Earthquaker Devices Palisades  [traced]

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Earthquaker Devices Palisades

Postby kmmoe » 26 Oct 2017, 14:35

Hi

Here is the schematic for a traced Palisades. There are three things I am uncertain about. The first thing is the orientation of the MPSA18 in the input buffer. I have checked it over and over, and the orientation seems to be correct the way it is drawn in the schematic, with 9V going to the emitter. The second thing is the flat top LED. It is water clear with a pinkish hue, but I am uncertain what color it is. The third is if the "no clipping diode" option is the way I have drawn it, or if it is linked.

Palisades schematic.png
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Re: Earthquaker Devices Palisades

Postby Nocentelli » 26 Oct 2017, 20:07

It seems almost certain that the input buffer should have the collector connected to +9v and the emitter be the output and connected via the 10k to ground - Look at the output buffer.

"No clipping" is likely to be just how you have drawn it: If you connect a short across the clippers, you'll turn the opamp into a buffer.

Not sure what to advise about identifying the LED - I'd be tempted to connect a battery and 10k resistor very briefly across the terminals to get it to light up, not sure whether this risks damaging the opamp, though.
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Re: Earthquaker Devices Palisades

Postby kmmoe » 26 Oct 2017, 21:16

Thanks for your kind sugestions Nocentelli.

I measured continuity again, and I am 99% certain that I have the MPSA18 in the input buffer drawn correctly. Based on other circuits, as well as the orientation of the MPSA18 in the output buffer, it seems logical that it should be oriented the other way. But as far as I can tell, it is not. I have traced the whole circuit, and looked it over many times.

The op-amp is socketed, so i pulled it and measured the diodes with a multimeter. The green diodes lit up, but not the water clear flat top. It did measure 1.247 V while in the circuit, if this could help anybody figure out what kind of diode this is.
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Re: Earthquaker Devices Palisades

Postby Nocentelli » 26 Oct 2017, 22:50

UV or IR, perhaps?
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Re: Earthquaker Devices Palisades

Postby Manfred » 26 Oct 2017, 23:17

The boost switch on the bottom right on the above schematic does not work in this arrangement.
The switches shall arranged in this a way:
BoostSwitchCorrection.jpg


Which function on the panel is assigned to the switch across the input buffer?
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Re: Earthquaker Devices Palisades

Postby Intripped » 27 Oct 2017, 00:53

Manfred wrote:Which function on the panel is assigned to the switch across the input buffer?


input buffer ON/OFF

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Re: Earthquaker Devices Palisades

Postby Manfred » 27 Oct 2017, 07:42

A BJT can also be operated in inverse order, but the diffrence is that the gain is significantly lower than in normal order.
I ran a simualtion of the buffer circuit and found the stage gains as follows.

Normal mode: 0.987
Inverse mode: 0.522

I suppose that was an intentional circuit design decision on the developer.

In that case the "Input Boost" is switched off if the circuit is active.

InputBufferModes.jpg
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Re: Earthquaker Devices Palisades

Postby kmmoe » 28 Oct 2017, 11:09

Based on the comments I now think that the unknown LED in the clipping section could be a IR diode. It seems unlikely that it is a UV diode. If anyone has a good way of confirming this, suggestions would be very welcome. I can not see the writing in the BAT41's too good either, so these could be BAT43's as well. I really do not want to desolder them to have a closer look. To me, this is now the only uncertaintys in the schematic.

And if I understand correctly, the oriantation of the MPSA18 in the input buffer seems likely the way I have drawn it.

I have updated my drawing with the comments on the switch orientation (found another switch the wrong way as well) and will post it later. This is my first trace and first schematic drawing, so there were bound to be some mistakes, however I am quite confident that this is now close to 100%
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Re: Earthquaker Devices Palisades

Postby Intripped » 28 Oct 2017, 14:16

Manfred wrote:A BJT can also be operated in inverse order, but the diffrence is that the gain is significantly lower than in normal order.
I ran a simualtion of the buffer circuit and found the stage gains as follows.

Normal mode: 0.987
Inverse mode: 0.522

I suppose that was an intentional circuit design decision on the developer.

In that case the "Input Boost" is switched off if the circuit is active.

InputBufferModes.jpg


I'm not big at interpreting these data, but if I'm not wrong, with the mpsa18 operating in inverse order the input signal-level is equal to the output, so you don't have differences in volume when you flip the buffer switch.

What I don't understand is why the signal gets boosted with the mpsa18 oriented in the conventional way; aren't buffers supposed to have unity gain at max?
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Re: Earthquaker Devices Palisades

Postby Manfred » 28 Oct 2017, 14:58

What I don't understand is why the signal gets boosted with the mpsa18 oriented in the conventional way; aren't buffers supposed to have unity gain at max?


The MPSA18 have no gain boost in the conventional way, because the collector circuit has nearly unity gain.
The less gain in the inverse mode is due to the dotation of the base-collector junction.

