Vintage Synth Repair

I have a Crumar Trilogy with some problems... 

First of all I need a CEM 3330 and a CEM 3320.
One voice board is dead due to these chips. Maybe also the CEM 3310 is dead, I�m not sure at the moment. Can anybody help?

Next there is a another strange problem:
When I switch on the unit, after appr. 1-2 minutes there is a hum, that can be heard best in the string section and in the synth section. If I only play the organ section I don�t hear it. 

The LFO speed is influencing the hum. Very nice effect... 

If I pull a few of the voice cards, it seems to be, that the hum is lower in volume, and that it is starting after 3-4 minutes after I switched on the machine.

What is the problem here?? PSU? Or anything else?

>>Next there is a another strange problem:
> When I switch on the unit, after appr. 1-2 minutes there is a hum, that can be heard best in the string section and in the synth section. If I only play the organ section I don´t hear it. 
> 
> The LFO speed is influencing the hum. Very nice effect... 
> 
> If I pull a few of the voice cards, it seems to be, that the hum is lower in volume, and that it is starting after 3-4 minutes after I switched on the machine.
> 
> What is the problem here?? PSU? Or anything else?<<

are there power regulation components on any of the voice cards? I don't know the trilogy, but if there are regs or smoothing caps local to each card, these could need replacing. the effect you describe sounds like something loading the supply beyond it's capacity to remove mains hum from the dc. are there any tantalum caps in there? maybe have a feel of the tops of the chips, see if anything's getting warm...

duncan.

Whenever I encounter hum I check for loose ground connections.

Take care
Arnar

----- Upprunalegt skeyti -----
Frá: "duncan" <ferrograph@...>
Til: vintagesynthrepair@yahoogroups.com

Sent: Mánudagur, 16. nóvember, 2009 20:16:16 GMT +00:00 Monrovia
Efni: [vintagesynthrepair] Re: Crumar Trilogy repair






>>Next there is a another strange problem: 
> When I switch on the unit, after appr. 1-2 minutes there is a hum, that can be heard best in the string section and in the synth section. If I only play the organ section I don´t hear it. 
> 
> The LFO speed is influencing the hum. Very nice effect... 
> 
> If I pull a few of the voice cards, it seems to be, that the hum is lower in volume, and that it is starting after 3-4 minutes after I switched on the machine. 
> 
> What is the problem here?? PSU? Or anything else?<< 

are there power regulation components on any of the voice cards? I don't know the trilogy, but if there are regs or smoothing caps local to each card, these could need replacing. the effect you describe sounds like something loading the supply beyond it's capacity to remove mains hum from the dc. are there any tantalum caps in there? maybe have a feel of the tops of the chips, see if anything's getting warm... 

duncan.

Do you have several pieces of equipment plugged into the same outlet?  This might be causing a ground loop that increases in strength after the equipment has been powered on for a short period of time.  Does the hum remain when no voices are being sounded?  More likely a ground loop.  Try plugging the other equipment into a different outlet across the room with an extention cord. 
 Is the hum only present when certain instrument voices are played and is not present when other voices are played?  More likely to be a voice programming issue.  The organ voice is most likely of all the voices to be a sine wave (or close).  A hum is usually a 120 Hz sine wave.  That is about the B or B flat in the octave below middle C.  Does playing that B flat note on organ voice sound either louder or softer than the other notes?  Does that B flat have a 'LFO-type' waving sound that the other organ tones don't have?  All signs of a ground loop.
  Do you have an oscilloscope?  Do you have a sound-card oscilloscope program?  Download a scope program and feed the hum from the synth into the PC audio line input.  Run the scope program and see if the hum actually is 120 Hz.  If not, it's a synth hardware issue. If it is, then it is a synth power supply problem or a ground loop.

AFAIK a cause for ground loop is using of different outlets in the  
room (different line circuits). Using only one outlet for all  
equipment can hardly be a reason for such ground loop.

Ground loop can be also avoided by ground lift on some equipment but  
it can be dangerous.

I had small hum problem in Japan because here grounding (earthing) is  
missing on power outlets. So I had to make my own grounding and now  
it's OK.

Frequency of hum caused by ground loops depends on net frequency, it  
can be 60 (USA} or 50 Hz (Europe}, Japan has 50 or 60 in different  
regions. Your 120 Hz looks like the second harmonics.

