Computer Controlled wrote:OK, is there a difference between 1uF and 1.0uF? Common sense tells me no. But i just wanna make sure.
Some of the OP's measurements as reported here show that reversing the cap can cause such drastic drops, their affect indeed being that the gain of the diff amp is sufficiently reduced so as to be audible, as several of the audio samples in the original and subsequent posts show. My post here shows how the gain will change with any leakage present by 'reversing' the capacitor, simply emulated (via SPICE simulation) by adding a resistor in parallel to C29, and sweeping its value. Further simulation results showing the affect on the overall frequency response of adding a 30k in parallel to C29 are shown in this post - to my mind these illustrate what is likely a quite tangible difference, and probably accounts for the audible differences in the audio samples.Robin-Whittle wrote:I guess a capacitor could leak so much that its voltage would drop
in a manner, such as to 3V or so, where the voltage across R106
(2.2k) is reduced sufficiently that the current through the Q21
pair is reduced so much as to cause clipping.
I think it would have to be a drastic drop to affect the gain of the
Q21 differential amplifier to any noticeable degree. If the
leakage was noisy, or erratic, that would probably cause audible
On looking over the thread whilst preparing this response, I believe it is clear that some 1uF capacitors when reversed at C29 are capable of producing audible changes - what is not so clear to me now is whether the caps that were tried backwards actually include the original cap that the TB-303 being used for the measurements was built with, or whether they were all a random selection from the OP's bag of pulled 1uF caps - perhaps he can elucidate?! (And apologies to anyone else who has reversed their cap and reported a difference - I haven't re-read the entire thread, only what I see as the larger 'key' posts..).I think it is quite likely that in all the TB-303s made, few, if any,
of these capacitors have ever failed to the point of audible
To me it looks like they are that cap symbol with the parallel plates with a little 'hatching' between them, as sometimes used to designate electrolytic caps (the quality of that section of the manual is possibly the result of several generations of photocopying, then the scanning, i.e. it is likely not representative of a 'factory fresh' PCB!?).cleaninglady wrote:Correct me if i'm wrong here but it looks like Diode symbols representing Capacitors here.
From memory (read: I'm not going to check back the rest of the thread!), it is the actual polarity marking of the silkscreen which is wrong, rather than the cap being placed incorrectly against the silkscreen (i.e. they were being built correctly according to what the silkscreen says).Doe's anyone think this may have been the reason for the C29 reversal in the Roland Factory ?
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