a matched pair for best gain and control voltage cancellation.
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: R.G. on March 09, 2007, 01:37:42 PM
Quote
RG, I looked in more detail at the 6G5, 6G14, 6G15 shcems available at the FIS, and don't see any phase inversion between the lowpass and highpass filters.  Apparently the extra inverter you mention wouldn't be needed, or if installed would produce a different effect from what we have.
That's correct, there isn't any signal inverter in the stock circuit. I put that in there because I believe that it would produce a more intense effect. In fact, a switch to feed the filters from either just the buffer or buffer plus inverse would be a good idea.

Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: R.G. on March 09, 2007, 02:22:27 PM
Wait a minute. I told you wrong. The filtering is not single-pole high and low pass. It's closest to the two halves of a twin-T. That makes for an even kinkier phase and amplitude response.

The result is that the response wiggles between bass heavy to mid-notch to treble heavy and back again.  It seems to wobble a mild notch filter around 300Hz, transforming to highpass or lowpass once it's much past 300 in either direction.

I think the other stuff is correct.
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: Steben on March 09, 2007, 03:09:32 PM
(http://library.thinkquest.org/C0111209/3/iu_jfet.gif)

Well, it looks tubey enough. Bringing "Ugs" (gate bias) down gives smaller amplitude. In a Fetzer II, the curve is more linear, which is in fact more triode-like, but reduces the amplitude change, which means you have to bring it down even more.
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: R.G. on March 09, 2007, 03:20:47 PM
I did a quickie markup of an old Phase 90 schematic to show one way to do a solid state version. It's up at GEO now.

I think this will get the right feel, if not be a perfect repro. The JFETs will probably introduce some soft distortion. That's NOT going to be the same as tube distortion, but it should be nice.
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: Sir H C on March 09, 2007, 04:55:52 PM
Having a brown amp, the trem is amazing.  That is why those amps are so cool. 

Now they are too expensive for me to ever think about buying again...
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: Eb7+9 on March 09, 2007, 06:19:07 PM
discussed here ...

http://www.diystompboxes.com/smfforum/index.php?topic=49413.0 (http://www.diystompboxes.com/smfforum/index.php?topic=49413.0)

class-A tremulant circuits won't sound the same exported to op-amp "loss-less" technology because of the low-end cancellation that takes place in the class-A case ...
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: R.G. on March 09, 2007, 07:40:31 PM
JC, did you even look at the schematic?

The circuit drives exactly the same network as in the Fender amp, then the result is buffered by the high impedance input of an opamp and the output of that is modulated by open-loop JFETs into a mixer. It's not a lossless opamp technology.

Next time, understand the circuit first, OK?

And that wasn't a discussion, it was a discharge into the ether. Discussion implies much more two-sided give and take than advice to look at patents for "electronic tremulant" and some amp schematics. I didn't see any discussion at all.
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: Dragonfly on March 09, 2007, 09:15:16 PM
I did a quickie markup of an old Phase 90 schematic to show one way to do a solid state version. It's up at GEO now.

I think this will get the right feel, if not be a perfect repro. The JFETs will probably introduce some soft distortion. That's NOT going to be the same as tube distortion, but it should be nice.


Hi RG...
 Interesting...i might "give this a go" on Sunday. I'm pretty curious as to the results, and it looks like an easy enough build. If I get a chance to build it, I'll be sure to report back with the results.
  Thanks,
    AC
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: R.G. on March 09, 2007, 10:21:52 PM
Cool.

The other thing I thought about was using a variant of the EA tremolo to do the amplitude variation before the mixing, but I didn't see a simple way to do the inverted LFO. At least not as simple as the design based on the Phase 90.
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: Eb7+9 on March 10, 2007, 07:20:34 AM
JC, did you even look at the schematic?

The circuit drives exactly the same network as in the Fender amp, then the result is buffered by the high impedance input of an opamp ...

right ... to be fair, at first I didn't look at the schematic because I kinda know by now how you "stand" so to speak on basic loading/drive issues ... :icon_wink:

so, I had a look and I was right, it's a lossless mixer ...

since you're a big fan of understanding, take a look at the redraw of the 6G7 Vibrato circuit

http://www.lynx.net/~jc/6G7vibrato.gif (http://www.lynx.net/~jc/6G7vibrato.gif)

at first glance it just seems like there's a split in the signal path, a low-bandpass leg and a high bandpass leg, the LFO causes an asymmetric change in gain to the diff pair these filtered legs are fed to and then into a resistive mixer to "add" the difference ...

at second glance there's something more going on ...

the oscillator puts out a sine wave that's around 6 v pk-pk ... by the time that voltage cross es the voltage divider and hits the grid there's about 3 to 4 volts pk-pk hitting the grid - that's with Intensity full up ... since the LFO has an inverter on one leg leading to the other side of the differential circuit that's a total of 6 to 8 volts of input voltage across the differential input circuit  ...

that means the diff pair is swinging almost (at least somewhat near) across it's fulldynamic range ... at the top end of these ranges the grid leak current rises to a considerable level relative to idling levels ... this translates in a (severely) reduced input resistance, well below 100k at the top input voltage extreme - vive-versa they go to higher than nominal resistance during the low part of the cycle ...

since this input resistance plays a dominant part in setting the high-low band-pass freq's then what happens is the bi-amp frequency moves up and down with the cycling ...  it's very much a part of the effect

in your circuit that frequency be static ...

so, what we have is varying bandwidth's being mixed at varying levels and drive ratios ... does this remind you of any other circuit ??

