Synth-DIY Yahoo! Groups Archives

Thread

Envelope problem, pops and "sensitive" pots (Crumar Composer)

2013-05-19 by Mikael

Hi all!

I bought a rare Crumar Composer I while ago but it has some problems. This synth has a mono synth section, a poly synth section, a organ section and a string section. All these sections can be combined. There is a separate output for every section and a main output. The separate outputs work but the volume for the main output and the main output itself do not work, could this be a problem in an amp-sircuit or something?

The problem I'm trying to look at now and ask about is an issue with the poly synth section. The problem is that the attack for the envelope is VERY slow, I can change the attack rate on the front panel pot but the fastest attack is about 15 seconds. Can anybody give me a hint where to look for the problem? Also there is a pop when I release the key on all keys it seems. The envelope of the poly-synth section is generated by a CEM3310 chip. There are also CEM3320 and 3330 chips on the poly section.

Last problem I'm having is that the release rate for the organ section is very sensitive, it seems that the effective range is about 30 degrees (1-1.5 on a scale from 1-10), if I turn the pot about 40 degrees I have a VERY long release time.

I would really like to get this synth in shape, it sounds so good and it's very rare, I think Crumar made only 500 of these.

Thanks in advance!

Re: [vintagesynthrepair] Envelope problem, pops and "sensitive" pots (Crumar Composer)

2013-05-19 by 65 Lotus

I'd do a full recap of the electrolytics and see what you get.

It may not be the most scientific approach, but...

Re: Envelope problem, pops and "sensitive" pots (Crumar Composer)

2013-05-20 by Mikael

Thanks for the answer. :) I have disassemled the synth completely and I'm in the process of mapping out all the capacitors I need. There are about 100 electrolytics in this synth, hopefully I will not break anything in the process of replacing. I will let you know how it went later. 

--- In vintagesynthrepair@yahoogroups.com, "65 Lotus" <Lotus@...> wrote:

Show quoted textHide quoted text

>
> I'd do a full recap of the electrolytics and see what you get.
> 
> It may not be the most scientific approach, but...
>

RE: [vintagesynthrepair] Re: Envelope problem, pops and "sensitive" pots (Crumar Composer)

2013-05-20 by Lorne Hammond

Photo the heck out of it before or during disassembly (I know too late) for
when you realize one went in backwards because you were tired and you can't
find the polarity mark on the board.  Also I would replace all power
regulators if you are going that intense as they take a lot of heat and wear
and tear.  Lorne in Canada

 

From: vintagesynthrepair@yahoogroups.com
[mailto:vintagesynthrepair@yahoogroups.com] On Behalf Of Mikael
Sent: Monday, May 20, 2013 5:52 AM
To: vintagesynthrepair@yahoogroups.com
Subject: [vintagesynthrepair] Re: Envelope problem, pops and "sensitive"
pots (Crumar Composer)

 

  

Thanks for the answer. :) I have disassemled the synth completely and I'm in
the process of mapping out all the capacitors I need. There are about 100
electrolytics in this synth, hopefully I will not break anything in the
process of replacing. I will let you know how it went later. 

--- In vintagesynthrepair@yahoogroups.com
<mailto:vintagesynthrepair%40yahoogroups.com> , "65 Lotus" <Lotus@...>
wrote:

Show quoted textHide quoted text

>
> I'd do a full recap of the electrolytics and see what you get.
> 
> It may not be the most scientific approach, but...
>

Re: Envelope problem, pops and "sensitive" pots (Crumar Composer)

2013-05-22 by Mikael

Hi,

I started with the power supply but gor problems already there. I replaced the voltage regulators. When I tested the power supply aftwerwards, the -12V rail shows -14.60V. What can cause this, is the new 7912 bad? When I remove power from the power supply the voltage of the 7912 decreases and stays on 12V for a while. Seems like the new 7912 can't handle the input voltage?

--- In vintagesynthrepair@yahoogroups.com, "Lorne Hammond" <lhammond@...> wrote:

