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PostPosted: 26 Dec 2015, 11:45 
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Location: Athens-Greece
I re-built the pre-amp section and one part of power supply. Noise still exist, too strong, but I listen music now. Soemthing that I noticed: when I switch off the pre-amp for a couple of seconds I listen good music with no hum, and then of course is disappeared , but that short time sound is the preferable one.

Something maybe in power supply. I attach again the power supply drawing. Could anybody tell me how can I have voltage anodes and filaments to all tubes and strong noise at same time?


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PostPosted: 26 Dec 2015, 12:04 
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Location: Arizona, USA
Hi, Yes post a copy of the schematic and a photo of the top and bottom of the chassis. If the hum goes away when the power is turned off then the PS is the problem.

Good listening
Bruce

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PostPosted: 26 Dec 2015, 12:16 
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Hi Bruce. I followed your schematics as attached. I replaced. So far all the section from 200V secondary up to LR8 section. Also, I replaced the LR8 and the capacitor of 4700 uf.

I did not touch yet the LR8 section up to tube anodes. I will attach a couple of photoz soon


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PostPosted: 26 Dec 2015, 12:21 
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Some photos. I placed tubes in series this time


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PostPosted: 26 Dec 2015, 21:01 
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Hi, A few questions, please excuse me if I already asked them but when working with several diyers at one time across 4 forums I occasionally lose track of who did what. Since I see no power transformer in the photos (higher rez would be helpful) did you build this with an external power supply? When I look at the photos.... hard to tell but there seems to be a lot of wiring and components just going every which way. This can lead to the sensitivity to pick up hum. Perhaps not in this particular case but always a factor. Now with the hum apparently going away when the power if off it leads me to think that one or more of the following problems may be present. Not necessarily in order.

A bad rectifier, either in the B+ or heaters
Bad filter capacitor or one that is not grounded well in either area
If the voltages are about right...skip this one .... failed LR8s.
If the transformer is in the chassis (not clear in the photos) then not enough shielding on it and the circuitry.
Possible multiple ground loop through the power supply. Particularly if external.

Things to check.
Voltages on all tube pins.
Resistance between the chassis and the signal ground.
Resistances from the tube pins to ground (some on the first two stages will be infinite)

Since I check my personal email more often than here ...PM me for more rapid response and the user ID for it. It can also handle hi-rez photos.

Good listening
Bruce

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PostPosted: 29 Dec 2015, 10:48 
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Location: Athens-Greece
I found that during re-building of the pre-amp, the grounding of LR8K circuit (from 470K and 1.0 uf) was missing!!! I forgot the small wire to connect to the star grounding. What could be the effect? Has something being burnt and be the cause of noise? Is it possible this lack of grounding wire to create problems to previous parts of power supply? I replaced the capacitors 4700 uf, 100 uf and 2.2 uf before LR8K with no results. I am thinking to change everything in blue box


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PostPosted: 29 Dec 2015, 13:36 
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Hi, Measure the voltage from the input to output of the LR8. If it is pretty much the same then it is fried. Be careful when measuring as a slip of the probe will instanteously fry it. The usually fail in the shorted through mode. I doubt that the caparitors were all bad. The grounding or lack of for some components can cause all sorts of issues. Generally noise and hum. In this preamp it is extremely important. I nearly didn't post the project over concerns that individuals would have trouble making it quiet. In this project , layout, grounding and a clean power supply are everything. It is possible to get great results. The first one I sent out to a friend who worked at the time in a major high end audio store thought it had failed when he first hooked it up. No hum or noise. Then with the gain on the system up higher than normal (because he didn't hear any noise) he put the stylus on the LP. I understand that everyone in the store was startled by the loudness. So we need to keep searching for your sources of hum/noise to get it up to the performance level it should have.

Good listening
Bruce

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PostPosted: 30 Dec 2015, 22:02 
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Hi I attached a photo of just the active portion of my latest version of the Groove... I call it the NuGroove. Someone snached the first stage tubes...not really they are Nuvistors.

Good listening
Bruce
Attachment:
NuGroove2.jpg


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PostPosted: 26 Jan 2016, 20:29 
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gofar99 wrote:
Hi I attached a photo of just the active portion of my latest version of the Groove... I call it the NuGroove. Someone snached the first stage tubes...not really they are Nuvistors.


Bruce! That's exciting. Which nuvistors are they? Can you share the resulting changed schematic? I'd like to give it a try.

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PostPosted: 28 Jan 2016, 21:43 
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Hi, They are 6S52N-V and are about $5US in quantity on the web. You can use NOS US ones ...but they cost more and the sockets are priced out of sight. These solder in place. The overall gain of the preamp is a little lower (about 3 db) but the sound is quite nice and the thing is quiet with a capital Q. Here is the circuit. As with all variations of the preamp grounding and shielding is extremely important. A single ground loop will kill the S/N.

Good listening
Bruce
Attachment:
Nuvistor Hybrid Phono Preamp Main Circuit December 4 2015.jpg


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