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voice problem (need to know if this is CEM related)

voice problem (need to know if this is CEM related)

2014-10-23 by berendnie@...

hi!


I just tested my second prophet that supposed to be in good working condition and discovered that one voice is verry low in volume. :( !!


now for the seller i'm in a hurry to clarify whats the problem here.


could this be cem related or is this an op amp problem or.. ?


i'm aware of cem's dying but i could not find anything on the web about them being low in volume,


it's not even half the volume as the others.


thank you!



Re: [prophet2000] voice problem (need to know if this is CEM related)

2014-10-23 by Martin Ator

Can you still hear the LFO and filter settings affecting the sample and also hear the sample OK on the bad voice(just that it's quiet)?


   

  On Thursday, 23 October 2014, 11:43, "berendnie@... [prophet2000]" <prophet2000@yahoogroups.com> wrote:
   

      hi!
I just tested my second prophet that supposed to be in good working condition and discovered that one voice is verry low in volume. :(  !!
now for the seller i'm in a hurry to clarify whats the problem here.
could this be cem related or is this an op amp problem or.. ?
i'm aware of cem's dying but i could not find anything on the web about them being low in volume,
it's not even half the volume as the others.
thank you!

Re: voice problem (need to know if this is CEM related)

2014-10-23 by berendnie@...

yes, resonance lfo filter adsr, sample sounds good not bend or anything, all work as it should!

only voice 8 is quiet /er than the rest.

I swapped alot of cems ;) also from my 2000, this is an p2002 plus btw. but all of them work fine.

do you have any id? thanks for responding btw!

I do feel like this is a minor problem, maybe a dead capasitor or something in the op-amp circuit?
i wish i had some fault finding skills because i'm just guessing..

also if anybody knows how to messure what comes out of the cem (with a simple multi-meter) please tell!
(also for future generation p2k owners. :) or do i need an oscilloscope for that, no problem in getting one.

maybe a good start to determine if the problem lies before or after the cem.










Re: [prophet2000] Re: voice problem (need to know if this is CEM related)

2014-10-23 by Martin Ator

There must be a control signal missing that controls the volume.
 

     On Thursday, 23 October 2014, 16:49, "berendnie@... [prophet2000]" <prophet2000@yahoogroups.com> wrote:
   

     yes, resonance lfo filter adsr, sample sounds good not bend or anything, all work as it should!
only voice 8 is quiet /er than the rest.
I swapped alot of cems ;) also from my 2000, this is an p2002 plus btw. but all of them work fine.
do you have any id? thanks for responding btw!
I do feel like this is a minor problem, maybe a dead capasitor or something in the op-amp circuit?i wish i had some fault finding skills because i'm just guessing..

also if anybody knows how to messure what comes out of the cem (with a simple multi-meter) please tell!(also for future generation p2k owners. :) or do i need an oscilloscope for that, no problem in getting one.
maybe a good start to determine if the problem lies before or after the cem.

Re: [prophet2000] Re: voice problem (need to know if this is CEM related)

2014-10-23 by berendnie@...

Hi again!

is this happening in the VCA section at page 047 of the service manual schematics file or..? (in the file section)

from the u325 4051 (CMOS demux chip ??) til the voice 8 adres line.

velosity and relative mix stil work.

so i asume the control voltage is there, only somehow its only half of what it should be..

could you explane in a little more detail what you mean ?

control signal missing that controls the volume of the cem right ?


do you think it's a minor problem ? because everyting works as it should exept that voice 8 is about half the volume.

first i have to get my hands on a scope!


looking at page 047 (if this is where the control voltages are) could you explane what to look at?

thank you! i appreciate it alot.


also, do you have experience in fixing this machine ?













