Well, I'm done with trying to eliminate this hum for now. I did have some marginal success with reducing it slightly. I was pretty much already done but I came across a few videos on youtube that showed troubleshooting a ground loop hum. I put the amp back on the bench and tried using a piece of wire to make a new ground path from various points. One of these was to place one end of the wire on the ground strap from the ground strap for the PCB to the opposite side of the board near C17. That took some of the edge off the hum but did not eliminate it. I decided to run a 16AWG wire from the strap to the pad for the jumper wire near C17 and leave it that. Maybe some day when I am feeling adventuresome I'll trace out the ground paths to see how many jumpers are used to tie into the perimeter ground plane to see if I can isolate and reground different points on the board. I will note that there is one track for the heater circuit that runs parallel to the ground for quite a bit of distance. The ground strap is at one end of this run and the place where I tied the new wire is at the other end.
Other thoughts - I don't know if I am expecting too much here or not. The hum can easily be drowned out with background noise and it is not noticeable when music is playing. I just notice it in the time between when the amp unmutes and the music starts. I'll also admit that my bench testing setup is not the best for testing this due to the small speaker I am using. There is a notable difference between a single 8" speaker and 3 x 12" speakers when it comes to 60hz hum.
Carl Haines
Hello Carl, I had a very similar "hum" issue on my 1948 Rockola 1428 Magic Glow. When I fist got this jukebox I rebuilt the amp and had the original crystal pick-up cartridge rebuilt by the outfit in West Virginia. It played great for about 5 years after which it started with the loud hum just as you stated when the amp heated up, but kinda disappeared, or subsided when the music started playing. I chased similar areas within the amp, but I had changed pretty much replaced everything out when I rebuilt it long ago. What I determined was the old rebuilt crystal cartridge had finally bit the dust. I got a modern Astatic 51 replacement and installed which cured the hum. Check the braided cable from cartridge to amp to insure braid is grounded and live internal wire is not grounded. You might want to try using another new or rebuilt cartridge to see if it fixes your hum. Regards,Walter "Britt" Abbott On Monday, February 6, 2023 at 11:40:10 AM EST, Carl Haines via Jukebox-list jukebox-list@lists.netlojix.com wrote:
Well, I'm done with trying to eliminate this hum for now. I did have some marginal success with reducing it slightly. I was pretty much already done but I came across a few videos on youtube that showed troubleshooting a ground loop hum. I put the amp back on the bench and tried using a piece of wire to make a new ground path from various points. One of these was to place one end of the wire on the ground strap from the ground strap for the PCB to the opposite side of the board near C17. That took some of the edge off the hum but did not eliminate it. I decided to run a 16AWG wire from the strap to the pad for the jumper wire near C17 and leave it that. Maybe some day when I am feeling adventuresome I'll trace out the ground paths to see how many jumpers are used to tie into the perimeter ground plane to see if I can isolate and reground different points on the board. I will note that there is one track for the heater circuit that runs parallel to the ground for quite a bit of distance. The ground strap is at one end of this run and the place where I tied the new wire is at the other end.
Other thoughts - I don't know if I am expecting too much here or not. The hum can easily be drowned out with background noise and it is not noticeable when music is playing. I just notice it in the time between when the amp unmutes and the music starts. I'll also admit that my bench testing setup is not the best for testing this due to the small speaker I am using. There is a notable difference between a single 8" speaker and 3 x 12" speakers when it comes to 60hz hum.
Carl Haines _______________________________________________ Jukebox-list mailing list -- jukebox-list@lists.netlojix.com To unsubscribe send an email to jukebox-list-leave@lists.netlojix.com %(web_page_url)slistinfo%(cgiext)s/%(_internal_name)s Searchable Archives: http://jukebox.markmail.org/
On Monday, February 6, 2023 at 11:40:10 AM EST, Carl Haines via Jukebox-list jukebox-list@lists.netlojix.com wrote:
Well, I'm done with trying to eliminate this hum for now. I did have some marginal success with reducing it slightly. I was pretty much already done but I came across a few videos on youtube that showed troubleshooting a ground loop hum.
If only someone made a board that used a continuous ground plane and would also take ceramic and magnetic inputs.
On 2023-02-07 15:16, Jay Hennigan via Jukebox-list wrote:
On Monday, February 6, 2023 at 11:40:10 AM EST, Carl Haines via Jukebox-list jukebox-list@lists.netlojix.com wrote:
Well, I'm done with trying to eliminate this hum for now. I didhave some marginal success with reducing it slightly. I was pretty much already done but I came across a few videos on youtube that showed troubleshooting a ground loop hum.
