Hi Hugo,
Thanks.
A close guess on my part then. I find it easier to measure voltage drops as that would exclude the other current draws from the rest of the circuit.
I would certainly change those caps out, I'd do the power supply, but not necessarily the large main filters. Tone board as well.
-Chris
Thanks.
A close guess on my part then. I find it easier to measure voltage drops as that would exclude the other current draws from the rest of the circuit.
I would certainly change those caps out, I'd do the power supply, but not necessarily the large main filters. Tone board as well.
-Chris
Did I send you guys the manual? Just say (mail) the word...
It will be the AU-6600 though. 🙂
/Hugo
It will be the AU-6600 though. 🙂
/Hugo
You may have sent it to me a while ago,But I seem to have lost it,if you did. 😕 (I promise I won't lose it this time! 😉 )
Thanks for the manual Hugo!
Do you guys think it would be a good idea to increase the size of the main filter caps? They're currently 4700uf 50V.
I think I have some 6800uf 63V caps around,and some others too.(Pulled from various amps/projects.)
Would those be okay,or do you think they might stress the power X-fmr or stock rectifiers/fuses too much?
Perhaps I could just put a pair of 1000uf caps close-by on the amp board,kinda Gainclone style?
(The main filter caps are connected by wires,not on the main amp board. -I've upped the size of the wire already.)
I've got the preamp-power supply,and power amp mostly re-capped now. (The new caps are physically much smaller!) and figured I'd ask about the main Filter caps while it's in pieces on the bench. 🙂
I'll probably have a go at the preamp/tone board later.Right now I just want to make the power amp safe/stable (I hate blowing speakers!) and see how she sounds,and go from there. 😉
Do you guys think it would be a good idea to increase the size of the main filter caps? They're currently 4700uf 50V.
I think I have some 6800uf 63V caps around,and some others too.(Pulled from various amps/projects.)
Would those be okay,or do you think they might stress the power X-fmr or stock rectifiers/fuses too much?
Perhaps I could just put a pair of 1000uf caps close-by on the amp board,kinda Gainclone style?
(The main filter caps are connected by wires,not on the main amp board. -I've upped the size of the wire already.)
I've got the preamp-power supply,and power amp mostly re-capped now. (The new caps are physically much smaller!) and figured I'd ask about the main Filter caps while it's in pieces on the bench. 🙂
I'll probably have a go at the preamp/tone board later.Right now I just want to make the power amp safe/stable (I hate blowing speakers!) and see how she sounds,and go from there. 😉
Okay,I got it back together..(for the moment,anyways)
I left the original filter caps,for now.I may change them later.
The power amp section seems to be rock solid now! 🙂
If I flip the "Separated/Connected" (disconnects the preamp) switch on the back,the drifty offset problem goes away,so it's surely something in the preamp/tone stages.
(Duh! Why didn't I think of that switch before!)
I managed to get the offset under 1mV on each channel,with some careful tweaking. 😀
So next,the preamp/tone board..
I left the original filter caps,for now.I may change them later.
The power amp section seems to be rock solid now! 🙂
If I flip the "Separated/Connected" (disconnects the preamp) switch on the back,the drifty offset problem goes away,so it's surely something in the preamp/tone stages.
(Duh! Why didn't I think of that switch before!)
I managed to get the offset under 1mV on each channel,with some careful tweaking. 😀
So next,the preamp/tone board..
I thought it might be helpful to others to ask my question in this thread as it is a wealth of AU-5500 knowledge.
I picked up a 5500 that was described as having "scratchy volume." Cleaning the pots didn't help. With the volume at minimum and attached to test speakers it has static/scratchy noise coming from mainly the right channel even with no input. Amp will go into protection shortly after sending the static signal to the speakers. It will then come out of protection.
I have >1 VDC on both channels. Measures +/- 35 V at the main filter caps. R37 looks burnt but shows an exact 100 R. R38 looks good and measures 102 R. Had a funny looking fuse at either F01 or F03 (sorry - I don't remember.) The fuse looked like it was full of sand, labeled F3.15/25OE. Any help would be greatly appreciated.
I picked up a 5500 that was described as having "scratchy volume." Cleaning the pots didn't help. With the volume at minimum and attached to test speakers it has static/scratchy noise coming from mainly the right channel even with no input. Amp will go into protection shortly after sending the static signal to the speakers. It will then come out of protection.
I have >1 VDC on both channels. Measures +/- 35 V at the main filter caps. R37 looks burnt but shows an exact 100 R. R38 looks good and measures 102 R. Had a funny looking fuse at either F01 or F03 (sorry - I don't remember.) The fuse looked like it was full of sand, labeled F3.15/25OE. Any help would be greatly appreciated.