Re: [prophet2000] Re: voice problem (need to know if this is CEM related)

2014-10-23 by Martin Ator

You could try to measure the voltage at pin 12 of the CEM and see if it is the same voltage on pin 12 of the other CEM's
 

     On Thursday, 23 October 2014, 21:28, "berendnie@... [prophet2000]" <prophet2000@yahoogroups.com> wrote:
   

     Hi again!
is this happening in the VCA section at page 047 of the service manual schematics file or..? (in the file section) 
from the u325 4051 (CMOS demux chip ??) til the voice 8 adres line.
velosity and relative mix stil work.
so i asume the control voltage is there, only somehow its only half of what it should be..
could you explane in a little more detail what you mean ?
control signal missing that controls the volume     of the cem right ?


do you think it's a minor problem ? because everyting works as it should exept that voice 8 is about half the volume.
first i have to get my hands on a scope!

looking at page 047 (if this is where the control voltages are) could you explane what to look at?
thank you!   i appreciate it alot.

also, do you have experience in fixing this machine ?

Re: [prophet2000] Re: voice problem (need to know if this is CEM related)

2014-10-23 by Martin Ator

Yes that should be the way to do it. Be careful not to slip and short circuit anything together. 
 

     On Thursday, 23 October 2014, 22:35, "berendnie@... [prophet2000]" <prophet2000@yahoogroups.com> wrote:
   

     I'll do that. but i'm really inexperienced here.
I assume the ground lead goes on the ground pin of the cem ? pin 10

Re: [prophet2000] Re: voice problem (need to know if this is CEM related)

2014-10-24 by berendnie@...

ok i've set up my "cheap voltcraft vc-11" multimeter.

and played a very long tone with alot decay in sequence.

at 20v dc i messured about it dropping from 4.62 on all cems

at 200 ac i messured about 09.1 on all cems

but forget all of this!!

now it gets wierder. (for me atleast!) :)

in preset banks 8 9 10 11 12 i dont have this problem, not with rom or sounds from disks

and in these presets i can play the sound numbers also with normal volume on all voices.

now when in preset banks 1 to 7 when i put forced outputs on the problem also disappears.
(i do not have this option in my prophet 2000 with system 3.0 i think)

in 8 to 12 I dont have to do this.. dynamic alocation off is fine.

am i missing something here ? or is this kind of wierd?

I also notised that the resonance and filters are actually stable in forsed output mode.

also this has system 4.0 on it.

sorry for the confusion, and mutch thanks for the help!

cheers !










Re: [prophet2000] Re: voice problem (need to know if this is CEM related)

2014-10-24 by Martin Ator

What size is this Prophet 2000, 256k or 512k and does it have a double sided disk drive, also have you double checked your findings were the sound was correct (preset banks 8 9 10 11 12) by editing the patch and making sure that only 1 voice is playing at a time?
It could be some kind of software bug maybe?
 

     On Friday, 24 October 2014, 1:21, "berendnie@... [prophet2000]" <prophet2000@yahoogroups.com> wrote:
   

     ok i've set up my "cheap voltcraft vc-11" multimeter.
and played a very long tone with alot decay in sequence.
at 20v dc i messured about it dropping from 4.62 on all cems
at 200 ac i messured about 09.1 on all cems 

but forget all of this!!
now it gets wierder. (for me atleast!) :)
in preset banks 8 9 10 11 12 i dont have this problem, not with rom or sounds from disks
   and in these presets i can play the sound numbers also with normal volume on all voices.
now when in preset banks 1 to 7 when i put forced outputs on the problem also disappears.(i do not have this option in my prophet 2000 with system 3.0 i think)

in 8 to 12 I dont have to do this.. dynamic alocation off is fine.
am i missing something here ? or is this kind of wierd?
I also notised that the resonance and filters are actually stable in forsed output mode.
also this has system 4.0 on it.
sorry for the confusion, and mutch thanks for the help!
cheers !

Re: [prophet2000] Re: voice problem (need to know if this is CEM related)

2014-10-24 by berendnie@...

my 2000 has 512k of memmory, i'm not sure about the drive tho..