If only someone made a board that used a continuous ground plane and would also take ceramic and magnetic inputs.
Looks nice! Did I miss the memo somewhere? I don't see where this is available. Nothing on the winsome-labs.com web page.
I do wonder if this message will make it through. I did post a reply to Rob and Britt that bounced.
Carl Haines
On 2/7/23 15:38, Carl Haines via Jukebox-list wrote:
On 2023-02-07 15:16, Jay Hennigan via Jukebox-list wrote:
On Monday, February 6, 2023 at 11:40:10 AM EST, Carl Haines vi If only someone made a board that used a continuous ground plane and would also take ceramic and magnetic inputs.
Looks nice! Did I miss the memo somewhere? I don't see where this is available. Nothing on the winsome-labs.com web page.
Winsome Labs is me. I haven't advertised it yet, made a couple for myself and put one in an amplifier I rebuilt for someone. Not sure exactly what price I'm going to put on it.
I also have a design for a replacement for the stereo one that can take 6GH8/6U8 instead of the scarce 7199. Not in production yet.
I do wonder if this message will make it through. I did post a reply to Rob and Britt that bounced.
Can you forward a copy of the bounced message to me privately? I think I've got things dialed in. Kind of a learning curve between Mailman 2 and Mailman 3. Thanks!
On 2023-02-07 19:56, Jay Hennigan via Jukebox-list wrote:
Winsome Labs is me. I haven't advertised it yet, made a couple for myself and put one in an amplifier I rebuilt for someone. Not sure exactly what price I'm going to put on it.
I also have a design for a replacement for the stereo one that can take 6GH8/6U8 instead of the scarce 7199. Not in production yet.
Good luck with the launch for both. It will certainly be a nice option to have especially if you have one that has not yet been recapped and consider the work needed to recap and potential damage to the board vs. installing a new board even if it comes as a kit requiring assembly. Mine had a previous repair where they lifted one track and I consider myself lucky that was the extent of the damage.
Carl Haines
I can see this chat has been going on for a while, but unfortunately this is the only one I have read.
Worth mentioning, but I have a 532 amp and had hum exactly as you have described. The problem turned out to be the bakelite remote volume socket and blanking plug. That was conducting to ground. I never used it anyway so I bypassed it and the hum disappeared. Apologies if this has already been mentioned, cheap and easy fix, worth a try.
Regards
Nigel, uk
On 8 Feb 2023 at 03:03, Carl Haines via Jukebox-list jukebox-list@lists.netlojix.com wrote:
On 2023-02-07 19:56, Jay Hennigan via Jukebox-list wrote:
Winsome Labs is me. I haven't advertised it yet, made a couple for myself and put one in an amplifier I rebuilt for someone. Not sure exactly what price I'm going to put on it.
I also have a design for a replacement for the stereo one that can take 6GH8/6U8 instead of the scarce 7199. Not in production yet.
Good luck with the launch for both. It will certainly be a nice option to have especially if you have one that has not yet been recapped and consider the work needed to recap and potential damage to the board vs. installing a new board even if it comes as a kit requiring assembly. Mine had a previous repair where they lifted one track and I consider myself lucky that was the extent of the damage.
Carl Haines _______________________________________________ Jukebox-list mailing list -- jukebox-list@lists.netlojix.com To unsubscribe send an email to jukebox-list-leave@lists.netlojix.com %(web_page_url)slistinfo%(cgiext)s/%(_internal_name)s Searchable Archives: http://jukebox.markmail.org/
On 2023-02-08 03:31, Nigel Pugh wrote:
I can see this chat has been going on for a while, but unfortunately this is the only one I have read.
Worth mentioning, but I have a 532 amp and had hum exactly as you have described. The problem turned out to be the bakelite remote volume socket and blanking plug. That was conducting to ground. I never used it anyway so I bypassed it and the hum disappeared. Apologies if this has already been mentioned, cheap and easy fix, worth a try.
No, that has not been mentioned in this thread. It was mentioned when I first posted several years ago. I think it was Wesley Dean that mentioned this and that it is likely caused by rodent urine. I don't have that problem and I did wire the volume control to bypass that connector at some point. I did see this mentioned somewhere else where as well so it does seem to be a common problem. I really do think I have this narrowed down to a ground loop problem with the circuit for the 6AU6. I'd have to look and trace out the grounds in this area, but I think I can fly a couple of the existing jumper wires and isolate the ground and apply a new ground wire to the copper strap.
