[leitmo]

Hi all of you!

it's been a long journey since i got Cornet2 PCB: getting components, soldering, some frustration time putting Cornet in "Unfinished projects folder"...

...but now it works and yes, sounds great!

here are some pics:















 

[david62]

What was the problem that prevented it from working?Enjoy your nice phono stage.
Dave

[leitmo]

Hi DAVID62!

2 years of frustration because a cold solder joint that blocked left channel to get proper HT voltage, just unsolder and resoldered components where i supposed was the problem and voila! voltages were OK.

I didn't want a standard Hammond enclosure so i decided to build a wood frame with handles (god bless Dremel tools )

[david62]

Leitmo,

    It must be a good feeling to have figured out what was wrong after so much time.How do you like performance of your phono stage?
Dave

[leitmo]

yes it was a great feeling when started to play music 

i hope tubes are breaking in, sound seems to be a little bit "dirty" and lack of bass, i played the same record on my "ripping system": technics sl1210mk2, Rod Elliott Phono Preamp, Motu 828mk2, Dynaudio Acoustics BM5A and sounds great.

maybe "ripping system" is better than "listening system": technics sl1210mk2, Cornet2, Nelson Pass B1 buffer preamp, Dynakit ST35, Marantz Imperial 5G speakers...

what do you think?

i'll try to rip some vinyl records through Cornet 2 and see what happens

[Bernie]

Hi guys. here is a tip on solder joints that I find very useful. I often use a magnify glass to inspect all joints. It's amazing what is revealed when doing so.

Bernie.

[leitmo]

good advice Bernie!

i started to measure continuity between components after every solder, it's tedious but i'm sure about all solder joints.

[Lengy]

I have also used a wooden enclosure and am having very bad problems with hum, can you tell me if you had similar problems and how did you earth everything? 

[leitmo]

hi Lengy!

i had no hum issues, i just connected RCA negative pin to Earth mains plug and and this to green aluminum plate, that's all

hope it helps!

[Lengy]

Hi Leitmo,

Thanks for the advice, was that input and output?  Did you use screened cable and if so which end of the screen do you not solder?  Lots of questions, I hope you can help!

Lengy

[leitmo]

sorry i think i missed something with my last answer, ok, here are my answers:

- i used microphone cable (shielded with cotton) but i tested with speaker cable and it also worked!
- ground connections: negative input from L and R  RCA jacks soldered together and then to PCB input, negative PCB output soldered to negative output RCA jacks. Mains Earth plug connected to Ground Bin Post (where we connect Turntable ground) and also connected to chassis...result: dead quiet Cornet2!

if you have any doubt don't hesitate asking again Lengy!

Regards!

[Lengy]

I've done this myself and the hum is unlistenable, any advice would be much appreciated.

Thanks

[poty]

I've done this myself and the hum is unlistenable, any advice would be much appreciated.

To give you concrete advices we should know (and better - see) your build.
There are several "universal" advices from other people in the forum:
1. The transformer and the PCB should be divided by a shield and be as far as possible from the input connectors.
2. ALL AC wires should be either twisted or twisted and shielded.
3. The signal wires should not cross AC power wires or (if it is impossible) cross it at 90 grad.
4. There should be only one grounding point and NO "spare connections". As other in the forum already pointed, the main mistakes are:
- not isolating RCAs "negatives" from the metal plate where they are mounted in.
- connecting RCA negatives to each other (and the single wire to the ground). Every RCA should have ITS OWN ground wire, connected to the central ground point.
- using metal standoffs (grounding the PCB in five point then).
- not connecting the ground wire from the power outlet to the system single ground point.
5. Use shielded or twisted signal-ground connections (including external interconnects).
6. Allocate the unit as far as possible from external sources of electromagnetic fields.
7. Checking "cold solder joints" in power supply (especially filter capacitors), checking heater circuits.

I'm not pretending to full coverage of factors, but IMHO point most frequent.

