[sdiy] Re: ARP Axxe popping..is this normal??

[Tom Wiltshire]

If it's popping when you press and key and pops when you've got the 
release up, could the problem be coming from the envelope generator? 
Could you get switching noise produced by a faulty EG?

On 2 Jan 2007, at 07:04, Bob Weigel wrote:

> I studied the diagram some more and realized that I didn't understand 
> it before because of some more fuzz that made me think the cvr pot was 
> one other than what it was..  And concluded that somewhere in between 
> it's got to do the job and sure enough apparently the control was just 
> too ditzy *right* in the spot where it needed to be....  I'd seen 
> someone replace all of them on the odyssey site I found yesterday and 
> added to my page.
> Anyway I have an idea the click is just part of it.  That got the 
> signal to noise ratio back on the map at least PROVIDED that I don't 
> have the RELEASE turned up at all.
>
> If the release is up there's a huge pop transitioning.  -Bob
>
> klosmon wrote:
>
>> I may as well be the one to ask the stupid question ("go with your 
>> strengths", they tell me):
>> have you checked/adjusted the VCA offset trim?
>> I haven't worked on one of these for a while, but I seem to recall 
>> that there WAS such a trim, and that it made a radical difference.
>>
>> ~G
>>
>>
>> At 09:08 PM 1/1/2007, you wrote:
>>
>>> Even with a slow attack, it's got all the charm of a machine gun at 
>>> the moment. :-)  No didn't see need to employ any energy discharge 
>>> techniques on this one. hehe. I had resonance down. This *is* the 
>>> ladder with three 3086 arrays; all replaced in sockets now. Nothing 
>>> changed like I said with all new transistors...and cant' see the 
>>> signal on the inputs to the op amp..just output.  Really bizarre as 
>>> always if I bring it up :-) -Bob
>>>
>>> harry bissell wrote:
>>>
>>>> Hi Bob...
>>>>
>>>> you didn't short the caps with a screwdriver did you ???   :^P
>>>>
>>>> ~seriously~
>>>>
>>>> Is this the ladder filter or the state variable ??? Usually the pop 
>>>> is a sudden DC level shift. If you use a slow envelope
>>>> does it ~not~ pop ???
>>>>
>>>> In the ladder case I'd look for bad matching in the two halves of 
>>>> the ladder...
>>>> that will cause a big DC swing...   I was able to look at the 
>>>> bottom of the ladder
>>>> and the DC level was changing a lot. Matching both halves cured 
>>>> that problem...
>>>> Maybe one transistor is shorted there ??? try with no resonance, 
>>>> measuring the
>>>> DC drops on both sides of the ladder. They should be equal...
>>>>
>>>> In the SVF maybe there is a bad offset voltage on an OTA stage...
>>>>
>>>>
>>>> Bob Weigel wrote:
>>>>
>>>>>
>>>>> I've never played one of these things but..I don't recall this 
>>>>> much pop when I hit a key on the odyssey I repaired.  It was a 
>>>>> later one I guess..but anyway... I can't figure out where this is 
>>>>> coming from.
>>>>> It originates, it seems at the output of the vcf op amp.  the 
>>>>> other half of which is in the vca, a 1458.  I replaced it thinking 
>>>>> it had gotten cross talky.  Didn't help much.  Maybe a little.  
>>>>> btw the sudden filter respond I talked about before was due to an 
>>>>> open resistor.  Got that solved and everything else in the vcf 
>>>>> replaced or verified except the dual fet and transistor pair.  All 
>>>>> new filter caps including local ones. -Bob
>>>>>
>>>>> harry bissell wrote:
>>>>>
>>>>>> Usually the glitch is from the triangle that feeds the sine 
>>>>>> shaper.
>>>>>> Its usually generated from the sawtooth, which causes a 
>>>>>> discontinuity
>>>>>> where the reset occurs. Best way around it is to use a triangle 
>>>>>> wave core...
>>>>>> which usually has its own problems to solve...
>>>>>> I did a little study on how to eliminate the glitch from the 
>>>>>> triangle... I'd predict
>>>>>> the reset time (perhaps with a comparator that is set just below 
>>>>>> the normal
>>>>>> reset point, then use a track-hold circuit to ride out the glitch.
>>>>>> Woah its pretty
>>>>>> complex but looks workable. Don't know if the distortion would be 
>>>>>> worse than
>>>>>> a small cap to cover the glitch... at least this method would 
>>>>>> keep the effects of the
>>>>>> glitch reasonable constant with frequency
>>>>>>
>>>>>> H^) harry
>>>>>>
>>>>>>
>>>>>> Paul Perry wrote:
>>>>>>
>>>>>>> The $64 question is, where does the blip at the peak come from?
>>>>>>> And, does it appear symmetrically at the lowest point of the 
>>>>>>> sine?
>>>>>>> ......and does it matter what diodes are used?
>>>>>>>
>>>>>>> paul perry melbourne australia
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>
>>>>
>>
>>
>>
>
>
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