Forums - Having Problems with My ZKIT Build

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Posts: 10

Having Problems with My ZKIT Build
01/27/22 at 14:38:42

Hello All!
New member here and I need help. I have built a P2P version of the SE84DIY based on the 3/10/19 revision with all anniversary mods. The only deviations to the schematic were the use of an Antek 1T300 toroidal PT, 6DJ8 driver, and 6P14P power tubes (had these on hand already). OPTs are Decware EMO493 I got used from Decware. I've triple-checked all paths and solder joints but I'm not getting sufficient volume or bass from the amp. I'm running Klipsch RP-600m speakers (94dB) in a near-field setting, on the other side of my work desk, running direct from a CD player. I get sufficient volume with rock and pop with the Alps Blue Velvet pot at wide open, but this is not enough volume for classical music's softer parts. I would also guess that I'm not getting anything under 150Hz or so. Without a sub handling 150 and below the sound I'm getting is only slightly better than my iphone. By comparison, when I run my Quicksilver GLA and passive preamp, the sub is relegated to only the lowest rumbles and can be turned off and not miss it. I cannot listen to the ZKIT amp without the sub on quite loud and at a high xover point. I DO get enough gain from the amp when I inserted 220uF cathode bypass caps (still need to go to max volume for classical) but I know this is not a proper solution for this circuit. Given the great reviews of the SE84 (albeit with tube rectification), I know something is wrong with my build. I've even begun to wonder if there are typos to the schematic (other than the power pin #'s). Any ideas? Thanks and sorry for the long and sad introduction. Thanks!

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Donnie Seasoned Member Why does it hurt when I pee? Posts: 2342	Re: Having Problems with My ZKIT Build Reply #1 - 01/27/22 at 17:11:08 How many volts does your CD player output? Maybe you aren't getting enough voltage on your input side. Just spitballing here.
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Ericus Rex Verified Member Posts: 10	Re: Having Problems with My ZKIT Build Reply #2 - 01/27/22 at 20:13:25 Hmmmm. I guess the standard 2v? I've now tried it with three different players; a Marantz SACD, a Yamaha SACD and a Denon DVD player. Same results with all players.
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Donnie Seasoned Member Why does it hurt when I pee? Posts: 2342	Re: Having Problems with My ZKIT Build Reply #3 - 01/27/22 at 22:42:53 Well crap, I'm out of ideas. But you need to understand that I'm not too technical. I'm betting that someone around here knows exactly what you need to know though. By the way, welcome to this joint!
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bobc Senior Member Posts: 67	Re: Having Problems with My ZKIT Build Reply #4 - 01/28/22 at 13:48:39 Check to see if you have the right parts/components. Particularly the 330K resistor to ground between stages of the amp. Also are all your voltages in line? Check your B+ voltage. Did you place a 330ohm vs Kohm in that spot? A schematic / photo would likely help...
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Ericus Rex

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Posts: 10

Re: Having Problems with My ZKIT Build
Reply #5 - 01/29/22 at 15:15:27

Now that's interesting, Bob! I read your post and thought to myself "330K resistor?" I then looked over the schematic I used (in the printed 2019 manual) and there is no 330k R shown. I then scrolled up the manual and traced the pic of the PCB and I found two more discrepancies between the PCB and the schematic. The 330K you mention (grid leak R, right?), which connects the coupling cap to ground is printed 1K, not 330K. Additionally, the plate resistors to the 6N1P are, on the schematic, connected directly to the 6.8K R, but on the PCB, the after-6.8K B+ passes through the 10k R's before the 47K plate R's. I tried to attach the PDF manual but the site is saying the file is too large. Are these misprints the root of all my problems?

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Ericus Rex Verified Member Posts: 10	Re: Having Problems with My ZKIT Build Reply #6 - 01/29/22 at 15:27:36 Here is the pcb pic from the 2019 manual
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Ericus Rex Verified Member Posts: 10	Re: Having Problems with My ZKIT Build Reply #7 - 01/29/22 at 15:32:12 And here is the printed 2019 schematic showing the three (possible) typos
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funch

Seasoned Member

Posts: 162

Re: Having Problems with My ZKIT Build
Reply #8 - 01/30/22 at 03:50:51

When I had my SE84UFO, I measured all the values of the components, diagramed the layout, and built my own clone using headphone output trannies. I just went back and looked at my notes, and the resistors after the 0.1 coupling cap's to ground are 330K metal film, and the ones to the output tube grids are 330R carbon composition. Of course, mine is P2P also. Hope that helps.