right ... the Univibe

btw, the very same one-stage variable-bandwidth variable-mixing idea is available as output in the the Jax Vibra-Chorus and Shin-Ei Resly Tone - but not the Univibe  ... though, again, the varying bandwidth component takes places through another mechanism in those circuits ... really interesting how this variable-bandwidth variable-mixing stuff pops up in different ways ...

then, there's a second amplitude thing going on at the plates of the differential triode circuit since the driving point impedances also varies considerably around it's nominal values as the bias on the tubes goes up and down ... this is another component that will sets the character of the signal envelope - the partial Trem component ...

the main thing is the variable frequencies occuring "before" the mixing - what I was referring to in  the post mentioned above ...  it's a product of wide-range loading variations // the opposite of losslessness ...

now, I'm not saying your circuit won't work or won't be appealing ... it just won't have that varying bandwidth component in it that's all - what I was saying ...

just to add to this, if we were to actually do a jFET emulation of the class-A mixer (with really well-matched FET devices) as it appears in the Fender schem then this component would be missing as well since the input resistance on a jFET hardly changes with bias ... combine this with the two-way device matching problems and this would explain why you don't see that version being explored much ... yeah, you could always rig up photocells and make the whole thing look even more ellegant ... then you've got that lower shut-off limit that tends to hit harder that the more gradual cutoff of tubes ...

very specific non-linear manifestos are built into this Fender circuit and it is what it is for those reasons ... otherwise, there's not much else going on ... it's one of those tube circuits tranny or op-amp emulators probably can't nail ...

let's see what the clips sound like ...
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: George Giblet on March 10, 2007, 08:36:14 AM
JC, thanks for the write up.  When you start looking at the finer point there's a lot going on.  It's the kind of circuit that easy to fob-off with a first pass glance only to realize it requires more detailed study.

> this translates in a (severely) reduced input resistance,

I'm not so sure that will happen to a large extent in the steady-state.  What I expect will happen is the coupling caps, 5n to the depth pot and 50n to the X-point will act as peak detectors with the grid diodes and eventually (after power up) a new set of DC conditions will be established such that the low resistance region is minimal.  I haven't actually analysed the circuit but the couple-cap grid diode DC shift is a common thing.

The other thing is the there's a lot of phase shifts due the low-pass filtering on the inverted LFO path - that's go to do something.

It's too late for me to think about this anymore today - I'm pooped.

Thanks for peaking some interesting into this ckt.

Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: d95err on March 10, 2007, 10:00:16 AM
Quote
RG, I looked in more detail at the 6G5, 6G14, 6G15 shcems available at the FIS, and don't see any phase inversion between the lowpass and highpass filters.  Apparently the extra inverter you mention wouldn't be needed, or if installed would produce a different effect from what we have.
That's correct, there isn't any signal inverter in the stock circuit. I put that in there because I believe that it would produce a more intense effect. In fact, a switch to feed the filters from either just the buffer or buffer plus inverse would be a good idea.

The tremolo used in the old Vox AC30 and AC15 uses a similar design which, if I remember correctly, also inverts the phase somewhere in there. I think it's actually even more complex...
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: R.G. on March 10, 2007, 10:34:02 AM
Quote
right ... to be fair, at first I didn't look at the schematic because I kinda know by now how you "stand" so to speak on basic loading/drive issues ...
OK. Your reply said as much.
Quote
so, I had a look and I was right, it's a lossless mixer ...
But neither your first reply nor the "discussed here" thread said anything about a lossless mixer. I guess if one looks hard enough they can find something to grouse about.

I don't suppose you read it where I said "I suspect that this gets 90% of the sound of the original, maybe even close enough not to need the other 10%." or "I think this will get the right feel, if not be a perfect repro. The JFETs will probably introduce some soft distortion. That's NOT going to be the same as tube distortion, but it should be nice."

But having not said that it would be perfect and then being told it's not perfect for thus-and-sundry reasons, lets look at it a bit, since I really am a big fan of understanding.
Quote from:  JC
at second glance there's something more going on ...

the oscillator puts out a sine wave that's around 6 v pk-pk ... by the time that voltage cross es the voltage divider and hits the grid there's about 3 to 4 volts pk-pk hitting the grid - that's with Intensity full up ... since the LFO has an inverter on one leg leading to the other side of the differential circuit that's a total of 6 to 8 volts of input voltage across the differential input circuit  ...
That's a great theory. But it's not what happens. I didn't happen to have a circuit board set up to try this, nor a 6G5 to measure, so I put the circuit into a simulator.

Before you read me the manifesto on simulators not being perfect and not trusting them, I'm well aware of the shortcomings of simulators as I used them for decades professionally. The simulator I'm using has certain issues, but biasing points with the tube models is not one of them. It's been very accurate, in that its results are inside the variations I see in real tubes when I breadboard the same circuit. So in lieu of a real amp to measure, I simm'ed the whole LFO/modulator circuit.

It turns out that the simulator seems to think that the voltage excursions are not that big. It shows a peak to peak on each of the modulator tube grids of about 1.5V. And the nonlinearities on the plates were at cutoff, not saturation. So forward grid conduction wasn't happening. Allowing for normal tube variation, I'm sure that some tubes would go into grid conduction somewhere, somehow in this circuit, but it's not the central effect. The plates hit cutoff only with intensity over 80%. Under that, they didn't even cut off.

So the theoretical basis for variable loading with LFO signal doesn't seem to apply. The LFO signals at the grids isn't that big, it doesn't seem to push them into positive grid bias range.