Show quoted textHide quoted text

>
> Photo the heck out of it before or during disassembly (I know too late) for
> when you realize one went in backwards because you were tired and you can't
> find the polarity mark on the board.  Also I would replace all power
> regulators if you are going that intense as they take a lot of heat and wear
> and tear.  Lorne in Canada
> 
>  
> 
> From: vintagesynthrepair@yahoogroups.com
> [mailto:vintagesynthrepair@yahoogroups.com] On Behalf Of Mikael
> Sent: Monday, May 20, 2013 5:52 AM
> To: vintagesynthrepair@yahoogroups.com
> Subject: [vintagesynthrepair] Re: Envelope problem, pops and "sensitive"
> pots (Crumar Composer)
> 
>  
> 
>   
> 
> Thanks for the answer. :) I have disassemled the synth completely and I'm in
> the process of mapping out all the capacitors I need. There are about 100
> electrolytics in this synth, hopefully I will not break anything in the
> process of replacing. I will let you know how it went later. 
> 
> --- In vintagesynthrepair@yahoogroups.com
> <mailto:vintagesynthrepair%40yahoogroups.com> , "65 Lotus" <Lotus@>
> wrote:
> >
> > I'd do a full recap of the electrolytics and see what you get.
> > 
> > It may not be the most scientific approach, but...
> >
>

Re: Envelope problem, pops and "sensitive" pots (Crumar Composer)

2013-05-22 by Mikael

And thank you for the help Lorne, I have taken a lot of photos from different angles so I can see every capacitor.

--- In vintagesynthrepair@yahoogroups.com, "Lorne Hammond" <lhammond@...> wrote:

Show quoted textHide quoted text

>
> Photo the heck out of it before or during disassembly (I know too late) for
> when you realize one went in backwards because you were tired and you can't
> find the polarity mark on the board.  Also I would replace all power
> regulators if you are going that intense as they take a lot of heat and wear
> and tear.  Lorne in Canada
> 
>  
> 
> From: vintagesynthrepair@yahoogroups.com
> [mailto:vintagesynthrepair@yahoogroups.com] On Behalf Of Mikael
> Sent: Monday, May 20, 2013 5:52 AM
> To: vintagesynthrepair@yahoogroups.com
> Subject: [vintagesynthrepair] Re: Envelope problem, pops and "sensitive"
> pots (Crumar Composer)
> 
>  
> 
>   
> 
> Thanks for the answer. :) I have disassemled the synth completely and I'm in
> the process of mapping out all the capacitors I need. There are about 100
> electrolytics in this synth, hopefully I will not break anything in the
> process of replacing. I will let you know how it went later. 
> 
> --- In vintagesynthrepair@yahoogroups.com
> <mailto:vintagesynthrepair%40yahoogroups.com> , "65 Lotus" <Lotus@>
> wrote:
> >
> > I'd do a full recap of the electrolytics and see what you get.
> > 
> > It may not be the most scientific approach, but...
> >
>

Re: [vintagesynthrepair] Envelope problem, pops and "sensitive" pots (Crumar Composer)

2013-05-23 by Hugh Vartanian

On the regulator problem, what is the input voltage to the 7912? More importantly, what are you using for a ground reference? Measure right at the regulator terminals, in and out, to its ground pin. Neg 14.xx volts might be a result of a loose ground floating positive a bit when power is applied. Remove power and the positive current draw and the 'ground' makes its way back to ground..... Just a thought.
-Hugh

Show quoted textHide quoted text

On May 19, 2013 5:36 AM, "Mikael" <wmc_mick@...> wrote:

Hi all!

I bought a rare Crumar Composer I while ago but it has some problems. This synth has a mono synth section, a poly synth section, a organ section and a string section. All these sections can be combined. There is a separate output for every section and a main output. The separate outputs work but the volume for the main output and the main output itself do not work, could this be a problem in an amp-sircuit or something?

The problem I'm trying to look at now and ask about is an issue with the poly synth section. The problem is that the attack for the envelope is VERY slow, I can change the attack rate on the front panel pot but the fastest attack is about 15 seconds. Can anybody give me a hint where to look for the problem? Also there is a pop when I release the key on all keys it seems. The envelope of the poly-synth section is generated by a CEM3310 chip. There are also CEM3320 and 3330 chips on the poly section.

Last problem I'm having is that the release rate for the organ section is very sensitive, it seems that the effective range is about 30 degrees (1-1.5 on a scale from 1-10), if I turn the pot about 40 degrees I have a VERY long release time.

I would really like to get this synth in shape, it sounds so good and it's very rare, I think Crumar made only 500 of these.

Thanks in advance!

Re: Envelope problem, pops and "sensitive" pots (Crumar Composer)

2013-05-24 by Mikael

The input voltage to the 7912 regulator is -22.2V. I replaced the new regulators with the old ones (made by Texas Instruments), I now have -12.25V as output for the 7912. I measured the voltages at the pins. The new 7912 was a L7912ACV. 

