I've gone through a Citation 12 and done a partial refurb for a friend, changing out all the passives at his request. I have different thread going regarding the input capacitors, which is another story entirely. I wanted to make a separate thread so things didn't get muddy.
The electrolytic caps have been replaced with new Nichicon KZ or similar, the resistors are now all Dale 1 percent tolerance metal film. I've added some ceramic discs across the regulators, and installed gold 5 way binding posts. The left channel now has a buzz through the speaker - sounds like a bad ground, or a power supply noise, but...
Before I rebuilt this thing the big filter caps were vibrating badly. After the work they're dead quiet both to the ear and to the touch, and so are the transformers. I've also re-flowed all the ground connections I could see, but the buzz is still coming through the speaker. Where could this be coming from?
The electrolytic caps have been replaced with new Nichicon KZ or similar, the resistors are now all Dale 1 percent tolerance metal film. I've added some ceramic discs across the regulators, and installed gold 5 way binding posts. The left channel now has a buzz through the speaker - sounds like a bad ground, or a power supply noise, but...
Before I rebuilt this thing the big filter caps were vibrating badly. After the work they're dead quiet both to the ear and to the touch, and so are the transformers. I've also re-flowed all the ground connections I could see, but the buzz is still coming through the speaker. Where could this be coming from?
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look at the side of the silent blocks of the power transformers and also look at the side of the connectors of the main pcb
Thank you for the advice. After reading that and re-reading my post I think I may have framed it improperly. The buzz isn't a physical buzz coming from the chassis, this is an electrical buzz coming through the speaker of the left channel.
I've edited the post to (hopefully) make things clearer, and I apologize for the bad writing.
Have you read this?
Citation 12 Power Amp
He had a hum problem in the left channel as well.
in case of a ground loop, try removing the input socket from the chassis or the input cable from the amplifier board.
Did you clean the pc board edge connectors as well as the socket?
Did you put any electrolytic caps in backwards? Accidently put in the wrong resistor value.
did you clean and retighten the screw on the power supply filter caps?
Compare the power supply +/- AC ripple voltage to each channel.
you have 2 mono amplifiers, you can compare everything between channels.
Citation 12 Power Amp
He had a hum problem in the left channel as well.
in case of a ground loop, try removing the input socket from the chassis or the input cable from the amplifier board.
Did you clean the pc board edge connectors as well as the socket?
Did you put any electrolytic caps in backwards? Accidently put in the wrong resistor value.
did you clean and retighten the screw on the power supply filter caps?
Compare the power supply +/- AC ripple voltage to each channel.
you have 2 mono amplifiers, you can compare everything between channels.
I saw that article a few days ago. His amp problem was different than this. I had the hum in this amp until I recapped it. Thats completely gone. The issue I hear now is a very bad buzz out of the left channel.
There was no need to clean the screws on the filter caps because I used all new hardware. I also fabricated new bus bars out of 10ga copper solid-core house wiring, with automotive-grade ring connectors at each end. I pulled the leads off the old bus wires and soldered them to the new bus bars as a package.
I verified values and directions on the passives multiple times, but it doesn't hurt to re-verify them so I'll check that. I didn't clean the board connections. Thats a great idea, so I'll put that on the list.
How do I check the AC ripple voltage? I have a scope, DMM, and an AWG if that helps.
DMM on A.C. volts same with the scope. On the scope you could check your buzz to see if it's 100/120 Hz or 50/60 Hz.
Would love to hear (your) amp.
Nice work Talon, I am a huge KZ fan!! Literally stock nearly every value, I use them so much ...pretty much across the board... KZs are a - big - open - window to the musical experience and lend to a very neutral sound, in all my work... I bet it'll sound fabulous.
Would like to hear "this amp" as you describe it *done up right*. I have never heard a "proper" Citation amp, with good [more current] parts.
Good luck on the buzz...
I struggle admitting, I reversed the input on one channel, in one amp build, and that channel buzzed... lucky that is all... Vision issues with age, is tough for me... reading glasses everywhere....
Nice work Talon, I am a huge KZ fan!! Literally stock nearly every value, I use them so much ...pretty much across the board... KZs are a - big - open - window to the musical experience and lend to a very neutral sound, in all my work... I bet it'll sound fabulous.
Would like to hear "this amp" as you describe it *done up right*. I have never heard a "proper" Citation amp, with good [more current] parts.
Good luck on the buzz...
I struggle admitting, I reversed the input on one channel, in one amp build, and that channel buzzed... lucky that is all... Vision issues with age, is tough for me... reading glasses everywhere....
I have some bench time today so I'm tackling this amp again. I'll warm up the Siglent and see whats coming out of the outputs, as you suggested.
I forgot to mention - I tried adjusting the bias and found the pots very uncooperative. One I was able to get adjusted, the other had a huge flat spot in the center and only changed the values at the extreme ends of the rotation. Since these are cheap old Amphenol open pots, I'd like to replace them with quality Vishay or Bourns sealed trimmers. Only issue... The originals are 10mm across (5mm lead spacing), all the new ones are 5mm across at the largest. The widest lead spacing I could find was 3.81mm, which since only two leads are active (this pot is strictly a trimmer and not a voltage divider) I guess I could make that work. But why does this original pot say "4.7k (5k) on it? Which value should I really shop for?
I forgot to mention - I tried adjusting the bias and found the pots very uncooperative. One I was able to get adjusted, the other had a huge flat spot in the center and only changed the values at the extreme ends of the rotation. Since these are cheap old Amphenol open pots, I'd like to replace them with quality Vishay or Bourns sealed trimmers. Only issue... The originals are 10mm across (5mm lead spacing), all the new ones are 5mm across at the largest. The widest lead spacing I could find was 3.81mm, which since only two leads are active (this pot is strictly a trimmer and not a voltage divider) I guess I could make that work. But why does this original pot say "4.7k (5k) on it? Which value should I really shop for?