(i dump al my samples with DSP quattro, this is a nice program.. a bit like the early Propellerhead Recycle
where midi sample dump was still avalible. and i store individual sounds in SysExLibrarian.

but i usualy get an iF. so could be that it is single sided.. it does not format or save anymore.
dit i read something in the manual about checking serial numbers of the drive to see if its sd or dd?

Now about the prophet 2002 plus (whitout the 8 output expantion)

yes i think i did this thoroughly. i played some presets loaded from disk, also individual sounds in sound number/ sound section (you know sound numbers press execute to get a point ;)!! )
and also tested the difference between presets 1-7 and 8-12 in midi mode 4 and how they respond to
forced output and dynamic alocation off..

this al gives me the same result: in preset 1 to 7 when dynamic alocation is on and also off
CEM 8 sounds a lot lower in volume.


yes i was already planning getting an eprom programmer! nice way to test this.. :)

hard to imagine it being something in the hardwear.. but i dont know how this all works..

for instance the fact that forced outputs option sounds different from dynamic alocation on and off, makes my head spin.. so it has to be that these two modes are different in the hardwhare part ? till the control voltages of the cem.. because the cutoff and resonance sounds steady in Fo mode.. instead of every voice having a slightly different filter timbre.

I also have this in my prophet 2000, there is a slight offset in volume and filter timbre.. but completly random

could it be that somehow the software does a sketchy job in preset 1-7 with dynamic alocation on and off
;) !

Ok.. i'm glad i can work with it now.




Re: [prophet2000] Re: voice problem (need to know if this is CEM related)

2014-10-25 by berendnie@...

Ok to get back at this.. i'm sorry again.

I did not do a proper test, in all presets in forced output mode, playing the 8th and 16th sound number it still has a lower CEM volume.

and off course it is different in the hardware part of it because it does not switch voices/cems

but in presets 8 to 12, when dynamic allocation is off i don't have a lower volume on cem-8 ,on any of the sound numbers. so when strumming a sample the 8th one is not lower in volume.. now maybe it's smart to measure if this cem is even playing in this mode when i test it like this! ;)
I will do that to confirm this.

still its a weird phenomenon. 2 things are possible at this point.. or dynamic allocation off works different in presets 8 to 12.. :S!! makes no sense but ok, like if you stack notes, play them on top of each other
it starts at cem1 and stacks it till cem8.. or again i don't have this problem when dynamic allocation is off.

I will get back on this after i measured activity with my cheap multimeter!

i'm afraid it's something like the first one and something is wrong around voice8.

thanks for the help

Re: [prophet2000] Re: voice problem (need to know if this is CEM related)

2014-10-25 by Martin Ator

Maybe there is a broken cable to the keyboard, or bad solder joint?How much quieter is it than the other voices, is it a little quieter, a lot, or almost silent?

 

     On Saturday, 25 October 2014, 11:44, "berendnie@yahoo.com [prophet2000]" <prophet2000@yahoogroups.com> wrote:
   

     Ok to get back at this.. i'm sorry again.
I did not do a proper test, in all presets in forced output mode, playing the 8th and 16th sound number it still has a lower CEM volume.
and off course it is different in the hardware part of it because it does not switch voices/cems
but in presets 8 to 12, when dynamic allocation is off i don't have a lower volume on cem-8 ,on any of the sound numbers. so when strumming a sample the 8th one is not lower in volume.. now maybe it's smart to measure if this cem is even playing in this mode when i test it like this! ;)I will do that to confirm this.

still its a weird phenomenon. 2 things are possible at this point.. or dynamic allocation off works different in presets 8 to 12.. :S!! makes no sense but ok, like if you stack notes, play them on top of each other it starts at cem1 and stacks it till cem8.. or again i don't have this problem when dynamic allocation is off.
I will get back on this after i measured activity with my cheap multimeter!
i'm afraid it's something like the first one and something is wrong around voice8.
thanks for the help

Re: [prophet2000] Re: voice problem (need to know if this is CEM related)

2014-10-25 by berendnie@...

this is about a 2002 so no keyboard but yes i thought about that to.
good moove to disconect and reconect the cable right ? and measure them.

