I don't think I'm going to mess with the front panel as it isn't mine. I have 16kR to 130R on the first track and 17kR to 2R on the second.
Do I need a power source, or do I just connect both emitters, both collectors through 100R resistor(s ?) and both bases through 1KR resistor(s ?) for the pair matching ?
Do I need a power source, or do I just connect both emitters, both collectors through 100R resistor(s ?) and both bases through 1KR resistor(s ?) for the pair matching ?
Getting back to my first concern on this amp, being the faulty volume pot, I got it out and one track is actually almost split in some point, it still works but as I said before it doesn't get the volume down all the way on the left channel. Any ideas on where I could find a replacement part (RM0503079-38M50KR*2 : 2 track 50KR with loudness pin at about half way).
I think some of the other amplifiers from this series might have the same so if anyone here has one for sale that would be great.
I think some of the other amplifiers from this series might have the same so if anyone here has one for sale that would be great.
Hi Depaj,
Try this method on your own stuff first I guess. It can take a long time to closely match transistors.
Normally you would use +/- 10 VDC, 9 V batteries are okay. I use a constant current source made from an LED and a transistor plus two resistors for the common emitter connection. Set the current to near the actual currents they will see in the circuit application. The two bases each connect to the mid point voltage through resistors (1K0 ~ 10K). The two collectors connect to the 100R resistors, and those are connected to the positive supply voltage. Your meter is connected between the two collectors. You are looking for a null (zero) voltage between the two collectors.
The goal is to select two transistors that are nearly alike. That has been achieved when the two collector voltages are the same (null = 0 ). A null < 10 mV is excellent and will perform very well. You will be surprised at how far the matching by beta meter can be.
-Chris
Try this method on your own stuff first I guess. It can take a long time to closely match transistors.
Normally you would use +/- 10 VDC, 9 V batteries are okay. I use a constant current source made from an LED and a transistor plus two resistors for the common emitter connection. Set the current to near the actual currents they will see in the circuit application. The two bases each connect to the mid point voltage through resistors (1K0 ~ 10K). The two collectors connect to the 100R resistors, and those are connected to the positive supply voltage. Your meter is connected between the two collectors. You are looking for a null (zero) voltage between the two collectors.
The goal is to select two transistors that are nearly alike. That has been achieved when the two collector voltages are the same (null = 0 ). A null < 10 mV is excellent and will perform very well. You will be surprised at how far the matching by beta meter can be.
-Chris
Thank you Chris.
If the original pair is fine is there still any benefit to have from changing it for a new pair closely matched ?
By the way, I had a volume pot from a pioneer sa-708 lying around and managed to fit that perfectly in the marantz. The fourth pin was on the wrong side but that was easily adapted and now it works perfectly, no sound at all when the knob is at zero and nicely balanced between the two channels.
If the original pair is fine is there still any benefit to have from changing it for a new pair closely matched ?
By the way, I had a volume pot from a pioneer sa-708 lying around and managed to fit that perfectly in the marantz. The fourth pin was on the wrong side but that was easily adapted and now it works perfectly, no sound at all when the knob is at zero and nicely balanced between the two channels.
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Hi Depaj,
Excellent! That is fantastic that you got a replacement control.
Yes, it is worth installing a closely matched diff pair. This is one of the things I do to greatly improve the sound quality. Its a real pain to do, but it also makes a big difference.
-Chris
Excellent! That is fantastic that you got a replacement control.
Yes, it is worth installing a closely matched diff pair. This is one of the things I do to greatly improve the sound quality. Its a real pain to do, but it also makes a big difference.
-Chris
Hello again,
My friend has been very happy with the Marantz 1090 so far but recently I got a message from him saying his right speaker tried to get out of its cabinet so I guess he got quite some DC on that channel. He brought the amp back but whatever I do I don't get any DC on either one of the channels (I'm testing with 1kHz and with some music on 8R dummy loads) even with the volume up until it starts clipping.
When I plug it in with the dim bulb though at a certain volume the output goes completely crazy, the bulb flickers and I got a lot of dc on both channels that I could trace back to the output of the preamp. I noticed this is exactly the same problem I got on a Marantz 1122DC. When using the "Main in" input I don't have this (same with the 1122dc). I assume this might be due to the voltage drop caused by the dim bulb.