Only choose a pot that will fit on the board properly, and be mechanically stable.
Pots have a wide tolerance, and are made only in rough values: 1k, 2k, 5k, 10k, etc.
Pots have a wide tolerance, and are made only in rough values: 1k, 2k, 5k, 10k, etc.
Since the pot is used as a variable resistor and not a voltage divider, there's no reason
to distinguish between 4.7k and 5k. And those are less than 10% apart anyway.
to distinguish between 4.7k and 5k. And those are less than 10% apart anyway.
Good to know, thank you.
Now I just have to find the right part to replace these things. I can find a wide variety of packages but nothing seems to allow me 3 leads in line with each other, with a 5mm spacing between them. The closest I've some is the Bourns 3386S, which gives me 3.8mm between the leads. I can spread the two live leads and make them fit, and then just ignore the dead lead.
Now I just have to find the right part to replace these things. I can find a wide variety of packages but nothing seems to allow me 3 leads in line with each other, with a 5mm spacing between them. The closest I've some is the Bourns 3386S, which gives me 3.8mm between the leads. I can spread the two live leads and make them fit, and then just ignore the dead lead.
That one would work electrically, but physically its too small. Also, it has a tripod arrangement, not in-line.
I think if I can't find a through-hole trimmer that meets the lead spacing, I'll cut the old trimmers out and leave their legs in place, then solder to those. Kludge, but it might be the only way to go.
If you look at the data sheet, it's available in either vertical or horizontal footprint.
Most such pots have a standard size and pinout.
Most such pots have a standard size and pinout.
Right. Looking over that data sheet I think the right one would be the 3362M, but it has a smaller lead spacing than the 3386S I was looking at earlier.
https://www.bourns.com/docs/Product-Datasheets/3386.pdf
The 3386S would get me to a 3.81mm spacing, which is workable. Unfortunately, neither Digikey nor Mouser have stock of that.
https://www.bourns.com/docs/Product-Datasheets/3386.pdf
The 3386S would get me to a 3.81mm spacing, which is workable. Unfortunately, neither Digikey nor Mouser have stock of that.
There have been a few trimpot styles with wider lead spacing, arranged in a triangle.
You may be able to find one of those.
Or just use a horizontal pot like this and bend the leads to fit the board.
These are very high quality trim pots.
https://www.bourns.com/docs/product-datasheets/3329.pdf?sfvrsn=337991f1_10
You may be able to find one of those.
Or just use a horizontal pot like this and bend the leads to fit the board.
These are very high quality trim pots.
https://www.bourns.com/docs/product-datasheets/3329.pdf?sfvrsn=337991f1_10
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I found the Bourns 3386S-1-502LF. Its got the right specs and a lead spacing I can work with. At 3.81mm spacing I just have to bend the wiper and one of the two outer pins enough to make up 1.2mm. If I can get the third pin far enough into its hole to anchor it, so much the better, but I'm not going to lose sleep over it if that doesn't work. I can always put a dab of hot glue on each pot package to secure them to the board.
Out of curiosity I pulled the input cables out of the jacks and ran the amp "headless" with just the speakers connected. The first thing I heard was a loud pop noise with a scratching noise accompanying it. I've now got a continuous waveform buzz coming out of both channels and it was LOUD. It sounded very similar to the buzz on old AM radio broadcasts.
Not only that - do you recall the sound that analog cell phones used to be able to push through nearby stereos when they were about to ring, or when a call was getting made? A kind of pulsating buzz. I now had that on top of the continuous buzz.
I removed the 4.7uF input capacitors that were recommended in my other thread and replaced them with 220uF 63v to balance out the feedback cap on the backside of the differential pair. The buzz was less but that pulsing noise was still there.
I then cut off the ceramic caps I'd put across the bridge rectifiers. That killed the pulsing noise. I have no idea what was going on there. Nelson Pass had suggested those as an option, and I guess they're contraindicated for this amp.
Connecting source cables to the inputs dropped the volume on the input buzz dramatically but I still have a very prominent buzz coming through on both channels. I didn't have a chance to hook up the oscilloscope and now its time to break for the evening. Hopefully I can get on this early tomorrow.
Not only that - do you recall the sound that analog cell phones used to be able to push through nearby stereos when they were about to ring, or when a call was getting made? A kind of pulsating buzz. I now had that on top of the continuous buzz.
I removed the 4.7uF input capacitors that were recommended in my other thread and replaced them with 220uF 63v to balance out the feedback cap on the backside of the differential pair. The buzz was less but that pulsing noise was still there.
I then cut off the ceramic caps I'd put across the bridge rectifiers. That killed the pulsing noise. I have no idea what was going on there. Nelson Pass had suggested those as an option, and I guess they're contraindicated for this amp.
Connecting source cables to the inputs dropped the volume on the input buzz dramatically but I still have a very prominent buzz coming through on both channels. I didn't have a chance to hook up the oscilloscope and now its time to break for the evening. Hopefully I can get on this early tomorrow.
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your buzz is present with a source connected to the input or also without a source?
mine, without connected source is noisy but once connected it is dead silence.
on the other hand if the holding is noisy with a source connected, try to disconnect only one side to see what happens.
mine, without connected source is noisy but once connected it is dead silence.
on the other hand if the holding is noisy with a source connected, try to disconnect only one side to see what happens.