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It is currently 16 Dec 2018, 13:56

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 Post subject: Re: 4S preamp project
PostPosted: 27 Nov 2018, 21:45 
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Joined: 19 Oct 2018, 15:30
Posts: 35
Location: Montréal, Québec
I’ve got new toys ! They will be helpful for shure
Tektronix 7623a oscilloscope (5$) and Weller WESD51


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 Post subject: Re: 4S preamp project
PostPosted: 27 Nov 2018, 22:02 
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Joined: 06 Apr 2009, 10:08
Posts: 1497
Location: US Pacific Northwest
Gab wrote:
Tektronix 7623a oscilloscope (5$) and Weller WESD51
Very cool. I love my WESD51! The variable temperature allows me to dial in for each type of soldering I do. make sure you get appropriate tips for each task. It really helps make things go smoothly.

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It's all about the Glass!
http://www.CascadeTubes.com
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 Post subject: Re: 4S preamp project
PostPosted: 27 Nov 2018, 23:12 
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Joined: 19 Oct 2018, 15:30
Posts: 35
Location: Montréal, Québec
Couldn’t wait to try my new iron. Viewed from outside, the back panel looks complete. The ground lift is installed and the output impedence selector is on its way.


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 Post subject: Re: 4S preamp project
PostPosted: 03 Dec 2018, 09:05 
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Joined: 19 Oct 2018, 15:30
Posts: 35
Location: Montréal, Québec
It’s done ! I didn’t have the opportunity to test it yet. It was to late to go out to buy some fuses. The led wires are not on the picture but are actually installed.


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 Post subject: Re: 4S preamp project
PostPosted: 03 Dec 2018, 19:04 
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Joined: 19 Oct 2018, 15:30
Posts: 35
Location: Montréal, Québec
So I plugged it into the wall. The fuse didn’t blew up and no smoke or odor were detected. I have a B+ of 284V after the filter. Next step is the audio test !


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 Post subject: Re: 4S preamp project
PostPosted: 03 Dec 2018, 20:14 
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Joined: 19 Oct 2018, 15:30
Posts: 35
Location: Montréal, Québec
It works ! But There is a constant buzz that is not changing with the volume. It doesn’t get louder or quieter when I adjust the volume on the preamp, but does get louder if I adjust the level on the power amp. I don’t really know where to start my search to be honest !

I still have to try different souces to make shure it’s really the preamp itself that is causing the noise.


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 Post subject: Re: 4S preamp project
PostPosted: 04 Dec 2018, 08:12 
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Joined: 19 Oct 2018, 15:30
Posts: 35
Location: Montréal, Québec
Found an error : I totally forgot to put the two 100r resistors between the heaters and the ground. I am not shure of the value I should use since I have a 12AU7 that is not on this circuit.


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 Post subject: Re: 4S preamp project
PostPosted: 04 Dec 2018, 21:33 
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Joined: 19 Oct 2018, 15:30
Posts: 35
Location: Montréal, Québec
I installed the two resistors that were missing. Now I get clean sound on the right channel, but there is still something wrong with the left channel. The overall sound is way better than it was and, honnestly, doesn't sound bad at all ! I tried it with different sources and with different 12AX7 and 12AU7 tubes from different brands.

Now back to my problem. I have checked both circuit and everything seems to be at the right place and to have the right value. I know for shure that it's not my sources or the power amp. The buzz I hear really sounds 60hz like to me. I suspect the AC part of the amp to cause this, but don't know eactly how to look at this kind of problem.


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 Post subject: Re: 4S preamp project
PostPosted: 05 Dec 2018, 21:42 
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Joined: 06 Apr 2009, 10:08
Posts: 1497
Location: US Pacific Northwest
Does the ground lift switch make any difference in the noise?
Is the noise the same in both channels?
Can you pos a high resolution picture of you wiring?

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


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 Post subject: Re: 4S preamp project
PostPosted: 06 Dec 2018, 16:48 
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Joined: 19 Oct 2018, 15:30
Posts: 35
Location: Montréal, Québec
The ground lift does make a difference, there was just distortion coming out when grounded with the chassis. Actually it making noise only in the left channel. The right channel is fine when compared with the left. For the high res pic, I guess i’ll have to host it outside of the forum because the 500k limit doesn’t allow me to post pics with more than 50% of the original quality from my iphone...


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