Picked up a NAD 1300 pre amp. Upon initial testing, knobs were scratchy, had a low hum and only one channel worked.
I used deoxit on all the knob/buttons, removed the old board glue (which I have heard can become a conductor) and inspected and resoldered some questionable joints, including the output RCA jack.
I also swapped out the RCA jacks from the pre amp to the amplifier and the bad channel appears to be the left side of the pre amp.
The hum is now gone as is the scratchiness, but still only have sound out of one speaker. However, when I plug in my headphones, both speakers work fine. Also, when the volume is all the way off, I can still faintly hear the music in the one working channel.
Any thoughts on what might be causing just the one speaker to work?
The one channel sounds great...would really like to hear what the pre amp sounds like in stereo!
I used deoxit on all the knob/buttons, removed the old board glue (which I have heard can become a conductor) and inspected and resoldered some questionable joints, including the output RCA jack.
I also swapped out the RCA jacks from the pre amp to the amplifier and the bad channel appears to be the left side of the pre amp.
The hum is now gone as is the scratchiness, but still only have sound out of one speaker. However, when I plug in my headphones, both speakers work fine. Also, when the volume is all the way off, I can still faintly hear the music in the one working channel.
Any thoughts on what might be causing just the one speaker to work?
The one channel sounds great...would really like to hear what the pre amp sounds like in stereo!
Some amps/preamps run the output through the switch of a headphone jack. So the speaker or output is disconnected by the switch when the headphone is plugged in. These jacks use cheap tinplate for switch contacts, so in the long run they can oxidize and cause the speaker or output to be permanently silent. Getting at them with a steel pick and scratching up the switch surface is about the best de-oxygen procedure, but obviouly won't be permanent.
You need for a preamp a meter with an AC volts scale of 2 v to trace the music to see where it stops. I've found $40 DVM tend to produce random numbers on music, they are fine at 60 or 50 hz AC wall socket frequency. $200 RMS DVM are popular, but they ignore any frequency over 7000 so they can miss ultrasonic oscillation. I prefer an analog VOM, particularly as they contain no electrolytic caps and will work as well in 50 years as they did on day one if you don't drop them or burn them up with too much voltage.
Aligator clip leads are also useful for tracing music through circuits. The regular ones work on the analog ground, but the tiny leads of resistors, caps & IC's, require a Pamona grabber or equivalent Q-ball tip.
Or there are scopes, the cheap versions of which are not rated over 80 vac input, which most brochures don't mention. You find out from the datasheet packed with the product. Scope probes are nice, but if you step on it you just blew $50. Grabbers are about $12 and are fine at audio frequencies. Scope probes are required for radio-TV etc.
You need for a preamp a meter with an AC volts scale of 2 v to trace the music to see where it stops. I've found $40 DVM tend to produce random numbers on music, they are fine at 60 or 50 hz AC wall socket frequency. $200 RMS DVM are popular, but they ignore any frequency over 7000 so they can miss ultrasonic oscillation. I prefer an analog VOM, particularly as they contain no electrolytic caps and will work as well in 50 years as they did on day one if you don't drop them or burn them up with too much voltage.
Aligator clip leads are also useful for tracing music through circuits. The regular ones work on the analog ground, but the tiny leads of resistors, caps & IC's, require a Pamona grabber or equivalent Q-ball tip.
Or there are scopes, the cheap versions of which are not rated over 80 vac input, which most brochures don't mention. You find out from the datasheet packed with the product. Scope probes are nice, but if you step on it you just blew $50. Grabbers are about $12 and are fine at audio frequencies. Scope probes are required for radio-TV etc.
Just spray the sockets with Deoxit or similar, and work jacks in and out.
If it clears up, you found the fault, and replace (or if not using),short out the jacks.
Tell us what happened.
And some circuits use the jack switch to run the mute circuit, unlikely here as one channel is on power.
Check the schematic.
And indianajo's suggestion of an analog meter is good, a hack would be a scrap VU meter with a 10 ohm series resistor...for the pre amp at least.
If it clears up, you found the fault, and replace (or if not using),short out the jacks.
Tell us what happened.
