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Old 18th February 2012, 01:24 PM   #11
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The schematic is totally wrong for the Deware Zbox. Gain is said to be close to unity and Zout ca 1k. According to the tech papers the Decware is a simple CF with a ECC83. Sound should be better without it as it can only add colouring. You then also get rid of the buzz.

The Zkit is completely different as it is a gainstage with the highly unlinear ECC82.
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Old 18th February 2012, 01:40 PM   #12
DF96 is offline DF96  England
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The Zkit looks strange because it has too much gain and a high output impedance. It is difficult to conceive of a system where it would not seriously damage the sound. Maybe it needs a CF to follow it!
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Old 18th February 2012, 05:00 PM   #13
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well, I removed the pot from the housing, the tube socket from the chasis to see if any basic wire bundling could be done. Of course, as luck would have it, as soon as I moved the POT and the tube socket, a few of the solder joints popped loose. So now we have cold solder joints to add to the mix. The picture I just upoaded is a PCB for the Zkit4, which I think is the same circut as the Zbox. It would have been great if this unit had a nice PCB instead of the point to point wiring with what looks like extra long wires. This thing is screaming to be redone.
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Old 18th February 2012, 05:11 PM   #14
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Quote:
Originally Posted by revintage View Post
The schematic is totally wrong for the Deware Zbox. Gain is said to be close to unity and Zout ca 1k. According to the tech papers the Decware is a simple CF with a ECC83. Sound should be better without it as it can only add colouring. You then also get rid of the buzz.

The Zkit is completely different as it is a gainstage with the highly unlinear ECC82.
I think the white papers is for current production. The Zbox ships with a 12AU7/ECC82. A lot of folks use 12BH7's. Using 12AX7's/ECC83's is reported to be problematic becuase of input over load. A POT is provided so that if you use tubes with other MU's , line level adjustments can be made. So basically, if you use a 12AT7 or 12BH7, there's some gain and may need to be rolled back. I found the box to be quieter using 6414's. The 6414 is a longer tube, and may be lest influenced by the effects of a starved AC heater as used in the Zbox. In any event, there's a lot of opportunity to put in a few mods as pointed out in this thread to quiet the unit down. I'm going to try them in order of level of effort. It would be great if I could come up with a measurements scheme so I can actually measure the effects of the changes. The buzz is pretty load, so maybe just a basic Iphone sound analyzer program. I dip into this over the next few days. more to follow.
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Old 18th February 2012, 05:41 PM   #15
DF96 is offline DF96  England
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Can we be clear: are we talking about the Zbox (cathode follower, gain<1, low o/p Z) or Zkit (degenerated grounded cathode, gain>1, high o/p Z)? Two very different circuits with different characteristics, although perhaps in similar boxes.

There is nothing wrong with p2p wiring, provided it is done properly. At least you can change it easily; a bad PCB design would mean starting from scratch.

If the buzz is loud then you don't need any instrumentation to show an improvement. All you need to do at first is sort out the PSU wiring, and ensure the heater supply has a voltage reference rather than being left to float. Then send the bill for your time to Decware!
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Old 18th February 2012, 08:03 PM   #16
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OK, I'm going to attribute this to 4 cold solder joints and poor wiring, which I would have not found if you guys did not talk me into doing something about the wiring. When I moved the POT and the tube socket, wires started to pop off their joints, so at least 4 cold solder joints where found. While in there, I move the tube socket 45 degrees so that the AC heater lines were not in the middle of the tube circuit components. I moved the turns on the ac heater lines as far forward to the tube as I could and hot glued the rest of the AC heater lines right to the box case. I positioned the B+ pink wire as far as I could from both the in and out lines and the lines going to the pot. I tied the in and out lines together and made sure they were not near AC or DC lines. Tested it out and there's no hum or buzz. Thanks for the input , I was going to dive right into a AC to DC conversion which would not have addressed the real issue. I decided not to do the two 100 ohm resister mod to the heater supply. The current loss would have been .1, I think the power supply can only handle .3 and the 12AU7 tube needs .3 for heater current so thats out. Thanks again everyone.
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File Type: jpg photo-2.JPG (596.1 KB, 152 views)
File Type: jpg photo-3.JPG (617.1 KB, 158 views)

Last edited by speakerfritz; 18th February 2012 at 08:20 PM.
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Old 18th February 2012, 08:30 PM   #17
DF96 is offline DF96  England
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Does the heater line have a DC reference? It should have. Ground is often sufficient - just ground the heater CT (valve pin 9). Don't do this if one side of the heater is already grounded.
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Old 18th February 2012, 09:29 PM   #18
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Quote:
Originally Posted by DF96 View Post
Does the heater line have a DC reference? It should have. Ground is often sufficient - just ground the heater CT (valve pin 9). Don't do this if one side of the heater is already grounded.
I'm buying you a beer. There was a faint background hum remaining but only noticeable a full volume with no signal. I checked pin 9 and it's not grounded. I confirmed that the whole AC heater circut is floating with no grounds. I grounded pin 9 and the system when totally dead quiet. No noise at all. Awesome. Thanks.
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Old 18th February 2012, 11:06 PM   #19
DF96 is offline DF96  England
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Glad you fixed it.
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