--- In vintagesynthrepair@yahoogroups.com, Hugh Vartanian <bouncev@...> wrote:

Show quoted textHide quoted text

>
> On the regulator problem, what is the input voltage to the 7912?   More
> importantly, what are you using for a ground reference?  Measure right at
> the regulator terminals, in and out, to its ground pin.  Neg 14.xx volts
> might be a result of a loose ground floating positive a bit when power is
> applied.  Remove power and the positive current draw  and the 'ground'
> makes its way back to ground.....  Just a thought.
> -Hugh
> On May 19, 2013 5:36 AM, "Mikael" <wmc_mick@...> wrote:
> 
> > **
> >
> >
> > Hi all!
> >
> > I bought a rare Crumar Composer I while ago but it has some problems. This
> > synth has a mono synth section, a poly synth section, a organ section and a
> > string section. All these sections can be combined. There is a separate
> > output for every section and a main output. The separate outputs work but
> > the volume for the main output and the main output itself do not work,
> > could this be a problem in an amp-sircuit or something?
> >
> > The problem I'm trying to look at now and ask about is an issue with the
> > poly synth section. The problem is that the attack for the envelope is VERY
> > slow, I can change the attack rate on the front panel pot but the fastest
> > attack is about 15 seconds. Can anybody give me a hint where to look for
> > the problem? Also there is a pop when I release the key on all keys it
> > seems. The envelope of the poly-synth section is generated by a CEM3310
> > chip. There are also CEM3320 and 3330 chips on the poly section.
> >
> > Last problem I'm having is that the release rate for the organ section is
> > very sensitive, it seems that the effective range is about 30 degrees
> > (1-1.5 on a scale from 1-10), if I turn the pot about 40 degrees I have a
> > VERY long release time.
> >
> > I would really like to get this synth in shape, it sounds so good and it's
> > very rare, I think Crumar made only 500 of these.
> >
> > Thanks in advance!
> >
> >  
> >
>

Re: [vintagesynthrepair] Re: Envelope problem, pops and "sensitive" pots (Crumar Composer)

2013-05-27 by Hugh Vartanian

Sounds like you have solved the regulator problem; no idea why the other part didn't work, assuming it was installed ok. Strange to have a defective part like that.

I deleted the rest of the thread; post a link to the schematics if you still need some thoughts on the other issues.

Hugh

Show quoted textHide quoted text

On Fri, May 24, 2013 at 5:14 AM, Mikael <wmc_mick@...> wrote:

The input voltage to the 7912 regulator is -22.2V. I replaced the new regulators with the old ones (made by Texas Instruments), I now have -12.25V as output for the 7912. I measured the voltages at the pins. The new 7912 was a L7912ACV.

--- In vintagesynthrepair@yahoogroups.com, Hugh Vartanian wrote:
>
> On the regulator problem, what is the input voltage to the 7912? More
> importantly, what are you using for a ground reference? Measure right at
> the regulator terminals, in and out, to its ground pin. Neg 14.xx volts
> might be a result of a loose ground floating positive a bit when power is
> applied. Remove power and the positive current draw and the 'ground'
> makes its way back to ground..... Just a thought.
> -Hugh
> On May 19, 2013 5:36 AM, "Mikael" >
> > **
> >
> >
> > Hi all!
> >
> > I bought a rare Crumar Composer I while ago but it has some problems. This
> > synth has a mono synth section, a poly synth section, a organ section and a
> > string section. All these sections can be combined. There is a separate
> > output for every section and a main output. The separate outputs work but
> > the volume for the main output and the main output itself do not work,
> > could this be a problem in an amp-sircuit or something?
> >
> > The problem I'm trying to look at now and ask about is an issue with the
> > poly synth section. The problem is that the attack for the envelope is VERY
> > slow, I can change the attack rate on the front panel pot but the fastest
> > attack is about 15 seconds. Can anybody give me a hint where to look for
> > the problem? Also there is a pop when I release the key on all keys it
> > seems. The envelope of the poly-synth section is generated by a CEM3310
> > chip. There are also CEM3320 and 3330 chips on the poly section.
> >
> > Last problem I';m having is that the release rate for the organ section is
> > very sensitive, it seems that the effective range is about 30 degrees
> > (1-1.5 on a scale from 1-10), if I turn the pot about 40 degrees I have a
> > VERY long release time.
> >
> > I would really like to get this synth in shape, it sounds so good and it's
> > very rare, I think Crumar made only 500 of these.
> >
> > Thanks in advance!
> >
> >
>; >
>

Re: Envelope problem, pops and "sensitive" pots (Crumar Composer)

2013-05-27 by Mikael

Yep, really strange I have to agree. It was connected correctly and it was working correctly only in the -13-17V range.

I would love to find the schematics for this synth but seems like they are not available (this synth is quite rare).