And some circuits use the jack switch to run the mute circuit, unlikely here as one channel is on power.
Check the schematic.
And indianajo's suggestion of an analog meter is good, a hack would be a scrap VU meter with a 10 ohm series resistor...for the pre amp at least.
Thanks for the feedback guys. I've sprayed all sockets with Deoxit but this hasn't resolved the channel issue. I'll trying "working" the jacks to see if that makes a difference.
I do own a DMM (Radio Shack brand...I know, insert laugh here 🙂... but it is of lower quality and I'm not sure if I have the skills to trace the music to see where it stops. The schematic for the NAD 1300 isn't as intuitive to me as other schematics that I've looked at. Likewise for scraping the VU meter with a 10 ohm resistor...I would need more specific instructions to complete the task.
I do own a DMM (Radio Shack brand...I know, insert laugh here 🙂... but it is of lower quality and I'm not sure if I have the skills to trace the music to see where it stops. The schematic for the NAD 1300 isn't as intuitive to me as other schematics that I've looked at. Likewise for scraping the VU meter with a 10 ohm resistor...I would need more specific instructions to complete the task.
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VU meters were analog Volume Unit meters in old stereos.
They are really analog volt meters with a different scale, so will work as a tracer for the signal.
You can find one in old sets, you may have one in scrap.
Or use a analog meter in its lowest AC volts scale, no more than 10V, more is not sensitive enough.
Hack no. 2 is a small 2 to 3 inch speaker....from a broken toy is fine.
One end to ground, through a resistor, and the other through a probe....
Leave the unit for a day after spraying and working jacks, allow the spray to penetrate. Then see how it responds.
They are really analog volt meters with a different scale, so will work as a tracer for the signal.
You can find one in old sets, you may have one in scrap.
Or use a analog meter in its lowest AC volts scale, no more than 10V, more is not sensitive enough.
Hack no. 2 is a small 2 to 3 inch speaker....from a broken toy is fine.
One end to ground, through a resistor, and the other through a probe....
Leave the unit for a day after spraying and working jacks, allow the spray to penetrate. Then see how it responds.
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I predict your radio shack meter will provide random number when measuring music or frequencies different than 50 or 60 hz. I trace music from a earphone jack of a $10 FM radio or a $15 kiddie keyboard, using 1/8" stereo plug to dual RCA plug adapter cable. Don't use a cell phone. Any DC or oscillation fed back from input of a defective product under test can blow a $600 phone.
The supply of used simpson 260 analog multimeters or equivalent triplett models with 2 vac scale in this country is huge. Even a $40 new analog meter from china with a 10 vac scale would be useful. They are often sold at hardware stores. I've never had a VU meter to scrap out.
With analog meter, you have to block DC from the ground probe with a series .047 uf capacitor, to keep them from reading DC voltage on the AC scale. Again a couple of alligator clip leads is necessary. They come in bundles of 10 usually, and don't buy the $40 alligator clip from Fluke. It is so safe from 600 vac that it is useless for microelectronics.
As far as music flow, major blockers are the volume pot, ribbon cables between boards or to from the front panel, or the output jack. If you get music (from portable radio earphone jack) going into output jack solder terminal but not coming out on a cable, there you are.
The supply of used simpson 260 analog multimeters or equivalent triplett models with 2 vac scale in this country is huge. Even a $40 new analog meter from china with a 10 vac scale would be useful. They are often sold at hardware stores. I've never had a VU meter to scrap out.
With analog meter, you have to block DC from the ground probe with a series .047 uf capacitor, to keep them from reading DC voltage on the AC scale. Again a couple of alligator clip leads is necessary. They come in bundles of 10 usually, and don't buy the $40 alligator clip from Fluke. It is so safe from 600 vac that it is useless for microelectronics.
As far as music flow, major blockers are the volume pot, ribbon cables between boards or to from the front panel, or the output jack. If you get music (from portable radio earphone jack) going into output jack solder terminal but not coming out on a cable, there you are.
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Really appreciate the additional insight. To be honest, I think I may be over my skis on this one. Generally speaking I'm following the advice being provided, but terms like "ultrasonic oscillation" are foreign for me. Clearing shows your knowledge level is many pay grades above mine!