He also asked if I could replace the speakers terminal by some binding posts for banana plugs. I have the posts but it's not possible to adapts the actual terminals for them. I can't find any that will anywhere, does anyone know of a place I could find those or should I make some myself and if yes with what material ?
My friend has been very happy with the Marantz 1090 so far but recently I got a message from him saying his right speaker tried to get out of its cabinet so I guess he got quite some DC on that channel. He brought the amp back but whatever I do I don't get any DC on either one of the channels (I'm testing with 1kHz and with some music on 8R dummy loads) even with the volume up until it starts clipping.
When I plug it in with the dim bulb though at a certain volume the output goes completely crazy, the bulb flickers and I got a lot of dc on both channels that I could trace back to the output of the preamp. I noticed this is exactly the same problem I got on a Marantz 1122DC. When using the "Main in" input I don't have this (same with the 1122dc). I assume this might be due to the voltage drop caused by the dim bulb.
He also asked if I could replace the speakers terminal by some binding posts for banana plugs. I have the posts but it's not possible to adapts the actual terminals for them. I can't find any that will anywhere, does anyone know of a place I could find those or should I make some myself and if yes with what material ?
Check the voltage regulators for the preamp section.
Try using some sheet plastic and install regular binding posts.
-Chris
Try using some sheet plastic and install regular binding posts.
-Chris
The voltages seem fine when the amp is playing normally, they just get really low when the dim bulb is in and I get the volume up to about half but I will check them tomorrow.
How come thousands of websites sell these binding posts but none sell any, lets call them plates to mount them on ?
I will see if I can find that somewhere, I will have to get the right tools as well but that might come in handy later anyway.
Thanks
How come thousands of websites sell these binding posts but none sell any, lets call them plates to mount them on ?
I will see if I can find that somewhere, I will have to get the right tools as well but that might come in handy later anyway.
Thanks
A dim bulb tester works (protects the amplifier) by reducing the supply voltage. That voltage drop is supposed to occur or it can't do any protecting at all. How difficult to understand is light bulb? - It is just a resistor that varies its resistance according to the load and glows brighter to show that the load is heavy, as with a short or unexpected low resistance somewhere inside. So when the bulb is cold, there is full line voltage delivered to the load, when it is glowing brightly, the supply voltage will be reduced to around 70V or less with a 220V mains supply.
"mounting plates" for binding posts are supplied as an assembly but only with standard 19mm centre spacing, which is too close for use with the monster posts now preferred. The individual posts you buy are mainly intended for use in holes drilled in the case by manufacturers or DIY constructors at whatever spacing they like.
"mounting plates" for binding posts are supplied as an assembly but only with standard 19mm centre spacing, which is too close for use with the monster posts now preferred. The individual posts you buy are mainly intended for use in holes drilled in the case by manufacturers or DIY constructors at whatever spacing they like.
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Hi Ian, don't worry I know exactly how the dim bulb works as a protection, and I also know it causes a voltage drop that gets more and more important in proportion to how bright the bulb gets. My last message was not clear but I was only wondering why in these two marantz models the power supply goes crazy when the power consumption of the amp gets higher whereas for example the pioneer SA 7800 just clips the signal when the supply rails get too low.
Ok so my only option here would be to just get some plastic sheet or other insulating material and drill the holes myself. Wouldn't it be beneficial for diy stores or even just electronic stores to sell standard mounting plates for these binding posts ?
Ok so my only option here would be to just get some plastic sheet or other insulating material and drill the holes myself. Wouldn't it be beneficial for diy stores or even just electronic stores to sell standard mounting plates for these binding posts ?
I haven't checked the different schematics yet but regulated power supplies, such as in preamps and often in larger amplifier designs, may "drop out" of regulation or normal operation at various supply voltages. The output may then distort badly if the supply voltage falls to perhaps 50% of the specified supplies whilst most will continue to operate almost normally, right down to a very low supply voltage like +/-6V .
There is an added complication of modern microprocessor controlled or analog protection circuits, relay controllers, even some VI limiters and similar local semiconductor protection circuits which can disrupt operation, cause bad distortion or no function at all, if the already small supply voltages used are reduced there too.
Some years ago, I tendered to service and repair a quantity of pro. PA amplifier boards but they behaved badly when powered with a +/-50V max. rated bench power supply. What a disaster! I had to add a second set of floating supplies in series with the 50V supplies to operate the amplifiers. They proved to require at least 55V of the specified 80V supplies originally fitted. I was caught out badly there, so it does happen.
