Welcome, Guest. Please Login or Register
Decware Audio Forums
11/27/14 at 06:58:25


Pages: 1 
Send Topic Print
Review of the ZKIT1 (Read 6466 times)
Jora Lebedev
Verified Member
**




Posts: 20
Review of the ZKIT1
08/05/12 at 21:03:22
 
Well, I'm not really that good at reviewing things but I'll give it a try.  Here goes...

I have a pretty strange system, somewhat mis-matched.  I built a pair of Sachikos about four years ago with the help of a cabinet maker friend of mine.  He loved them so much he kept them at his shop using them instead of his Altec A7's and it was only the fact that I bought a new house that allowed me to guilt him into giving them back.  These use the limited edition Fostex FE206ES-R drivers that came out about six years ago and are about 98db efficient.  I built them because I'd wanted to hear what the single ended triode phenomenon was all about.  Well, shortly after they were built I met my wife to be and spent the next three years getting her over to the states from her native England so audio pursuits took a back burner for a while in favor of getting married, buying a house, renovations, etc.

Initially I was using the Sachikos with a 25 year old boom box but that got old really fast.  It wasn't a very powerful one and although I could rock the entire house with it I needed a better solution as its limitations were very apparent.  I had a bunch of transformers and tubes from projects I'd been planning to build and never finished but I really wanted to find something that I knew would see completion.  That, and the wife really wanted good tunes.  One of the (many) reasons I married her is that she's a total music head and she was very excited and encouraging about my audio hobby.  She's a fantastic gal but she was getting impatient with the boombox/horn system.

I stumbled across the ZKIT1 and it seemed tailor made as a project that was a proven design that a beginner could finish in a short period of time.  I ordered the power transformer from Edcor and all the parts on the components list.  I had some output transformers from an SE EL84 amp that I'd planned on building so I didn't think I'd need output trannies.  Well, all the parts arrived and unfortunately it took a long time for the Edcor power transformer to get here but in the meantime I also sourced a couple of Svetlana SV83 tubes along with a JJ E88CC driver tube plus fuse holder, power cable, etc.  

Finally the power transformer arrived and it was time to solder.  I went over the instructions and much to my dismay the primary impedance on the output trannies needed to be 9.6K rather than the 5K of the Edcors I had on hand!  So much for RTFM!  Somewhat dismayed I rummaged through my audio geek stash and came across a pair of One Electron transformers with 3.5K primaries but 4, 8 and 16 ohm secondary taps.  I decided that since the FE206ES-R's impedance never dropped below eight ohms I could use the four ohm taps and the reflected impedance to the output tubes would be 7K - not the 9.6K of the recommended transformers but since the speakers weren't a difficult or reactive load I figured it would be just fine and I might get a little more power output to boot.  I decided to proceed.

Now, I do HVAC tech support for a living which mostly involves reading manuals to people too lazy to do it themselves but I have to say that it was a bit frustrating to have the info on the website not match the board.  I was a bit worried but after reading many of the posts on the forum I was able to suss out that the CCE mod was now incorporated into the board and how to wire the transformers properly.  The board is well made and I was able to stuff it and get it all wired on a slab of plywood in the space of an afternoon.  

Then the moment of truth.  I connected the boom box speakers (with their 3 ohm load) to the terminals of the board and powered it up.  After a few seconds, no smoke, no fire but I could hear the hum through the little loudspeakers.  I never thought I'd be so happy to hear hum!  Next I powered it down and connected my Wavelength Proton to it, fired it up and my wife and I were surprised to hear very nice sounding music!  I was so happy!  I decided to let it play for a little while to make sure that an early component or tube failure wouldn't take out my irreplaceable loudspeaker drivers.  As it warmed up I could hear the sound improving even on those old boombox speakers.  

Finally I couldn't take it any longer and I decided it was time to bite the bullet and wire it into the Sachikos and my other source - a Wavelength Crimson.  Yes, I said earlier that my system is a bit lopsided.  After a few tense minutes wiring it all up with zip cord speaker cables and a pair of 20+ year old freebie interconnects I got with some component long ago I turned the volume up and the whole house was filled with incredible sound.  I don't know who was happier, me or my wife!  She absolutely loves music of all sorts and had been really pushing me to get a good system going.  She was thrilled with the sound quality as was I.  I've heard my Crimson DAC on some very high end systems and I know very well what it's capabilities are.  Immediately I could tell that these six hundred dollar baltic birch single driver speakers and three hundred dollar two watt triode amp connected to a DAC costing ten times that weren't the mismatch I thought they'd be.  Detail.  Slam.  Depth.  Imaging.  Being curious, I turned up the wick more and it just got louder and louder with no strain until I was well above the level I'd be able to listen for any real length of time.  These things ROCKED.  We stayed up very late that night listening to track after track marveling at the little circuit board, rats nest of wires and lumps of iron and the sound they were making.  As the night wore on the sound got better and better as the components broke in.  Finally we reluctantly called it a night and I headed to bed a very happy guy.

