[gosha68]

My first attempt was to build a Claricorn version and it was scrapped because I was never been able to get rid of hum on Cornet's side. I took the Cornet pcb out an installed it into it's own enclosure with a smaller (stock) PT with grey wire pulled out and connected to the grounding post. I've also made and aluminum cover for the transformer wires, just in case. So here is my "take 2":

   
 
Ok, this version gives less hum but it is still audible on both channels (and at the level I am not really comfortable with) when connected to my 60watt push-pull with volume control 1/3 up and with TT disconnected. When I plug in TT hum gets louder. My TT is a cheapish Denon DP-300F with built-in switchable phono stage (of course turned off) and no ground post. I opened it up and added ground wire to the TT - when I connect it to the Cornets' grounding post the hum gets even louder.

Well, I've ordered another pcb and built a brand new stock version. The only deviation from stock components are ClarityCaps on inputs (the only 0.1uf pair I had on hands) and shielded sockets for the AU7s. So here is my "take 3":



   

Guess what? I've got exactly the same hum as with "take 2"... 
I am pretty sure I know how solder - used to do it professionally, I followed instructions, I've checked and matched all the resistors and caps prior to soldering them in, all voltages are within range. What am I doing wrong? Where else to look? What else to try?
I'd appreciate any help and suggestions.

Forgot to mention that I've also built Jim's AC line conditioner and all equipment is connected through it:



On a positive note - my Clarinet is almost completed - will post some pics once it's done.
 

[poty]

Well... I can understand 1 fault, but 3 in the succession... Amazing!
The first suggesttion - don't accept anything on faith. The checking procedure in your case should be total and careful (so - time consuming).
I think you should begin with checking the "external environment". I mean basically 2 things - 1. the source and the next amplifying stage and 2. AC supply.
First check means that you should isolate your source (short out the input jacks, disconnect everything from your ground post) and your amplifier (if possible - try with other amplifiers, if it is not possible - short out the output jacks). If you still have hum - then the problem lies in some ground loops. They can easily be in your amplifier too. Then you should try to avoid the loops.
The second check is more difficult. The Cornet is Class 1 safety device and there is no ground breaker to the signal ground. It brings several thoughts. 1. Do you really have the earth wire in your mains? 2. How "clean" is the earth connection? 3. Is there a possibility for ground loops here?
If you really have experience with electricity (and only if you have!) you can (with all precautions):
- fully disconnect the Cornet from the power outlet,
- disconnect the "earth" wire from the ground post (isolate!!!),
- made all the connections to your amplifier, short out the inputs and disconnect everything from the ground post of the Cornet, switch the power on button to ON position,
- switch ON the amplifier, listen to the noise, plug the Cornet into the outlet directly (without any filters) and listen to the noise again (do not touch Cornet!!!),
- unplug the Cornet, switch off the amplifier, restore the safety connection to the ground post!
Without saying you can check (try another pair?) all interconnects, power cords...
If you still have noise - report here your findings on every step and we'll go further in chasing the problem.

[gosha68]

Poty, Thank you so much for your input! I will try to follow all the steps and will report back with results.

[hagtech]

Try tracking the hum down with your fingers.  If you touch a piece of chassis does the hum get louder?  If so, then you need to scrape away the black anodize to make sure all chassis pieces make electrical contact.  Use a countersink bit dig out the #6 corner screw holes.  The anodize is an insulator.

Are the RCA jack shields connected to chassis?  It looks like they are not, which is correct.

Do you have hum with nothing connected to input?  What if you remove the first 12AX7?  Does that fix it?

jh

[gosha68]

Here are my results so far:

- Cornet plugged into wall outlet directly, no external connections to ground post, nothing connected to inputs, outputs connected to the amplifier -> kind of white noise hissing, way too noticeable with volume 1/2 up;
- Inputs shorted to shields -> same hissing as above;
- IC cables connected to Cornet inputs only -> AC-like hum, louder than hissing above;
    - shorting inputs to shields on the other end of ICs quiets down hum only a little bit;
    - shorting inputs to ground post -> hum gets louder;
- TT outputs connected to Cornets inputs -> same hum as with just ICs connected;
- TT outputs connected to Cornets inputs, TT ground to Cornet ground -> hum gets noticeably louder;
- Touching different parts of the chassis, transformer, ground post with fingers during the tests above had no effect on the noise level;
- Removing first 12AX7 quiets down Cornet almost completely, some negligible noise with the volume all the way up;
- Earth wire disconnected, inputs disconnected -> hum is much louder;
- Earth wire disconnected, TT connected -> getting my "normal" hum as in other steps.

Tried with 2 different amps, ICs and power cables - results are pretty much the same.
Would be nice to try my Cornet in different system/house but I do not have anyone nearby to try it with.
Anodizing had been stripped from the interlocking parts of the chassis during initial assembly and ground continuity checked, RCA shields isolated from the chassis and connected to the dedicated PCB points.