Carl Haines
With machine unplugged, tip a selection pin, plug machine in. It will start scanning as normal. Does the hum begin immediately OR does it only begin as the tubes warm up?
I ask because these amps have multiple voltage sources for the entire machine. Sometimes poor grounds can cause AC (60Hz) to leak into other non-related circuits.
If the hum were to start as soon as power was turned on, this would be a sure sign of that happening.
RobNYC
On Sunday, February 5, 2023, 04:30:07 PM GMT-8, Carl Haines via Jukebox-list jukebox-list@lists.netlojix.com wrote:
Well, I'm done with trying to eliminate this hum for now. I did have some marginal success with reducing it slightly. I was pretty much already done but I came across a few videos on youtube that showed troubleshooting a ground loop hum. I put the amp back on the bench and tried using a piece of wire to make a new ground path from various points. One of these was to place one end of the wire on the ground strap from the ground strap for the PCB to the opposite side of the board near C17. That took some of the edge off the hum but did not eliminate it. I decided to run a 16AWG wire from the strap to the pad for the jumper wire near C17 and leave it that. Maybe some day when I am feeling adventuresome I'll trace out the ground paths to see how many jumpers are used to tie into the perimeter ground plane to see if I can isolate and reground different points on the board. I will note that there is one track for the heater circuit that runs parallel to the ground for quite a bit of distance. The ground strap is at one end of this run and the place where I tied the new wire is at the other end.
Other thoughts - I don't know if I am expecting too much here or not. The hum can easily be drowned out with background noise and it is not noticeable when music is playing. I just notice it in the time between when the amp unmutes and the music starts. I'll also admit that my bench testing setup is not the best for testing this due to the small speaker I am using. There is a notable difference between a single 8" speaker and 3 x 12" speakers when it comes to 60hz hum.
Carl Haines _______________________________________________ Jukebox-list mailing list -- jukebox-list@lists.netlojix.com To unsubscribe send an email to jukebox-list-leave@lists.netlojix.com %(web_page_url)slistinfo%(cgiext)s/%(_internal_name)s Searchable Archives: http://jukebox.markmail.org/
Resend due to a bounce earlier...
On 2023-02-06 16:34, Chan Gade wrote:
With machine unplugged, tip a selection pin, plug machine in. It will start scanning as normal. Does the hum begin immediately OR does it only begin as the tubes warm up?
I ask because these amps have multiple voltage sources for the entire machine. Sometimes poor grounds can cause AC (60Hz) to leak into other non-related circuits.
Thanks for the suggestion. The hum only occurs once the amp is warmed up. As far as I can tell the hum is not from the B+ supply. The hum is only there when it is unmuted. I pretty much have isolated the source to the 6AU6. I will point out that it is not a loud hum. I really do think that this is due to a ground loop on the PCB itself.
On 2023-02-06 15:49, Britt Abbott via Jukebox-list wrote:
Check the braided cable from cartridge to amp to insure braid is grounded and live internal wire is not grounded. You might want to try using another new or rebuilt cartridge to see if it fixes your hum.
I've been doing some testing on the bench, so the hum source is not input into the app. Now that you bring this up, several years ago I converted the amp from Cobra to a magnetic cartridge + preamp. The input to the amp is basically line level now which makes it easier to test on the bench.
Carl Haines
Carl, I didn’t know you had done this conversion.
First, you can NOT use the same RCA female or shielded tonearm cable on the arch after converting to a mag cart. The shell is electrically touching the arch and creates a ground loop. The cart must be “floating” and not touch ground till it reaches the preamp.
The stereo models use a multiprong connector that does not touch anything, so it can be used when converting those machines.
The preamp must be grounded to either the arch or the amp chassis, just as you would with any other turntable.
Finally, even after all this, those amps were never “broadcast silent” –there was always some alight hum. It is usually obscured by the turntable rumble J RobNYC
On Tuesday, February 7, 2023, 08:09:11 PM GMT-5, Carl Haines via Jukebox-list jukebox-list@lists.netlojix.com wrote:
Now that you bring this up, several years ago I converted the amp from Cobra to a magnetic cartridge + preamp. The input to the amp is basically line level now which makes it easier to test on the bench.
Carl Haines _______________________________________________ Jukebox-list mailing list -- jukebox-list@lists.netlojix.com To unsubscribe send an email to jukebox-list-leave@lists.netlojix.com %(web_page_url)slistinfo%(cgiext)s/%(_internal_name)s Searchable Archives: http://jukebox.markmail.org/
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