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It is currently 28 May 2018, 02:49

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PostPosted: 27 Apr 2017, 00:54 
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Joined: 29 Oct 2014, 12:32
Posts: 95
Location: Russia Komi republic
alahti wrote:
Hi, thank you for the answers. I have already separated LL1678 to the metal chassis and seems to work much better in this way.
Question is about signal ground, have I connected it right? Cause I still hear some little hum.

Another question is how or is it possible to attach my Grados 80i - 32 ohm to the output. Now is the volume not enough.

BR/Alahti
Attachment:
1.jpg

I would have connected differently.
All the earths - red and blue I would connect in a star. (You have this point, where blue segments come).
And the point where the red segments come in should be connected to the body.
Also, you can create local stars for convenience, and bring them to the global one.

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PostPosted: 28 Apr 2017, 06:35 
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Joined: 24 Oct 2010, 07:05
Posts: 257
alahti wrote:
... about signal ground, have I connected it right? Cause I still hear some little hum.
Agreed with zyu - the "star" you pointed as S (means "signal" I hope, orange wire goes here in your picture) is not signal ground at all. The "true" system star you marked as P is in the bottom of the schematic. More than that, points you marked as P is also in signal path!
alahti wrote:
Another question is how or is it possible to attach my Grados 80i - 32 ohm to the output.
Directly - no. Adding a headphone amp - yes.


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PostPosted: 28 Apr 2017, 18:04 
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Joined: 04 Jun 2008, 20:59
Posts: 3649
Location: Arizona, USA
Hi, I tend to prefer a main ground point at the location where the signal input enters the chassis (not connected to the chassis). I use something like a 12 gage copper wire and run it between all the ground terminals on the input and output jacks. From there individual ground wires go to the parts of the unit that need grounding. One to the main active circuitry, one to the power supply, and so on. Essentially it is a star system with the star at the inputs. Doing this I can achieve exceptionally quiet operation. I have not found other ways to work as well. BTW the star is isolated from the chassis by a X2 capacitor and parallel resistor. I have seen diodes used there are well but my personal preference is the X2/R arrangement.

Good listening
Bruce

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PostPosted: 14 May 2017, 15:27 
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Joined: 10 Nov 2013, 05:03
Posts: 9
Hello, tried to measure the response and got very strange results with the Spectralab. I always thought that bass is too much and that I can now see on graph. What could cause that problem? I see this on both channels.
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PostPosted: 14 May 2017, 17:59 
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Joined: 24 Oct 2010, 07:05
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Please tell something more about your build and the method you use for testing. From the graphs I can only say that there is some difference in gain values, but
- I'd use common base point - 1kHz, both graphs should cross zero dB here.
- What is the source of the test signal? Is may be that source linearity problem, impedances mismatch and so on...
- It may be wrong tube, passive components mistakes, build errors...


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PostPosted: 15 May 2017, 01:13 
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Joined: 10 Nov 2013, 05:03
Posts: 9
poty wrote:
Please tell something more about your build and the method you use for testing. From the graphs I can only say that there is some difference in gain values, but
- I'd use common base point - 1kHz, both graphs should cross zero dB here.
- What is the source of the test signal? Is may be that source linearity problem, impedances mismatch and so on...
- It may be wrong tube, passive components mistakes, build errors...

Hello, I'm using Spectralab. There is a Freq sweep thats creating own signal and measure it.
Have tried either with ecc82, same result. I will check once again all passive components.
Connected this way.
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PostPosted: 15 May 2017, 05:56 
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Joined: 24 Oct 2010, 07:05
Posts: 257
You have "base" signal connected to the R input. Could you estimate the linearity of the signal (frequency response)?
Could you also check a simple input-R3-output response (in case you have big input capacitance of your audio card)?


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PostPosted: 15 May 2017, 12:22 
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Joined: 10 Nov 2013, 05:03
Posts: 9
Think found the problem, used wrong nominal- 680R vs 680K.


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PostPosted: 16 May 2017, 10:33 
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Joined: 13 May 2017, 11:24
Posts: 1
Stupid question of the day.........I’m looking to build the Groovewatt Preamp and looking at the schematics (ver. 5/21/16 found in the forum not the site). I’m trying to get a parts list together. I’ve looked at all the drawings and the entire thread on the forum and cannot find the Resistor types and watt rating for the circuit. I see that the majority of the power section seems to be all Metal film type resistors from what I’ve seen in the pictures and online. If not noted at 1W which value should I use 1/2W, 1/4W, or 1W? also should they all be metal film or should carbon be used in some places? I have heard pros and cons on both for use in tube audio circuits. This will be my first Tube build and I’ve done some SS non audio builds . I do have past experience with Solid State Audio repairs as well as custom Home/ Mobile / Marine Audio- Video design and installations. I already have the transformer on order from Edcor and I’m looking forward to this build but I want to have everything ready before I start.


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PostPosted: 18 May 2017, 00:54 
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Joined: 10 Nov 2013, 05:03
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alahti wrote:
Think found the problem, used wrong nominal- 680R vs 680K.

Sorry, 30nF was done with 2 caps of 15nF each in series, so I got only 7,5nF. So I put them in parallel and got 30nF. My fault.
Now it looks almost ok. Maybe cables are not so good.
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