More to follow.

Back to top
 
« Last Edit: 08/05/12 at 21:15:30 by Jora Lebedev »  
  IP Logged
Lon
Seasoned Member
****


"Love without
guts is
worthless!"
Philip K. D*ck

Posts: 7817
Re: Review of the ZKIT1
Reply #1 - 08/05/12 at 21:59:07
 
Congrats!

Yes, I've found the better the source you throw at these amps, the better the sound. You have great reason to be proud and happy!
Back to top
 
 

Decware:ERR,HR-1,ZP3,CSP2+,Torii Mk III,PS Audio PWT+DS,PowerBases,PPP,AC-12 pcs, Denon DVD-A1UDCI, Rega RP3 +TTPSU,white belt+Exact2, VooDoo Cable:Stradivarius, Ultra Linear+Evo ICs, Iso-Pods,Mapleshade:Double Heiix Plus,Samsonv2+v3 +4" platforms,Herbie's Iso-Cup
  IP Logged
dank
Seasoned Member
****


pair of dual 18
Imperials

Posts: 275
Re: Review of the ZKIT1
Reply #2 - 08/06/12 at 12:56:44
 
Back when the parts came with the Zkit1, there were 2 output transformer options:  9800 ohm and 3300 ohm.  The 9800 ohm was the default and works fine with 4 ohm speakers, but the winding ratio is simple too large to get full power to an 8 ohm speaker load.  So for 8 or 16 ohm speakers, the 3300 ohm transformers worked better.  Either your 5k or your 7k transformers should work ok with your 8 ohm speakers, I'd guess your 5k's might be the best fit.

Dan
Back to top
 
 
  IP Logged
Jora Lebedev
Verified Member
**




Posts: 20
Re: Review of the ZKIT1
Reply #3 - 08/06/12 at 15:04:15
 
Lon, thanks for the kind words!

Dank, thanks for the info.  I was going by the schematic of the circuit that showed 9800 on the website (I don't know where I got the 9.6K in my review) but it's good news to me that I'll be able to use the Edcor 5K transformers and potentially get better performance and a little more power output.
Back to top
 
 
  IP Logged
Jora Lebedev
Verified Member
**




Posts: 20
Re: Review of the ZKIT1
Reply #4 - 03/03/13 at 15:56:28
 
Wow, I can't believe that it's been since last August that I built this.  Well, a few more impressions and an update:

The amp has stood the test of time and remains in my system.  It sounds great but I have done some mods.  

First, the Cornell Dubilier coupling caps on the recommended parts list are a waste of time and I wouldn't bother with them.  After about a week I spent the princely sum of around four dollars and replaced the recommended caps with Sprague 716P film and foil caps.  The results were spectacular - for the money I can't even imagine buying the CD caps unless you want to see for yourself how much a difference upgrading to the 716P caps makes.  716P capacitors are one of the best bangs for the buck in all of DIY audio in my opinion.

Second, the 5W bias resistor for the output tubes has left a nice scorch mark on the board.  I have it mounted WELL proud of the board but I do have the board built so I have the tubes up top and all the other stuff underneath.  I have the amp sitting on standoffs and the resistor has also made a dark mark on the wood underneath the amp.  Now I've been running this amp constantly since last August but I think an uprated part might be in order.  I may get myself two 5w 300 ohm resistors and wire them in parallel at the same spot split apart sort of like a "Y".  I'll do a temp reading of the resistors pre and post mod and let you all know how it works out.

I really hadn't done much beyond that, I hooked up some of Nordost's low end speaker wire, used a pair of Nordost Blue Heaven interconnects and that was it.  I sat back and enjoyed the music.  The hum was a pain, though.  My Sachikos use the 98db 1W/1M Fostex FE206ES-R drivers and there was a lot of hum, even after the resistor mod.  I also wondered what the amp would sound like with a tube rectifier and choke input.  My goal was to make a minimum of changes to the board itself, merely adding a level of filtering between the power transformer and the existing power supply circuit.  