Thanks,
Mikael

--- In vintagesynthrepair@yahoogroups.com, Hugh Vartanian <bouncev@...> wrote:

Show quoted textHide quoted text

>
> Sounds like you have solved the regulator problem; no idea why the other
> part didn't work, assuming it was installed ok.  Strange to have a
> defective part like that.
> 
> I deleted the rest of the thread; post a link to the schematics if you
> still need some thoughts on the other issues.
> 
> Hugh
> 
> 
> On Fri, May 24, 2013 at 5:14 AM, Mikael <wmc_mick@...> wrote:
> 
> > **
> >
> >
> > The input voltage to the 7912 regulator is -22.2V. I replaced the new
> > regulators with the old ones (made by Texas Instruments), I now have
> > -12.25V as output for the 7912. I measured the voltages at the pins. The
> > new 7912 was a L7912ACV.
> >
> > --- In vintagesynthrepair@yahoogroups.com, Hugh Vartanian <bouncev@>
> > wrote:
> > >
> > > On the regulator problem, what is the input voltage to the 7912? More
> > > importantly, what are you using for a ground reference? Measure right at
> > > the regulator terminals, in and out, to its ground pin. Neg 14.xx volts
> > > might be a result of a loose ground floating positive a bit when power is
> > > applied. Remove power and the positive current draw and the 'ground'
> > > makes its way back to ground..... Just a thought.
> > > -Hugh
> > > On May 19, 2013 5:36 AM, "Mikael" <wmc_mick@> wrote:
> > >
> > > > **
> > > >
> > > >
> > > > Hi all!
> > > >
> > > > I bought a rare Crumar Composer I while ago but it has some problems.
> > This
> > > > synth has a mono synth section, a poly synth section, a organ section
> > and a
> > > > string section. All these sections can be combined. There is a separate
> > > > output for every section and a main output. The separate outputs work
> > but
> > > > the volume for the main output and the main output itself do not work,
> > > > could this be a problem in an amp-sircuit or something?
> > > >
> > > > The problem I'm trying to look at now and ask about is an issue with
> > the
> > > > poly synth section. The problem is that the attack for the envelope is
> > VERY
> > > > slow, I can change the attack rate on the front panel pot but the
> > fastest
> > > > attack is about 15 seconds. Can anybody give me a hint where to look
> > for
> > > > the problem? Also there is a pop when I release the key on all keys it
> > > > seems. The envelope of the poly-synth section is generated by a CEM3310
> > > > chip. There are also CEM3320 and 3330 chips on the poly section.
> > > >
> > > > Last problem I'm having is that the release rate for the organ section
> > is
> > > > very sensitive, it seems that the effective range is about 30 degrees
> > > > (1-1.5 on a scale from 1-10), if I turn the pot about 40 degrees I
> > have a
> > > > VERY long release time.
> > > >
> > > > I would really like to get this synth in shape, it sounds so good and
> > it's
> > > > very rare, I think Crumar made only 500 of these.
> > > >
> > > > Thanks in advance!
> > > >
> > > >
> > > >
> > >
> >
> >  
> >
>

Re: Envelope problem, pops and "sensitive" pots (Crumar Composer)

2013-06-11 by Mikael

Hi again!

I have now replaced all the electrolytics in the Crumar Composer. I also cleaned the pots and replaced an MC1741C op-amp in the end stage. The main output is now working. :) Quite a few of the electrolytics had leaked so I guess it was good to replace them all. 

The sound of the mono-synth, organ and string section is now clean. Some problems remain, mainly the envelope on the poly-synth section. The envelope and filter of the poly-synth is controlled by the same pots as the mono-synth, so it's possible to use the pots for one section at a time. The envelope and filter work great for the mono-section.

Problems with the poly-section:
- Attack at lowest is slow, and seems to vary betwwen 1 second and 10 seconds (maybe due to warm up or something).
- At the start of a note, there is sometimes a "pop"-sound and always when I release the key or when the attack has reached maximum (then sound stops).
- Sustain level is always zero (the sustain pot has no effect).
- The decay setting works sometimes and the release seem to work normally.
- The filter cutoff is always quite high, I can change it with the pot but the lowest cutoff frequency is still quite high.

I have uploaded a photo of the poly-synth board to help troubleshooting. Maybe some of you can spot components that are likely to fail etc.

https://dl.dropboxusercontent.com/u/26435295/crumar_p-975.jpg

The envelope is controlled by a CEM3310, and the filter is a CEM3320 and the VCA is a CEM3330. The mono synth is controlled by another set of the same CEM chips. There are trimmers by the CEM chips for calibrating, but I have no idea which trimmer does what. I guess I could replace the CEM chips from the mono-section but I'm afraid there is some other problem that could do damage to those chips. Anybody have any of these CEM-chips for sale btw?

