Brown source schematic - tone switching

[mikeb]

I've been looking at this to work on a PCB layout - the schematic supplied doesn't seem to make sense WRT the tone switching. Pos 1 should be 'tone off' (i.e. throws 12, 4, and 8 engaged) but this doesn't lead to the signal being carried from the tone section through to the final part of the opamp at all .... it seems a connection is missing from (say) pin 12 to pin 4.

Help!

Mike

[mikeb]

Bump ... I can't go any further without sorting this out!  

Mike

[puretube]

link us to the schem...

[mikeb]

Certainly .... this is Marcos's schematic...

http://prophecysound.com/temphost/lovetonebrownsource.jpg

... I think the rotary switch diagram is based of a preliminary schematic by FP, but am not completely sure of it's accurary - as it stands there isn't a path for the signal with the tone switch in the 'off' position. I don't have a PCB track-side picture either.

Mike

[marrstians]

there's a couple of minor errors in the shem... first off i believe that the .022's are actually .22's... the cap labeled .0033 should just be a .033... the tone switch is a little misleading...  try this and see if it works... http://tinypic.com/55vo3

[marrstians]

one other odd thing about the circuit... i could only get it to work with a pnp instead of a npn... with the npn i got constant oscialation and it sounded like crap, i used a 2n3906 and it sounds right... odd...

[Marcos - Munky]

I don't know if the tone switch is correct. I drew the schematic based in a pic of the board, two schematics, a copy of the original layout and Marrstians' help. The only thing that I know is that the switch used in my schematic is different from the original unit, based in the schematics that I have (maybe easier to get?), but I believe it's wired to work like the original switch.

[Arno van der Heijden]

Can you post the pic of the board and the layout?

[marrstians]

i just used a simple 4 postion 3 throw rotary switch from mouser...  A should connect to 1-4, B to 4-8, and C to 9-12... that way A connects to B and #4 of the switch bypassing the tone section on the fouth positon...  most caps are labeled 33n except for the .022's in the schem (which are labeled U22 that i believe are .22) and the .047 (which is labeled 47k63).. the rest of the schem works, i've bulit one up, it would only work with a pnp tranny though....

[mikeb]

Thanks for the responses, all. I'll puzzle over what is here and the info I have (I drew the copy of the PCB layout - hence I'd be quite reticient to post that openly here!). Likely if anyone is to blame for errors it's me so I'll go and quietly try and fix them now ... (sneaks away) ....

Mike

[marrstians]

the layout could be the problem but i think the schem's a little off so that probably didn't help you... i hope that small schem for the tone section helps you out... i have a layout in express pcb but it's exact copy of the origional so i don't know if it's kosher...

[cd]

marrstians - regarding the small tone control pic you posted above, can you confirm what connections are made from lug #4?  Is lug #4 connected to lug B, or is it connected to the tone control?  I think I almost have the whole thing worked out (see schem link below - with apologies to the original maker of the schem, I didn't want to redraw the whole thing).

http://img11.exs.cx/img11/3630/lovetonebrownsource1.gif

The way I'm thinking it works because:

Position 1 (as pictured, arrow full up): tone control works as normal
Position 2 (next one down): .033u added in parallel with high pass filter in tone control, shifting frequency from 1237Hz to 618Hz (more mids) - also, HP added at volume control (with 220 ohms resistor) kills highs above 22kHz.  Tone control works.
Position 3: .22u added in parallel with high pass filter in tone control, shifting frequency from 1237Hz to 161Hz (LOT more mids) - also, HP added at volume control (with 220 ohms resistor) kills highs above 22kHz.  Tone control works.
Position 4 (lowest position): Tone control bypassed???  This is the position that doesn't make sense!

[mikeb]

Yeah, the tone control bypassed bit *is* correct! Thanks for posting that, too, it's help me finish the schematic. Layout in progress....

Mike

[cd]

Yeah, the tone control bypassed bit *is* correct! Thanks for posting that, too, it's help me finish the schematic. Layout in progress....

Mike

Whoops - you're right!  You know what, I redrew the pencil sketch I made and got the lug #4 connection wrong - I had it connected to lug C in my sketch.  Dang, what a lucky coincidence!

OK I'm going to sim the rest of the circuit to see if the component values make sense.

[mikeb]

I'm still puzzing over that 220n/22n value though. U22, to me, implies 22n. Oh well, I'll the layout and we can suss it out later....

Mike

[marrstians]

i did a search online and every where i came up with (backwards)U22 = .22uf... that's just what my search came up with... all the .033's are labeled 33n on the parts so i don't know... i don't think that a .022 would make a big difference from the .033 in the tone section so i think the .22 would make more sence for a different postion on the tone... not 100% sure...