Welcome, Guest. Please Login or Register
Decware Audio Forums
03/29/24 at 16:01:50 




Pages: 1
Send Topic Print
ZKIT2 -> ZKIT1 build and the next one. (Read 2674 times)
bobc
Senior Member
***




Posts: 64
ZKIT2 -> ZKIT1 build and the next one.
10/17/20 at 16:40:14
 
Was looking for a lock.down project earlier this year... So I built two of these, based on ZKIT2 board. Identical, with the idea to have 2 amps I could bridge etc.... The box in back is a Z-stage I built using the online schematic, and is a simple switch box/gain control.

I built the ZKIT2 as spec'd, chased a few grounding issues, and got obsessed over the small hum I could hear about 6in from cone on my RP-600m. 1.1mv

As many on the forums mentioned, I threw capacitors at the issue. Using UF diodes, and smoothing at 47k and first filter at 94 k. This quieted things down substantially, but x2 was stressing transformer with the 2 kits as mono blocks...

Couldn't leave things alone, so these 'morphed' into a sort of anniversary ZKIT1. I converted to a single power supply and modified parts to match ZKIT1 anniversary version, with. the 47/94 filter stage. And boom.... started with 6922/EL84M, but I found 6N1P/6P15V to have best sound. Only issue is I need extra input tubes.... Smiley

I am actually using one of these in my kitchen system with an old set of BW LM1 and a sub, at surprising levels, and perhaps most importantly, my better half has actually noted the sound quality improvement.

So begins the next phase of my journey on a p2p version of the SE84 with tube rectification, meters, real center taps etc... This amp, even on a prototype layout is outstanding. That said, I had the same issue with the ~1.1mv of hum. Not hearable from my listening seat with high efficiency speakers, only at about 6in from cone or less. This is not a complaint, rather just an observation. Some of my other other tube stuff (bob latino kits) is dead quiet, and I enjoy... but the little zen circuit is magic.

I appreciate the balancing act of PS responsiveness linked to sound quality.  So now I need to decide if I should quiet things down with a choke as first filter stage and a big ass filter cap. Ive been doing some a/b and I think 'as designed' is defintely faster. Now Im playing around with bypassing all the caps to speed things up. Not sure where I will land on the final power supply build, but I just ordered a nice brushed stainless steel plate to mount everything so marching on!

ForZKIT 2 the chassis,I used a custom front panel express chassis. It was a little expensive but nice and solid. For the panel on my P2P build I went another direction, check out this company called sendcutsend. I designed the panel in sketchup. Uploaded and with all the laser cut holes etc. it ended up being $50. They can laser cut all sorts of metals (titanium or copper plate anyone?), and are very quick.

Here is the ZKIT2 / stage chassis. Was playing with knobs when picture was taken...


Very grateful to Steve for putting his designs out there, and for this incredible piece of audio simplicity.

Here to learn, share and connect with this great community after lurking for 6 months...

Back to top
 

IMG_1725.jpg
  IP Logged
jdb996
Verified Member
**




Posts: 6
Re: ZKIT2 -> ZKIT1 build and the next one.
Reply #1 - 02/04/21 at 01:32:04
 
I'm in the same boat. I too built ZKIT2 in a stereo configuration and have the same hum. It looks like i'll need to change a few things in the PS.

I'm running a 7DJ8 for the preamp and it sound amazing.

I'm also working on building a P2P based on the 25th anniversary schematic with tube rectification, most likely a 5U4G.....still working that bit out.

Maybe we can convince Steve to add an optional PS circuit like he did for the ZKIT4. Wink
Back to top
 

IMG_1921_2.JPG
  IP Logged
RonFranks
Verified Member
**




Posts: 13
Re: ZKIT2 -> ZKIT1 build and the next one.
Reply #2 - 11/29/21 at 03:36:16
 
Hi, I built the ZKIT2 as monoblocks and I’m getting great sound from them.  However, I’m getting hum that I can just barely hear from my listening position.  If I unplug the RCA input cable, almost all the hum disappears.  All components are on the same AC circuit.  I tested it by lifting the ground with a two prong AC plug and it had no effect.  Anything I hook up to the amp causes hum.  Since it’s a ground loop, I don’t understand why lifting the ground had no effect.  Any thoughts on what might be going on or how to solve the problem?  I don’t know what else to try.  Any help would be greatly appreciated!
Back to top
 
 
  IP Logged
bobc
Senior Member
***




Posts: 64
Re: ZKIT2 -> ZKIT1 build and the next one.
Reply #3 - 11/29/21 at 21:18:52
 
Measure hum at outputs. There is a paper here somewhere how to measure with simple vom. Chances are you are hearing slight b+ ripple. You can try artificial center tap on heaters (2x100ohm) if it’s not wired on the board, also you can double cap in second stage to add more filtering in the power supply. 1.2mv can be “enough” to hear. I would be careful in wiring input jacks and volume control as another area to check.
Back to top
 
 
  IP Logged
RonFranks
Verified Member
**




Posts: 13
Re: ZKIT2 -> ZKIT1 build and the next one.
Reply #4 - 11/29/21 at 21:32:26
 
Thanks for your reply.  I should have stated that I’m pretty much a novice as far as troubleshooting.  Doesn’t the fact that that there’s no hum with the input disconnected point to a ground loop issue or a problem outside the amplifier?  The amp has no volume pot so I assume it’s running wide open and not humming until an RCA cable is connected.
Back to top
 
 
  IP Logged
bobc
Senior Member
***




Posts: 64
Re: ZKIT2 -> ZKIT1 build and the next one.
Reply #5 - 11/29/21 at 21:37:53
 
You should always measure hum with the inputs shorted. If there is no hum at speakers, then the source of hum is upstream (ie not the amp). In this case it could be anything, including a ground loop, or even your cable tv connected to cable box.
Back to top
 
 
  IP Logged
RonFranks
Verified Member
**




Posts: 13
Re: ZKIT2 -> ZKIT1 build and the next one.
Reply #6 - 11/29/21 at 21:57:34
 
Just out of curiosity, I attempted earlier to short the input and the result was a bad screeching noise from my speaker.  I don’t know if it was oscillation or what.  I immediately removed the shorting RCA plug.  Thoughts?
Back to top
 
 
  IP Logged
bobc
Senior Member
***




Posts: 64
Re: ZKIT2 -> ZKIT1 build and the next one.
Reply #7 - 11/29/21 at 22:24:39
 
Each input to ground. Connecting them together? I dunno.
Back to top
 
 
  IP Logged
Pages: 1
Send Topic Print