About the op-amps (MC1741 and MC1458). Can I replace the MC1458s with low noise alternatives like NE5532?

As always, I'm greatful for any help!

As a sidenote, I bought a proper desoldering gun. Using that the recapping was a walk in the park, a long walk but.. I feel it was worth buying the desoldering gun only for this job. :)
 

--- In vintagesynthrepair@yahoogroups.com, "Mikael" <wmc_mick@...> wrote:

Show quoted textHide quoted text

>
> Hi all!
> 
> I bought a rare Crumar Composer I while ago but it has some problems. This synth has a mono synth section, a poly synth section, a organ section and a string section. All these sections can be combined. There is a separate output for every section and a main output. The separate outputs work but the volume for the main output and the main output itself do not work, could this be a problem in an amp-sircuit or something?
> 
> The problem I'm trying to look at now and ask about is an issue with the poly synth section. The problem is that the attack for the envelope is VERY slow, I can change the attack rate on the front panel pot but the fastest attack is about 15 seconds. Can anybody give me a hint where to look for the problem? Also there is a pop when I release the key on all keys it seems. The envelope of the poly-synth section is generated by a CEM3310 chip. There are also CEM3320 and 3330 chips on the poly section.
> 
> Last problem I'm having is that the release rate for the organ section is very sensitive, it seems that the effective range is about 30 degrees (1-1.5 on a scale from 1-10), if I turn the pot about 40 degrees I have a VERY long release time.
> 
> I would really like to get this synth in shape, it sounds so good and it's very rare, I think Crumar made only 500 of these.
> 
> Thanks in advance!
>

Re: Envelope problem, pops and "sensitive" pots (Crumar Composer)

2013-06-17 by Mikael

I found a broken trace (at a connector) that stopped the sutain-signal arriving at the CEM3310. The brake was impossible to see, even with a magnifying glass. I also managed to fix the problem with the attack-signal. The socket for the CEM3310 was bad and I replaced it. ALL chips on this synth are socketed and it seems the sockets are not so good anymore, I suspect the remaining problems are likely due to bad sockets also. 

Maybe if somebody with more experience would have seen the synth they had instantly suspected the sockets, but now I now, I just also read tips about repairing arcade machines and there they said that edge connectors and ic sockets are one of the most common causes for failures.

I will update my progress later in hope that it helps somebody else.

--- In vintagesynthrepair@yahoogroups.com, "Mikael" <wmc_mick@...> wrote:

Show quoted textHide quoted text

>
> Hi again!
> 
> I have now replaced all the electrolytics in the Crumar Composer. I also cleaned the pots and replaced an MC1741C op-amp in the end stage. The main output is now working. :) Quite a few of the electrolytics had leaked so I guess it was good to replace them all. 
> 
> The sound of the mono-synth, organ and string section is now clean. Some problems remain, mainly the envelope on the poly-synth section. The envelope and filter of the poly-synth is controlled by the same pots as the mono-synth, so it's possible to use the pots for one section at a time. The envelope and filter work great for the mono-section.
> 
> Problems with the poly-section:
> - Attack at lowest is slow, and seems to vary betwwen 1 second and 10 seconds (maybe due to warm up or something).
> - At the start of a note, there is sometimes a "pop"-sound and always when I release the key or when the attack has reached maximum (then sound stops).
> - Sustain level is always zero (the sustain pot has no effect).
> - The decay setting works sometimes and the release seem to work normally.
> - The filter cutoff is always quite high, I can change it with the pot but the lowest cutoff frequency is still quite high.
> 
> I have uploaded a photo of the poly-synth board to help troubleshooting. Maybe some of you can spot components that are likely to fail etc.
> 
> https://dl.dropboxusercontent.com/u/26435295/crumar_p-975.jpg
> 
> The envelope is controlled by a CEM3310, and the filter is a CEM3320 and the VCA is a CEM3330. The mono synth is controlled by another set of the same CEM chips. There are trimmers by the CEM chips for calibrating, but I have no idea which trimmer does what. I guess I could replace the CEM chips from the mono-section but I'm afraid there is some other problem that could do damage to those chips. Anybody have any of these CEM-chips for sale btw?
> 
> About the op-amps (MC1741 and MC1458). Can I replace the MC1458s with low noise alternatives like NE5532?
> 
> As always, I'm greatful for any help!
> 
> As a sidenote, I bought a proper desoldering gun. Using that the recapping was a walk in the park, a long walk but.. I feel it was worth buying the desoldering gun only for this job. :)
>  
> 
> --- In vintagesynthrepair@yahoogroups.com, "Mikael" <wmc_mick@> wrote:
> >
> > Hi all!
> > 
> > I bought a rare Crumar Composer I while ago but it has some problems. This synth has a mono synth section, a poly synth section, a organ section and a string section. All these sections can be combined. There is a separate output for every section and a main output. The separate outputs work but the volume for the main output and the main output itself do not work, could this be a problem in an amp-sircuit or something?
> > 
> > The problem I'm trying to look at now and ask about is an issue with the poly synth section. The problem is that the attack for the envelope is VERY slow, I can change the attack rate on the front panel pot but the fastest attack is about 15 seconds. Can anybody give me a hint where to look for the problem? Also there is a pop when I release the key on all keys it seems. The envelope of the poly-synth section is generated by a CEM3310 chip. There are also CEM3320 and 3330 chips on the poly section.
> > 
> > Last problem I'm having is that the release rate for the organ section is very sensitive, it seems that the effective range is about 30 degrees (1-1.5 on a scale from 1-10), if I turn the pot about 40 degrees I have a VERY long release time.
> > 
> > I would really like to get this synth in shape, it sounds so good and it's very rare, I think Crumar made only 500 of these.
> > 
> > Thanks in advance!
> >
>

