PAL800 v3: the switches

[martre]

What do you think about replacing the 10n cap (c13) with 22n? I also see r13 (10K) in the pedalpal is 4k7 (r12), do you think it can affect the sound)

 

[temol]

Replacing 10n with 22n would cut some mid/high freq.

 

[martre]

Ok, tried all, bet result is to bypass R19 (equivalent to use trimpot to maximum), my question is what about to add the 470n in series to the bridged r19 (like the m800)? Remember I still have an electrolytics 1uF just after (really strange).

 

[temol]

Not sure if I understand you correctly... 470n in series with R19 or 470n in series with 1u (because R19 is bridged)?

 

[martre]

470 in series with 1 uF...In this way the only differences between pedalpcb circuit and pcbmania will be the 1uF

 

[temol]

Green plot - no 470n, blue plot - with 470n.

 

[martre]

Green plot - no 470n, blue plot - with 470n.

View attachment 11339

That's interesting...What about removing the 1uF electrolytics?

 

[temol]

There's almost no difference in frequency response between 470n+1u and 470n only.

 

[martre]

There's almost no difference in frequency response between 470n+1u and 470n only.

What's general rule about this cap? Higher values will raise bass or is the opposite? I would like to get more scooped mids...

 

[temol]

Then I would suggest adjusting values of the tone stack components - R10 and C6. You can try 47k and 330p.
Install Tone Stack Calculator and play with the values.

 

[martre]

Tried to work on the tonestack, best result by using 100k pot for treble. No differences with the 470n in series at r19, HUGE DIFFERENCES bypassing the 1uF cap just at the output (not present in the pedalpcb circuit), it opens alot the sound by rising the mid-high freq. Bypassing it make all sound darker

 

[equinox]

I just heard about this pedal and reviewed multiple videos tonight.
I found the pedal sound VERY good.
The one thing in the V3 I did notice was that the notes still tended to die out. I would prefer them to ring indefintely in the Boost-mode. The information from the site says 6dB of boost being applied to the original channel. I would say that needs to be kicked up to 20dB imo and for my liking.
I look forward to understand the design of the V3 100% and then getting it tweaked for my liking. I will stay tuned to this thread for further developments.

 

[Quentin]

Hello, I have a question about the PAL800, the JCM800 Emulator, the PedalPCB version is the M800:

http://www.pedalpcb.com/docs/M800.pdf

The schematic is a jfet version of a JCM800 preamp: six transistors with five trimpots. That was the old version of the PAL800.

There's a V3 version, now, that includes the same controls, but with a 3-way toggle switch that change the bass and mid response, especially at low gain setting. At max gain setting (from the official web site information) it doesn't make anything.
Another toggle switch for the #34 mod and a footswitch to alternate the stock high input with the low input.

Here's the official page:

PedalPalFx - PAL800-V3 GOLD Overdrive

In this new version we keep the original design of the GOLD Overdrive but adding more features making it even more versatile.

www.pedalpalfx.com

And this is a gutshot I found:

You can see there's only three... transistors? Those thing are called Q1, Q2 and Q3 and look strange. But just three? And the trimmer? There's just one for the inner master tone control.

The #34 Mod I know is some parts changed or added in the JCM800 preamp. How in this circuit a SPDT switch can make just one change and reach more or less the same mod?
And does the I/II footsiwtch follow the original JCM800 schematic?

What do you think about all this?

Do you think we will see a modified version of the m800 that includes these two switches?

 

[Elijah-Baley]

Well... I wish!

 

[Gebrey]

Do you think we will see a modified version of the m800 that includes these two switches?

Hi, I've isolated the switches and boost part of the circuit.

The boost probably involve the input resistor like switching between Hi - Lo inputs.
Here I identify: 68K 68K 15K 1M ..... 220R

Since this pedal is not new to multiple resistor in series (see the led CLRs or the bias pairs) maybe the thing is:
- BOOST OFF: 68K resistor (original schematic)
- BOOST ON: add a series pair 68K+15K in parallel to original 68K resistor > 37K results

(Usually marshall amps has 33K Hi input and 68K Lo input)

Im not sure if this change modify the tone. If so maybe the near 2 red caps are for tone compensation.

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Voicing: MAYBE in the tonestack, connect to [node 33K, 22n, 22n] a capacitor and a resistor in series to create a LPF.
IF NOT located there, probably elsewhere.
But voicing is usually achieved with a cap variation in a LPF (like 1.5kHz and 7kHz).


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Mod #34: hypotesis
- Add some filter caps to source resistors (off: all ground linked MODGND but disconnected / on: MODGND to GND)
- parallel capacitor of 1n5/1n8 to 470pF of the 1st filter to achieve 2n2 OR simply swap between 2n2 and 470p

--------

Ive seen 2 caps at top left: red one i think is a 0.1 input decoupling cap. The ceramic old style cap is instead a high freq filter full audio spectrum (like 22kH LPF).

Further investigation are apreciated.

Cheers

 

[Gebrey]

Well... I wish!

I know that these photos are a limitation but look at what I ve tracked down. Probably is fine to suppose the mods and then try.

 

[Gebrey]

Here the V4 gutshot. As you can see the VOICING switch has gone (in fact is a bit useless since you can tweak guitar tone pot, pickup selection, TMB pots, presence and even the internal trimmer)

Also, the mod34 emphatise the highs.

The MOD switch is a ON/OFF/ON 3PDT
Mod34 (well known) and Mod07 (no info found)

Also the BOOST has gone.