Yes, it is possible that my simulator is wrong. But it's been right many, many times about things like this. I trust it more than just eyeballing a schematic or my sometimes-faulty calculations.
Quote
this translates in a (severely) reduced input resistance, well below 100k at the top input voltage extreme - vive-versa they go to higher than nominal resistance during the low part of the cycle ...
There is an abrupt change from near-infinite impedance to low impedance at a grid when the input voltage gets just a hair over the source voltage. And I'm using the word correctly - abrupt. It's not a lazy, slew-the-response kind of thing. Tubes will give razor-sharp distortion when driven into positive grid voltages from a high impedance, as the circuit here is doing. One can soften that transition with a low-impedance drive to a grid, but that's not what's happening here. The grid goes from repelling electrons to sucking them in.  The forward biased grid resistance for a 12AX7 tube is something between 5K and 10K depending on the degree of forward bias, by the way.

The grid impedance may go from near-infinity to nearer infinity as you make it more negative, but given the rest of the circuit component values, this produces no change. Normal tube grid impedance is negligible loading on a 1M grid resistor. Making it many times negligible, even if that were to happen, has no effect.

Since I wanted to be sure of my facts, I dug out the Radiotron Designer's Handbook, fourth edition. They say:
Quote
When a valve is used at audio frequencies, it is sometimes assumed that the grid input impedance is infinite. In most cases, however, this assumption leads to serious error, and careful attention is desirable to both its static and dynamic impedances.
EEK! I could be wrong. But then, I always consider that to be a possibility. Only the naive believe they're always right.

There follows a long string of equations describing how to calculate the input admittance (inverse of impedance). The meat of the discussion boils down to the equation showing that for frequencies up to 10MHz, the input admittance is
G = 1/rg +jw(Cgk +Cgp)

There follows the two comments:
- "If the grid is negatively biased to prevent the flow of positive grid current, the grid resistance becomes very high and 1/rg may be negligible in the expression for G. [G being the name for the overall grid admittance.]
- "the short circuit input admittance is affected by the transit time of electrons, the inductances of the electrodes (particularly the cathode) and the capacitance between grid and cathode. The capacitance term is practically constant." (my italics)

So out of this - there are a bunch of special cases to consider in the general case for critical applications. But the special cases don't seem to matter to this discussion. The 1/rg term is neglegible under these conditions and the capacitive term is constant. No varying bandwidth based on grid bias.

The rest of the discussion digs into the effects of interelectrode capacitance, gas leakage, grid emission of electrons, and transit time of electrons across the tube. All reasonably esoteric, but something the professional tube designer needs to take into account for industrial designs.

Quote from: JC
the main thing is the variable frequencies occuring "before" the mixing - what I was referring to in  the post mentioned above ...  it's a product of wide-range loading variations // the opposite of losslessness ...
But I thought the only losslessness you found was in the mixer. That's what you just said. Or wait - what was it you said? Can you explain how the losslessness was the mixer, but then wasn't, it was before the mixer?

And as we've seen, the variable loading doesn't happen, so the losslessness doesn't matter, eh?

Quote from: JC
really interesting how this variable-bandwidth variable-mixing stuff pops up in different ways ...
Sure is. Especially if you look really, really hard for it.

Quote from: JC
now, I'm not saying your circuit won't work or won't be appealing ... it just won't have that varying bandwidth component in it that's all - what I was saying ...
Where I said "I suspect that this gets 90% of the sound of the original, maybe even close enough not to need the other 10%." or "I think this will get the right feel, if not be a perfect repro. The JFETs will probably introduce some soft distortion. That's NOT going to be the same as tube distortion, but it should be nice." it wasn't enough?

By the way, Merriam-Webster says that "manifesto" means:
Quote
  a written statement declaring publicly the intentions, motives, or views of its issuer
I didn't know that circuits had manifestos. I didn't know they could write. But is is a fancy sounding word, all right.
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: Ghandi on March 19, 2007, 08:09:44 AM
anybody tried it jet?
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: Ben N on March 19, 2007, 01:57:30 PM
Easy, now fellas!

(Ducks, runs...)
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: Processaurus on April 21, 2007, 02:13:10 AM
RG, I was looking over the schematic for your fender style tremolo, and was wondering if it was an error that the two 1M resistors from the complementary hipass and lowpass filter's opamp's non inverting inputs meet, and then go through another 1M to Vref, rather than straight to Vref as a typical opamp design would?  As is the channels might bleed a bit into each other.

Very cool circuit, by the way, I'm thinking of stealing the filters to add onto the end of my stereo EA based trem mutant, since the panning is happening already.  I think I can do it in stereo too (one channel getting darker as the other gets brighter), with a six pack of opamps, 4 for the filters and 2 for mixing/recovering gain with each channel's respective filters.  I'm excited to hear how it will sound combined with the eccentricities of the phase shift LFO.
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: nordine on April 21, 2007, 10:49:43 PM
forgot to say it, but i breadboarded that emu-circuit RG made

have to say its a very beautiful sound.... really difficult to explain.. its bouncy, but solid through all the swirl

one thing that i had while testing it, is that the oscillator worked only at fast speed, and did cease to function if i went past certain (lower) speed.. had me wondering what could it be
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: R.G. on April 21, 2007, 11:05:31 PM
Quote
the oscillator worked only at fast speed, and did cease to function if i went past certain (lower) speed.. had me wondering what could it be
Thanks for the build report.

If the 10uf cap is leaky it might cause that. Can you try a different 10uF cap in the LFO?
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: rockgardenlove on April 21, 2007, 11:30:02 PM
Did you by any chance make a PCB?
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: nordine on April 21, 2007, 11:36:43 PM
Quote
the oscillator worked only at fast speed, and did cease to function if i went past certain (lower) speed.. had me wondering what could it be
Thanks for the build report.