Hi jbush,
2SC1134 may be getting leaky. I don't understand why you would have greater than 1 VDC offset on both channels. There are no common power supply components except the main supplies.
You can check for oscillation or a common ground point that has come loose (power supply PCB?).
Also, all electrolytic caps are suspect since they are old.
The sand filled fuse is a time delay type.
-Chris
2SC1134 may be getting leaky. I don't understand why you would have greater than 1 VDC offset on both channels. There are no common power supply components except the main supplies.
You can check for oscillation or a common ground point that has come loose (power supply PCB?).
Also, all electrolytic caps are suspect since they are old.
The sand filled fuse is a time delay type.
-Chris
Thanks anatech, I'll look into that. I will also replace all the fuses with new quick-acting ones.
-Jeremiah
-Jeremiah
Well, I guess I'm going to need a service manual. That way I can test for the correct voltages at the correct points. I will probably order it online. Are there any companies you would recommend (or stay away from)?
Jeremiah
Jeremiah
I know this is an old post but when I see something wrong I think it should be corrected? Replacing cheap variable resistors with multiturn types is the common-sense way to go because they are sealed and therefore don't oxidize the insides so they will be working like new 50+ years down the road, that's why most TOTL Hi-Fi gear manufacturers use them. Multiturn variable resistors are never ever noisy, not in my experience and I've never heard of anyone else saying they are noisy except for this once? plus they are much more precise.
Hi redrooster,
I appreciate your comments, however you are wrong about the fact they are sealed. I'm a journeyman calibration technician for electronic instruments. We have had to replace tons of multi-turn controls. These are expensive ones and not something the average person would buy. These are properly called "sem-fixed resistors" and are not intended to be adjusted much.
Another thing that is true is that the contact are between the wiper and track is very small compared to normal good quality single turn controls. This is important when used as bias setting controls where there is current that flows through the wiper circuit. Most being designed as potentiometers. Lately there is a multi-turn control designed to allow this, but the Ebay types most people use are neither sealed or designed for current flow through the wiper.
Now for the most important point. There isn't anything wrong with a single turn control to begin with. I restore audio equipment and controls 40 years + old are working just fine.
Multi-turn controls are not better than single turn controls. They are just different. They each have an application where they suit better than the other one. Bias circuits are generally best served by using a single turn control where the circuit has been designed so that the range of resistance is useful instead of covering everything from cutting the transistor off to allowing it to operate almost full on. In those applications where the range is too great, the person that designed the circuit was either lazy, or not knowledgeable enough to design it.
-Chris
I appreciate your comments, however you are wrong about the fact they are sealed. I'm a journeyman calibration technician for electronic instruments. We have had to replace tons of multi-turn controls. These are expensive ones and not something the average person would buy. These are properly called "sem-fixed resistors" and are not intended to be adjusted much.
Another thing that is true is that the contact are between the wiper and track is very small compared to normal good quality single turn controls. This is important when used as bias setting controls where there is current that flows through the wiper circuit. Most being designed as potentiometers. Lately there is a multi-turn control designed to allow this, but the Ebay types most people use are neither sealed or designed for current flow through the wiper.
Now for the most important point. There isn't anything wrong with a single turn control to begin with. I restore audio equipment and controls 40 years + old are working just fine.
Multi-turn controls are not better than single turn controls. They are just different. They each have an application where they suit better than the other one. Bias circuits are generally best served by using a single turn control where the circuit has been designed so that the range of resistance is useful instead of covering everything from cutting the transistor off to allowing it to operate almost full on. In those applications where the range is too great, the person that designed the circuit was either lazy, or not knowledgeable enough to design it.
-Chris
I'm not going to tread lightly because you are a moderator, in fact, I'm doubling down because you of all people should know better than this? I've been re-building, re-capping amplifiers, etc, for at least the past 10 years with hardly any breaks between. Most people who are going to go to the trouble of re-building their amplifier are going to use Bourns, Vishay, etc... VRs. Who in their right mind is going to want to save a few cents on some ebay rejects/seconds or whatever you get in that Chinese lucky dip? The most common advice given on audio forums when changing out intractable single-turn noisy Bias and DC VRs is, ''Use good quality Bourns, Vishay, etc, multi-turn VRs'' Another thing is that the current-carrying capacity of sealed VRs is not an issue at all, look at the datasheets? This is what they were designed for? My AU-11000 has a 50ma bias. I repeat 50ma! My AU-D907F has a 10mv bias (needs to be converted to ma by ohms law) These are tiny currents, we are not dealing with the big collector or emitter type currents here? You don't appear to have a proper grasp on electronic theory in this area? I've never come across a noisy sealed VR ever for that matter, in fact, this is the first time I've ever heard of it?