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bobc Senior Member Posts: 67	Re: Having Problems with My ZKIT Build Reply #9 - 01/30/22 at 13:32:11 You will have better luck with this schematic, which seems to have been updated. The one you posted had some errors. https://www.decware.com/newsite/ZKIT1.pdf or this one... https://www.decware.com/Select/select_schematic.pdf
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Ericus Rex

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Posts: 10

Re: Having Problems with My ZKIT Build
Reply #10 - 02/01/22 at 17:50:49

Bobc, you are a genius! Your schematic links were the key. I've found 5 errors, so far, in the 2019 schematic. The most sonically egregious is the 1k grid leak resistor instead of 330k. I changed that straightaway and now I have ample gain and rich, full bass. Thank you!

Now, a couple of questions about the 5U4 option. The schematic doesn't list power tranny specs. I'm currently running a toroid, 300-0-300v 200VA. Is this adequate? This trans also has an extra, unused 6.3v/4a filament winding. Can I run this through a potential divider network to get my 5v? Or is this a bad idea?

Thanks!

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bobc

Senior Member

Posts: 67

Re: Having Problems with My ZKIT Build
Reply #11 - 02/02/22 at 00:14:08

A Hammond 272 fx is a good reference. The circuit when running draws roughly 60ma +\-. The fx is rated for 170ma I’d use this transformer buildin from scratch. It pulls more current as things settle down.

Never powered a 5u4 from 6.3 tap. If amps are right I suppose it would work. I’d be cautious about using only resistors, but maybe a few diodes to drop closer to 5v. I have to defer on this one… there are 6v heated rectifiers, but you’d have to look at current and voltage drop… dunno.

Glad it got sorted. Enjoy! It’s a nice sounding circuit.

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funch Seasoned Member Posts: 162	Re: Having Problems with My ZKIT Build Reply #12 - 02/02/22 at 03:38:13 The 272FX Hammond is the tranny I used in my build as well. Use the yellow/black center tap wire for B+.
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JBzen

Seasoned Member

Posts: 1525

Re: Having Problems with My ZKIT Build
Reply #13 - 02/02/22 at 14:48:54

A .22 ohm 5 watt resistor tied to the each of the 5U4’s cathodes should work. At least it did for this guy at https://el34world.com/Forum/index.php?topic=22066.0

Not sure how it would affect the B+ and as bobc said be cautious!

You guys that built a point to point using schematics of ZKIT1 and SE84C-S try any of the variants? 33uf or 40uf in the PS? 1k ohm resistor with the .1 uf suppressor grid cap as compared to 330 ohm without the suppressor grid?

I am almost ready to give this build a go being the transformers can be had in short order. Just trying to set a clear course.

Thanks for any info that can be provided.

John

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LoopA[AMC CD8b>XO3>Stokes DAC>Carver C-9]LoopB[Ortofon 2M Black>JVC QL-F4/Otari MX5050B2>ZP3]LoopC[Cambridge CXN2>ZDAC>ZBOX>Zrock2]}CSP2+>SE8425th>9AWG silver/copper braid>lii Crystal 10" Huijgen Cabinets. Isolation. AC filtering. Room Treatment.

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Ericus Rex Verified Member Posts: 10	Re: Having Problems with My ZKIT Build Reply #14 - 02/02/22 at 23:41:32 You are all talking sense. If I had to save a few bucks and use this tranny then I'd get a dedicated 5v power transformer to run the 5U4. JBzen, will follow for responses r.e. the variants. What OPTs were you planning to go with? The Edcors recommended in the schematic now have an estimated May delivery....
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JBzen

Seasoned Member

Posts: 1525

Re: Having Problems with My ZKIT Build
Reply #15 - 02/03/22 at 09:59:51

ER,
Still searching for OPs. Seems to be plenty of options. Trying to find ones with 10w, 8k impedance, and wide frequency response. Going to steer away of sketchy eBay offerings.

I found answers to some of the questions. The cathode cap to suppression grid is an old mod(Hazen) by Steve back in 2009. It makes good sense to use in the diode scheme to eliminate some of the hash and ringing created by the solid state device. He recommended it originally to use it in all his offerings. It had great positive feedback from users. So it will be a keeper in my build. If anything it helps clear some of the noise from the mains.

There is a recent thread about filter caps and rectifiers limits. It was mentioned that 40uf is the max a 5u4 should see at the first cap in the filter. Any higher capacitance will shorten the life of the tube because inrush current at startup is hard on the rectifier. Steve also wrote a paper on rectifiers and recommends using NOS rectifiers for the best reliable service. He also notes that any current production rectifier is junk(my word). I am thinking of using the 40uf caps and getting a NOS rectifier.

John

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LoopA[AMC CD8b>XO3>Stokes DAC>Carver C-9]LoopB[Ortofon 2M Black>JVC QL-F4/Otari MX5050B2>ZP3]LoopC[Cambridge CXN2>ZDAC>ZBOX>Zrock2]}CSP2+>SE8425th>9AWG silver/copper braid>lii Crystal 10" Huijgen Cabinets. Isolation. AC filtering. Room Treatment.

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