Small Stone trouble

[JimiB]

I put a DPDT switch in my old small stone to true bypass it as It was noisy even when it was off, and now when the depth switch is in the up pos. it makes this noise that raises and lowers in pitch even when the pedal is off. I don't understand how it could be doing this as the wire from the tip of the in jack is conected only to the tip of the out jack thru the switch. What gives?

[sir_modulus]

Maybe high gain? Crossed I/O wires? Faulty switch? If you have a 3PDT, I'd try the input grounding technique (see offboard wiring at Tonepad).

Cheers,

Nish

[JimiB]

I'm using a DPDT and its wiried exactly like the Offboard Wiring 1 schematic. I don't understand how the circuit could be introducing signal when the switch is off. I have tried 2 different switches.

[puretube]

Hi gain is no issue in the (almost) unity gain Small Stone...

Wrong wiring is, however:

in the unmodded SS, there`s always a connexion to the circuit`s input -
this has to be interrupted by the 2nd "pole" of the 2P2T, when the input jack is routed to the output jack by the 1st pole, when in "bypass".

[sir_modulus]

Are you sure it's a DPDT? (I dunno, I thought I'd take a stab at the high gain thing....Vintage Pulsar isn't exactly high gain either, but with no input grounding, theres an LFO tick.)

Listen to Puretube! He's almost always right  

Cheers,

Nish

[JimiB]

this is how I have it wired
1 2
3 4
5 6
Input jack to 3
Input to board to 1
output jack to 4
output from board to 2
5 and 6 are conected

The input jack has 3 wires attached. One to each lug
the two not mentioned previously are I believe dissconecting the - from the batt. when the input is unplugged.
The out put jack has 2 wires attached one from the switch = tip
and one from the color switch which goes to sleeve = ground.

The noise only happens when the color switch is in the up pos. = the wire going to ground at ouput jack is no longer connected.

[JimiB]

please  

[puretube]

is your old SS by chance an old orange lettered box with 6 ICs?

[JimiB]

no its the chrome one.

[JimiB]

any ideas?

[palthegiraffe]

I put a DPDT switch in my old small stone to true bypass it as It was noisy even when it was off, and now when the depth switch is in the up pos. it makes this noise that raises and lowers in pitch even when the pedal is off. I don't understand how it could be doing this as the wire from the tip of the in jack is conected only to the tip of the out jack thru the switch. What gives?

Sorry to bump such an old thread, but I wondered if any resolution was found for this problem, as I just installed a DPDT in an old Small Stone myself and it is having exactly the same problem (noise in bypass that is at the same speed as the effect when on, and only with the color switch in the on position).

[Mark Hammer]

The Small Stone Coor switch is kind of the poor man's cousin to the 4-way rotary switch on the MXR Phase 100.  It controls two parameters at the same time: sweep width, and regeneration.  When the color is "off", the sweep is more limited in range and the regen is turned off.  When the color is turned "on" the regen is increased (though not to the max possible) and the sweep width is increased.

Actually, I lied.  It adjusts three things.  The change in the LFO sweep also seems to bump the speed a bit too.  I wish I knew enough about OTA-based oscillators to be able to separate those latter two.

Since your problem with the noise appears to occur only when there is regeneration/feedback introduced, that points the way to possibly identifying the source of the problem.

When a SPDT switch is used, the input jack goes directly to the board (which is going to be a reasonably short lead on the SS) and the switch is used for selecting between the input jack and the output of the board.  When a DPDT switch is used, the input jack has to be run to the stompswitch, then to the place on the board where it is normally tied.  That provides a lot of opportunity for any stray signal to be picked up by the wires to the input and fed back through the regen loop.  With the color/regen off there may well be the same noise picked up, but it isn't fed back and reamplified by the circuit.

As such, the first place to start would be using a piece of shielded cable between the input jack and the stompswitch, the shield doesn't have to find its way right to the stompswitch, but at least make sure its tied to ground at the jack.

See if that makes it go away, and then report back.

[palthegiraffe]

Will do. Thanks for your help!

See if that makes it go away, and then report back.

[palthegiraffe]

Okay, I replaced the input-jack-to-stomp-switch wire with a shielded wire. The braided shield part of the wire is soldered to the ground tab on the input jack. The chirping sound is still there in bypass mode when the color switch is up, so I remain confused. Any other ideas?

[tennisdude]

Yes. This may be totally off the mark, and I am by not means an electronics expert, but this is my opinion:
1. use shielded wire for the input and output wires
2. use a 3pdt. this way, you can ground the input to the PCB when bypass is activated. See "offboard wiring 5" on tonepad. http://www.tonepad.com/getFile.asp?id=76
an LED would be nice anyway, so its a good opportunity to include one 
3. run the wires along the side of the enclosure as much as you can. In fact, tape them to the sides of the enclosure. Then, double and triple check that none of the wires are overlapped.
4. throw a hissy fit if the above 3 don't work 

good luck
John

[palthegiraffe]

Problem solved at last!

I replaced the DPDT with a 3PDT, and used the third set of lugs to switch on and off the connection from the input jack ground to the PCB, so that with the pedal off that connection is broken and the true bypass has no connection at all to the PCB. Now it works well and sounds great!

On to the next broken pedal...