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Review of the ZKIT1 (Read 5570 times)
Jora Lebedev
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Re: Review of the ZKIT1
Reply #15 - 03/17/13 at 02:07:47
 
So, it appears that you lose about four volts with the choke filter but the ripple is reduced by a huge amount.  

The green curve on the simulation is voltage point B in the schematic.  The ripple on point B goes from 2mV to .2mV with the addition of the choke.
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« Last Edit: 03/17/13 at 02:16:51 by Jora Lebedev »  
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Jora Lebedev
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Re: Review of the ZKIT1
Reply #16 - 03/17/13 at 02:43:20
 
Here is the supply with the Triad C-7X choke in the supply.  The specs say the choke has 270 ohms of DC resistance but I measured 235.  Ripple on point A is now down to 2mV.  Actual voltage at point A drops to 343.6 in the simulation.
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Stock_PS_with_C-7X_Choke.png
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Jora Lebedev
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Re: Review of the ZKIT1
Reply #17 - 03/17/13 at 02:46:18
 
Here is a shot of the ripple:
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Stock_PS_ripple_with_C-7X_choke.png
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Jora Lebedev
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Re: Review of the ZKIT1
Reply #18 - 03/17/13 at 14:59:27
 
OOPS!

I didn't put the correct secondary power transformer winding resistance in the impedance calculator in PSUD so the correct impedance for the recommended transformer is actually 46.91 ohms instead of what I have in the previous posts.  It makes very little difference in the simulation but I figured I'd let people know if they're trying it on their own.
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Lon
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Re: Review of the ZKIT1
Reply #19 - 03/17/13 at 17:49:56
 
Jora, you're really working it! So glad you've found improvements. Hope you're really enjoying the sound.
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Jora Lebedev
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Re: Review of the ZKIT1
Reply #20 - 03/17/13 at 21:25:12
 
Okay, I've got the amp wired with solid state rectifiers, Triad C-24X choke and the separate properly center tapped filament transformer.  

Upon fire up there were no flashes or puffs of smoke so that's good.  There is very little audible hum unless you put your ear right up against the speaker but it is not completely silent.  Before the choke was added you could easily hear the hum from the listening position.  I have the choke wired so that I don't have to de-solder anything to change it out.  I'm currently getting 352 volts at point A on the circuit as configured so even with the choke I'm still getting a bit more voltage than I should be.  That's not really surprising since the secondary winding of the transformer is rated for 150mA and the circuit only pulls 80.  

I would rate the sound definitely superior to the way it was originally when I had it with the un-center tapped filament supply and no choke.  The hum was really loud back then and it really distracted you from the music, especially in quiet passages.  Is it better than when I had it with the tube rectifiers?  I don't think so.  I'll have to try it with chokes with higher henry ratings and see if they improve things.  I can say that adding a choke that costs less than eight dollars and a 33uF cap should be a no brainer for anyone building this amp.  It's not the ultimate but it will go a long way towards making the amp more fun to listen to.

Currently I'm running One Electron output transformers on their four ohm taps to an eight ohm speaker.  This is presenting a 7K impedance to the output tubes.  My single driver speakers never drop below eight ohms so I'm going to hook up my Edcor 5K/8 ohm transformers as well, this should give me a bit more power at the expense of a little bit more distortion.
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mboxler
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Re: Review of the ZKIT1
Reply #21 - 03/20/13 at 16:30:00
 
Hi Jora

Sorry for the newbie questions, but regarding the stock PS options...

How do you get the PT resistance?

How did you arrive at the current tap values?

I thought the two 20uf capacitors in series would result in 10uf, not 40uf.

I have a 250 volt (measuring 287 with no load) R-core transformer, and I'm trying to use this program to determine component changes.  Not sure if the transformer can be used, but would like to try.  I also have two OT with 5K input and 4 and 8 ohm output to play with.

