6V6 line preamp - Page 92

cjkpkg · 23rd June 2012, 11:42 AM

This is the best I can do now...the wiring and placement is just temporary until I get everything sorted out...

tinitus · 23rd June 2012, 12:11 PM

keep power supply wires away from signal wire

amp board and supply board should shift/change place

cjkpkg · 23rd June 2012, 02:07 PM

yup...rearranged to this and did two more things...
1. tried a toroid just to rule out xformer noise
2. yanked out the rca outputs from the chassis

with the toroid the hum comes on immediately and is even louder.

After I rearranged it with the EI core xformer it came on and played nicely for about a minute and then the humm came back. Thats when I tried the toroid.

So I am at a total loss here...I even threw in a pair of EL34's again to rule out the tubes...and same thing...hummmmmmmmm

I am about ready to throw in the towel on this one...

cjkpkg · 23rd June 2012, 02:08 PM

forgot to attach pic...

Salas · 23rd June 2012, 02:13 PM

Its either you got something traced totally wrong regarding the audio schematic on PCB or you get a strong oscillation, which sounds like hum if high amplitude. Maybe that is why it comes and goes. In an open loop pre with a reg you can either get it from the interaction with the reg, or with the signal run and the grid. Are there 1K grid stoppers tightly soldered to the grid pins? I suggest you hard wire it.

Salas · 23rd June 2012, 02:23 PM

I also see wide loop area on your B+ GND reg output wires. Twist those tightly.

cjkpkg · 23rd June 2012, 02:34 PM

should I try and increase the grid stopper value to 1.5K or 2K maybe?

I triple checked the board traces and they are correct...the 1K grid stoppers are very close to the pin 5 on both channels.

Salas · 23rd June 2012, 02:37 PM

Do you have a scope?

Salas · 23rd June 2012, 02:48 PM

If you got one, set it to AC input and check the B+ line at 5mV and 50uSec. If it ain't a horizontal line, but its a sine or a thick mess, its power line oscillation. If you have not got a scope its difficult to know. I would start by twisting B+ GND wires. Are the ''triodizing'' resistors tight for pins 3,4? Larger grid resistors I doubt they would change something.

cjkpkg · 25th June 2012, 11:31 AM

And they did not...I tried 1.5K and 2.1K and same result.

I think that for the principle of the matter I will P2P this I just need to reorder some resistors. I have all the other stuff.

I cant believe that 2 different PSU's I use on 2 other amps I have are that noisy. It must be something in the layout of my PCB.

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23rd June 2012, 12:11 PM	#912
tinitus diyAudio Moderator Join Date: Nov 2005	keep power supply wires away from signal wire amp board and supply board should shift/change place

23rd June 2012, 02:07 PM	#913
cjkpkg diyAudio Member Join Date: Aug 2008 Location: Roswell GA	yup...rearranged to this and did two more things... 1. tried a toroid just to rule out xformer noise 2. yanked out the rca outputs from the chassis with the toroid the hum comes on immediately and is even louder. After I rearranged it with the EI core xformer it came on and played nicely for about a minute and then the humm came back. Thats when I tried the toroid. So I am at a total loss here...I even threw in a pair of EL34's again to rule out the tubes...and same thing...hummmmmmmmm I am about ready to throw in the towel on this one...

23rd June 2012, 02:13 PM	#915
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	Its either you got something traced totally wrong regarding the audio schematic on PCB or you get a strong oscillation, which sounds like hum if high amplitude. Maybe that is why it comes and goes. In an open loop pre with a reg you can either get it from the interaction with the reg, or with the signal run and the grid. Are there 1K grid stoppers tightly soldered to the grid pins? I suggest you hard wire it.

23rd June 2012, 02:23 PM	#916
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	I also see wide loop area on your B+ GND reg output wires. Twist those tightly.

23rd June 2012, 02:34 PM	#917
cjkpkg diyAudio Member Join Date: Aug 2008 Location: Roswell GA	should I try and increase the grid stopper value to 1.5K or 2K maybe? I triple checked the board traces and they are correct...the 1K grid stoppers are very close to the pin 5 on both channels.

23rd June 2012, 02:37 PM	#918
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	Do you have a scope?

23rd June 2012, 02:48 PM	#919
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	If you got one, set it to AC input and check the B+ line at 5mV and 50uSec. If it ain't a horizontal line, but its a sine or a thick mess, its power line oscillation. If you have not got a scope its difficult to know. I would start by twisting B+ GND wires. Are the ''triodizing'' resistors tight for pins 3,4? Larger grid resistors I doubt they would change something.

25th June 2012, 11:31 AM	#920
cjkpkg diyAudio Member Join Date: Aug 2008 Location: Roswell GA	And they did not...I tried 1.5K and 2.1K and same result. I think that for the principle of the matter I will P2P this I just need to reorder some resistors. I have all the other stuff. I cant believe that 2 different PSU's I use on 2 other amps I have are that noisy. It must be something in the layout of my PCB.