Not sure how to test for noisy house grounding, jumped under the house and found out that my outlets are grounded to the copper water pipes (grounding to water mains used to be a normal practice). Would it help if I install a dedicated house grounding rod? My house is sitting on a rock so it's not going to be an easy task...

Thank you,

[poty]

- Cornet plugged into wall outlet directly, no external connections to ground post, nothing connected to inputs, outputs connected to the amplifier -> kind of white noise hissing, way too noticeable with volume 1/2 up;

Then - the Cornet itself does not add hum! Something is induced from outside, presumable from input side. It is also possible that the hum is from the ground wire. Even if you

- Earth wire disconnected, inputs disconnected -> hum is much louder;

the ground wire is connected by interconnects->amplifier->mains.
About hissing... This design sometimes suffers from its simplicity. The first stage is rather common, but needs attention to trifles. It may be possible that your amplifier has surplus amplification too. I'd begin with checking if all RIAA parts are soldered right (hi-frequencies should be attenuated to 20-40dB, so the result should be far from "white noise"). The second checkpoint - input resistors R200 (soldered right, good quality). Then tube rolling for V200. Then try to determine if the 1/2 volume is too loud to listen to the real turntable input. I'd also use best quality parts for R202, C200 (also check if soldered good). In my case the tube was the most demanding for this position. After rolling around 15 tubes I stay with one of Russian 6N2P-EV (6Н2П-ЕВ), which gives me the best result in hiss battle and the quality of sound. But I'm using my own board, which enables to switch heaters to different pinout of the tube.

- Inputs shorted to shields -> same hissing as above;
- Removing first 12AX7 quiets down Cornet almost completely, some negligible noise with the volume all the way up;

It proves that the hiss begins in the first stage.

- IC cables connected to Cornet inputs only -> AC-like hum, louder than hissing above;
    - shorting inputs to shields on the other end of ICs quiets down hum only a little bit;
    - shorting inputs to ground post -> hum gets louder;

I can only guess here. Normal shielded interconnects should not have such effect. So... Something wrong with shields on all your interconnects (it's possible if you use modern "esoteric" designs - "nose pull - tail gets stuck")?  Agressive EMI pollution? Bad RCA-to-PCB wiring? Bad ground? Need checks...

- TT outputs connected to Cornets inputs, TT ground to Cornet ground -> hum gets noticeably louder;

IMHO you do NOT have proper grounding for mains. So attaching even more "antennas" to not grounded wire and devices only aggravates the situation. But my thoughts need more clarifications.
Is it possible to do one more "experiment"? I believe you said you have something like DIY filter. Is it possible to use the filter to connect all audio gear (TT, Cornet, Amp) without ground wire from mains connected to any of the devices?

[hagtech]

Yes, you should have a nice warm-sounding "hiss" with nothing connected to the inputs.  That is the sound of a 47k resistor through a phonostage.  With a cartridge plugged in, the resistance is in parallel with the 47k and the hiss level should go way down.

jh

[gosha68]

Poty, Jim, thank you so much for you help – I think I’ve figured out my issues now and happy to report that the hum I was experiencing wasn’t coming from Cornet after all but was a combination of several other issues, mainly way too much of a combined gain in my system and improper internal wiring in my TT.

By following all of the suggested test I’ve found out that Cornet itself (with inputs disconnected) does not add any noise. My system is not entirely quiet and apparently has some other issues which I initially blamed on Cornet, but even at moderate listening levels this noise is not noticeable. I should have played some music first and then listen to hum/noise without touching volume controls. I was just hunting that noise instead with volume all the way up. I did installed an 8 feet grounding rod to ground just one outlet to which all of my components are connected – didn’t noticed any difference though.

The real hum was injected only when TT was connected. My TT have built-in interconnects so I was not been able to try another pair. It also does not have external ground connection (power cord has a 2-prong plug). I opened it up and found out that signal grounds are connected to the internal grounds. I’ve ended up installing a pair of RCAs plugs connecting each channel’s wires to their respective RCA only – that completely eliminated the hum that was previously heard with TT connected to Cornet! Problem solved!!! 

I’ve then reinstalled my original Cornet PCB, so now I have an extra assembled Cornet2 PCB – anyone interested?

Once again, thank you guys for your help, If left on my own I’d probably just gave it up not knowing what to do. Next step is to figure out what amp would be a good match for Clarinet and to build it so I can retire my integrated pp. Hope I will not end up rebuilding the whole house while trying to figure out issues in my next project.

[poty]

My congratulations! Since my first replica of Cornet 2 (with Cornet 3 mods and several other improvements) I constantly changing the device and there are still many ideas what to do better.

I was just hunting that noise instead with volume all the way up. I did installed an 8 feet grounding rod to ground just one outlet to which all of my components are connected – didn’t noticed any difference though.
...
Hope I will not end up rebuilding the whole house while trying to figure out issues in my next project.

I know it was me who suggested to weaken you rock basement! Sorry for that! But you reported so odd things like connecting open interconnects which induced hum, that I cannot think of anything else!