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PostPosted: 08 Jun 2011, 22:55 
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Hi, I suspect that you have created a ground loop through the chassis. In nearly all instances I have seen where someone used the chassis as a ground there were ground loops. Especially in stereo equipment (different paths for the signal to go through the ground). I would disconnect everything from the chassis and run only a type X2 capacitor of about .1uf to .22 uf and a parallel 120-150 ohm 1/2 watt resistor between the signal ground on the circuit board and chassis. That way the chassis can act as a shield for the board and not be part of the signal path. Then connect your grounds to the pot in a more conventional manner. It is best to use only a single ground wire for both channels between the pot and the board. Use shielded wire for inputs and between the pot and board. In the K-12 there is a tendency to oscillate. The cure is to also attach a ground wire to the pot housing. If yours behaves, then skip it. The actual wire if used on the pot housing can go to either the chassis (like a shield) or to the signal ground, try both ways as one will usually be better than the other. Be sure that the speaker negative terminals are not attached to the chassis either. They are already grounded to the signal ground on the circuit board. Finally, check the color codes on the wires. Everyone including myself has hooked them up wrong at one time or another. Keep us posted on the progress.

Good listening
Bruce

I just saw your later answer. Even though it works, I would still separate the grounds.

Enjoy the music

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PostPosted: 11 Jun 2011, 18:57 
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Thanks for the excellent advice bruce! Going to get on that once I get more parts in for modding. For now, just want to enjoy some headache free (indeed, newer stereos give me a headache) music.

Another question that I had is... has anyone experimented with different .22uf capacitors to replace the ones that come with the kit? I did some reading and found some interesting opinions/results/flames. I'm on parts express and was going to upgrade to Auricaps, but at $13 X6 I'm a bit hesitant... Has anyone tried the less expensive "Audiocap PPT Theta 0.22uF 600V Film/Foil Capacitor" (1/2 the cost of the Auricaps)? (or the ?lesser? Dayton Audio, or medium priced Jantzen?) Just trying to get some more input as to what works/doesn't work, and to get a good balance of price and audible quality difference.

Not saying that I don't have the money for the Auricaps, but why spend twice the price for a small difference? :)

-AJ

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PostPosted: 11 Jun 2011, 20:59 
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Hi, Yes I have experimented with the caps. First, you can eliminate the one at the input. So you really need only 4. Just put a jumper where the first cap was. I used Auricaps in mine and it was the single biggest improvement IMHO in the whole thing. Since then I have experimented with several brands of caps in my projects. Particularly in my line stage preamp (project is on the web site) where there is only one cap per channel and it makes a huge impact on the sound. The ones I like the best are Jantzen Silver Z caps. They however are more costly than the Auricaps. Some lower priced ones that give good results are the Jantzen CrossCaps (quite inexpensive), KimberKaps ( about halfway between in cost). I have used the Dayton Audio Precision cap and Solens and they just don't seem to be that much of an improvement IMHO. I have not tried the Dayton Film and Foil caps - so if someone else has just chime in with an opinion. Cost in general is not a great indicator of how well a given cap will work in any particular circuit. That said, up to say the $10-20 range, you get what you pay for. For a budget upgrade I would use the CrossCaps. To do it justice go for the Auricaps. If you can source out some physically small Russian K40 series paper in oil caps they work quite nicely as well. Most are physically too large. Price varies with quantity, but can be quite reasonable ($2-3 each), check ebay. I use them in the kits my company sells. Any value over .2uf and 250 volts is fine.The K40Y-9 series seems to be about the best.

Good listening
Bruce

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PostPosted: 12 Jun 2011, 10:56 
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I tried Auricap, Dayton, I don't like.....K40Y9 is little bit better.

I advise You best Russian interstage caps
МБГЧ - http://www.lzelectronics.net/catalog/pr ... ucts_id=82,
МБГО, МБГП - very similar - http://www.ljclub.net/materqli/kondenza ... zatori.htm /about 20-50 cents in Bulgarian store/
and ФТ-3 http://meshok.ru/item/3154359_%CA%EE%ED ... C_2_%F8%F2 - http://saratov.molotok.ru/ft-3-luchshij ... 61276.html /the best audiocap for tube amplifiers, according this link/.
I sow and tried the similar caps, like МБГ...from West and East Germany.

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PostPosted: 12 Jun 2011, 11:40 
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>>If you can source out some physically small Russian K40 series paper in oil caps they work quite nicely as well. Most are physically too large. <<<

I bought 10 of the Russian 0.22uf K40 PIO caps for my K-12 build. Cost was around $25 including shipping off of eBay. Unfortunately they are just to big and heavy to fit on the small PCB of the K12 without some thoughtful modifications. I decided not to install them for that reason.

The Auricaps I have now are fine indeed small, light and sweet. I wanted to do a comparison with the K40s but the amount of work involved was just too steep due to their size. My K-12 sounds sweet indeed. If it ain't broke don't fix it with an extensive mod. So I let it go.