Hi redrooster,
Well gee whiz. I'm obviously out of my depth here I guess.
I've been professionally rebuilding and designing equipment (getting paid for this) for over 40 years now. In addition I am a Metrologist - I mentioned that already. Between University training, training programs and on the job training, I've been continuously upgrading my skills as well. I was approved for warranty service for brands like Nakamichi, Revox, Carver, Marantz. I could go on but I find it boring. I owned and operated a service facility where I trained technicians for 16 years before I sold it. Before I got into servicing in a big way, I sold electronic parts and had to learn all about their individual characteristics. Especially since I was recommending various parts to industrial service engineers. Learned a lot. I recommend maybe you should look into this.
Okay, I did mention that some newer multi-turn controls were rated for some current through the wiper circuit. But the fact remains that multi-turn controls were originally designed as potentiometers. That means very little current through the wiper in case you aren't paying attention. Most people recommend changing to multi-turn controls for reasons that escape me entirely. It is painfully obvious that a single turn control has a larger wiper and contact area. This means you can use your eyeballs before talking. Larger contact area means they can handle higher current through the wiper connection. It's true, the same physical thing holds true for switches. The larger the contact area, the higher the current the contact can support.
Generally speaking, most people talking on the internet have no training or real work experience. That includes the huge number of hackers out there that call themselves technicians. Looks like you want to join that club from your attitude. You could have just asked politely.
Okay, now I do know you can't read a schematic completely. You're saying the bias current for your output stage is 50 mA - right? So, do you think this current runs through the bias control? News flash for you. It doesn't. The bias current is set a stage or two back, normally by a Vbe multiplier. The pot controls the base current in a shunt transistor so that the standing current for that circuit is divided between the drivers or predrivers, and the Vbe multiplier transistor. The currents in that circuit are normally reasonably light. In the bad old days, the bias control passed whatever current didn't go through the driver transistors. That amounted to mA depending on the unit.
So before you go after anyone in the future, you should attempt to get a grip on what you are talking about first. You might consider trying to assess what your target knows first as well.
One of the most common reasons for a multi-turn control being used for bias control is pure laziness. If you size the resistors correctly, you can get fine control with a single turn control without large dead zones at one or either end. Now here is a shocker for you. Bias current is approximate at best. It changes with ambient temperature, and often mains voltage which may change hour by hour. Then there is the temperature of the heat sinks. Hey wait! That means that bias current changes dynamically! Yes, it does. So, the main use of a multi-turn control is for a very fine adjustment for accurate voltages or currents. Mostly in test equipment or industrial instrumentation (test equipment). I have a very nice voltage reference that I have to replace all the pots in now. They are single turn, but scaled properly by the surrounding fixed resistors. The used value of that instrument is over $2,000 US. It isn't in high demand so it's price hasn't gone through the roof. I have rebuilt a couple Sansui AU-11000 int amps this year alone. Also a number of other high end pieces of equipment.
I'll let you in on a secret you would be well to keep in mind. Often, people who aren't well versed in various activities, like restoration of older equipment, will often buy the more expensive components - because they are better, right? Look at the world of capacitors and the expensive ones people wreck their equipment with because the leads are too large for the holes in the PCBs, and the component body won't fit where the old one did. Common sense would suggest that maybe you shouldn't use the large part. The industrial parts are often better than the boutique parts. As long as you understand what parameters are important, you can test and select the truly superior parts. I use an HP 4263A LCR meter. It wasn't cheap when I bought it new. What do you use? Hint, an ESR meter is useless for selecting capacitors that pass signals. Power supply and crossover caps okay, but not everything else.
I've actually told you a lot of helpful things if you care to pay attention. In the future you might consider that challenging someone isn't the proper way to get explanations or to learn anything.
Lastly, I'm a normal member with extra work to do. When I act as a moderator (all of us), you will see the following symbol ...
-Chris
Well gee whiz. I'm obviously out of my depth here I guess.
I've been professionally rebuilding and designing equipment (getting paid for this) for over 40 years now. In addition I am a Metrologist - I mentioned that already. Between University training, training programs and on the job training, I've been continuously upgrading my skills as well. I was approved for warranty service for brands like Nakamichi, Revox, Carver, Marantz. I could go on but I find it boring. I owned and operated a service facility where I trained technicians for 16 years before I sold it. Before I got into servicing in a big way, I sold electronic parts and had to learn all about their individual characteristics. Especially since I was recommending various parts to industrial service engineers. Learned a lot. I recommend maybe you should look into this.