What I ended up with was a 360-0-360 secondary power transformer going into a 22uF capacitor, then into an 8H choke that has 149 ohms of series resistance.  The rectifiers I used were a pair of 6AX4-GT damper diodes.  I also used a proper center tapped 6.3V supply for the signal tube heaters.  Modeled on PSUD2 it didn't look bad at all and when assembled the voltage at A on the ZKIT1 schematic is about ten volts higher than the schematic says it should be and I can live with that.

The result?  There is no hum.  Nada.  Zilch.  None.  I put my ear an inch from the cones of the Fostex drivers when I hooked the amp up to the system and at first I thought I'd disconnected something when I moved the breadboarded amp over to the speakers.  I was wrong.  I pressed play and the music just came out of nowhere - I was actually startled by it.  This addition to the power supply has unmasked more detail and helped a great deal with microdynamics.  I'd recommend this mod to anyone who is buying a new board or has a board lying around waiting to be used.  6AX4-GT damper diodes are ultra cheap and even cheaper if you buy the 12 volt versions (12AX4-GT) and use an outboard 12V filament transformer for your rectifier tubes which is a good idea anyway.  The beauty of this mod is that the only real change to a fully stuffed board is the removal of the two solid state rectifiers.

So what's next?  Well, I'm going to experiment with resistors and possibly replace the 22uF cap before the choke with a 20uF polypropylene in oil motor run cap just to see what difference it would make.

I'll be sure to let everyone know how it goes.
Back to top
 
« Last Edit: 03/03/13 at 16:04:12 by Jora Lebedev »  
  IP Logged
opnlybafld
Ex Member



Re: Review of the ZKIT1
Reply #5 - 03/03/13 at 22:06:48
 
Thanks for the update!
Back to top
 
 
  IP Logged
jpv
Seasoned Member
****


Cause inside
everyone is a heavy
metal kid

Posts: 112
Re: Review of the ZKIT1
Reply #6 - 03/06/13 at 13:21:13
 
Jora,
  Can you post some pictures of the mods you have done. A parts list and a schematic. I have a hum problem with my ZKIT1 - see "first time build". The hum is strange as it sometimes a buzz - 120HZ? or more of a grunting sound that starts off low and gets louder and stops over a period of about 1 second. The both are heard when the volume is set high and gets louder as you turn it up.
 I look foward to the other mods you are doing, I know we can do better.
John
Back to top
 
 

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.
  IP Logged
Jora Lebedev
Verified Member
**




Posts: 20
Re: Review of the ZKIT1
Reply #7 - 03/06/13 at 19:33:42
 
I just came up with a simpler power supply that won't require the use of a new transformer but will require a different choke.  I'll post once I've wired it up and let you all know about the results.
Back to top
 
 
  IP Logged
Jora Lebedev
Verified Member
**




Posts: 20
Re: Review of the ZKIT1
Reply #8 - 03/06/13 at 23:30:13
 
JPV, normally hum is pretty constant in level and continuous, what you're describing doesn't really sound like hum except that it gets louder when you turn up the volume.  I really don't know what it would be but I'd be happy if my mod corrected the issue.

I was wondering today if there was a way to use tube rectifiers and a choke without using a different power transformer and I think I've found out how to do it.  It will require different value power supply capacitors but they're not very expensive.  I'm ordering the parts and once I know it works I'll do a write up with parts lists.  It will also solve the center tap issue because it uses the six volt tap on the recommended Edcor power transformer as a filament supply for the 6AX4-GT rectifiers and you then use a separate 6.3VAC transformer with a center tap for the filament supply for the signal tubes.

Here's to hoping it works.
Back to top
 
 
  IP Logged
Jora Lebedev
Verified Member
**




Posts: 20
Re: Review of the ZKIT1
Reply #9 - 03/14/13 at 03:47:32
 
I've received the components.  I'm hoping to try my ideas this weekend.
Back to top
 
 
  IP Logged
Jora Lebedev
Verified Member
**




Posts: 20
Re: Review of the ZKIT1
Reply #10 - 03/16/13 at 23:32:14
 
Okay, so I'm getting started on this thing.  I'm not going to post about how my amp is currently wired as even though the voltage checks out okay on the board it looks like I was running the simulations incorrectly in PSUD2.  It seems that you're supposed to put the unloaded secondary voltage along with the secondary impedance of the transformer, not the rated voltage and secondary winding resistance of your power transformer into the simulation.  

PSUD2 actually has an impedance calculator built into the program and by measuring your wall voltage, power transformer winding resistance and measured unloaded secondary voltage you can come up with the impedance of your transformer.  It turns out my earlier calculations were way off because of this but let's see what happens in reality.  

