Tone-O-Matic

[moosapotamus]

This is the Tone-O-Matic from Boscorelli's Stompbox Cookbook. It is apparently designed to duplicate the passive and active tone control functions of the Ampeg SVT.

Tone-O-Matic

One thing that I cant quite figure out is the two DP3T switches. Here's how one of them is represented in the schematic...



I'm familiar with how a Lorlin rotary DP3T switch works, but I've never seen a double pole triple throw switch represented this way. I'm assuming that it represents a 3-position toggle switch, but which poles are connecting to what for each of the switch's 3 positions? Does anyone know of an actual switch that works like this and that is also currently available?

Thanks
~ Charlie

[tommy.genes]

I'm thinking those horizontal bars between the switch pins represent the contacts, so in position 1 they tie the first column of pins to the second column of pins in their respective rows. Position 2 ties the second column to the third column, and position 3 ties the third column to the fourth column.

This is just a gut read, and isn't based on any analysis of the circuit, however. Cool circuit, though...

[edit] I found it helpful to compare it to the controls on this PHOTO of an SVT (view full size to be able to read the labels). SW2 and SW4 are pretty obvious, and I'm guessing SW3 is the "ultra-hi" switch. I'm not seeing a SW1 in the schematic.

-- T. G. --

[Ben N]

I believe TG is correct.

[moosapotamus]

Thanks for the feedback, guys!

SW1 is the overall bypass switch. I left the true bypass switching out of my re-draw.

So, does such a DP3T toggle switch really exist? Where? I've never seen one.
I suppose, now that both of you have confirmed the way that switch works, that I might be able to do it with a rotary. But I'd rather have the toggle.

Thanks
~ Charlie

[slotbot]

I think usually this type of switch is a slider.

It sort of makes sense if you think of it. the 2 parallel pars "sliding" across the 8 contacts, connecting 2 adjacent pole pairs at a time, just as TG stated.

Im not sure if these would be exactly it:

http://cgi.ebay.com/DEFOND-DP3T-SLIDE-SWITCHES-6-5A-250VAC-10-PCS_W0QQitemZ320409436147QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item4a99e3fff3#ht_578wt_939

....but something along those lines.

I dont think it was an SVT but I remember playing some sort of vintage ampeg that had 3 position rocker switches that did something similar.

There are DP3T ON/ON/ON toggles but i *think* usually they work as say, left poles connected to center poles, both left and right poles connected to center poles and just right poles connected to center poles. which i dont think will work quite for this schem.

[Ben N]

In the original '70s Ampegs I'm pretty sure those switches were rockers.

[moosapotamus]

Yeah, I think the amp originally used rocker switches. You can see them in the picture that TG posted.

I'm not optimistic about finding a switch that works like that. Might just have to try adapting a rotary switch.

FTTB, I'm going to keep looking, tho.

[DougH]

The impedance selector in my amp works like this. You might try looking for impedance selector switches at places that sell amp parts. Maybe get a part number and then get it cheaper at Mouser or something too.

Edit: It's a slide switch.

Here are some ideas:

http://www.google.com/products?q=2p3t+slide+switch&oe=utf-8&rls=org.mozilla:en-US:official&client=firefox-a&um=1&ie=UTF-8&ei=Vm7ES_CrPJPaNZOCqYMO&sa=X&oi=product_result_group&ct=title&resnum=11&ved=0CDEQrQQwCg

http://www.mouser.com/_/?Keyword=2p3t+slide+switch

[tommy.genes]

I suspect the original Ampeg switches really are slide switches, but with a 'rocker' mechanism in front (no pun intended) that moves the slide based upon the rocker position. I recall having seen a similar arrangement somewhere before, although I'm pretty sure I've never opened up an Ampeg amp to have a look. It must have been one of those many calculators, clock radios etc. that I dissected as a youth.

-- T. G. --

[WGTP]

I had an Ampeg VT-22 back in the day.  Ampeg was big on those "Rocker" switches.  They were used for input padding, lo and high cut/boost (depending on guitar or bass amp) mid-range shift, etc.  Had a nice feel to them.  Not sure what was underneath it.  Might check other schematics.  V-4b, VT-40, etc.

[DougH]

I used to play with a bassist with one of those old Ampeg heads, long ago. I asked him what all those switches were for. He said, "Different sounds"...

Pretty much summed it up...

[moosapotamus]

Good suggestions for running down those switches. Thanks! I hunted around a little and decided, based on the consensus of how they are supposed to work, to just redraw the schematic with representations of "normal" switches. So here's how I think it ought to look...

Tone-O-Matic v2

The way I've drawn them, they could now be implemented with 3-position rotary switches. If anyone has a chance to take a look and spots what might be a mistake, please let me know. I'll probably try to get this breadboarded within the next couple of weeks... Then I'll see if it really does make "different sounds".

~ Charlie

[Ben N]

Thanks, Charlie, that's awesome. Let us know how it comes out. BTW, was this intended for a dual supply?

[moosapotamus]

Yes, it is intended for a dual supply, as shown going to pins 4 and 11 on U1a. Boscorelli wrote that this circuit likes a lot of headroom, so a +/-15V or even +/-18V should be considered. There's a pretty nice little circuit in the stompbox cookbook that uses a DC-DC converter with a dual output to provide +/-15V from a +9V supply. The converter is a little pricey at ~$14, but it works quite well. I'll probably give this a try with +/-9V a la LT1054 or MAX1044, too.

~ Charlie

[nofretsplz]

Bump! Hey, I remember seeing this circuit years ago in Boscorelli's book, and thought I should put it on my bucket list. Anyone try a build on this?