[Lengy]

Thanks, a couple of silly questions:

Are the stand-offs a problem if I have a wooden top plate?
Are you saying not to use shielded/twisted cable for the signal/interconnect
I'm not sure what you mean when you say spare connections

I've included a few images of the amp, I have rewired the input and output with shielded cable, but this is humming as before.  I have also added a  single earth and earthed the input/output cables and moved the amp as far away from stray fields as posable, but again the hum is still there.

[poty]

Are the stand-offs a problem if I have a wooden top plate?

No, but in that case you do not have any transformer shielding.

Are you saying not to use shielded/twisted cable for the signal/interconnect

No, I ment just opposite.

I'm not sure what you mean when you say spare connections

Lets look at and
I can't see it clearly, but it seems you have soldered both ends of shields from the input connectors (to the connectors and to the PCB). It means that (for example) for the left connector (on the first photo) there are 3 connection to the ground (1. yellow wire, 2. blue wire + shielding to PCB (from the right connector) + PCB-to-ground, 3. shielding to PCB (from the connector) + PCB-to-ground) - 2 of them are parasitic!
You have different setup (from leitmo), because he has aluminium plate on top, serving as shielding. I also can't see where is you cord to outlet connects, where is the transformer, what are the two wires connected to presumable ground point, where is the ground terminal for turntable and many-many other things.
I think you should start with determining the source of hum. Shorten the inputs (is the hum from the otside?), take off the first tube (the hum induced in the first stage?), the second - compare the intensity of the hum. Recheck power supply - maybe problems lie here.

[Lengy]

I think the output is the problem as that was the only side connected yesterday and the hum was still there.



Here's a close up of the output.

I've just discovered that the red wire from the transformer had not been crimped and was loose.  I've re-crimped it and it has reduced the hum. 
Another silly question, sorry: will there be more hum if I connect a MC cartridge to the Cornet2 without the Piccolo?

Johnathan

[poty]

I think the output is the problem as that was the only side connected yesterday and the hum was still there.

Should it be readed as "the output is not the problem"? It was just example of ground loops. And your close-ups just prove that the loops exist.

I've just discovered that the red wire from the transformer had not been crimped and was loose.  I've re-crimped it and it has reduced the hum.

It is an example of power supply problems. Enable your DVM and carefully check all voltages.

will there be more hum if I connect a MC cartridge to the Cornet2 without the Piccolo?

First of all, even in working Cornet the output level of MC cartridge is more than 10 times less than nesessary. Second, the load (47k) is too high. If you want to do this you should use some step-up transformer or preamplifier like Piccolo. Then the MC cartridge would be like MM cartridge from the point of view of Cornet.

[galyons]

Another silly question, sorry: will there be more hum if I connect a MC cartridge to the Cornet2 without the Piccolo?

This will depend on the output of the MC. High output MC will likely be fine.  HOMC's are typically loaded at MM standard 47K.  But then again, it is pretty easy to switch out the loading resistors,

Any output less than 1mv may be a challenge.  I did run a VdH Frog @ .65mv for a while, actually worked pretty well.  I could hear a light tube rush and dynamics were slightly compressed compared to use with the Piccolo. My Cornet2 is hum free, though. My system is all tube, so that contributed to the tube noise background when turning the volume up on the pre to accommodate the Frog's low-medium output. I currently run a SoundSmith Voice @2.12mv and it is more than fine! 

But the hum issue needs to be solved. Is it 60hz?

Cheers,
Geary

[Lengy]

After many hours searching problems out and creating a few for myself, I've got the Cornet and Piccolo working.  The Cornet now has a copper top plate, no ground loops and the Piccolo is safely in it's case.  The pair sound excellent and I'm looking forward to spending many happy hours listening to music again, instead of the rollercoaster ride of fault finding!

Thanks everybody

Johnathan

[leitmo]

happy to hear you're now enjoying your cornet2 Lengy!!!!

after getting mine working i realised it's not a novice project, grounding it's a bit tricky if not using standard enclosure but....hey! you have a customized and exclusive Cornet!

congrats again!

Leitmo