Dr. Z - Z-Wreck  [schematic]

Tube or solid-state, this section goes to eleven!
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stringgz301
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Post by stringgz301 »

Hey all. Anyone have a source for a Z-Wreck schematic? I know it's a variation on a Rocket, but was hoping to get specifics.

Thanks in advance.

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wyatt
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Post by wyatt »

Pretty much a Rocket with vintage Vox filter cap values and dropping resistor wiring.

Ultimately... '60's Vox power supply+Vox Top Boost preamp+AC30 power amp=Z Wreck circuit...that's it.
Z wreck Differences to the Rocket are,

1. V1 signal cap to volume pot is 470pf ceramic disc, Treble cap in tone stack is 47pf.
2. The 220k/220k voltage divider exiting the tone stack into the PI.
3. Long tail section - 976k R's instead of 1M, 47.5K R instead of 47K.
4. 250uf bias cap for power tubes.

5. B+ dropping string is paralleled from the output tube screen node to all stages and not in series as is the Rocket.
PI = 27k
CF = 22k
V1 = 27k

Input jack resistor to earth is also a 976k not 1M.
All signal resistors are 1/2w metal film.

The only other obvious difference is the way the CF stage is split between V2a and V2b, Not V1a and V2a.

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modman
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Post by modman »

ZWRECK REV 1.pdf
Dr Z. Z-Wreck schematic
(220.36 KiB) Downloaded 549 times
ZWRECK REV 1-3.jpg
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POTL
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Post by POTL »

Almost 100% VOX AC30.
When I look at the schematics of boutique replica classic amps, I wonder, "Hey guys why can't you add master volume?"
R13 + R14 is almost equal to a 500kΩ potentiometer.
Why not give the opportunity for more flexible sound settings?

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soulsonic
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Post by soulsonic »

POTL wrote: 18 Jul 2020, 20:48 Almost 100% VOX AC30.
When I look at the schematics of boutique replica classic amps, I wonder, "Hey guys why can't you add master volume?"
R13 + R14 is almost equal to a 500kΩ potentiometer.
Why not give the opportunity for more flexible sound settings?
Replace C12 with 1uF, and you've got an effective master volume right there.
"Analog electronics in music is dead. Analog effects pedal design is a dead art." - Fran

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soulsonic
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Post by soulsonic »

soulsonic wrote: 19 Jul 2020, 00:19
POTL wrote: 18 Jul 2020, 20:48 Almost 100% VOX AC30.
When I look at the schematics of boutique replica classic amps, I wonder, "Hey guys why can't you add master volume?"
R13 + R14 is almost equal to a 500kΩ potentiometer.
Why not give the opportunity for more flexible sound settings?
Replace C12 with 1uF, and you've got an effective master volume right there.
I believe the pull switch on the "Cut/Master" control in the Mesa Transatlantic TA-30 is exactly this. Changes the typical Vox cut control into a master volume by making the cap bigger.
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modman
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Post by modman »

POTL wrote: 18 Jul 2020, 20:48 Almost 100% VOX AC30.
Some time ago some panties got waddled on facebook over the 500pF coupling cap. I remarked that the 2.2nF after the first stage is the place to look for fattening up the tone on that amp. Buddy stated "I seen coupling caps as low as 500pF in Vox etc.."

So here it is, but my question is: why is the 220k there as plate resistor?
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Post by POTL »

220 kΩ gives more gain.
Much more interesting is another point, in the original VOX circuit, the 2 halves of the triode in the first stage have a common cathode resistor and capacitor, in this circuit, the second half of the triode is turned off (how wasteful), which means Dr. Z should have changed the component values ​​1.5 kΩ = 3 kΩ and the capacitor 22 mF = 10 mF
Since in such a connection, the components are considered as connected in series.

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Post by soulsonic »

Higher value plate resistor can make it slightly darker sounding as well.
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Post by klingo »

For those interested in the Z-Wreck Jr, i saw the doctor wired V2 like a bootstrapped cathode follower (2 split resistors & a cap on the socket).
Usefull informations in the Merlinb books. However V2a 1k5 cathode resistor is still bypassed with a 22uf...no grid stopper; no arc protection on the CF...
From the pics it's hard to see if he used 47K's, 56K's or a mix of that, the cap looks like a 0.1uf Xicon.

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