If the 10uf cap is leaky it might cause that. Can you try a different 10uF cap in the LFO?


i already took the circuit apart, but will try if it was the cap, then i'll report

ps: no man, no pcb (i've never etched a circuit), sorry
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: QSQCaito on April 21, 2007, 11:53:00 PM
Wow.. I was thinking of making a tremmolo,  for what said, this would be a good solution unique sounding.

Is there anything that can be done by me to help?

A PCB design I could make if the circuit is correct, I'd have no problem.

Bye bye

DAC
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: joelap on April 22, 2007, 01:19:15 AM
I'd also be interested in keeping up to date on this circuit.  Actually, I've had the watchful eyes (aka my friends) keeping a lookout for me for any '62 or '63 blonde bandmasters that might pop up, which also has this same type of oddball vibrato/tremolo circuit.  If I can snag one, I'd gladly do a side by side comparison if a PCB layout is made of this circuit.  That's a big if, since they are more difficult to find, but should I get a hold of one, I'd gladly record clips of the real deal versus R.G.'s work.
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: skiraly017 on April 22, 2007, 01:26:11 AM
I'm just the idea man.  :icon_mrgreen:

I hope it works out. I'm interested in hearing clips.
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: markm on April 22, 2007, 11:55:55 PM
I too am very interested in this circuit.
What about this one in casey's gallery?
http://aronnelson.com/gallery/Tremolos-and-Vibratos/tube_vibrato (http://aronnelson.com/gallery/Tremolos-and-Vibratos/tube_vibrato)

Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: nordine on April 23, 2007, 12:40:25 AM
What about this one in casey's gallery?
http://aronnelson.com/gallery/Tremolos-and-Vibratos/tube_vibrato (http://aronnelson.com/gallery/Tremolos-and-Vibratos/tube_vibrato)

hey that's cute,
its like an ancient EA Tremolo  ;D
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: puretube on April 23, 2007, 02:06:57 AM
I too am very interested in this circuit.
What about this one in casey's gallery?
http://aronnelson.com/gallery/Tremolos-and-Vibratos/tube_vibrato (http://aronnelson.com/gallery/Tremolos-and-Vibratos/tube_vibrato)



it`s a Trem...
(similarly working to the one, TTG wrote about a while ago).
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: R.G. on April 23, 2007, 10:16:58 AM
Quote
Did you by any chance make a PCB?
If enough of you are interested, I can make one.

I actually did two approaches to the same circuit. The one up on the web page is based on the infrastructure of the Phase 90, perverting the phase JFETs to do tremolo. I did another version using the infrastructure of the EA tremolo - two EA trems run out of phase by an enhanced LFO and added filtering.

I'd expect the P90 circuit to work more simply, the EA version to work more tube-i-ly. Whether that makes a difference or not depends on your ears...  :icon_biggrin:
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: jakenold on April 23, 2007, 11:47:30 AM
Quote
Did you by any chance make a PCB?
If enough of you are interested, I can make one.

I actually did two approaches to the same circuit. The one up on the web page is based on the infrastructure of the Phase 90, perverting the phase JFETs to do tremolo. I did another version using the infrastructure of the EA tremolo - two EA trems run out of phase by an enhanced LFO and added filtering.

I'd expect the P90 circuit to work more simply, the EA version to work more tube-i-ly. Whether that makes a difference or not depends on your ears...  :icon_biggrin:

I take one of each, please! Great work, mr. Keen!  :D
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: markm on April 23, 2007, 12:38:12 PM
Would love to both hear and see the results RG,
I guess I was thinking this could be easily acheived by using the ROG emulation technology to produce a "simple" JFET circuit that would emulate the Brown Vibrato......from reading this entire thread, I may be VERY wrong huh?!
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: Ptron on April 23, 2007, 01:24:38 PM
Would there be any way to sneak an intensity control into this circuit? How about a dual-gange 1M pot wired as a rhoestat in place of the 1M bias resistors? I see the 3.3M and 1M resistors forming a 3:1 voltage divider from the lfo output to virtual ground (bias voltage) so a pot halfway down would be a 6:1 and so on... Does that make any sense?

Or perhaps a dry/wet mix pot.
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: Processaurus on April 23, 2007, 09:05:59 PM
Departing from the emulation of the traditional fender sound, but the voltage controlled bass/trble/panning chip in this threadhttp://www.diystompboxes.com/smfforum/index.php?topic=56630.0 (http://www.diystompboxes.com/smfforum/index.php?topic=56630.0) could make an interesting, low parts tremolo!
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: Ptron on April 24, 2007, 08:51:02 AM
Quote
Would there be any way to sneak an intensity control into this circuit? How about a dual-gange 1M pot wired as a rhoestat in place of the 1M bias resistors? I see the 3.3M and 1M resistors forming a 3:1 voltage divider from the lfo output to virtual ground (bias voltage) so a pot halfway down would be a 6:1 and so on... Does that make any sense?

O.k. Now I see a R.G. Phase90 schematic at GEOfx that does just this. http://www.geofex.com/FX_images/p90ramp.pdf
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: markm on April 29, 2007, 07:40:27 PM
I found this page with amp trem info......It would be very cool to get a brown-face trem circuit going!  :icon_cool:
How about the Swamp Thang.....anyone know what's going on inside of that one?
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: skiraly017 on April 29, 2007, 10:06:35 PM
I found this page with amp trem info......It would be very cool to get a brown-face trem circuit going!  :icon_cool:
How about the Swamp Thang.....anyone know what's going on inside of that one?

