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Deluxe Memory Man Troubleshoot

4/18/1997 11:54 PM
Rob Prosper	Deluxe Memory Man Troubleshoot When I started this repair, I had a distored ghost note on the wet signal. I was intending to tweak the trim pots on the MN 3005 delay line. I didn't get around to it and when I put it back together I didn't get ANY wet signal. I don't have a signal generator but I do have a scope so I improvised a signal by plugging in a guitar and plucking the low E. Looking at the schematic, the input signal appears to come in at pin 7 on the MN3005. When I put the scope probe their and pluck the note I get a signal. When I hook up the probe to the ouput (pin 3 or pin 4) my scope shows two parallel horizontal lines that do not react when the note is plucked. The next MN3005 demonstrates the same picture on the output pins. The input of the second delay chip does not show a signal either. It appears the signal is not getting through the first MN3005. Two questions....are the two parellel lines on the outputs what you are supposed to see? Is my guess right that the chip is not passing the signal and it will have to be replaced? Rob

4/18/1997 11:54 PM

Rob Prosper

Deluxe Memory Man Troubleshoot

When I started this repair, I had a distored ghost note on the wet signal. I was intending to tweak the trim pots on the MN 3005 delay line. I didn't get around to it and when I put it back together I didn't get ANY wet signal.

I don't have a signal generator but I do have a scope so I improvised a signal by plugging in a guitar and plucking the low E.

Looking at the schematic, the input signal appears to come in at pin 7 on the MN3005. When I put the scope probe their and pluck the note I get a signal. When I hook up the probe to the ouput (pin 3 or pin 4) my scope shows two parallel horizontal lines that do not react when the note is plucked. The next MN3005 demonstrates the same picture on the output pins. The input of the second delay chip does not show a signal either. It appears the signal is not getting through the first MN3005.

Two questions....are the two parellel lines on the outputs what you are supposed to see?

Is my guess right that the chip is not passing the signal and it will have to be replaced?

Rob

7/25/1997 5:36 PM
CJ Landry	looking at my Panasonic BBD specs, check to make sure that you have a good clock signal at pins 2 and 6. The databook unfortunatly does not give much in the way of an explanation of the BBD's operation but they do mention that the " Electrical charges corresponding to analog signals are transferred from one stage to another by a two phase clock." Also, it states "electrical signals flow unidirectionally from the input to the output with a time delay which can be controlled by the clock frequency." BBD's are a number of silicon gate stages which consist of a capacitor that stores elctrical charges and are switched with a tetrode transistor. Then the charge is transferred to the next stage and so on... Think of a BBD as a series of pitchers in line and the first is full of water. Then it fills the next pitcher and that pitcher fills the next pitcher and so on.... I hope I didn't get carried away, but this may help in finding the problem. I personally have never replaced a MN3005. SAD1024 yes, but not the MN3005's. Christian CJLectronics

7/25/1997 5:36 PM

CJ Landry

looking at my Panasonic BBD specs, check to make sure that you have a good clock signal at pins 2 and 6. The databook unfortunatly does not give much in the way of an explanation of the BBD's operation but they do mention that the " Electrical charges corresponding to analog signals are transferred from one stage to another by a two phase clock." Also, it states "electrical signals flow unidirectionally from the input to the output with a time delay which can be controlled by the clock frequency."

BBD's are a number of silicon gate stages which consist of a capacitor that stores elctrical charges and are switched with a tetrode transistor. Then the charge is transferred to the next stage and so on...

Think of a BBD as a series of pitchers in line and the first is full of water. Then it fills the next pitcher and that pitcher fills the next pitcher and so on....

I hope I didn't get carried away, but this may help in finding the problem. I personally have never replaced a MN3005. SAD1024 yes, but not the MN3005's.