RE: Envelope problem, pops and "sensitive" pots (Crumar Composer)

2013-10-24 by <wmc_mick@...>

New sockets fixed some problems. One socket even had two legs broken. The biggest problem now is the ADSR and other controls for the poly synth section. Can you tell me if it's safe to connect a 5V signal directly to the input controlling attack on the CEM ADSR chip and also to the input controlling resonance amount on the CEM filter chip? The resonance level is now fluctuating a lot, so it's seems like either the filter chip is getting a fluctuating signal or the filter chip has a problem. Same goes for the ADSR chip. Greatful for any advice!

---In vintagesynthrepair@yahoogroups.com, <wmc_mick@...> wrote:

I found a broken trace (at a connector) that stopped the sutain-signal arriving at the CEM3310. The brake was impossible to see, even with a magnifying glass. I also managed to fix the problem with the attack-signal. The socket for the CEM3310 was bad and I replaced it. ALL chips on this synth are socketed and it seems the sockets are not so good anymore, I suspect the remaining problems are likely due to bad sockets also.

Maybe if somebody with more experience would have seen the synth they had instantly suspected the sockets, but now I now, I just also read tips about repairing arcade machines and there they said that edge connectors and ic sockets are one of the most common causes for failures.

I will update my progress later in hope that it helps somebody else.

Show quoted textHide quoted text

--- In vintagesynthrepair@yahoogroups.com, "Mikael" <wmc_mick@...> wrote:
>
> Hi again!
>
> I have now replaced all the electrolytics in the Crumar Composer. I also cleaned the pots and replaced an MC1741C op-amp in the end stage. The main output is now working. :) Quite a few of the electrolytics had leaked so I guess it was good to replace them all.
>
> The sound of the mono-synth, organ and string section is now clean. Some problems remain, mainly the envelope on the poly-synth section. The envelope and filter of the poly-synth is controlled by the same pots as the mono-synth, so it's possible to use the pots for one section at a time. The envelope and filter work great for the mono-section.
>
> Problems with the poly-section:
> - Attack at lowest is slow, and seems to vary betwwen 1 second and 10 seconds (maybe due to warm up or something).
> - At the start of a note, there is sometimes a "pop"-sound and always when I release the key or when the attack has reached maximum (then sound stops).
> - Sustain level is always zero (the sustain pot has no effect).
> - The decay setting works sometimes and the release seem to work normally.
> - The filter cutoff is always quite high, I can change it with the pot but the lowest cutoff frequency is still quite high.
>
> I have uploaded a photo of the poly-synth board to help troubleshooting. Maybe some of you can spot components that are likely to fail etc.
>
> https://dl.dropboxusercontent.com/u/26435295/crumar_p-975.jpg
>
> The envelope is controlled by a CEM3310, and the filter is a CEM3320 and the VCA is a CEM3330. The mono synth is controlled by another set of the same CEM chips. There are trimmers by the CEM chips for calibrating, but I have no idea which trimmer does what. I guess I could replace the CEM chips from the mono-section but I'm afraid there is some other problem that could do damage to those chips. Anybody have any of these CEM-chips for sale btw?
>
> About the op-amps (MC1741 and MC1458). Can I replace the MC1458s with low noise alternatives like NE5532?
>
> As always, I'm greatful for any help!
>
> As a sidenote, I bought a proper desoldering gun. Using that the recapping was a walk in the park, a long walk but.. I feel it was worth buying the desoldering gun only for this job. :)
>
>
> --- In vintagesynthrepair@yahoogroups.com, "Mikael" <wmc_mick@> wrote:
> >
> > Hi all!
> >
> > I bought a rare Crumar Composer I while ago but it has some problems. This synth has a mono synth section, a poly synth section, a organ section and a string section. All these sections can be combined. There is a separate output for every section and a main output. The separate outputs work but the volume for the main output and the main output itself do not work, could this be a problem in an amp-sircuit or something?
> >
> > The problem I'm trying to look at now and ask about is an issue with the poly synth section. The problem is that the attack for the envelope is VERY slow, I can change the attack rate on the front panel pot but the fastest attack is about 15 seconds. Can anybody give me a hint where to look for the problem? Also there is a pop when I release the key on all keys it seems. The envelope of the poly-synth section is generated by a CEM3310 chip. There are also CEM3320 and 3330 chips on the poly section.
> >
> > Last problem I'm having is that the release rate for the organ section is very sensitive, it seems that the effective range is about 30 degrees (1-1.5 on a scale from 1-10), if I turn the pot about 40 degrees I have a VERY long release time.
> >
> > I would really like to get this synth in shape, it sounds so good and it's very rare, I think Crumar made only 500 of these.
> >
> > Thanks in advance!
> >
>