searching for a good way for cleaning ribbon cable holders now.. do you have an id?

in my 2000 i can see alot of oxidation on stuff on the pcb like that sample input volume trim pod.. and on the chassis/ case. also there are 3 types of cems with different batch numbers. but this one looks super clean on the inside, not that thats a good indication but ok.

you where thinking that preset's 8 -12 use differen data lines or ? again i'm guessing here with my limited skills!

and about the volume..

its a bit over half of what it should be. when i look at my input channel and gain my input so that its just about 0 db, voice 8 comes in about half of the vu meter in my daw.

now whats also maybe usefull to point out,is that the first 4 voices come in at about -5% from 0db then voice 5 at about -4%, then voice 6 at about -2%, than voice 7 is at 0db(this is the loudest) and 8 at -45% or so.. I hope you get what i mean.












Re: voice problem (need to know if this is CEM related)

2014-10-25 by berendnie@...

ok next thing i measured this.

in preset 8 to 12 in midi mode 4 with dynamic allocation off it only plays the first 4 voices.. so it actualy becomes a 4 voice.. this is wierd. :| in these presets and mode, i can only play a 4 note chord.
this is also when playing individual sound numbers.


1 to 7 does play all the cems and is 8 voice polyphonic so normal except for voice 8.

now i did another measurement on all cem.

and in 200 ac (or should i do this in 20 dc?) i measure

06.8 on the first 4 cems.. and

09.1 on the last 4

this is a bit of a wierd thing.. any id's ? thank you.. i know what to do from now!

cheers




Re: [prophet2000] Re: voice problem (need to know if this is CEM related)

2014-10-28 by James Ulibarri

Call this guy and pick his brain. I have talked to him before.

http://phoenix.craigslist.org/evl/msd/4645633025.html
Show quoted textHide quoted text
On Sat, Oct 25, 2014 at 1:32 PM, berendnie@...m [prophet2000] <prophet2000@yahoogroups.com> wrote:

ok next thing i measured this.


in preset 8 to 12 in midi mode 4 with dynamic allocation off it only plays the first 4 voices.. so it actualy becomes a 4 voice.. this is wierd. :| in these presets and mode, i can only play a 4 note chord.
this is also when playing individual sound numbers.


1 to 7 does play all the cems and is 8 voice polyphonic so normal except for voice 8.

now i did another measurement on all cem.

and in 200 ac (or should i do this in 20 dc?) i measure

06.8 on the first 4 cems.. and

09.1 on the last 4

this is a bit of a wierd thing.. any id's ? thank you.. i know what to do from now!

cheers





Re: [prophet2000] Re: voice problem (need to know if this is CEM related)

2014-10-29 by James Ulibarri

I have no idea, bud. I'll see if I can get his email address for you.

Hold on. Let me call him.

Call Forat, or email him too. Bruce@...


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On Wed, Oct 29, 2014 at 1:07 PM, berendnie@... [prophet2000] <prophet2000@yahoogroups.com> wrote:

i live in the netherlands.. if only he had an email adres.


but good moove to contact a repair center in the netherlands.

what do you think about this voice volume/level problem ?

easy repair? or ?

thank you


Re: [prophet2000] Re: voice problem (need to know if this is CEM related)

2014-10-29 by James Ulibarri

Also, try Grant.

grant@...

He's did some work on my 440 and knows the Pro One really well. He may have ran into this before on the 2000/2002.

Show quoted textHide quoted text
On Wed, Oct 29, 2014 at 1:25 PM, James Ulibarri <jamesulibarri@...> wrote:
info @ forat dot com

http://forat.com/

On Wed, Oct 29, 2014 at 1:22 PM, berendnie@... [prophet2000] <prophet2000@yahoogroups.com> wrote:

ok that would be nice!


forat ? bruce@... ?



Re: [prophet2000] Re: voice problem (need to know if this is CEM related)

2014-10-29 by James Ulibarri

jo?? who's jo? :)

anyways. The guy in Phoenix from that Craigslist advertisement is Dean from Five Star Engineering.
He said you can contact him at:

fivestareng@...