For me to trace the music path it sounds like I will need to upgrade to a new DMM or use some sort of proxy device (small speaker, earphone jack, etc.) and also need to get comfortable reading the schematic to determine the exact path on the board to trace. I think finding a proxy testing device should be easy enough. However, I'm not sure I can confidently read the pre amps schematic to the level necessary to know exactly the tracing steps. Again, I've had limited success in the past reading schematics from older equipment (e.g., Pioneer SX receivers) but those schematics seemed to be more complete and easier to read.
Any suggestions on how to figure out the path or am I out of luck here?
For me to trace the music path it sounds like I will need to upgrade to a new DMM or use some sort of proxy device (small speaker, earphone jack, etc.) and also need to get comfortable reading the schematic to determine the exact path on the board to trace. I think finding a proxy testing device should be easy enough. However, I'm not sure I can confidently read the pre amps schematic to the level necessary to know exactly the tracing steps. Again, I've had limited success in the past reading schematics from older equipment (e.g., Pioneer SX receivers) but those schematics seemed to be more complete and easier to read.
Any suggestions on how to figure out the path or am I out of luck here?
Learning this hobby is more fun that crossword puzzles & more remunerative IMHO. Keeps products out of the dump, and keeps you from running to the store to buy another 3 year life (or shorter) product. The lords of commerce expect the latter, and design their products to fail sooner (consumer) or later (professional grade). They do things like patenting their batteries or connectors to keep aftermarket parts dealers from selling parts. Like the Apple earphone jack, changes with every model or two.
"ultrasonic oscillation" of an amp/preamp means your fan is running hard, or the heat sinks or transistors are heating up, your analog meter reads significant AC voltage out, but you can't hear anything. The frequency is too high for your ears. Audio circuits can do it, but aren't supposed to. Op amp swapping can cause it, or just bad design.
You can hope your board is labeled with Q#s (transistors) R#s (resistors) C numbers (capacitors) U#s (ICs) to help you follow the music flow through the circuit boards. Those reference disignations will be on the schematic diagram. If not, music generally flows from the input connector, loop to the volume pot on front panel, then back and towards the output jack.
If you have transistor or IC part type numbers, you can look up the manufacturer's diagram on sources like datasheetcatalog.com for a picture of name of each pin.
I don't expect much help from tracing sound with a speaker on a preamp. Some 32 ohm speakers are available for use with computers, but anything 8 ohm or below will just sit there doing nothing. You can build a sound probe, which is an amplifier/speaker combination with an input that is protected to prevent damage from DC or too much AC voltage. Working computer speakers were ideal, but they are cheap and mostly blew up a decade ago. Protector is two .047 uf caps (roughly) series the hot and ground. after that, a 2 k resistor series each hot & ground. After that two red LED's across the outputs of the resistors, one plus to plus, one plus to minus. Plus of an LED is the long lead. The LED's clamp the input to 2.2 v, about line level max. Then to the hot & ground input of the amp. You probe around with aligator clip leads or pamona grabbers.
Basic knowledge can be gained in a hurry by reading a local community college textbook on electronics. I liked "electronic devices the electron flow version" I picked up for $2 at Goodwill resale shop. Problems go obsolete in textbooks, in 2 years. They lose their value and are flogged off or donated. Lots of parts were invented since I went to college & studied the "GE transistor manual 6th edition" which was obsolete in 1968 anyway. Interstage transformer coupled amps went the way of the dodo bird about 1965.
"ultrasonic oscillation" of an amp/preamp means your fan is running hard, or the heat sinks or transistors are heating up, your analog meter reads significant AC voltage out, but you can't hear anything. The frequency is too high for your ears. Audio circuits can do it, but aren't supposed to. Op amp swapping can cause it, or just bad design.
You can hope your board is labeled with Q#s (transistors) R#s (resistors) C numbers (capacitors) U#s (ICs) to help you follow the music flow through the circuit boards. Those reference disignations will be on the schematic diagram. If not, music generally flows from the input connector, loop to the volume pot on front panel, then back and towards the output jack.
