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Old 12th March 2006, 02:35 PM   #1
Paper mache horn fabricator
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Default ZV7-T (transformer)

Hi all,

I'm fabricating the ZV7-T.

I'm in the process of submitting my pics and ideas for discussion.

Here's a drawing of Nelson's original artwork, but with colored lines to show where the onboard and offboard circuits belong. If I've made a gross error, please inform me. I'm especially curious to know how close the 1K resistors need to be in relationship to their perspective FETs.

All the best to the diyers out there,

John Inlow
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Old 21st March 2006, 03:51 AM   #2
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Default Man, oh man...

I completed one channel. I have the voltages dialed in, all but the dc offset, that is. The power supply is a pair of Nebraska Surplus' 34 volt 14amp specials coupled to a CLCLC filter (the chokes are 10mH @ .1ohms. Caps are surplus 20k uF each). The current supply transformers are Plitron 1000 V/A. They have found a permanent home!

This is an amazing sounding amplifier. I honestly enjoy it more than my AX. I scoped it to the best of my abilities and everything seems normal. The square wave had no outragous characteristics.

The sound is probably colored, but so warm and lush. Nothing harsh or brassy, thin or brittle--just warm and very sweet, like my sweetheart's concert grand piano. Just amazing...

I don't have a digital camera, so I'll have to take snapshots and scan them for you guys.

I can't wait to get the other channel up.

I assume that the dc offset is adjusted with pots P1 and P2 to the gates of Q1 and Q2?

Nelson, can you tell me how to adjust for minimal distortion. I have an HP 332A coming my way soon.

All the best,

John Inlow
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Old 21st March 2006, 06:04 AM   #3
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Nice to see you have ignited the beast : You are definitely a bold guy

I’m not qualified to go over the topology but could suggest some tweaking to see if it makes some improvement soudwise. Of course I’m not Nelson to come and suggest changes on the values but never the less I would try it.

You could replace P3 with a voltage divider now that you know you need 7V to the gate of the CCS if you are not planning to change the bias of the circuit. On the long run is better.

C3 is a bypass for Z1, as I understand it, it looks small in value and to work the best it should have a series resistor to load it. All of this with an eye to see if it does not produce thumps at turn on or off.

As Nelson says, the amp has very low input impedance (3K balanced), I remember you mentioned using a balanced line but can’t recall which one. The reason to ask is that you need a very low source impedance to drive this beast with authority. If it sounds bland you may need a lower impedance pre or add, as suggested by NP, an input buffer a la Z4.
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Old 21st March 2006, 06:13 AM   #4
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Default Re: Man, oh man...

Quote:
Originally posted by carpenter

I assume that the dc offset is adjusted with pots P1 and P2 to the gates of Q1 and Q2
If you reread Nelson's paper you will see that that is correct
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Old 21st March 2006, 12:39 PM   #5
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Default Thanks, Tony

I'm so consumed with getting to this stage of completion that I can't remember the finer details. Glad to have guys like you around to keep me walking straight.

Now where's my papers...

John
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Old 25th March 2006, 05:05 PM   #6
Magura is offline Magura  Denmark
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Have you tried playing around with different types of mosfets?

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Old 25th March 2006, 06:14 PM   #7
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Default different MOSFETs?

I'm chuckling because I've blown up at least a dozen MOSFETs just getting to this point in time with this amp.

I've reconfigured the PS to an LCLC format that gives me exactly 30 volts out. The amp reads as follows:

transformer center tap 30 volts
R-6 2.48 volts
Q1 gate 9.61 volts
Q1 drain 28.7 volts
Q1 source 5.25 volts
dc offset 1.5 millivolts (pretty cool huh?)

I'm reluctant to push the little fellow harder Another volt makes the difference between warm and supernova...

Eric Clapton never sounded so good!

John Inlow
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Old 25th March 2006, 11:23 PM   #8
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Default listening impressions

My ears are ringing a bit...

I just connected my mono version (stereo compliment to be completed in the next several weeks) to my Aphex single ended input/balanced output processor then the single ended dvd/cd player--cheap little eight-nine dollar unit. I didn't feel like pulling apart my main system until the ZV7-T is fully functional.

Today, the center channel is my test speaker which consist of two eminence twelves, two jbl eights, and one baby butt cheek tweeter. I'd place this at close to 100 db 1 watt 1 meter and rate it as a four ohm load.

This amplifer slams! It also tickles and sparkles I'm not biased up as high as Nelson's original (yes, I'm a bit chicken), and my heatsinks are barely warm (of course they have 5-1/2" x 5-1/2" fins!) but it hits the bottom octaves hard, much harder than I would have expected for a four ohm load! The quality is very apparent, you can tell this is upper end class A sound It holds it own against my AX, which seems more than a little unfair considering how simple and quickly the ZV7-T materialized--point to point on a copper padded perf board, took several several minutes of soldering interspersed with a couple hours of head scratching--way easier than remodeling a kitchen! Who would have thought...

My hat's off to Nelson... honestly, how would I have discovered such a wonderful sound without him. Thank-you! If there's anything I can do for you, Nelson, just give a yell. Oregon's not far from Nevada.

I'll have pics up soon.

John
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Old 28th March 2006, 01:32 PM   #9
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Default where to go from here

Hi everyone,

I enjoy this Zen configuration so much that I'd like to remain here for quite some time. My question is this: how do I improve the output transformer and associated sound quality?

If there is nothing else that can be done with the output transformer, fine. But surely there must be improvements if one knows were to look. This is where I hope you tube guys can help...

Any thoughts?

Thanks for reading,

John Inlow
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Old 28th March 2006, 03:16 PM   #10
Zen Mod is offline Zen Mod  Serbia
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first thing-its just splitted choke,not output xformer ( and believe me -you are lucky that you don't need one )

when you touch it -is it hot ?
if not-do not change it from saturation reasons

when you listen to it -are you satisfied with bass?
if yes-do not change it from "not enough inductivity " reasons.

chokes and xformers have some other (different )qualities,comparing to CCS-es (active or passive) ; these "qualities" are somewhat under suspicion from guys who believe in many zeros after decimal point....

if you are satisfied with sound,do not change iron...
try with different currents,parts etc-but leave iron where it is
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