Thanks, Mike
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Jora Lebedev
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Re: Review of the ZKIT1
Reply #22 - 03/21/13 at 14:09:02
 
The ohm rating of the transformer in the program is not the resistance but the impedance.  There is an impedance calculator in the program that uses measured input (wall) voltage, resistance of the primary and secondary winding of the transformer and the unloaded voltage output.  

When you right click on the tranformer in the program to edit, both parameters have a button after the data entry box with "..." in them.  Click on the resistance box and it will help you calculate impedance.

The current tap ratings were a guess based on tube ratings.  At some point I will measure the current draw of the small signal tube and subtract that from the total 80mA of current draw.

You are of course right about the capacitors in series.   Embarrassed  

Is the R core transformer 250 center tapped, i.e. 250-0-250?
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« Last Edit: 03/21/13 at 14:12:46 by Jora Lebedev »  
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mboxler
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Re: Review of the ZKIT1
Reply #23 - 03/21/13 at 19:33:07
 
Thanks for the info!  No, the R-Core is not center-tapped, so I chose bridge (SS) for the rectification.  Just trying to see if the 17% voltage reduction will still work.  It seems like 250 volts diode rectifed would be higher than 300 volts tube rectifed (I.E., the non kit amp).

Glad there are not a lot of components to the amp.  Makes playing (and learning) a lot cheaper.

Oh...how did you get the ripple to display in reply #17?  All I can get are the voltage curves as you have in reply #16.

Again...thanks for the help.  There is so much to learn!

Mike

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Jora Lebedev
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Re: Review of the ZKIT1
Reply #24 - 03/21/13 at 21:05:02
 
You can use the zoom in and zoom out buttons on the display graph, I zoom out then click and hold on a point to the upper left of the graph then drag to create a box around the area you want to look at.  Doing this repeatedly allows you to zoom in on a very small part of the graph so you can see the actual ripple which can get very small.
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Jora Lebedev
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Re: Review of the ZKIT1
Reply #25 - 03/21/13 at 23:09:08
 
Home now, hooked up the lamented (for bargain seekers) no longer available Radio Daze RDC-100 choke, rated 8H at 125mA and with a series resistance of 149 ohms.

Voltage at point A in the schematic is 343.  Supply is even quieter now, I have to turn the wick all the way up to hear any noise on my 98db efficient Sachikos.

I think I'm going to get some ASC polypropylene in oil motor run caps from Angela Instruments to replace the electrolytics in the power supply.  I've also built a tubecad stepped attenuator to replace the volume pot and I hope to do a report on what difference that makes, if any.  I'm also going to take a pic of the zkit-enstien so you can see what my breadboarded mess looks like.

I've also just received my Wavelength Crimson back from being upgraded to current spec with the high speed mod.  I was using my Wavelength Proton in the meantime and the ZKIT 1 definitely let me know how much better the Crimson is.  The limit is the amp at this point but the great thing is that with a single driver loudspeaker it's like listening through a microscope, all improvements are RIGHT THERE.  

I've also switched from using iTunes as my music player to Audirvana Plus and it also made a gigantic improvement.  I had to get a newer computer (a mac mini) to allow the program to work in integer mode (the highest resolution) but for the money Audirvana Plus is a spectacular sounding program if you're a Mac user.  

Thanks to those that have chimed in with kind words and encouragement, I hope folks are finding my messing around useful/interesting.
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« Last Edit: 03/21/13 at 23:10:39 by Jora Lebedev »  
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mboxler
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Re: Review of the ZKIT1
Reply #26 - 03/22/13 at 02:40:41
 
You got my attention!  

Can't wait to see those speakers!  

Mike
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« Last Edit: 03/22/13 at 02:41:58 by mboxler »  
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jpv
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Re: Review of the ZKIT1
Reply #27 - 05/08/13 at 03:03:40
 
Jora,
 How are the modifications coming along? I am ready interested in the tweaks / changes you are making. Please keep us updated.
John
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VPI Scoutmaster, Grado Sonata1, Counterpoint pre amp and amp (modded by Altavista Audio), Proac sp. and home made subs. Lots of room treatment. Anti-cable sp cables, Decware IC, ZKit 1.
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