Good luck man.
Show quoted textHide quoted text
On Wed, Oct 29, 2014 at 1:43 PM, berendnie@... [prophet2000] <prophet2000@yahoogroups.com> wrote:

thanks jo! I will contact them and post my findings here.


hope this is a common problem.. we wil see.


Re: voice problem (need to know if this is CEM related)

2014-11-30 by berendnie@...

Hi!

it uses 4.0

for a moment i also thought it may be a firmware problem..

actualy i cant think of anything else that could cause the wierd behaviour(playing only the first 4 cems in the last couple of presets)

could be both firmware/bad eprom and control voltages defect.. right? :S

are there any known problems with 4.0 ?

i'm going to swap it with the 3.0 eprom in my prophet 2000.

also anyone out there with a image of the 4.3b firmware?


@ James Ulibarri

thanks again for you help.. had no luck with the people i emailed



Re: voice problem (need to know if this is CEM related)

2015-04-04 by jhn_llwllyn@...

Now that I have my p2000 up and running again (thanks, Paul!) I also find that I
have a problem with one of the voices...
Every eighth note I play is distorted/clipped and a bit hissy.
Which resistors need to be checked ?

Re: [prophet2000] Re: voice problem (need to know if this is CEM related)

2015-04-04 by paul le secq

On my P2000 I have found a dead resistor around the CEM IC.
You can check if you find the same value on each resistor around the CEM circuit.
If i remember correctly the very fist note you play us the Voice 1 CEM( from left to right )
If you put the P2000 on and count the note number you have the voice number that have a problem.
Check also the capacitors around the CEM.

Le 4 avr. 2015 à 15:07, jhn_llwllyn@... [prophet2000] a écrit :


Now that I have my p2000 up and running again (thanks, Paul!) I also find that I
have a problem with one of the voices...
Every eighth note I play is distorted/clipped and a bit hissy.
Which resistors need to be checked ?


Re: voice problem (need to know if this is CEM related)

2017-01-13 by berendnie@...

Alright, after years i finally got the knowledge to fix it :). it was a bad 2.2uf cap around the CEM (voice 8), it was probably something i should have considered from the start. But it's hard to pinpoint these things without a scope etc.

Anyways it works now :) and i'm very happy.. on a side note, i modded 8 external outs with some op amps on stripboard.. i might get some pcb's made. If anyone is interested in a pcb, should be something like 5,- ex shipping and unpopulated off-course. Please let me know.

Best,

Berend

Re: [prophet2000] Re: voice problem (need to know if this is CEM related)

2017-01-13 by charles copp

I for one would be interested in anything schemamtic you can share , and a board
too
Show quoted textHide quoted text
> ---------- Original Message ----------
> From: "berendnie@... [prophet2000]" <prophet2000@yahoogroups.com>
> Date: January 13, 2017 at 7:34 AM
> 
> 
> Alright, after years i finally got the knowledge to fix it :). it was a bad
> 2.2uf cap around the CEM (voice 8), it was probably something i should have
> considered from the start. But it's hard to pinpoint these things without a
> scope etc. 
> 
>  Anyways it works now :) and i'm very happy.. on a side note, i modded 8
> external outs with some op amps on stripboard.. i might get some pcb's made.
> If anyone is interested in a pcb, should be something like 5,- ex shipping and
> unpopulated off-course. Please let me know.
>  
> 
>  Best,
>  
> 
>  Berend

Re: [prophet2000] Re: voice problem (need to know if this is CEM related)

2017-01-14 by berendnie@...

Sure, its just the original op-amp circuit times 8 and because the factory made prophets that did not came with the output expansion have the summing amp on board. We can just ''split'' the signal, as in keep pin 12 of the cem seated. The board will have footprints for jacks etc. to minimise wiring.

Maybe shoot me a pm with your email adres. i'll probably start a topic on another forum to get somewhat more interrest.

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