I'm going to bring the amp back to stock form with silicon rectifiers and the recommended transformer and use a separate proper 6.3VCT filament transformer and do some measurements of voltages with the stock supply and see how they compare with the PSUD2 simulations.  In my haste to change to tube rectifiers I neglected to take voltage readings of the stock supply and write them down.  

I'm such a tool sometimes.  

Embarrassed

So, there is good news and bad news.  I'd hoped to be able to replace the first voltage dropping resistor (1K 6W) with a choke with high resistance.  Well, that ain't gonna happen because the supply rings like mad.  What appears to work is adding a choke input filter (Triad C-24X) and a 33uF capacitor filter to the existing silicon rectified power supply.  This doesn't drop the voltage much but it drops the power supply ripple a LOT.  So it appears that with around ten bucks expenditure you can get a lot less power supply noise.  

So...  first bring it back to stock form and see how that performs (with a proper filament transformer) and then see how it sounds with the little choke.  I'll post the PSUD2 sims as well so you can see the circuit.  

Back to top
 
 
  IP Logged
Jora Lebedev
Verified Member
**




Posts: 20
Re: Review of the ZKIT1
Reply #11 - 03/17/13 at 01:56:08
 
Here is a simulation of the stock power supply:

Back to top
 

Stock_PS_Simulation.png
  IP Logged
Jora Lebedev
Verified Member
**




Posts: 20
Re: Review of the ZKIT1
Reply #12 - 03/17/13 at 02:00:51
 
Here is the stock power supply with a 33uF cap and C-24X choke:
Back to top
 

Stock_PS_with_C-24X_choke.png
  IP Logged
Jora Lebedev
Verified Member
**




Posts: 20
Re: Review of the ZKIT1
Reply #13 - 03/17/13 at 02:03:03
 
Here is the stock power supply ripple at voltage point A on the schematic, about 1/2 volt of ripple:
Back to top
 

Stock_PS_ripple.png
  IP Logged
Jora Lebedev
Verified Member
**




Posts: 20
Re: Review of the ZKIT1
Reply #14 - 03/17/13 at 02:04:24
 
Here is the PS ripple with the choke:

Back to top
 

Stock_PS_ripple_with_C-24X_choke.png
  IP Logged
Jora Lebedev
Verified Member
**




Posts: 20
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.
Back to top
 
« Last Edit: 03/17/13 at 02:16:51 by Jora Lebedev »  
  IP Logged
Jora Lebedev
Verified Member
**




Posts: 20
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.
Back to top
 

Stock_PS_with_C-7X_Choke.png
  IP Logged
Jora Lebedev
Verified Member
**




Posts: 20
Re: Review of the ZKIT1
Reply #17 - 03/17/13 at 02:46:18
 
Here is a shot of the ripple:
Back to top
 

Stock_PS_ripple_with_C-7X_choke.png
  IP Logged
Jora Lebedev
Verified Member
**




Posts: 20
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.
Back to top
 
 
  IP Logged
Lon
Seasoned Member
****


"Love without
guts is
worthless!"
Philip K. D*ck

Posts: 7817
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.
Back to top
 
 

Decware:ERR,HR-1,ZP3,CSP2+,Torii Mk III,PS Audio PWT+DS,PowerBases,PPP,AC-12 pcs, Denon DVD-A1UDCI, Rega RP3 +TTPSU,white belt+Exact2, VooDoo Cable:Stradivarius, Ultra Linear+Evo ICs, Iso-Pods,Mapleshade:Double Heiix Plus,Samsonv2+v3 +4" platforms,Herbie's Iso-Cup
  IP Logged
Jora Lebedev
Verified Member
**




Posts: 20
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.
Back to top
 
 
  IP Logged
mboxler
Senior Member
***




Posts: 85
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
Back to top
 
 
  IP Logged
Jora Lebedev
Verified Member
**




Posts: 20
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?
Back to top
 
« Last Edit: 03/21/13 at 14:12:46 by Jora Lebedev »  
  IP Logged
mboxler
Senior Member
***




Posts: 85
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

Back to top
 
 
  IP Logged
Jora Lebedev
Verified Member
**




Posts: 20
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.
Back to top
 
 
  IP Logged
Jora Lebedev
Verified Member
**




Posts: 20
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.
Back to top
 
« Last Edit: 03/21/13 at 23:10:39 by Jora Lebedev »  
  IP Logged
mboxler
Senior Member
***




Posts: 85
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
Back to top
 
« Last Edit: 03/22/13 at 02:41:58 by mboxler »  
  IP Logged
jpv
Seasoned Member
****


Cause inside
everyone is a heavy
metal kid

Posts: 112
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
Back to top
 
 

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.
  IP Logged
Pages: 1 
Send Topic Print