chirping tubescreamer ! ?

[bluedreamin]

Gez , heres a link to the best ts5 schematic I could find http://www.freeinfosociety.com/electronics/schemview.php?id=1087  , don't know if it will help ?? Sure hope we can get this figured out , I like the sound of this ugly little pedal ...but not the switching noise ! Thanks all !

[gez]

Will have a look later (though can't promise to have a fix - other's might though), as I need to go out soon.  

[gez]

Hi,

Sorry I dont have time to look it up exactly but changing resistor values in the mirror image FET switching circuitry to TS9 values helped the TS10. Maybe this info can help someone with more time tell you what to try.

R30 & R31 in the schematic BlueD.  Also check C16 & C17.  Compare these values with original schematic.

If it's oscillation follow Pauls advice about using screened cable.

[bluedreamin]

Yes , these parts in the ts5 are the same as the ts9 , still stumped ! I can't be the only one this has happened to ...as far as shielded wire , please explain the only wire is the batt. wire and LED wire . Any other ideas gentlemen ?

[Paul Perry (Frostwave)]

...as far as shielded wire , please explain the only wire is the batt. wire and LED wire . ?

I didn't realise that! but, if you are turning the electronics off at the same time as you are bypassing, then no wonder, because plenty of circuits oscillate (or behave in strange ways) immediately after the power is switched off, as the caps in the circuit discharge.

What circuit should I be looking at??

[bluedreamin]

Hi Paul , this is a ts5 circuit and I have a schematic link posted earlier in this thread . It happens switching on or off unless I turn down the volume which I prefer maxed ...pretty weird eh . Hopefully we can get this figured out . Thanks again !

[bluedreamin]

Hello again , anybody have any other advice on this ts5 problem ? I've tried many suggestions but nothing seems to work ! Thanks you guys !

[Paul Perry (Frostwave)]

IN the absence of an osciloscope, I'd suggest using an audio probe (in this case a 100K resistor in series with a .01 cap going to an audio amp) to check where in the circuit the chirp comes from. (don't forget the earth connection!)
In particular, I'd like to know if the outputs of the op amps chirp.
And now I've actually looked at the circuit, I'm wondering whether the flip flop (the 2 transistors) are switching fast enough, because if they switch slow, that makes a temporary positive feedback loop via the fets , whilehey are both in transit from off to on & on to off. Maybe smaller caps in the flip flop, to speed it up!

[bluedreamin]

Thanks for your reply Paul , is the flip flop the FETs or the 2 transistors in the switching circuit ? Please tell how to use this "probe " you speak of , can I use it with an amp , how would I hook it up and use it ? Are you talking about the .047 caps ...making them smaller ? I appreciate your patience and help very much ! ! !

[Paul Perry (Frostwave)]

The 'flip-flop' (or Eccles-Jordan as they were called in my childhood, see http://www.du.edu/~etuttle/electron/elect36.htm ) is the 2 transistors, the fets are the switching circuit that their outputs control.

C4 & C5 are the caps I would try making smaller, say 1/10 approx what they were. Experiment, nothing will break.

An 'audio probe' is just a cable to your amp, with the shield of the cable connected to ground, and the active inner wire connects to your circuit via a .01 microfarad cap, the idea is that this helps you track how far the signal gets in your circuit.

[bluedreamin]

I will give that a try Paul , will have to locate parts first but am willing to try anything ! I found this interesting ...I added an extra .047 to each of  the 2 existing .047 from the backside of the board , it didn't help BUT if I remove just one of the added ones it only chirps one way ...depending on which cap I take out, it only chirps once , either when switching off or on ! I thought that was strange but maybe not ! ?

[Gus]

try changing the c3 value

[bluedreamin]

Up or down Gus ?

[Paul Perry (Frostwave)]

Up or down Gus ?

Try both ways, you can't break anything! Personally I would back smaller. The fact that adding one cap made a difference (chirp one way only) shows that we might be on the right path!! Also, if you have a spare fet, try swapping one over. I think the problem is, the switcvhing happens too slowly., and as it does, there is a time when BOTH fets are partly turned on, which makes a feedback loop around the effect & it oscillates (= chirp).
Come on, there must be an EE in the house :roll:

[bluedreamin]

Hello again , no luck on these caps either . I went from 1000pf (stock)down to 100pf on all three of the ceramic caps , tried c3 first , then all three then just c4&5 . I've already tried different fets Paul ...no change . This is very weird , it is totally stock so I would think it's a bad part but I have been hearing that many ts5's do this ! ? Seems like another dead end but that one way chirping thing with just one extra .047 cap seems to be pointing in some direction doesn't it ? Beats me !

[gez]

Seems like another dead end but that one way chirping thing with just one extra .047 cap seems to be pointing in some direction doesn't it ?

Which one is the .047 cap on the schematic you linked to (it has no values).

[bluedreamin]

there are two of them , side by side and are tied to two diodes also . What are ya thinkin Gez ?

[gez]

there are two of them , side by side and are tied to two diodes also .

You mean C16 and C17?

[gez]

I think Paul was onto something, i.e. both FETs open at the same time.  The op-amps are non inverting so if both FET's channels are open during switching it would be easy for the output to feed back to the input.

Try Paul's suggestion and make C16 and C17 smaller.  Or buy some more FETs and try different ones out til you get some joy.

[bluedreamin]

back in the thread Paul suggested larger values for c16 &17 but smaller for C4 & 5 , I have no more fets to try but I will keep messin with it ! Thanks all !