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PostPosted: 26 May 2010, 07:02 
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Joined: 24 May 2010, 10:50
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mwhouston wrote:
Hiss will ocure in most tubes at various levels. It can also be controlled by reducing the filament voltage/current. See if you can reduce the filament volatge by 0.1V. A series resistor with the filament should work.

What voltage is across your filaments at the momment?
Is the hiss the same in both channels?

Thanks for your help so far!

The hiss is present even when the AA batteries are not connected, so I think the problem doesn't lie in the tubes but somewhere else.
The hiss sounds the same in both channels.

I connected an external power source to the 9V connections and removed the AA batteries, played around with different voltages, but it's still there...


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PostPosted: 26 May 2010, 07:18 
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mahalaleel wrote:
The hiss is present even when the AA batteries are not connected, so I think the problem doesn't lie in the tubes but somewhere else.
The hiss sounds the same in both channels.

I connected an external power source to the 9V connections and removed the AA batteries, played around with different voltages, but it's still there...

The preamp cannot generate sound if the AA batteries are out. I think it is not the preamp. It's like saying a car with no petrol runs rough.

Do the filaments light-up? You need a very dark room to see them.

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PostPosted: 26 May 2010, 09:23 
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mwhouston wrote:
The preamp cannot generate sound if the AA batteries are out. I think it is not the preamp. It's like saying a car with no petrol runs rough.

So this means that the problem lies in the power supply section or something? I'm positive that the hiss starts whenever I connect a 9V battery, regardless of the presence of AA batteries.
However, I only hear the tubes "ring" when touched if the AA batteries are connected.

By the way, I connected an almost flat 9V battery and I heard a very loud buzz, so I guess it is the power section that's generating the hiss?

mwhouston wrote:
Do the filaments light-up? You need a very dark room to see them.

Yes, they light up after the device has been powered on for about 15 seconds.


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PostPosted: 26 May 2010, 11:46 
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mwhouston wrote:
You need a very dark room to see them.

LOL, and you need to be in that dark room for some time in order to get your eyes accustomed.

Here's mine from another thread: viewtopic.php?f=9&t=1281&start=62


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PostPosted: 26 May 2010, 17:38 
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mahalaleel wrote:
mwhouston wrote:
The preamp cannot generate sound if the AA batteries are out. I think it is not the preamp. It's like saying a car with no petrol runs rough.

So this means that the problem lies in the power supply section or something? I'm positive that the hiss starts whenever I connect a 9V battery, regardless of the presence of AA batteries.
However, I only hear the tubes "ring" when touched if the AA batteries are connected.

By the way, I connected an almost flat 9V battery and I heard a very loud buzz, so I guess it is the power section that's generating the hiss?

mwhouston wrote:
Do the filaments light-up? You need a very dark room to see them.

Yes, they light up after the device has been powered on for about 15 seconds.

There are some small valued caps around the regulator chip, are all these the correct value. Are all electros in the right way?

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Projects:“Salt Cellar” - Mono 807 triode integrated amp |
"Rosso" - E88CC SRPP preamp | ”Salt Cellar II” - 6EM7 mono wine box triode amp | “MWH” - 1920s UX-171A preamp |


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PostPosted: 26 May 2010, 17:40 
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Beftus wrote:
mwhouston wrote:
You need a very dark room to see them.

LOL, and you need to be in that dark room for some time in order to get your eyes accustomed.

Here's mine from another thread: viewtopic.php?f=9&t=1281&start=62

No wonder 2 X AAs will power the heaters for years. Good photo by the way.

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Projects:“Salt Cellar” - Mono 807 triode integrated amp |
"Rosso" - E88CC SRPP preamp | ”Salt Cellar II” - 6EM7 mono wine box triode amp | “MWH” - 1920s UX-171A preamp |


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PostPosted: 26 May 2010, 20:16 
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mahalaleel wrote:
The hiss is present even when the AA batteries are not connected, so I think the problem doesn't lie in the tubes but somewhere else.
The hiss sounds the same in both channels.

I connected an external power source to the 9V connections and removed the AA batteries, played around with different voltages, but it's still there...

mwhouston wrote:
The preamp cannot generate sound if the AA batteries are out. I think it is not the preamp. It's like saying a car with no petrol runs rough.

The opamp which follows the tube will run off only the 9v supply.

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PostPosted: 27 May 2010, 02:40 
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Joined: 26 May 2010, 23:00
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Hi, everyone have the schemtic of this version :D and can I use it for high Z headphone(300ohm such as Sen HD600).

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Bab English.


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PostPosted: 27 May 2010, 03:53 
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Gio wrote:
mahalaleel wrote:
The hiss is present even when the AA batteries are not connected, so I think the problem doesn't lie in the tubes but somewhere else.
The hiss sounds the same in both channels.

I connected an external power source to the 9V connections and removed the AA batteries, played around with different voltages, but it's still there...


mwhouston wrote:
The preamp cannot generate sound if the AA batteries are out. I think it is not the preamp. It's like saying a car with no petrol runs rough.


The opamp which follows the tube will run off only the 9v supply.


I built a single stage OPA627 (AU$50 a chip for one opamp per chip) and I gave it too much gain with too smaller feed back network. It had a hiss. When I told a friend, who put me onto the chip and has a few hundred opamps in his system, that it hissed he said I had too much gain. The way I fixed it was just didn't turn the input pot up too much. You can't hear the hiss until you crank the input. There is plenty of gain down low so no need to push it. Some of the hiss was coming from my CD player and with the high gain preamp it was too much. Do you get the same hiss with the inputs shorted??

See that you have the right Rs as FB Rs around the chip. Can you make the one from the opamp output to the input R smaller (less gain)?

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Projects:“Salt Cellar” - Mono 807 triode integrated amp |
"Rosso" - E88CC SRPP preamp | ”Salt Cellar II” - 6EM7 mono wine box triode amp | “MWH” - 1920s UX-171A preamp |


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PostPosted: 27 May 2010, 11:11 
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mwhouston wrote:
There are some small valued caps around the regulator chip, are all these the correct value. Are all electros in the right way?

Around IC2 (L4949) all the caps are 22µF. The PCB marks them as 10µF but the instructional booklet says that 22µF should work as well. They're all inserted correctly.
The non-electrolytic caps are all marked 2A104J, so they should be 0.1µF as needed.

The resistors all have the correct value.

mwhouston wrote:
Can you make the one from the opamp output to the input R smaller (less gain)?

Are these R7 and R8 on this schematic?
Image


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