There is an added complication of modern microprocessor controlled or analog protection circuits, relay controllers, even some VI limiters and similar local semiconductor protection circuits which can disrupt operation, cause bad distortion or no function at all, if the already small supply voltages used are reduced there too.
Some years ago, I tendered to service and repair a quantity of pro. PA amplifier boards but they behaved badly when powered with a +/-50V max. rated bench power supply. What a disaster! I had to add a second set of floating supplies in series with the 50V supplies to operate the amplifiers. They proved to require at least 55V of the specified 80V supplies originally fitted. I was caught out badly there, so it does happen.
So it's probably the way this amps regulated supply is designed that would explain this behaviour. Nothing to worry about than really as it should never be used with a dim bulb while listening anyway.
The supply rails, when pushing it with the dim bulb, dropped all the way to 16v (coming from 42) so yes that's quite low. The power amp section which is not regulated keeps doings it's job.
I suppose that does get some repairs harder to carry out !!!
The supply rails, when pushing it with the dim bulb, dropped all the way to 16v (coming from 42) so yes that's quite low. The power amp section which is not regulated keeps doings it's job.
I suppose that does get some repairs harder to carry out !!!
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Hi Depaj,
That is possible. The lamp is dim, so no catastrophic shorts.
I disagree with the light bulb test procedure. I've used a variac (variable AC transformer) since I was in my teens to safely bring up equipment. Only a couple sets didn't like the variac. One drew high current at low voltages (a Pioneer), and the others were Carver units that had a type of regulated AC supply. All you do is watch the current meter as you increase the voltage. It's nice to always be aware of what voltage the test unit is seeing. To each his own, but the lightbulb "tester" doesn't tell you much, and you don't know what voltage your unit under test is seeing.
-Chris
That is possible. The lamp is dim, so no catastrophic shorts.
I disagree with the light bulb test procedure. I've used a variac (variable AC transformer) since I was in my teens to safely bring up equipment. Only a couple sets didn't like the variac. One drew high current at low voltages (a Pioneer), and the others were Carver units that had a type of regulated AC supply. All you do is watch the current meter as you increase the voltage. It's nice to always be aware of what voltage the test unit is seeing. To each his own, but the lightbulb "tester" doesn't tell you much, and you don't know what voltage your unit under test is seeing.
-Chris
I never see a DBT mentioned in service manuals only Variacs. Never heard of a DBT until I got onto these forums. Like Chris I've been at this nearly 40 years and have never blown up anything using a Variac. How many posts have we seen and wasted time on only to find the reason a unit doesn't work because it's on the DBT? I guess on initial turn on it may be useful but after that it needs to go, certainly you can't do any alignments or measurements with it in the circuit. Also using the Variac you can adjust your mains voltage to what it's supposed to be and THEN do your alignments.
Craig
Craig
I know, I really need to get one, I haven't been doing this for very long and getting all the necessary stuff takes time and money. But I will get there. The dim bulb has helped me a lot so far and I only had a few setbacks with it so I still consider a quite useful tool.
I think the choice is down to skill and commercial demands. If you're raised on variacs and dealing with manually applied current limiting, you get accustomed to it. My local service shop used large DBTs back in tube days then changed to variacs, only because his service agency agreements and conditions began to make it necessary. In his own workshop, he stuck to DBTs and preferred them in audio service work to the end.
However, perhaps as Craig is suggesting, the real reason for a DBT is protection, particularly at first power-up on unchecked circuits. This foolproof type of protection is almost mandatory for newbie builders and also what a lot of threads are about, driving home the realities of build errors and junk components. Often, there is no specific need to vary the supply voltage. A DBT protects cheaply, reliably and with visual indication. It's a pleasure to use for the simple task of getting up and running with minimal casualties.
A variac provides protection only to the degree of operator attention to the voltage and current level - responding with skill learned in constant use. i.e. professional repairers. If you power on at some arbitrary voltage or crank up from zero until you see signs of life, you'll still see the magic smoke escape unless you know exactly what you're doing and act quickly.
I use a Variac too when I need to do reliability checks but not the cheap auto-transformer type that is still not considered safe to use here, earthed case or not. For even only 750VA capacity, a fully isolated transformer variac is out of reach of most newbies. Unless a collector of gadgets, why would anyone pay more money to buy test equipment than the value of the little DIY that many guys actually undertake? That only makes sense to pro. repair businesses where the money can be justified in returns. With a few large amplifier repairs, it might pay for itself. You'd never pay anything off repairing a few domestic amps for yourself and friends though.