I had one awhile back and don't recall it capturing "that sound" but it's also been quite some time since I played one. I did play the brownface Pro again today. It's really hard not to buy the amp just for the vibrato.
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: markm on April 29, 2007, 10:49:13 PM
I found this page with amp trem info......It would be very cool to get a brown-face trem circuit going!  :icon_cool:
How about the Swamp Thang.....anyone know what's going on inside of that one?

I had one awhile back and don't recall it capturing "that sound" but it's also been quite some time since I played one. I did play the brownface Pro again today. It's really hard not to buy the amp just for the vibrato.

BUY IT!!  :D
I'd like to know what type of circuit the Swamp Thang is......LDR or FETs?
Anyone looked under the hood?
The clips sound amazing!  8)
If I could build one that sounded like that.....my love affair with the EA would be over.
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: Ghandi on May 01, 2007, 07:14:15 AM
the swamp thang is a modded diaz tremadillo.
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: markm on May 01, 2007, 08:19:58 AM
the swamp thang is a modded diaz tremadillo.

FET based I assume?
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: Ghandi on May 01, 2007, 12:35:33 PM
nope, it's based on the NTE123AP silicon npn transitor.
oh and it's called "Texas Tremodillo" instead of tremadillo, whatever! ;D
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: markm on May 01, 2007, 12:49:40 PM
nope, it's based on the NTE123AP silicon npn transitor.
oh and it's called "Texas Tremodillo" instead of tremadillo, whatever! ;D

Interesting.
I guess that means it's not optical based which was where I was headed with this!
I am in the minority but I dislike Opto-Trems for the most part......the TremLune just really does nothing for me.  :icon_neutral:
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: nordine on May 01, 2007, 05:55:57 PM
hi there,

well, i breadboarded again the circuit  ;D

RG, this time the oscillator worked perfectly but, sadly, my recording means (a small cam-recorder) are so lo-fi, that the captured sound of the samples doesn't do any justice to whats really sounding -so you could tell it really does the fender thing- ..besides, i did record it on bass, then it's somewhat muddy

anyways, what i can report on the circuit is:

-Vref 15uf cap must be upgraded to 100uf at least, to prevent oscillator thumping
-for a more pronounced effect (depth), i changed both 3.3m resistors for 1.2m resistors
-a LED freq indicator mod suits it really well  ;) (think p45)
-if one takes Q2 out (the fet on the treble path), one get a pleasing bassy-phasing.. pretty cool
-i get the best performance out of the circuit  biasing the fets at 0V (is that a bad thing?)

now,

markm, on the Swamp Thang issue... i did a little research, and got some info that might interest you:

you like the Swamp Thang, right? ..then we know this effect is a modded Diaz Tremodillo (according to Jack Orman, the most noticeable change, is the true bypass conversion)

take a look at this:
http://www.pedaldoctor.com/images/DiazBrd6.jpg

right, thats a tremodillo board

if one looks at it, having in mind its an npn based tremolo, and taking note on the number of electrolytics it has, the resistor values, and number of transistors (besides the number of pots and the 1/2 freq switch), it seems to be none other than this:

http://topopiccione.atspace.com/pjimages/SchallerTremolo.sch.jpg

a schaller tremolo replica ( a very sweet tremolo on its own)

so.. if you clone a Schaller Tremolo, and true bypass it, you might get a very close Swamp Thang  ;D

cheers
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: markm on May 01, 2007, 08:50:08 PM
if you clone a Schaller Tremolo, and true bypass it, you might get a very close Swamp Thang  ;D

No Kiddin'!
That's tremendous news nordine......a great Big Thank You for that tid bit of info and the pic is really a great shot too!
I have been looking over the Schaller schem which I printed out a couple of weeks ago but have yet to do anything with it.
Maybe it's time to do something about it.
I didn't think the Schaller was as smooth as the Diaz or Swamp Thang.
Who knew?!!  :icon_lol:
Again, THANK YOU my friend!
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: Ghandi on May 02, 2007, 05:06:15 PM
anybody did a pcb for the ersatz fender pro tremolo jet?

@nordine
how would you compare the "ersatz fender trem" to the "schaller trem"?
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: momiel on May 03, 2007, 03:30:05 PM
Its me or the Ersatz Tremolo doesn't have any depth pot?
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: nordine on May 03, 2007, 11:12:59 PM
No Kiddin'!
That's tremendous news nordine......a great Big Thank You for that tid bit of info and the pic is really a great shot too!
I have been looking over the Schaller schem which I printed out a couple of weeks ago but have yet to do anything with it.
Maybe it's time to do something about it.
I didn't think the Schaller was as smooth as the Diaz or Swamp Thang.
Who knew?!!  :icon_lol:
Again, THANK YOU my friend!

hey man, thats a lot of happiness!  ;D
well i'm pretty glad this info served you, i expect the circuit fulfills your expectatives as well.. good luck on that! ..let us informed on how it comes out

ghandi, the ersatz has obviously different sound from the schaller, because the first one uses phase shifting plus AM, and the other one only amplitude modulation.. ... now, the oscillator in the schaller is sweeter (asymmetrical sine wave i think) than the ersatz, which is a square wave at all lights

momiel, right it doesn't have a depth pot, but you can set the depth with the bias pot (not the best way to do it, but it works)
 
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: nordine on May 03, 2007, 11:49:46 PM
here:

http://www.youtube.com/watch?v=Ya9s_0f0eFE

a sound sample of the ersatz tremolo,

notice, again, that in bass and at that recording quality, the effect maybe is not much apreciable, but it gives an idea (also have in count that i subbed the 3.3M resistors, so it's sounding deeper/squarer than intended.. did that for experimenting purposes)
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: John Blund on May 04, 2007, 08:31:10 AM
This thing sounds great. after reading through the post I even tried to set up a kinda faux version on the computer with plugins based on R.G. instructions, and well I don't know how well these plugins simulate the real deal, but after listening to the youtube sample I'd say I wasn't to far off, this is a must build, just gonna get a bredboard and some opamps. what kind is recommended?