Christian
CJLectronics

7/25/1997 8:53 PM
Mark Hammer	I'm looking at an information sheet for the MN3005 provided by Dave Tarnowski of A/DA. Lines 3 and 4 are the output lines. They are summed together with a pot that balances the two parallel delayed signals from each chip. The key thing to keep in mind is that absolutely NADA will be shifted by those teensy capacitors and FET's if the bias signal is not set right. This is (in my picture here) a 20k trimpot with one end tied to ground, the opposite end tied to minus 15v (or whatever) and the wiper feeding in a bias voltage to the op-amp immediately prior to the MN3005. Since the illustration only shows one 3005, I couldn't tell you whether the procedure needs to be repeated for successive chips. In any event, what you want to look for is a DC bias voltage of somewhere between -5 to -10 vdc going into pin 7 of the MN3005. Your signal rides on top of that. The two parallel lines you see on your scope may well be the bias voltage, just not enough (or too much) of it. Try and find the source of the DC bias voltage and play with it so that it is somewhere in the range indicated.

7/25/1997 8:53 PM

Mark Hammer

I'm looking at an information sheet for the MN3005 provided by Dave Tarnowski of A/DA. Lines 3 and 4 are the output lines. They are summed together with a pot that balances the two parallel delayed signals from each chip. The key thing to keep in mind is that absolutely NADA will be shifted by those teensy capacitors and FET's if the bias signal is not set right. This is (in my picture here) a 20k trimpot with one end tied to ground, the opposite end tied to minus 15v (or whatever) and the wiper feeding in a bias voltage to the op-amp immediately prior to the MN3005. Since the illustration only shows one 3005, I couldn't tell you whether the procedure needs to be repeated for successive chips.

In any event, what you want to look for is a DC bias voltage of somewhere between -5 to -10 vdc going into pin 7 of the MN3005. Your signal rides on top of that. The two parallel lines you see on your scope may well be the bias voltage, just not enough (or too much) of it. Try and find the source of the DC bias voltage and play with it so that it is somewhere in the range indicated.

8/22/1997 3:32 PM
Rob Prosper	Just an update on how this is going. With the guitar plugged in and watching for a wet signal on the scope, I was able to trim both MN3005 to get a signal. I then set for minimum distortion and now have a pretty good signal but a little hum. I have changed the 220 mf 50v filter cap to a 1000uf 50 v cap and it has reduced the hum in half. I still have the weird knocking problem. I know I have received replies on this but I can't find them. In review......when using a compressor before the delay...as the input signal is increased I continue to get a nice wet signal. Once the input signal is a little high, instead of a nice delay response , the wet signal turns into a loud "knock". It sounds like the plectrum pluck multiplied by a thousand. When playing a 'chicken-picken country solo..it will be interspersed with these loud knocks'. I believe one of the replies was to check to see if a component immediately preceding the input rc4558 was still to specification. I can't remember which one. In other words..adjust one of the component parameters to reduce the input signal. This sounds like a good idea if I can be reminded how to do it. I wonder if it is a problem with the compander? Is it possible that the snap of a highly compressed signal is challenging the noise reduction ability of the compander? Thanks for your time. Rob

8/22/1997 3:32 PM

Rob Prosper

Just an update on how this is going. With the guitar plugged in and watching for a wet signal on the scope, I was able to trim both MN3005 to get a signal. I then set for minimum distortion and now have a pretty good signal but a little hum.

I have changed the 220 mf 50v filter cap to a 1000uf 50 v cap and it has reduced the hum in half.

I still have the weird knocking problem. I know I have received replies on this but I can't find them. In review......when using a compressor before the delay...as the input signal is increased I continue to get a nice wet signal. Once the input signal is a little high, instead of a nice delay response , the wet signal turns into a loud "knock". It sounds like the plectrum pluck multiplied by a thousand. When playing a 'chicken-picken country solo..it will be interspersed with these loud knocks'.

I believe one of the replies was to check to see if a component immediately preceding the input rc4558 was still to specification. I can't remember which one. In other words..adjust one of the component parameters to reduce the input signal. This sounds like a good idea if I can be reminded how to do it.

I wonder if it is a problem with the compander? Is it possible that the snap of a highly compressed signal is challenging the noise reduction ability of the compander?