RE: Envelope problem, pops and "sensitive" pots (Crumar Composer)

2013-10-25 by <sounddoctorin@...>

I did a lot of documentation on the instrument AND have one here for sale if anyone is interested. They are fabulous. I did the original videos on the machine after taking a chance on one from ebay and fixing it up. Pleasant surprise :-)

---In vintagesynthrepair@yahoogroups.com, <wmc_mick@...> wrote:

Show quoted textHide quoted text

--- In vintagesynthrepair@yahoogroups.com, "Mikael" <wmc_mick@...> wrote:
>
> Hi again!
>
> I have now replaced all the electrolytics in the Crumar Composer. I also cleaned the pots and replaced an MC1741C op-amp in the end stage. The main output is now working. :) Quite a few of the electrolytics had leaked so I guess it was good to replace them all.
>
> The sound of the mono-synth, organ and string section is now clean. Some problems remain, mainly the envelope on the poly-synth section. The envelope and filter of the poly-synth is controlled by the same pots as the mono-synth, so it's possible to use the pots for one section at a time. The envelope and filter work great for the mono-section.
>
> Problems with the poly-section:
> - Attack at lowest is slow, and seems to vary betwwen 1 second and 10 seconds (maybe due to warm up or something).
> - At the start of a note, there is sometimes a "pop"-sound and always when I release the key or when the attack has reached maximum (then sound stops).
> - Sustain level is always zero (the sustain pot has no effect).
> - The decay setting works sometimes and the release seem to work normally.
> - The filter cutoff is always quite high, I can change it with the pot but the lowest cutoff frequency is still quite high.
>
> I have uploaded a photo of the poly-synth board to help troubleshooting. Maybe some of you can spot components that are likely to fail etc.
>
> https://dl.dropboxusercontent.com/u/26435295/crumar_p-975.jpg
>
> The envelope is controlled by a CEM3310, and the filter is a CEM3320 and the VCA is a CEM3330. The mono synth is controlled by another set of the same CEM chips. There are trimmers by the CEM chips for calibrating, but I have no idea which trimmer does what. I guess I could replace the CEM chips from the mono-section but I'm afraid there is some other problem that could do damage to those chips. Anybody have any of these CEM-chips for sale btw?
>
> About the op-amps (MC1741 and MC1458). Can I replace the MC1458s with low noise alternatives like NE5532?
>
> As always, I'm greatful for any help!
>
> As a sidenote, I bought a proper desoldering gun. Using that the recapping was a walk in the park, a long walk but.. I feel it was worth buying the desoldering gun only for this job. :)
>
>
> --- In vintagesynthrepair@yahoogroups.com, "Mikael" <wmc_mick@> wrote:
> >
> > Hi all!
> >
> > I bought a rare Crumar Composer I while ago but it has some problems. This synth has a mono synth section, a poly synth section, a organ section and a string section. All these sections can be combined. There is a separate output for every section and a main output. The separate outputs work but the volume for the main output and the main output itself do not work, could this be a problem in an amp-sircuit or something?
> >
> > The problem I'm trying to look at now and ask about is an issue with the poly synth section. The problem is that the attack for the envelope is VERY slow, I can change the attack rate on the front panel pot but the fastest attack is about 15 seconds. Can anybody give me a hint where to look for the problem? Also there is a pop when I release the key on all keys it seems. The envelope of the poly-synth section is generated by a CEM3310 chip. There are also CEM3320 and 3330 chips on the poly section.
> >
> > Last problem I'm having is that the release rate for the organ section is very sensitive, it seems that the effective range is about 30 degrees (1-1.5 on a scale from 1-10), if I turn the pot about 40 degrees I have a VERY long release time.
> >
> > I would really like to get this synth in shape, it sounds so good and it's very rare, I think Crumar made only 500 of these.
> >
> > Thanks in advance!
> >
>