 ;D
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: Processaurus on May 05, 2007, 11:18:44 PM
Hi, I just made a version of this as an add on to an existing panning EA tremolo, and had a problem.  What I did was feed the two panning outputs to the two filters (one side to the series 470K and one to the series 220K).  The low pass filter side (with the series 470K and the .05uF to ground) doesn't make sound.  This makes sense now, looking at the schematic, as that RC filter combination gives a frequency rolloff of 6.8Hz.  As is it sounds like a normal, albeit bassless tremolo.

I took a peek at a better resolution Fender 6G5 schematic referenced before here (http://www.cnjradio.net/fenderamps/pro_6g5_schem.gif), the filter part RG emulated is right in the middle.  Ah ha, its a .005, not .05! :icon_wink:

Edit:  With the right cap it sounds really cool!  Even tasteful perhaps (a rarity for pedals I build :icon_biggrin:).  Like people said, it has something reminiscent of a univibe or phaser, but not as identifiable.  It also sounds very cool and subtle with the depth of the panning turned down some, to add a slight watery sounding shiftiness. 

Darn it anyway, for it to be perfect, it needs a knob to blend in the brownness with the normal trem, rather than a switch.  But the enclosure is drilled, and its pretty cozy inside, with this new daughter board...  the box is drilled, dude...
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: R.G. on May 06, 2007, 10:28:03 AM
Oops - sorry about copying that value wrong.

It's interesting that you reworked this on the EA trem body. Shortly after I did the P90 based one, I did an EA trem based version that I sent Mark a print of to try. Convergent evolution is powerful!

I'll put that one up on at GEO if there's enough interest. Mine had the filters before the modulators, like the Fender circuit, but it works either way.

Good work!
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: markm on May 06, 2007, 10:31:49 AM
Would love to take a look at the EA based version RG, please post it!
Thank you.
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: Ghandi on May 07, 2007, 03:37:17 AM
yeah, me too!
please post it!
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: d95err on May 07, 2007, 03:53:25 AM
Interesting... I've been toying with the idea of making an EA trem based version too. Only on paper so far thogh...
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: SeanCostello on May 08, 2007, 12:09:41 AM
I had never heard this type of vibrato before, just read about. Found a sound file of a tube-based circuit:

http://home.everestkc.net/jgehring/Revibe.mp3

This is the Ted Weber ReVibe - basically a cross between the old stand-alone reverb and the three-tube vibrato.

After hearing this, I realized that Neil Young sounds like he was playing through this type of vibrato on the live album with Crazy Horse from 1970 that came out late last year. Anyone know what amp he was using?

Anyway, it is a great sound, and it would be cool to have in a pedal. Maybe the Spin Semi FV-1 would be a good candidate in the emulation? (might be able to shoehorn a spring reverb simulaton as well...)

Sean Costello
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: gez on May 08, 2007, 03:15:27 AM
Wow, sweet sound!  Thanks for the clip Sean.
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: Ben N on May 08, 2007, 12:46:17 PM
Weber has the Revibe schem posted:

https://taweber.powweb.com/store/5h15_schem.jpg
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: Processaurus on May 09, 2007, 07:21:21 AM
Anyone know what amp he was using?

I read a (pretty cool actually) article on his crazy setup, he uses a few amps, mixed together, one of them is a Magnatone.

The modulation I'm getting seems similar to that revibe sample, I'll try to record something when its all boxed up.

I'm going to work in the knob to blend in the brownness (the normal trem on one end, fender pro style on the other), it just sounds too cool in the in between settings, to add some mysterious character to the basic tremolo sound.  I'm using a simple pan like is in the Geofex "Panning for Fun" article,  using a 10K pot, the only thing that's weird is I used extra resistance on the trem side of the pan circuit, because it is louder than the pro side, which makes sense, because of inevitable losses in the previous filter part.  R=15K on the pro side, R=30K on the trem side.  I tried the two polarities of the trem to blend in, and preferred the trem in sync with the treble, rather than the bass.  Though the other way wasn't terrible exactly, it just sounded less tremolo like.  Only problem with this panning arrangement is there is a little volume boost in the middle of the pan knob, because when the knob is centered, the two sides are at ~.707x their voltage, rather than 1/2, one could use a dual pot wired as alternating volume controls, but whatever, the EA has a volume control.

Bang Bang
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: reverberation66 on May 09, 2007, 11:55:06 AM
  yeah it's probably that magnatone amp neil is using, those are supposed to be the only amps that ever had true pitch shifting vibrato.  I think he uses one of those old magnatones and also a fender tweed deluxe together. 
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: Steben on May 09, 2007, 12:11:50 PM
A little closer translation brings me to this.
Only thing you need is a well-leveled modulation signal (simple oscillator like ROG phoser?) "A" with inverted "B".
And, yes, a lot of trimming...  ::)
Fet's could be matched ones like sold for Ph45 or Ph90.

(http://aronnelson.com/gallery/albums/Stebens-fuzzy-pot/vibratrem.gif)
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: markm on May 09, 2007, 12:20:47 PM
That looks interesting...... 8)
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: SeanCostello on May 09, 2007, 12:57:38 PM
A little closer translation brings me to this:

(http://aronnelson.com/gallery/albums/Stebens-fuzzy-pot/vibratrem.gif)

That schematic is real purty. What software did you use?

