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For goodness sake, the CP500 uses a Bourns rotary encoder for the volume control. It is the same one, right down to the last digit in the part number, that Panastereo have been using for about 8 years in their processors (that's right folks, Panastereo did it first and Dolby copied them). But you will not find a Panastereo this side of hell that "ticks".

Now seriously, step fader noise!!! A rotary encoder talks directly to the microprocessor. There is no direct connection the the VCA. This is getting really annoying....

IT IS A FAULT IN THE PROCESSOR. IT NEEDS A REPLACEMENT BOARD!!!

HOW .. MANY .. PEOPLE .. LIVE .. IN .. YOUR .. HOUSE???

Yes, I am an arrogant Son of a Bitch, but I really do know my stuff when it comes to sound, which is why I am known as the Sound Pro - and I DO NOT suffer fools or stupid uneducated suggestions.

Sorry Paul, you are probably a really nice guy and only trying to help. My suggestion .... DON'T.

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<Pulling out BSEE degree> Mind if I speak, from my arm-chair? ;-)

The Rotary encoder, as used by the CP-500 is a two-bit quadrature device. That is, it has two "outputs" typically called "A" and "B". If one were to hook up an O'scope to it and start spinning the dial at a constant speed, you would see two square waves on the two channels. The square waves would be separated by 90 degrees (that is the quadrature part). By comparing the two outputs to one another, it can be "decoded" as to which direction the knob is being turned. That is, if "A" is leading "B" or vice-versa. Once decoded and the desired resolution is obtained (who is to say that the engineer designing the circuit wanted the same number of pulses as the device puts out?). The rest of the circuit (counter) can then pulse up or down, depending on the direction of the knob. There is a finite range the counter can count based on practicality (just how many steps does one really need to give a smooth transition?

My suspicion (I have not looked at Dolby's circuit, myself) is that their counter is the limiting factor on the actual volume range. Lets do some base 2 math...we have found that 9.2 or 9.3 is top of range...someone else said that around 2.6, things went down real fast...2^6 = 64...

9.2-6.4=2.8. Again, this is a real stab in the dark but it seems they are using a 6-bit counter for the volume. 2^7 would yeild 128 steps and would cover the whole range.

Once this binary number is coverted to an analog current, it can drive the VCAs which I'm pretty positive are done in the analog domain.

So why the ticks? Beats me! It could be anything from noise on the line to how things are wired to the way the PCBs are made causing chatter or even an unstable design/layout. I would rule nothing out.

<throwing crumpled up degree back in the corner>

If it does it on some but not others, have you tried swapping some boards out (Like the output card and the main module) Just to see if the problem moves?

It kind of makes sense to me, as even some of the sound cards used in Personal Computers would register real low
key "thumps" that were plainly audible when listening carefully in a pair of headsets as the slider was snagged and moved with the mouse. The faster the slider was moved, the louder the thumps would get. I would guess the VCA's are seeing that as an extremely rapid change in the ramp voltage. What do you think?

As such, I can only speculate on Dolby's design. But the volume knob and counter shouldn't be inherently noisy since they are in the digital domain. BUT, and here is another place for the noise to creep in, lets say there is some connection between the digital ground and the analog ground, then the noise from the digital steps could indeed show up in the analog ouputs (it might not even be the steps of the rotary encoder but the digital words moving about on the PCB).

Once their processor has it's level, it has to go through some form of D-A conversion for the VCA's to deal with it. Certainly, how they handle this signal could result in a "tick" being impressed on the sound.

I thought I read that some units have the noise and some don't. If it is an intrinsict design flaw (or "feature") then it should show up in all units. If some units do not have the problem then I would try to locate which module(s) are participating in the problem.

Steve

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"Old projectionists never die, they just changeover!"

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The only CP-500 I installed in our theater chain was about 3 years ago. It has been trouble free, and because of that, the very little I learned I have forgotton.

As to the quadrature optical encoder (which IS what Dolby is using in the CP-500)...I have actually used the same part Dolby is using (a Bourns part)...

You have to understand "state machines" to understand how it works. To decode the encoder, you compare the two outputs (A and B). If say A leads B in a clockwise direction, lets set up a situation for the state machine:
A and B are both "high", if the next change has A go low, then we know the knob is rotating clockwise. Now we have A high and B low. If the next change has A go high again, the knob was turned back. You can set up all four states and see that you can uniquely determine what action had been taken on the knob.

Furthermore, there is often more than several state changes between "clicks" in an optical encoder (in fact, Bourns offers the products with two different resolutions last I checked). To prove (or amuse yourself) to yourself this, take the knob and rock it back and forth between "clicks" without actually advancing the knob (ie the finger dimple doesn't go around) and you can raise or lower the volume.

Steve

Here we have a bunch of guys speculating about something they obviously do not fully understand.

It is one thing to offer advice to others when you really know what you are talking about. The problem arises when people make statements on this and other web sites and present them as fact when they are really nothing more than idle speculation.

Steve and Gordon, from your many posts you are clearly very knowledgable and articulate and I was not directing my "arm chair expert" reference to either of you. It is the proliferation of incorrect and inaccurate statements from some others that just confuse the hell out of the poor guy who asked the original question, and this only serves to enhance the spread of mis-information. The Internet should be renamed the "Mis-Information Superhighway".

Just for the record, the rotary encoder used in the CP500 is indeed as Steve has stated a "quadrature" encoder, but it is NOT as he also said, an "optical" rotary encoder. It is fact a three terminal "contact" encoder consisting of dual rings of metal contacts which are offset to each other in such a way that when a rotating blade makes contact alternatively with the contacts on each ring, an effective phase difference of 90 degrees is achieved.

However it would be highly unconventional to use a hardware "counter" with such a device in a professional design. Because this would impose absolute limits on the encoder's effective rotation in either direction, and this in turn would make it impossible to have simultaneous parallel control from other sources, such as the CP500's remote control.

The normal encoder interface is for a microprocessor to "read" and decode the pulses and use the direction and number of steps "information" to increase or decrease the volume setting. So the idea that such a counter could be the limiting factor in the volume range is not realistic.

The most likely cause of the ticks is digital bleedthough either in the volume DACs (did I say VCAs) or via a defective ground system as Steve suggested.

I reiterate by my orginal statement that the problem is a FAULT which is cured by swapping out one of the boards. Now it is a while since I saw this problem so I don't remember if it was definitely the audio output card but I can tell you that when we swapped the offending card with another processor the fault went with it. The serial cable was not a part of the equation.

Now THIS is FACT and not speculation, boys and girls!

Do I hear the referee counting?

Nobody's getting "testy".

Nothing worthwhile has ever been achieved in human existance by people sitting smiling across a table at each other.