Daniel Forro

On 17 Nov 2009, at 10:29 AM, Alan Probandt wrote:

> Do you have several pieces of equipment plugged into the same  
> outlet?  This might be causing a ground loop that increases in  
> strength after the equipment has been powered on for a short period  
> of time.  Does the hum remain when no voices are being sounded?   
> More likely a ground loop.  Try plugging the other equipment into a  
> different outlet across the room with an extention cord.
>  Is the hum only present when certain instrument voices are played  
> and is not present when other voices are played?  More likely to be  
> a voice programming issue.  The organ voice is most likely of all  
> the voices to be a sine wave (or close).  A hum is usually a 120 Hz  
> sine wave.  That is about the B or B flat in the octave below  
> middle C.  Does playing that B flat note on organ voice sound  
> either louder or softer than the other notes?  Does that B flat  
> have a 'LFO-type' waving sound that the other organ tones don't  
> have?  All signs of a ground loop.
>   Do you have an oscilloscope?  Do you have a sound-card  
> oscilloscope program?  Download a scope program and feed the hum  
> from the synth into the PC audio line input.  Run the scope program  
> and see if the hum actually is 120 Hz.  If not, it's a synth  
> hardware issue. If it is, then it is a synth power supply problem  
> or a ground loop.

-If you can take the "ground loop" out of the equation, the most likely cause is power supply filtering capacitors that have gone dry  and arent doing what theyre supposed to.

I see this as a regular thing here in my shop.

Caps are easy to get and fairly cheap and replacing them drops troubleshooting time way down

Just doing that may make your troubles flee

Scott in Burrrrrrrr-mont

Re: Crumar Trilogy repair

It is not a normal ground loop problem. The hum seems to be directly related to
the number of voice cards in the machine. So I think, the power supply could be
the problem.

I think, a recapping of the power supply should be the way to go.

On the other hand, there is a tantalum on every voice card. I think, changing
the tantalums on the voice cards shouldn´t be a bad choice either.

Anybody of you got some spare CEM´s?
One 3330 and a 3320 as well are broken. For one of my other machines I´m also looking for a CEM3340.



--- In vintagesynthrepair@yahoogroups.com, "Scott" <painintheamp@...> wrote:

>
> 
> 
> -If you can take the "ground loop" out of the equation, the most likely cause is power supply filtering capacitors that have gone dry  and arent doing what theyre supposed to.
> 
> I see this as a regular thing here in my shop.
> 
> Caps are easy to get and fairly cheap and replacing them drops troubleshooting time way down
> 
> Just doing that may make your troubles flee
> 
> Scott in Burrrrrrrr-mont
>

I had to replace a tantalum on my Roland RS202 to fix a bad note. Do tantalums have the same limited life that electrolytics have?
Ta
Susie
http://www.myspace.com/susangardener

--- In vintagesynthrepair@yahoogroups.com, "ambrosia800" <Second-Edition@...> wrote:

>
> Re: Crumar Trilogy repair
> 
> It is not a normal ground loop problem. The hum seems to be directly related to
> the number of voice cards in the machine. So I think, the power supply could be
> the problem.
> 
> I think, a recapping of the power supply should be the way to go.
> 
> On the other hand, there is a tantalum on every voice card. I think, changing
> the tantalums on the voice cards shouldn´t be a bad choice either.
> 
> Anybody of you got some spare CEM´s?
> One 3330 and a 3320 as well are broken. For one of my other machines I´m also looking for a CEM3340.
> 
> 
> 
> --- In vintagesynthrepair@yahoogroups.com, "Scott" <painintheamp@> wrote:
> >
> > 
> > 
> > -If you can take the "ground loop" out of the equation, the most likely cause is power supply filtering capacitors that have gone dry  and arent doing what theyre supposed to.
> > 
> > I see this as a regular thing here in my shop.
> > 
> > Caps are easy to get and fairly cheap and replacing them drops troubleshooting time way down
> > 
> > Just doing that may make your troubles flee
> > 
> > Scott in Burrrrrrrr-mont
> >
>

--- In vintagesynthrepair@yahoogroups.com, "Susie" <gardens@...> wrote:
>
> I had to replace a tantalum on my Roland RS202 to fix a bad note. Do tantalums have the same limited life that electrolytics have?
> Ta
> Susie
> http://www.myspace.com/susangardener
> 
> Tantalums have a different construction but are more susceptible
to over-voltage damage and they blowup if you put them in backwards.
They dont dry out like old electrolytics.
>