Thanks for your time.

Rob

8/22/1997 8:48 PM
CJ Landry	Rob, Have you looked at your voltage levels. Are they all a clean DC level? ie no ripple? This can sometimes cause hum. Is there hum only when you play or can you here it if you hold the strings of your guitar? Christian CJLectronics

8/26/1997 11:13 AM
Rob Prosper	Christian: I hear the hum all the time, including when I hold the strings. The hum has been reduced considerably with the changing of two filter caps. I have not checked the voltages for ripple. I did some experimenting trying to determine when I got the "knock". The problem is most pronounced when the guitar string is struck firmly but muted. This will happen with or without a compressor, although far more prevalent with a compressed signal. As stated previously I have trimmed the mn3005 for the cleanest signal. I have no idea how to trim the other trimpots. These are the balance trim after the second mn3005 and the gain trims on the 4558s that follow each of the delay stages. When I turn these trims it affects the output volume....but I don't know where these should be set. I'm not terribly concerned about the low level hum but I do want to solve the knock. Thanks, Rob

8/26/1997 11:13 AM

Rob Prosper

Christian:

I hear the hum all the time, including when I hold the strings. The hum has been reduced considerably with the changing of two filter caps. I have not checked the voltages for ripple.

I did some experimenting trying to determine when I got the "knock". The problem is most pronounced when the guitar string is struck firmly but muted. This will happen with or without a compressor, although far more prevalent with a compressed signal. As stated previously I have trimmed the mn3005 for the cleanest signal. I have no idea how to trim the other trimpots. These are the balance trim after the second mn3005 and the gain trims on the 4558s that follow each of the delay stages. When I turn these trims it affects the output volume....but I don't know where these should be set.

I'm not terribly concerned about the low level hum but I do want to solve the knock.

Thanks,

Rob

8/26/1997 4:00 PM
Mark Hammer	If memory serves, the DMM is a companded device. If it is companded, most likely there is a Signetics NE570 or 571 in there. People often complain about thunks, ticks, and assorted other transient gremlins when using dynamic control devices like noise gates, limiters, duckers, etc. The cure often involves adjusting the timing aspects of the device so that it isn't asked to respond faster than is practical given what it has to do. Perhaps the compander on the DMM is responding too fast to transients; i.e., the attack time is set too fast, and the "untamed" transient demands more headroom of the MN3005 than it can deliver. This is, as always, mere speculation on my part, but it's worth a shot. The attack/decay characteristics of the NE570/571 are set by a capacitor between pin 1 and ground (pin 16 on the second gain cell on the chip). Higher values yield longer attack and decay times (i.e., more sluggish response, which may be what you want). Since there are two channels that need to be matched for mirror image compression/expansion, whatever you do to one channel, you need to do to the other. Since the values likely to be used for the desired timing range are likely electrolytic, be sure you are attentive to capacitor polarity.

8/26/1997 4:00 PM

Mark Hammer

If memory serves, the DMM is a companded device. If it is companded, most likely there is a Signetics NE570 or 571 in there. People often complain about thunks, ticks, and assorted other transient gremlins when using dynamic control devices like noise gates, limiters, duckers, etc. The cure often involves adjusting the timing aspects of the device so that it isn't asked to respond faster than is practical given what it has to do. Perhaps the compander on the DMM is responding too fast to transients; i.e., the attack time is set too fast, and the "untamed" transient demands more headroom of the MN3005 than it can deliver. This is, as always, mere speculation on my part, but it's worth a shot.

The attack/decay characteristics of the NE570/571 are set by a capacitor between pin 1 and ground (pin 16 on the second gain cell on the chip). Higher values yield longer attack and decay times (i.e., more sluggish response, which may be what you want). Since there are two channels that need to be matched for mirror image compression/expansion, whatever you do to one channel, you need to do to the other. Since the values likely to be used for the desired timing range are likely electrolytic, be sure you are attentive to capacitor polarity.

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