Korg Delta Adsr /Release problem. More info.

2013-10-27 by plat@simnet.is

Having problems getting the adsr to work properly on my Korg Delta.
No proper techs here in Iceland so I have got to fix things myself.

On a working Delta the VCO itself will have pretty long release independant of the ADSR.
I am missing this release from the VCO itself.

When I disconnect the VCO from the filter/vca board the release comes back on the VCO.
As soon as I connect the VCO to the filter/Vca the VCO release is cutoff.
Obviously this affects both the Synth and String Release as there is no signal to release.

The problem is therefore on the filter/Vca Board...is seems.
I assume its a problem with the "Release Control" signal sent to the VCO?
On a healthy Delta I would have a nice trigger signal coming in to the Vco via the "Release Control going to the vca board-transistor-IC 324 , but on mine there is nothing?

So far I have checked the 324 ,tl 072 and the 4007 , all seem to be working properly although I am not getting the "Release Control" signal from the 324?
Can anyone tell me the function of each IC / 324 / 072 / An 6551 and the 4007 ?

I am kind of confused as to how the ADSR works on this synth , probably something to do with its "polyphonic" nature.

The envelope seems to work on the filter an the filter is working perfectly.
The noise however goes straight through the VCA without any envelope applied to it, which is strange?

Havent gotten much further so far.

If anyone could give me any pointers as to where/how to trace this properly?
I am a novice but I have a scope , the schematics and and I am eager to learn.

Its driving me slightly nuts at the moment. :P

Thanks
Arnar

RE: RE: Envelope problem, pops and "sensitive" pots (Crumar Composer)

2013-10-30 by <wmc_mick@...>

I found your documentation when I started repairing my Crumar Composer, thanks a lot for that, it helped me a lot. :) I have also watched some of your repair videos, those have also helped me.

I have put a lot of hours into this synth, even replacing all caps, but it sounds SO good and is very inspiring so I think it's worth it. It had a lot of problems, now there's just a few left (unable to select one of the string presets and the organ presets sometimes all light up). Those problems are to bad solder joints I think, I have found several bad solder joints and replaced ic sockets since some were bad.

I'm still a beginner with synth repair but by repairing this synth I have learned a lot, not finding a schematic has made it harder.

Vintage Synth Repair

Envelope problem, pops and "sensitive" pots (Crumar Composer)

Envelope problem, pops and "sensitive" pots (Crumar Composer)

Re: [vintagesynthrepair] Envelope problem, pops and "sensitive" pots (Crumar Composer)

Re: Envelope problem, pops and "sensitive" pots (Crumar Composer)

RE: [vintagesynthrepair] Re: Envelope problem, pops and "sensitive" pots (Crumar Composer)

Re: Envelope problem, pops and "sensitive" pots (Crumar Composer)

Re: Envelope problem, pops and "sensitive" pots (Crumar Composer)

Re: [vintagesynthrepair] Envelope problem, pops and "sensitive" pots (Crumar Composer)

Re: Envelope problem, pops and "sensitive" pots (Crumar Composer)

Re: [vintagesynthrepair] Re: Envelope problem, pops and "sensitive" pots (Crumar Composer)

Re: Envelope problem, pops and "sensitive" pots (Crumar Composer)

Re: Envelope problem, pops and "sensitive" pots (Crumar Composer)

Re: Envelope problem, pops and "sensitive" pots (Crumar Composer)

RE: Envelope problem, pops and "sensitive" pots (Crumar Composer)

RE: Envelope problem, pops and "sensitive" pots (Crumar Composer)

Korg Delta Adsr /Release problem. More info.

RE: RE: Envelope problem, pops and "sensitive" pots (Crumar Composer)

Move to quarantaine