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 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

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It is currently 12 May 2021, 12:31

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PostPosted: 12 Jul 2020, 11:33 
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Joined: 01 Jul 2020, 11:33
Posts: 6
Ok, so i have a new problem. I recently changed the power supply of my amplifier and hear a humming/buzzing noise. So, i disconnected the input (i am using a pc) and connected an earphone. I can still hear the humming/buzzing noise but when i touched the case (aluminium) the noise disappeared and if i let go, the noise comes back. And if i connected my amp to my pc, there is constant noise no matter if i touch the case or not. I don't think the power supply caused this because i tried another power supply and the noise is still there. Can anyone help? Thanks!


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PostPosted: 12 Jul 2020, 22:08 
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Joined: 23 Feb 2017, 02:02
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Never connect the ground of the amplifier to the case, you connect the case to directly earth of mains, then you parallel another wire from earth of mains to amp ground.
I suspect a grounding prolbem


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PostPosted: 31 Aug 2020, 01:30 
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Joined: 30 Aug 2020, 20:52
Posts: 2
Hi all! I´m new to the forum, and also taking my first steps into tubes. I built this circuit in a bread board and used an infamous 12AX7 I happened to have as an ornament in my house.

I can read several times in this threat that the 12AX7 is NOT an adequate tube for this circuit. I don't have the expierence with tubes to judge by myself how the AX sound, so I ordered two 12AU7s to see what the differences are. They should be arriving this week.

Currently I have the circuit working with the AX and I'm happy with how it sounds. I only needed a 100k pot to get the bias at the mosfet down to 5.75 V wich is half the 11.5 V my PC power supply is giving me. Aside from a very strong ripple from the PSU and an FM station getting in the middle, it works. I need to make a proper PCB and shield the cables accordingly.

-----------------------------------------

Things I can't understand yet, no matter how much I read. I hope someone can give me a good explanation:

- I can read the 12AX7 is NOT a good tube because of it's high gain. Isn't gain a good thing? Why is it bad? Doesn't it mean that the tube can drive the headphones harder?

- I read there would be a lot of noise and distortion because of gain. Is there any way to lower the gain? Maybe a pot at the input? Why another tube should be used?

Hope someone can give me a headsup. I'm dying trying to understand these concepts!

Thanks!


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PostPosted: 02 Sep 2020, 22:43 
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Joined: 30 Aug 2020, 20:52
Posts: 2
Well, nevermind my latest post, the 12AU7 arrived and I think I now understand all the thing that were wrong.

- Signal now is crystal clear, no FM interference from nearby antennas.
- Now I have more volume.
- I also had a loud "brightness" in the sound I wasn´t aware of, now it´s gone.

I now understand better the concept of gain. I had to turn the volume at the input very low to get no distortion, but that also means the signal is near the noise floor of the signal, wich is bad. It doesn´t make the AX7 unusable, but an AU7 is more robust overall and sounds best without much effort. Luckily I could get one NOS really cheap.

Thanks to the project author and the admins of this site! Definitely going to stay around :)


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PostPosted: 08 Dec 2020, 14:14 
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Joined: 08 Dec 2020, 13:48
Posts: 1
Hi, I am new here :headphones:
I find this project very interesting and I am going to build it myself.
Currently I am not really sure which power supply I should use. Is a normal 12v 2a PSU enough?
And how about filtering? Do I have to mind anything?
I am not very familiar (ok, the basics + a little bit here and there) with electronics, but I have a oscilloscope and can use it :D
But I don't know how much ripple is acceptable?
Thank you in advance!
Best regards from Austria


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PostPosted: 01 Jan 2021, 01:45 
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Joined: 01 Jan 2021, 01:39
Posts: 1
this project is build for a 50ohm headphone, right?
what should i do if i want to power it to a 600ohm one, change the r4 ( resister with the lm317)?
if so what should i put


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PostPosted: 20 Jan 2021, 12:30 
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Joined: 13 Jan 2021, 06:31
Posts: 1
Not sure if this thread is still active but I just built this amp and it sounds great. Got a mullard 12AU7 in there and it sounds delightful. However, I'm struggling to get rid of a static sound with the board.

I have two 12AU7 and tried both and even run without the tube in and I can still here it. It sounds like a mix between rushing water and background freeway noise (don't have an oscilloscope but would guess that it's about 600-1000hz).

For context I'm using a lab bench power supply which is where I believe is the cause of the noise (I've checked soldering and the noise is coming through on both channels).

I've tried putting a 470uF capacitor across the voltage rails and it deals with a smaller amount of the noise (higher frequency) but it doesn't get rid of all of it. Do I need a bigger capacitor like a 1000uF or is that still not going to make enough of a difference?


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PostPosted: 21 Jan 2021, 00:18 
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Joined: 06 Apr 2009, 10:08
Posts: 1748
Location: US Pacific Northwest
PieGeters wrote:
It sounds like a mix between rushing water and background freeway noise (don't have an oscilloscope but would guess that it's about 600-1000hz).
Your description sounds like power supply noise. Capacitors across the line won't squash it. You need a choke in line with the power supply. I'd start with an RF hash choke and, if that doesn't work, place a good sized LC pair on the power supply.

_________________
Matt
It's all about the Glass!
http://www.CascadeTubes.com
Cascade Tubes Blog


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PostPosted: 14 Feb 2021, 01:44 
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Joined: 01 Jul 2020, 11:33
Posts: 6
Does anyone know how much this amp outputs? Also, which is better to use 12au7 or 12at7?


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PostPosted: 18 Feb 2021, 23:55 
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Joined: 11 Aug 2014, 06:54
Posts: 10
"I'd start with an RF hash choke and, if that doesn't work, place a good sized LC pair on the power supply."

Suncalc-

Can you suggest specs for the RF hash choke and LC pair?

Thanks


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