I had totally forgotten to short negative phase to ground on the SE inputs, so I did it. Unfortunately it did not solve the hum issues.
Here's a few pictures for you master ZM! 🙂
Thanks
Do
Here's a few pictures for you master ZM! 🙂
Thanks
Do
pics OK
not really hum related in this case ( important in case of catastrophe) - those small NTCs in each PSU - are too small ; put ones having 8-10mm Dia
now - I know it's bother, but you must try - move those RCores outside ( at least 30-40cm) from box, then observe hum level
there is shorter way of trying it - try preamp in proper Bal In/Bal Out arrangement, and hum will not exist if everything is OK..... balanced operation will kill hum induced by magnetics
not really hum related in this case ( important in case of catastrophe) - those small NTCs in each PSU - are too small ; put ones having 8-10mm Dia
now - I know it's bother, but you must try - move those RCores outside ( at least 30-40cm) from box, then observe hum level
there is shorter way of trying it - try preamp in proper Bal In/Bal Out arrangement, and hum will not exist if everything is OK..... balanced operation will kill hum induced by magnetics
I have several CL-60, would you recommend those?
ok, I will try everything balanced first and see the outcome.
Thanks
Do
ok, I will try everything balanced first and see the outcome.
Thanks
Do
Just tried balanced input and output and same result...
I think I will change the transformers to test... Will use toroids and put everything away. Weird though as r-core have very low magnetic stray field.
Other than this, everything adjusted easily and properly and looked ok on the scope...
Do
I think I will change the transformers to test... Will use toroids and put everything away. Weird though as r-core have very low magnetic stray field.
Other than this, everything adjusted easily and properly and looked ok on the scope...
Do
as long cable is connected OK (meaning - relays are functional as prescribed), doesn't matter where red is - left or right
and, count on that - our nosy friend is having final iteration, with big MoBo; no changes in audio part (except arrangement on big pcb) but now positive is common for relays etc.
and, count on that - our nosy friend is having final iteration, with big MoBo; no changes in audio part (except arrangement on big pcb) but now positive is common for relays etc.
Just wanted to start with a big thank you to everyone who chimed in to help, this is greatly appreciated! 🙂
So... I ended up replacing those NTC with bigger ones, then connected a ground cable from the PCB chassis ground directly to the chassis star ground, isolating that standoff. All this didn't seem to do any good...
Then checking those all XLR and RCA jacks on the back and measuring ground to chassis and audio ground to chassis. Ended up noticing something weird with those male XLR... I bough a different brand (io audio) than the usual Neutrik just because Neutrik was out of stock... Something was weird with them... When I was measuring the chassis ground pin with chassis star ground on the Neutrik, I was getting ~0.02 ohm, but with both io audio XLR jacks, I was getting ~3.2 ohms... Something was not proper... I decided to scavenge on another preamplifier some male Neutrik and once installed, they measured like all the other ones ~0.02 ohm.
Once I connected the preamplifier, I was getting a lower fast hum, but increasing the volume did not increase the hum. Now I'll test fully balance and ear if it's still there.
Do
So... I ended up replacing those NTC with bigger ones, then connected a ground cable from the PCB chassis ground directly to the chassis star ground, isolating that standoff. All this didn't seem to do any good...
Then checking those all XLR and RCA jacks on the back and measuring ground to chassis and audio ground to chassis. Ended up noticing something weird with those male XLR... I bough a different brand (io audio) than the usual Neutrik just because Neutrik was out of stock... Something was weird with them... When I was measuring the chassis ground pin with chassis star ground on the Neutrik, I was getting ~0.02 ohm, but with both io audio XLR jacks, I was getting ~3.2 ohms... Something was not proper... I decided to scavenge on another preamplifier some male Neutrik and once installed, they measured like all the other ones ~0.02 ohm.
Once I connected the preamplifier, I was getting a lower fast hum, but increasing the volume did not increase the hum. Now I'll test fully balance and ear if it's still there.
Do
these two NTCs are connected to chassis/safety GND through bolt - mounting pad at left front corner of pcb; so be sure that there is continuity
easiest to check - each channel GND must show NTC value ref. to chassis
IEC mid pin - you can bolt its wire to chassis or solder to pad - right back mounting screw of pcb
easiest to check - each channel GND must show NTC value ref. to chassis
IEC mid pin - you can bolt its wire to chassis or solder to pad - right back mounting screw of pcb
ok, added bigger NTC
Tried just about anything, including external transformers (different ones) and nothing will do. It's only when I hit volume position 8 that the hum starts to be noticeable. Positions 1-7 is barely audible, you need to have your ear to the tweeter, but then position 8, hum starts... The infamous "bzzzzzz"...
I noticed that I have the best result when earth ground is not connected to chassis.
Still looking...
Do
Tried just about anything, including external transformers (different ones) and nothing will do. It's only when I hit volume position 8 that the hum starts to be noticeable. Positions 1-7 is barely audible, you need to have your ear to the tweeter, but then position 8, hum starts... The infamous "bzzzzzz"...
I noticed that I have the best result when earth ground is not connected to chassis.
Still looking...
Do
now I need bunch of proper big pics
best directly on e-mail or, in case of too many, uploaded somewhere
when done properly, you can't hear it's powered on, without signal
best directly on e-mail or, in case of too many, uploaded somewhere
when done properly, you can't hear it's powered on, without signal
Hi ZM,
For sure Something is wrong somewhere but I've been searching and testing many different things and cannot put my finger on it yet...
I sent you a Dropbox link with many pictures. If you need more, please let me know and I will add them to the folder.
You will see in there two different power supplies (i mean just transformers), one internal and one external. On the picture, only the relays transformer is external, but I have tried fully external as well. Also, earth ground is also not connected as there's more hum when connected. I've also isolated the IEC inlet metal casing so it does not ground to chassis for testing.
Thanks a million for all your support, it is really appreciated!
Do
For sure Something is wrong somewhere but I've been searching and testing many different things and cannot put my finger on it yet...
I sent you a Dropbox link with many pictures. If you need more, please let me know and I will add them to the folder.
You will see in there two different power supplies (i mean just transformers), one internal and one external. On the picture, only the relays transformer is external, but I have tried fully external as well. Also, earth ground is also not connected as there's more hum when connected. I've also isolated the IEC inlet metal casing so it does not ground to chassis for testing.
Thanks a million for all your support, it is really appreciated!
Do
Hi Do,
Here are some troubleshooting ideas, maybe you have tried them already.
- Move the preamp so it's further away from the amplifier or other electric devices
- try a DC power supply to feed the pumpkin
Danny
Here are some troubleshooting ideas, maybe you have tried them already.
- Move the preamp so it's further away from the amplifier or other electric devices
- try a DC power supply to feed the pumpkin
Danny
Hi Danny,
On the test bench, all amplifiers are at least 3 feet away. Good idea with the DC supply!
Do
On the test bench, all amplifiers are at least 3 feet away. Good idea with the DC supply!
Do
no need to waste time with DC supply , I mean - any
everything is already on board and it works flawlessly
I'm at home,have some chores today and I'll take a look at pics
they're downloaded in my Drop folder
everything is already on board and it works flawlessly
I'm at home,have some chores today and I'll take a look at pics
they're downloaded in my Drop folder
Probably a stupid question... On my source selector I've got 6 positions but 5 sources.
I know that position 2-6 are my input sources but position 1, is it a mute? I'm looking at the schematics but can't find what it is.
Do
I know that position 2-6 are my input sources but position 1, is it a mute? I'm looking at the schematics but can't find what it is.
Do