Okay, I did mention that some newer multi-turn controls were rated for some current through the wiper circuit. But the fact remains that multi-turn controls were originally designed as potentiometers. That means very little current through the wiper in case you aren't paying attention. Most people recommend changing to multi-turn controls for reasons that escape me entirely. It is painfully obvious that a single turn control has a larger wiper and contact area. This means you can use your eyeballs before talking. Larger contact area means they can handle higher current through the wiper connection. It's true, the same physical thing holds true for switches. The larger the contact area, the higher the current the contact can support.
Generally speaking, most people talking on the internet have no training or real work experience. That includes the huge number of hackers out there that call themselves technicians. Looks like you want to join that club from your attitude. You could have just asked politely.
Okay, now I do know you can't read a schematic completely. You're saying the bias current for your output stage is 50 mA - right? So, do you think this current runs through the bias control? News flash for you. It doesn't. The bias current is set a stage or two back, normally by a Vbe multiplier. The pot controls the base current in a shunt transistor so that the standing current for that circuit is divided between the drivers or predrivers, and the Vbe multiplier transistor. The currents in that circuit are normally reasonably light. In the bad old days, the bias control passed whatever current didn't go through the driver transistors. That amounted to mA depending on the unit.
So before you go after anyone in the future, you should attempt to get a grip on what you are talking about first. You might consider trying to assess what your target knows first as well.
One of the most common reasons for a multi-turn control being used for bias control is pure laziness. If you size the resistors correctly, you can get fine control with a single turn control without large dead zones at one or either end. Now here is a shocker for you. Bias current is approximate at best. It changes with ambient temperature, and often mains voltage which may change hour by hour. Then there is the temperature of the heat sinks. Hey wait! That means that bias current changes dynamically! Yes, it does. So, the main use of a multi-turn control is for a very fine adjustment for accurate voltages or currents. Mostly in test equipment or industrial instrumentation (test equipment). I have a very nice voltage reference that I have to replace all the pots in now. They are single turn, but scaled properly by the surrounding fixed resistors. The used value of that instrument is over $2,000 US. It isn't in high demand so it's price hasn't gone through the roof. I have rebuilt a couple Sansui AU-11000 int amps this year alone. Also a number of other high end pieces of equipment.
I'll let you in on a secret you would be well to keep in mind. Often, people who aren't well versed in various activities, like restoration of older equipment, will often buy the more expensive components - because they are better, right? Look at the world of capacitors and the expensive ones people wreck their equipment with because the leads are too large for the holes in the PCBs, and the component body won't fit where the old one did. Common sense would suggest that maybe you shouldn't use the large part. The industrial parts are often better than the boutique parts. As long as you understand what parameters are important, you can test and select the truly superior parts. I use an HP 4263A LCR meter. It wasn't cheap when I bought it new. What do you use? Hint, an ESR meter is useless for selecting capacitors that pass signals. Power supply and crossover caps okay, but not everything else.
I've actually told you a lot of helpful things if you care to pay attention. In the future you might consider that challenging someone isn't the proper way to get explanations or to learn anything.
Lastly, I'm a normal member with extra work to do. When I act as a moderator (all of us), you will see the following symbol ...
-Chris
I'm not trying to make trouble or go after you or challenge you? I'm just pointing out somethings you said that were wrong? It doesn't matter to me who you are if you were Albert Einstein and you were wrong about something you would be just as wrong as Bill Bloggs down the road. Don't worry about it I've been pulled up myself for somethings I've said that was wrong, its no big deal? I think I should point it out so that any newbs don't get the wrong idea?
Hi redrooster,
Actually, you did in fact "go after me"
As for your main point (multi-turn trimmers) I'll say it again. They aren't the right part for the job.
So given that you believe I'm in error, please explain why these are better. Now before getting too far, consider that the controls that are already in place before people start messing with things were designed in by teams of engineers. These people have far more education than the people you are listening to.
-Chris
Actually, you did in fact "go after me"
As for your main point (multi-turn trimmers) I'll say it again. They aren't the right part for the job.
So given that you believe I'm in error, please explain why these are better. Now before getting too far, consider that the controls that are already in place before people start messing with things were designed in by teams of engineers. These people have far more education than the people you are listening to.
-Chris
You say that expensive sealed Bourns type Variable Resistors are not sealed? Read the Datasheets? You said the wiper is not big enough to carry the correct current? But if you read the Datasheets on these VRs you will see you are wrong again? As for expensive sealed VRs going noisy? I've never heard of that happening, ever? Your sarcastic and insulting comments towards me speak volumes about your suitability as a moderator here. This conversation if you could call it that? Is finished.
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