Sean Costello
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: Ben N on May 09, 2007, 01:03:58 PM
Looks nice. Just a suggestion: Why not include a simple one-tranny phase inverter, like in a transformerless octave, so that you have only a single LFO input?
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: R.G. on May 09, 2007, 01:04:48 PM
Actually, that comes pretty close to the EA Trem version, which is here:
http://geofex.com/FX_images/FakeFenderVib2.pdf (http://geofex.com/FX_images/FakeFenderVib2.pdf)

Differences are
- JFETs biased for bigger signals without distortion
- Modulation circuit shown; you'd need something like the LFO to make the A and B signals
- Modulation applied to source instead of gate, which seems to be less touchy

Edit: looking at it on line I notice that there's a drafting bug. The place where the signal out of Q1 crosses ground going to the 220K resistor should have a cross-over bump, and does not.

A note about my schemo drafting conventions:
- One wire which meets another at a right angle connects.
- There should never be a four-wire crossover; if there is, it does not connect. There should be a crossover hump just to make this blindingly clear, but sometimes I miss them.

Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: markm on May 09, 2007, 01:17:09 PM
That looks interesting...... 8)

Thank you RG.  ;)
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: Steben on May 09, 2007, 02:00:41 PM
Actually, that comes pretty close to the EA Trem version, which is here:
http://geofex.com/FX_images/FakeFenderVib2.pdf (http://geofex.com/FX_images/FakeFenderVib2.pdf)

Differences are
- JFETs biased for bigger signals without distortion
- Modulation circuit shown; you'd need something like the LFO to make the A and B signals

sorry RG, haven't seen your version yet.
the LFO: yeah of course, I didn't draw it yet since LFOs seem a bit generic to me. one could also use the typical opamp LFO, or the phozer's/EA trem....

Quote
- Modulation applied to source instead of gate, which seems to be less touchy

really? I believe you yet I wonder why. Do you mean the biasing stuff?

Quote
A note about my schemo drafting conventions:
- One wire which meets another at a right angle connects.
- There should never be a four-wire crossover; if there is, it does not connect. There should be a crossover hump just to make this blindingly clear, but sometimes I miss them.

Solution: a dot where it connects. no discussion.
Actually I draw the humps as well to stress it a bit.
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: Steben on May 09, 2007, 02:02:33 PM
A little closer translation brings me to this:
http://aronnelson.com/gallery/albums/Stebens-fuzzy-pot/vibratrem.gif

That schematic is real purty. What software did you use?

Sean Costello

Autocad, my friend.  ;)  Pure vector style.
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: R.G. on May 09, 2007, 02:38:44 PM
Quote
sorry RG, haven't seen your version yet.
Oh, no, no apologies are needed. Convergent evolution happens all the time.

Quote
Solution: a dot where it connects. no discussion.
I know. I just hate going back and putting a dot at each intersection. I inevitably forget a dot here or there. It seems to me that my error rate is lower with the only-three-wires version. I forget crossover humps less than I forget dots.  %-)
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: rocket on May 10, 2007, 04:30:22 AM
- Modulation applied to source instead of gate, which seems to be less touchy

I don't quite understand your circuit, for me it looks like like the fets at the sources (Q5,6) are acting as parallel restors to the source resistor, not varying the bias of the fets (Q2,3).


- Modulation circuit shown; you'd need something like the LFO to make the A and B signals

What is the frequency range that you can achieve with such a phase shift oscillator.
I would like 1:20 (1Hz to just audible, for ring mod sounds, even though that's probably not suiting for the brownface trem)  but only could achieve maybe 1:3 or 1:4  both in reality and with ltspice.
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: rocket on May 15, 2007, 09:30:39 AM
Any news on the brownfacetrem?
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: markm on May 16, 2007, 08:17:28 PM
Just a thought but,
What about some mods to the original Phozer circuit from the fellas at ROG?
It use the LFO from the EA, perhaps it could become an EA with some slight phasing and maybe.....just maybe "fake" the BrownFace Trem sound reasonably well?

(http://i17.photobucket.com/albums/b72/mmarkmm/phozer.png)
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: R.G. on May 16, 2007, 10:50:41 PM
Quote
I don't quite understand your circuit, for me it looks like like the fets at the sources (Q5,6) are acting as parallel restors to the source resistor, not varying the bias of the fets (Q2,3).
Yes. That's what it does, and that's what I meant by modulation at the sources.

Quote
What is the frequency range that you can achieve with such a phase shift oscillator.
I would like 1:20 (1Hz to just audible, for ring mod sounds, even though that's probably not suiting for the brownface trem)  but only could achieve maybe 1:3 or 1:4  both in reality and with ltspice.
By changing two of the resistors in parallel as I did, you can get more than 1:4, but probably not more than 1:10.

Yes, we would all like to get wide speed ranges, but it's very hard to do with such simple circuits. I have designed much wider range LFOs, but they are a completely different design, and do not produce sine waves like a phase shift oscillator does.

Quote
Any news on the brownfacetrem?
Yes. I breadboarded it and I like it. A couple of other people have reported they like it here. I've posted two different designs which work. I'd say that's pretty good news.
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: sfx1999 on May 17, 2007, 01:07:29 AM
Brownfacetrem? I thought this was about the brownface VIBRATO (I mean the TRUE vibrato, some brown Fenders had it).

Leo Fender has confused us all.

