my kick drum is working perfectly, so i do not exactly have the need
to reply to this, but...

mda231, this was by far the best troubleshooting post i īve read since
a long time - very insightful and explanatory. exactly what i would
want to find if i had a problem with my gear!

thanks for the good read.

creekree

--- In tr-707@yahoogroups.com , "mda231" <mda231@...> wrote:
>
> Hello Alexis,
>
> From what you write, I think I may know what has gone wrong with your
> TR-707. I had a similar problem myself, and here is what I did to
> repair it:
>
> 1) The kick drum sound travels to the output via an op-amp which is
> configured as an inverting amplifer. The individual volume control for
> the kick drum is the feedback resistor. As you may know, the gain of
> an inverting amplifier is calculated by dividing the feedback
> resistance (Rf)by the input resistance (Ri), in symbols, Gain = Rf/Ri.
>
> 2) Now, when Rf is at a minimum (i.e. zero), the gain will also be
> zero, so you won't hear a sound. But when Rf is at its maximum, the
> gain will also be at its maximum, remember, Ri is a fixed resistor,
> not a variable one.
>
> 3) Here is my diagnosis: your kick drum makes an incredibly loud
> buzzing sound. - That description sounds to me like distortion. When
> do we normally get distortion - Easy! When we turn the volume up too
> loud, i.e. when we apply excessive gain. -From this I conclude that
> excessive gain is being applied to the kick drum.
>
> 4) Remember that the volume of the kick drum is controlled by the
> volume slider which is infact the feedback resistor, Rf. -What would
> happen if Rf became extremely large - Well, massive amplification
> would be applied to the kick drum. What does massive amplification
> cause Easy! DISTORTION! e.g. a "loud buzzing sound" when you'd
> normally hear a solid thump.
>
> 5) It seems to me that your kick drum's volume slider has failed. The
> type of failure is most likely an open-circuit, i.e. its resistance
> has become excessively large. Hence massive amplification is now being
> applied.
>
> 6) How do you test the theory - As I recall, the individual volume
> sliders all have the same value (check this). So all you need to do is
> swap one that you know is working for the presumably faulty kick drum
> slider.
> If the kick drum sound returns to normal, then you've solved the
problem.
>
> If you have a multimeter, you can also measure the resistance of your
> apparently faulty slider. If it's far too high, then you have located
> your problem. Since you write that the slider has no effect on the
> kick drum's volume, I suspect this is what you will find.
>
> 7) If this is what has gone wrong, all you need to do is replace the
> defective kick drum slider.
>
> Hope this assists you.
>
> MDA231
>
> --- In tr-707@yahoogroups.com , "bronxed01" <bronxed01@> wrote:
> >
> > I bought a 707 a while ago for cheap because supposedly some of the
> > buttons weren't functioning correctly. When i got it, i found out
that
> > the only problem was that the kick drums didn't work, they just make
> > an incredibly loud buzzing sound. I'm guessing this is because the
ROM
> > chips for the kick must be broken. How can i fix it
> >
> > Alexis
> >
>