Kramer DMZ4001A preamp help - decode schematic?

[bloke_zero]

I recently acquired a Kramer DMZ4001A from @roger (thanks Roger!) and I'm wondering about what the preamp does.

 

I can see one of the switches is series/parallel and the knobs are volume and what looks like passive tone.

 

So all I really need to know is what the 3 position switch next to the volume control does (switching it it seems like it gives a lot of boost!). There is a schematic here but I can't read them:

http://www.vintagekramer.com/Electric/wiring-dmz4000preamp.jpeg

 

Anyone know? My googling leads me to various sold listings with slightly dubious technical descriptions - the linked schematic seems the most spot on.

[BigRedX]

According to the schematic it should give three pre-set tone shapes. 

 

However Kramer from that period were notorious for changing specifications as parts availability demanded it. Also that circuit board looks very home-made, so without checking the components against the schematic you simply can't know. 

[sandy_r]

2 hours ago, bloke_zero said:

 

 - the linked schematic seems the most spot on.

 

Wow - what were the others like?!?

 

What to say about a schematic which:

• takes pain to state the circuit is 'positive' ground - but then shows both transistors as types which would require 'negative' ground (NPN type);
• doesn't show any bias voltage arrangement for the 1st transistor (unless - it's really a PNP type... in which case  they have the collector & emitter connections drawn incorrectly)

...but apart from that - we can trust the remainder of this circuit absolutely, yes?

 

Good ol' Uncle Ernie!

 

PS.  if that foil is uninsulated, it might be an idea to check it can't make contact with any component leads on the PCB

 (...and if you ever get any hum or other elec type noise, more shielding wouldn't go amiss 😉)

 

Edited March 19 by sandy_r

[bloke_zero]

4 hours ago, BigRedX said:

According to the schematic it should give three pre-set tone shapes. 

 

However Kramer from that period were notorious for changing specifications as parts availability demanded it. Also that circuit board looks very home-made, so without checking the components against the schematic you simply can't know. 

That certainly jibes with what I hear, so I think that makes sense.

[bloke_zero]

3 hours ago, sandy_r said:

 

Wow - what were the others like?!?

 

What to say about a schematic which:

• takes pain to state the circuit is 'positive' ground - but then shows both transistors as types which would require 'negative' ground (NPN type);
• doesn't show any bias voltage arrangement for the 1st transistor (unless - it's really a PNP type... in which case  they have the collector & emitter connections drawn incorrectly)

...but apart from that - we can trust the remainder of this circuit absolutely, yes?

 

Good ol' Uncle Ernie!

 

PS.  if that foil is uninsulated, it might be an idea to check it can't make contact with any component leads on the PCB

 (...and if you ever get any hum or other elec type noise, more shielding wouldn't go amiss 😉)

 

I didn't find another schematic, just the other descriptions all had 'coil tap' as one of the switches, where it is surely series/parallel.

 

Thanks for having a look guys!

 

I'm thinking of them as 'big, bigger & biggest' settings right now.

 

With the PU too close to the strings I think I can hear some overdrive in the preamp so some further experimentation required (battery is fresh).