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PostPosted: 13 Jun 2011, 14:13 
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Hi All, As can be seen from the previous few posts..... We all hear different things and like slightly different tonal qualities in our equipment. It is one reason I usually hesitate to recommend anything... Sort of do you like chocolate or vanilla ice cream? I figure that caps and inductors in particular have flavors and while the manufacturers always claim them to be pure and clean, they usually are not perfect. :soapbox: Jumping down now....I'm really glad to have new folks join the audio diy community. Keep up the momentum :wizard: Regarding K-12s..... Something I have always wanted to try is to use the Edcor GXPP 10K 10 watt transformers for outputs. I used Hammonds and they are fine, but since then I have had great results with Edcors in my projects and would suspect the GXPPs would be great on the K-12s. Cheaper as well. :)

Good listening
Bruce

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PostPosted: 13 Jun 2011, 16:13 
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Indeed Bruce- different folks, different strokes. I'd love to do a side-by-side comparison of different capacitors and different parts in order to build something that fits my listening needs but alas... space and money does not permit such spending. I'm actually quite content with the current setup tbh, but then again I don't have a good stereo to compare to at this point as anything sounds better than my Pioneer VSX-820 :(

Continuing.... I'll be swinging by HSC (halted.com) tomorrow to pick up some more supplies and to make a nice Discharging tool for Capacitors so that I can seperate the chassis from the board and build a nice insulated case. They have a wealth of capacitors there but as my knowledge is so limited, I'll play it safe and go with the recommendations here (really want to try those Russian capacitors) but also ask them to see if they have a recommendation of their own.

I'm going to do what Bruce said too- seperate the chassis from the board with a resistor and X2 capacitor and I'm sure with my IEC EMI Filter (3A YB03A1 Panel Mount320 C14 thanks to ebay) I should be able to get rid of that stubborn hum that I have. I'll be adding 2 switches along with this- one for power to the transformer, then transformer to the board- I'm getting a HARSH clicking noise whenever I turn the board OFF and it doesn't happen always, but it sure doesn't sound very nice :|

Should I be using .47uf or 1uf Snubber Capacitors in ceramic or Metallized Polyester Film? Tons of reading and tons of different methods leaves me to more questions than answers, haha, but I guess that's just part of the learning game.

-AJ

P.S.: I've read about installing bleeder resistors/capacitors from ?B+ to ground? so that stored voltage within the board gets bled off over a period of time in order to extend the life of the on board capacitors and to potentially prevent a potentially lethal shock of voltage if you haven't touched the board in a while, get lazy, and forget to see if there is any residual voltage in the system- how would I go about doing this? If I wrote anything wrong there, please correct me- again, I'm still new to this kind of electronics. :beer:

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PostPosted: 13 Jun 2011, 18:17 
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Hi, Sounds like you are on a roll. Snubbers for use in parallel with electrolytics are typically 1% of the value of the bigger cap. So for a 100uf I use a 1uf. You can actually bypass that one too with a value in the .005 to .001 range. What you are trying to do is allow for the problem that electrolytics have rather poor high frequency response and will not get rid of crud in the power supply over a few 1000 HZ. Polys have generally good high frequency response and work well in getting the junk out. Snubbers for use across tube heaters the values most used are in the .1uf to 1uf range. I generally size them according to the current draw of the individual tube heater. Up to 0.3 amps I use 0.1uf, above that 1uf. To be most effective they must be right at the tube socket. The inexpensive green molded polys, usually with 100 volt ratings are quite good on the heaters. For use across filter capacitors you need to use one with voltage ratings about 1.5 times greater than the expected voltage in that part of the circuit. Since I aim for really high quality audio in my circuits, I use audio grade capacitors across the electrolytics. Most commonly Jantzen Cross caps or Solens. :soapbox: A thing that many builders forget it that the power supply is half the audio chain. It just doesn't provide juice for the audio part....is part of the audio circuit. So skimping on power supply components can easily turn a good design to junk. I don't generally use bleeders in my circuits, but they certainly can be added. A common way to figure out what size is to compute one to draw about 1 to 10ma. If you have 100 volts then the resistor would be 100/.001 = 10K to 100/.01 = 1K. TO figure out the power it is current squared (in amps!) times the value of the resistor. so in the example 10,000 times .001 squared =about .01 watts. Really zilch a 1/2 watt resistor is fine. At 10ma it would be .1 watt, still small and a 1/2 watt would be fine. For a k-12 the B+ is in the 250 volt range so I would personally use a value between 10K and 25K . Just to be safe I would size it at 1 watt. There are several places it could go in the filter string. To be most effective in discharging all the caps I would put it in the middle. Remember it doesn't discharge the caps immediately. Allow for several minutes, better yet use a voltmeter and measure the charge on the caps before working on the amp. Some folks like to use much larger currents for discharging the caps. It will shorten the time for them to get to a safe level, but depending on the circuit and how robust the power supply is it may cause the B+ voltage to be lower. Again in tube amps like the K-12 which run in class A mode (current is drawn at all times) the tubes will draw nearly a normal amount of current off the caps and bring the voltage down quickly while they are still hot and starting to cool down.

Good listening
Bruce

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PostPosted: 29 Jul 2011, 11:31 
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Just a bit of an update- I haven't had much of any time to mess around with my k-12 because it just sounds so darn good and I hate to have to pull it from my system (as it's the only amp I run now. I removed my digital pile of crap :D ).
By a stroke of luck, however, I found a k-12 for a steal and it's on my way to my door... so I'll FINALLY be able to tinker around with the one I built :)

I have wood set aside for a surround for the current unit, along with the upgraded russian caps I want to make work. I have yet to build 2 other oatley kits (buffer/headphone amp). Recently busted out my Korg MS-2000 keyboard and Korg padKontrol for some musical inspiration, so I've had other things on my mind aside from vintage tubes ;)

Will finally be posting updates once the unit arrives next week. Cheers all!

-AJ

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PostPosted: 29 Jul 2011, 12:20 
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the4ork wrote:
Just a bit of an update- I haven't had much of any time to mess around with my k-12 because it just sounds so darn good and I hate to have to pull it from my system (as it's the only amp I run now. I removed my digital pile of crap :D ).

Yup, sound like you need backup amps. :twisted:
the4ork wrote:
By a stroke of luck, however, I found a k-12 for a steal and it's on my way to my door... so I'll FINALLY be able to tinker around with the one I built :)

:up: Don't forget a backup single-ended amp too! ;)

Let us know how you make out.

Cheers

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