The "boost" works in reverse function in that case, the circuit would better named as input attenuator,
but "boost" is a common term in the pedal world and clear for the user.
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Re: Earthquaker Devices Palisades  [traced]

Postby kmmoe » 28 Oct 2017, 20:24

I have updated the schematic. Found another slight mistake. The asym clipping is the 1n416 diodes, while the sym clipping is the 1n4148 diodes. Sorry about that.

Some additional information. all resistors are metal film exept the 10M, which is a carbon film for some reason. Could be supply. The pedal I have traced have 3mm green LED's, however I have seen some pictures with 5mm green LED's as well. Even though the earlier Palisades are said to be able to be run at up to 18V, EQD now states that it should only be run at 9V.
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Re: Earthquaker Devices Palisades

Postby albru80 » 28 Oct 2017, 20:51

Thanks mate!
Easy fix!
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Re: Earthquaker Devices Palisades

Postby Intripped » 29 Oct 2017, 14:48

@Manfred:
Please excuse me, but something is still not clear to me.
There are 2 switches on the pedal: A toggle switch for buffer bypass, AND a footswitch for activating the boost circuit (a dedicated little circuit, that has nothing to do with the input buffer)

I say this because I have the feeling that you're talking about the buffer switch as it was the boost switch... Please excuse me if I misunderstood your posts.

Back to the simulation that you've made:
As I said before I'm not big at reading those data.
What I see is that you feed the 2 circuits with a 1kHz, 1Vpk (peak to peak?) signal.
In the first circuit (mpsa18 conventionally oriented) you get at the output 1.97V(p-p), and in the second circuit 962mV(p-p).
What does this "(p-p)" stand for? Is it peak to peak? If it is, doesn't that mean that in the first circuit you get an increase in signal-level, from 1Vpk to 1,97(p-p)? While in the second circuit (mpsa18 in the unusual configuration) you get almost the same signal-level as at the input?

But you said that the gain factor is 0.987 in normal mode, and 0.522 in inverse mode...
So, how do you calculate the gain factor?

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Re: Earthquaker Devices Palisades

Postby Manfred » 29 Oct 2017, 15:46

Please excuse me, but something is still not clear to me.
There are 2 switches on the pedal: A toggle switch for buffer bypass, AND a footswitch for activating the boost circuit (a dedicated little circuit, that has nothing to do with the input buffer)

Sorry, my fault.
I have mixed up buffer and boost.
The "buffer ON" switch turns the input buffer on or off.
The foot switch "boost" turns the boost circuit on or off.

Vp-p means the peak-to-peak voltage.
Ignor this values, because they changes during the simulation, there are random values at the time of screenshot.

But you said that the gain factor is 0.987 in normal mode, and 0.522 in inverse mode...
So, how do you calculate the gain factor?


The input level is 0.707 Volts_rms

The Output level at normal mode is 0,698 Volts_rms.
Hence, the normal mode gain is 0.698 Volts_rms / 0.707 Volts_rms = 0,987.

The Output level at normal mode is 0,369 Volts_rms.
Hence, the normal mode gain is 0.369 Volts_rms / 0.707 Volts_rms = 0,522.

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Re: Earthquaker Devices Palisades

Postby Intripped » 29 Oct 2017, 16:17

Thanks a lot, now all is clear.

So, in the original pedal, if you switch the buffer on, the signal should get a significant drop in volume.
...why did they do it this way?

I have another question: does the signal-phase stay the same when the mpsa18 is used inversely?
If so, then this could be the answer.

PS: I've just read the description of this buffer-switch on the EQD site.
They say:
Buffer: Turns the input buffer on or off. ON is a tighter and brighter tone while OFF is a warmer tone with more sag.
And also:
[...] a buffer on/off switch to tighten up the tone and make it sparkle when set to “ON” or warm it up and make it sag when set to “OFF”.
...something else is going on with the inverted mpsa18?
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Re: Earthquaker Devices Palisades

Postby Nocentelli » 29 Oct 2017, 17:17

"warm it up and make it sag" suggests less treble (more loading from lack of buffer) and hotter signal (from the increased output from no buffer). As to why, it suggests squeezing two benefits out of the buffer/no buffer option.
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Re: Earthquaker Devices Palisades

Postby Manfred » 29 Oct 2017, 18:47

I have another question: does the signal-phase stay the same when the mpsa18 is used inversely?
If so, then this could be the answer.


The signal-phase stay the same.

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Re: Earthquaker Devices Palisades

Postby modman » 01 Nov 2017, 14:23

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Re: Earthquaker Devices Palisades

Postby kmmoe » 07 Nov 2017, 11:54

Albru80's layout have now been confirmed over at tagboardeffects. There is still the mystery diode, but as both the pictures shown in this post by modman, and the comments over at tagboardeffects show, diffused red 3mm have been used by EQD, and sounds good.
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Re: Earthquaker Devices Palisades

Postby storyboardist » 07 Nov 2017, 15:35

Here's a perf/pcb layout for this. Pots are board mounted, switches are off board. Best fit is going to be in a 1790NS like the original.

Image

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