Marlboro - Quadra Sound Blender QBS  [schematic]

Discussion regarding early stompbox technology: 1960-1975 Please keep discussion focused and contribute what info you have...
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Zokk
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Post by Zokk »

Hey folks

I'm not sure of the manufacturing date of my unit... I hope I post in the good section.

I've done a full recap on my old QSB as it was really too much noisy...
I've not found pictures anywhere, so I've taken some photos of its guts, just for the curious because it is not a real good reverb unit (the only one spring measures around 20 cm and is really "boingy" :mrgreen: ).
After recap' it's dead silent, and I even think I've more headroom, but it's still a bad reverb for guitar: it sounds better when used for dub drum kits :lol:
So here are the pictures before changing the electros (you can see the new caps laying under the unit on one picture: Lelon & Panasonic 105°C hi grade caps, but I'm not sure this effect really worth such a luxury):
Attachments
IMGA0089.JPG
IMGA0091.JPG
IMGA0092.JPG
IMGA0093.JPG
IMGA0094.JPG

Bernardduur
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Post by Bernardduur »

Nice!

I just scored a Marlboro G50-R amp which is a 2x10 SS amp with a QSB already inside it!

The amp sounds just wonderfull. A bit of hissssss so I'll also do a cap job.The amp sounds remarkable tube like with enough volume. The bright input works perfect for my HB guitars, the normal for my SC guitars and the mellow is just dark, dark and bassy. With bass it is just a bit too much!

The reverb is also a bit boingy and feeds back a bit on the highest settings

The QSB effect is a weird one;
- The tremolo is a hard, choppy tremolo with maximum depth
- The vibrato is a less choppy tremolo (same as above with lower depth setting)
- The echo setting is tremolo on the reverb so you'll get a reverb wash that is cut on volume SIMULATING an echo sound

Sounds nice! Schematic will follow when I get the time to trace it!
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Post by soulsonic »

Bernardduur wrote: - The echo setting is tremolo on the reverb so you'll get a reverb wash that is cut on volume SIMULATING an echo sound
:!:
This is a really cool idea for a standalone pedal! I'm now imagining doing something like this with a Belton brick.... :idea:
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Post by Intripped »

something like this?
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tremverb.png
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Post by Zokk »

Nope, the tremolo is located after the reverb tank, inorder to chop the reverb tail :wink:

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Post by Bernardduur »

Yep! The decaying reverb wash is chopped by the tremolo. You can spot that on the higher tremolo settings: the wash is still going strong (although the reverb isn't that great........ I think I need to upgrade that one!!
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Post by Bernardduur »

DSCF5328.jpg
DSCF5329.jpg
DSCF5330.jpg
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Post by soulsonic »

I'm definitely going to start on a design for a pedal version of the weird echo-reverb from this.
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Post by Bernardduur »

Schematic time:
Preamp.JPG
Reverb.JPG
Tremolo.JPG
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Post by Bernardduur »

PSU.JPG
Poweramp.JPG
Much simpeler then I would guess.........

On further search one of the speakers is dead........ see if I can revive that one :)
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Post by allesz »

Hallo, thank you for the schematic.
It's so simple I would like to try it myself, always wanted to try a spring reverb pedal, and the tremolo, quasi echo, idea would be a nice one to try.
Mr Bernaddurr, can you tell me the voltages V1, V2 and V3 coming from the power supply?

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Post by Bernardduur »

allesz wrote:Hallo, thank you for the schematic.
It's so simple I would like to try it myself, always wanted to try a spring reverb pedal, and the tremolo, quasi echo, idea would be a nice one to try.
Mr Bernaddurr, can you tell me the voltages V1, V2 and V3 coming from the power supply?
Not yet, I'll first recap the unit and then measure some voltages.
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Post by tube-exorcist »

The emitter resistors of the output transistors probably will be 0,51 Ohm instead of 0,15 Ohm.

The output driver dransformer is drawn wrong. The primary winding doesn´t have a tap (and no connection to the lower trimmer. The secondary winding doesn´t have a tap there are two seperate windings. The upper is shown correct but no connection to the base of the lower output transistor. The second winding is between the lower trimmer and the lower base, identical to the upper half.
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Post by Bernardduur »

I'll look into it!
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Post by Bernardduur »

I think you are right!

I was guessing the transformer wiring as there are many (also unused) pads on the print. They are all filled with solder. I desoldered the unit.
Poweramp.JPG
Better?
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Post by Bernardduur »

Now the PSU with voltages!
PSU.JPG
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Post by tube-exorcist »

Bernardduur wrote:I think you are right!

I was guessing the transformer wiring as there are many (also unused) pads on the print. They are all filled with solder. I desoldered the unit.
Poweramp.JPG
Better?
Much better....
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Post by Intripped »

Am I wrong if I say that you had better take those two 20n capacitors off?
I mean C1 and C2, aren't they two "death caps"?

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Post by Bernardduur »

Yep, and already done!

They were also part of the noise in my unit
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Post by Mattyr »

I've used a qsbII for many years and I love it. Recently my reverb broke and upon inspection I found that the small wires that hold the spring had broken. The wires have what appears to be a small magnet that sits between the two bars connected to the transducer. How can I repair this and where would I get parts, including a new spring as I would like to alter the effect slightly. I have no education in electronics but I'm not stupid so I think with some direction I should be able to do this. Any input would be greatly appreciated.

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