If you have transistor or IC part type numbers, you can look up the manufacturer's diagram on sources like datasheetcatalog.com for a picture of name of each pin.
I don't expect much help from tracing sound with a speaker on a preamp. Some 32 ohm speakers are available for use with computers, but anything 8 ohm or below will just sit there doing nothing. You can build a sound probe, which is an amplifier/speaker combination with an input that is protected to prevent damage from DC or too much AC voltage. Working computer speakers were ideal, but they are cheap and mostly blew up a decade ago. Protector is two .047 uf caps (roughly) series the hot and ground. after that, a 2 k resistor series each hot & ground. After that two red LED's across the outputs of the resistors, one plus to plus, one plus to minus. Plus of an LED is the long lead. The LED's clamp the input to 2.2 v, about line level max. Then to the hot & ground input of the amp. You probe around with aligator clip leads or pamona grabbers.
Basic knowledge can be gained in a hurry by reading a local community college textbook on electronics. I liked "electronic devices the electron flow version" I picked up for $2 at Goodwill resale shop. Problems go obsolete in textbooks, in 2 years. They lose their value and are flogged off or donated. Lots of parts were invented since I went to college & studied the "GE transistor manual 6th edition" which was obsolete in 1968 anyway. Interstage transformer coupled amps went the way of the dodo bird about 1965.
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the headphone output is the output of the preamp- -thus if you signal at the headphones the preamp is working-however the RCA outputs are connected to the headphones via a relay- which would be my first point of interest does it click?
indianajo - completely agree, I always prefer to try to revive the older equipment than to see it thrown away. I've had great success fixing older turntables, especially the older Duals and Elacs. I'm not about to give up on the NAD pre amp. Thanks for all of the feedback/information.
pwdiya12 - regarding the relay click, are you asking if the relay clicks when the headphone jack is inserted, directly after taking out the jack or when the pre amp is initially turned on with no headphones inserted? Want to make sure I understand the timing of when the relay should click.
pwdiya12 - regarding the relay click, are you asking if the relay clicks when the headphone jack is inserted, directly after taking out the jack or when the pre amp is initially turned on with no headphones inserted? Want to make sure I understand the timing of when the relay should click.
Does relay ever click?
Schematic should show what it is for. Source selector, or output turn off for some reason? Power supply to relay could have blown, PS regulators zener diodes & filter capacitors are high failure parts. You know your main power supply is working without measuring because one channel works.
Dirty relay contacts can stop music. Need to be gold or palladioum or rhodium plated contacts @ 2 vac 2000 ohm source. Most preamps don't have a relay.
Edit, downloaded schematic from electrotanya. Relay is controlled by SW601-2 & Q522. Not obvious what is driving Q522 and this version doesn't say what S601-2 is for. Relay definitely blocks output. Shunts output jacks to ground if not pulled in.
Schematic should show what it is for. Source selector, or output turn off for some reason? Power supply to relay could have blown, PS regulators zener diodes & filter capacitors are high failure parts. You know your main power supply is working without measuring because one channel works.
Dirty relay contacts can stop music. Need to be gold or palladioum or rhodium plated contacts @ 2 vac 2000 ohm source. Most preamps don't have a relay.
Edit, downloaded schematic from electrotanya. Relay is controlled by SW601-2 & Q522. Not obvious what is driving Q522 and this version doesn't say what S601-2 is for. Relay definitely blocks output. Shunts output jacks to ground if not pulled in.
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Whoa! Failed 100 uf electrolytic cap. Who knew?
If it was mine I would change ALL .the electrolytics. 2 at a time followed by checks to point out where I just installed a bad solder joint or incorrect part.
I use 3000 hours service life parts up, to avoid doing the job again in 4 years. Lots of 500 hour caps for sale. You can get 10000 hour caps in the 100 uf size.
If it was mine I would change ALL .the electrolytics. 2 at a time followed by checks to point out where I just installed a bad solder joint or incorrect part.
I use 3000 hours service life parts up, to avoid doing the job again in 4 years. Lots of 500 hour caps for sale. You can get 10000 hour caps in the 100 uf size.
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