If you are actually doing a tremolo, is there any change of getting a Magnatone vibrato pedal?
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: markm on May 17, 2007, 07:18:57 AM
Brownfacetrem? I thought this was about the brownface VIBRATO (I mean the TRUE vibrato, some brown Fenders had it).

Yeah, that's the one.
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: R.G. on May 17, 2007, 11:09:28 AM
Quote
Brownfacetrem? I thought this was about the brownface VIBRATO (I mean the TRUE vibrato, some brown Fenders had it).
Leo Fender has confused us all.
Yes, he has. It's the amplifier "vibrato" that does tremolo, not the guitar "tremolo" that does true vibrato.
Quote
If you are actually doing a tremolo, is there any change of getting a Magnatone vibrato pedal?
There's a really good chance - the Magnatone vibrato is a true vibrato, done by making a phase shifter without adding the dry signal in. In that sense, every phaser with the dry signal disconnected is a vibrato in the style of a Magnatone vibrato.

A long time ago, maybe ten years, I built up a vacuum tube version of the Univibe along the Magnatone lines. Worked fine. The exact operation of the Magnatone amps can no longer be built, as the critical part, a softly varying voltage variable resistor (varistor) is no longer made and old stocks have been depleted. The newer varistors are specialized devices which have a sharp, snap action variable resistance for limiting transient voltages, and are not suitable for the smoothly varying resistance that a Magnatone styled varistor needs. But you can do the same thing with LDRs (which I did), JFETs, PWM resistors, and so on.
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: markm on May 17, 2007, 12:57:05 PM
I found this quite sometime ago on the net.....
I don't even know where but, maybe it could be useful?  ???
The description states that it produces "phasing".
Any thoughts RG?

(http://i17.photobucket.com/albums/b72/mmarkmm/vibrato.jpg)

Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: markm on May 17, 2007, 12:59:56 PM
Oh yeah.....
Or this?

(http://i17.photobucket.com/albums/b72/mmarkmm/vibrafet.gif)
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: R.G. on May 17, 2007, 01:12:55 PM
Quote
I found this quite sometime ago on the net.....
I don't even know where but, maybe it could be useful? 
The description states that it produces "phasing".
It doesn't. It's amplitude modulation - tremolo. It's interesting though. That's only the second time I've seen a current-mode phase shift oscillator, the first being the univibe.

Quote
Oh yeah..... Or this?
Input fed to a highpass on one side, lowpass on the other, the two blended back together. Presumably A and B are places to insert a current (and hence gain) modulating LFO, possibly out of phase between A and B.

It looks like my first concept of the Fender Concert/brownface/Pro tremolo, a single pole filter on each side. It won't have the phase funnies that the Fender circuit does, but it might be useful. It will be harder to balance out the LFO; that's probably what the 25K pot is for.
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: Ben N on May 17, 2007, 01:43:48 PM
Are the 10k pots just bias adjustment?
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: stm on May 17, 2007, 02:20:25 PM
Quote
I found this quite sometime ago on the net.....
I don't even know where but, maybe it could be useful? 
The description states that it produces "phasing".
It doesn't. It's amplitude modulation - tremolo. It's interesting though. That's only the second time I've seen a current-mode phase shift oscillator, the first being the univibe.
I see there is at least a resistor missing on that schem, probably in series with the power supply or somewhere between the supply and Q1's collector.  As drawn it won't oscillate since there is no feedback path in the oscillator.  Also, the modulation control signal is taken directly from the supply voltage.
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: SeanCostello on June 30, 2008, 01:41:46 AM
It looks like my first concept of the Fender Concert/brownface/Pro tremolo, a single pole filter on each side. It won't have the phase funnies that the Fender circuit does, but it might be useful. It will be harder to balance out the LFO; that's probably what the 25K pot is for.

What sort of phase funnies are in the Fender circuit? You had mentioned that it was closest to a twin-T filter. Are the filters 2nd order that it crossfades in between? Or is it one of those weird circuits like the Fender tone controls, that has to be explained by a fairly complicated equation in the s-plane?

I am assuming that the circuit can be simulated by a weighted balance between two time-invariant circuits, and that the input mix does not affect the cutoff frequencies of the lowpass and highpass filters. The crossfading will affect the notch frequency and phase shift of the output, but this is standard. It reminds me of the knob on the old Oberheim SEM-1 module, that crossfaded between the lowpass and highpass outputs of a state-variable filter. Or a Big Muff tone control - is this a close relative of this circuit?

Thanks,

Sean Costello (I decided to revisit the spring reverb/brown Fender vibrato recreation for the FV-1 that I mentioned earlier)
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: SeanCostello on July 02, 2008, 02:02:00 AM
On an older thread on a different forum, there is a link to results of a simulation of the harmonic vibrato in the Showman, but the link is no longer valid:

http://www.fenderforum.com/forum.html?topic_number=327608 - about 2/3rds of the way down the page.

Does anyone here have an analysis of the crossover network / frequency response that they would be willing to share?

Thanks,

Sean Costello
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: Ben N on July 02, 2008, 02:49:36 AM
There was an email link over there, so I emailed the guy to ask if he would share.
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: Steben on July 03, 2008, 07:43:43 AM
It won't have the phase funnies that the Fender circuit does

Euhhhh...... why?  :-\
Title: Re: Fender brownface vibrato in a stomp...does it exist? What about with JFETS?
Post by: R.G. on July 03, 2008, 03:56:03 PM
The Fender vibrato is not a simple first-order crossover filter, so it has excess phase shift in both sections. That's another way of saying that the sections are not designed to be complementary to eliminate the phase changes around the crossover frequency. Phase linearity at the crossover frequency is a common issue in designing hifi speaker crossovers.