However, perhaps as Craig is suggesting, the real reason for a DBT is protection, particularly at first power-up on unchecked circuits. This foolproof type of protection is almost mandatory for newbie builders and also what a lot of threads are about, driving home the realities of build errors and junk components. Often, there is no specific need to vary the supply voltage. A DBT protects cheaply, reliably and with visual indication. It's a pleasure to use for the simple task of getting up and running with minimal casualties.
A variac provides protection only to the degree of operator attention to the voltage and current level - responding with skill learned in constant use. i.e. professional repairers. If you power on at some arbitrary voltage or crank up from zero until you see signs of life, you'll still see the magic smoke escape unless you know exactly what you're doing and act quickly.
I use a Variac too when I need to do reliability checks but not the cheap auto-transformer type that is still not considered safe to use here, earthed case or not. For even only 750VA capacity, a fully isolated transformer variac is out of reach of most newbies. Unless a collector of gadgets, why would anyone pay more money to buy test equipment than the value of the little DIY that many guys actually undertake? That only makes sense to pro. repair businesses where the money can be justified in returns. With a few large amplifier repairs, it might pay for itself. You'd never pay anything off repairing a few domestic amps for yourself and friends though.
It's great to get some different opinions about this. I for one don't inspire for commercial use and definitely consider myself as a newbie. I love how simple to use and straight forward the dim bulb tester is, it has helped a lot and saved me some money on components. I can understand why at some point a variac would be considered more accurate and "professional" but also needs more understanding on how to use it and an activity that justifies the investment. Just out of curiosity I started looking and I found a lot that were affordable, but I think those are probably the "cheap auto-transformer" you are talking about.
HI Ian,
Why buy decent equipment? Because, you know for certain what is going on and using good stuff makes the hobby pleasureable.
I have yet to see any hobbyist look at expenditures from an economic viewpoint. Whether the hobby is quilting (my wife has good stuff so she doesn't have to fight it), or some path in electronics, money has to be spent and equipment acquired over time. That's the fun of a hobby. Look at a HAM shack some day and add their stuff up.
You can couple a variac with an isolation transformer and create a perfectly safe test solution for not too much money. But don't think of it as protection, it is a way where you can partially power unknown equipment up in order to measure some key parameters. That way you can stop turning it up if something looks off.
Meters and 'scopes. It's important that your equipment doesn't lie to you. Get at least one good meter that you can check the horde of cheap ones against. A used analog scope is often better than a new cheap digital because they will handle higher voltages that would kill a cheaper DSO.
I know a lot of hobbyists that do better work and know more than many service technicians that don't have an interest in the subject. Part of being good and enjoying the hobby comes from being sure of your measurements so you can make intelligent decisions and learn. From the days when we started, today's hobbyist has it a lot better, and a lot less expensive than we did. I still have my main meter I used in my early teens. A Heathkit IM-18 VTVM. I built it and used it for years. Too bad you can't really do that anymore.
-Chris
Why buy decent equipment? Because, you know for certain what is going on and using good stuff makes the hobby pleasureable.
I have yet to see any hobbyist look at expenditures from an economic viewpoint. Whether the hobby is quilting (my wife has good stuff so she doesn't have to fight it), or some path in electronics, money has to be spent and equipment acquired over time. That's the fun of a hobby. Look at a HAM shack some day and add their stuff up.
You can couple a variac with an isolation transformer and create a perfectly safe test solution for not too much money. But don't think of it as protection, it is a way where you can partially power unknown equipment up in order to measure some key parameters. That way you can stop turning it up if something looks off.
Meters and 'scopes. It's important that your equipment doesn't lie to you. Get at least one good meter that you can check the horde of cheap ones against. A used analog scope is often better than a new cheap digital because they will handle higher voltages that would kill a cheaper DSO.
I know a lot of hobbyists that do better work and know more than many service technicians that don't have an interest in the subject. Part of being good and enjoying the hobby comes from being sure of your measurements so you can make intelligent decisions and learn. From the days when we started, today's hobbyist has it a lot better, and a lot less expensive than we did. I still have my main meter I used in my early teens. A Heathkit IM-18 VTVM. I built it and used it for years. Too bad you can't really do that anymore.
-Chris
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