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Balanced Zen Line Stage Preamp
Balanced Zen Line Stage Preamp
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Old 4th April 2019, 09:39 PM   #51
elwood625 is offline elwood625  United States
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Location: Illinois
jfuquay - I went back and reread the NP article, check this out:
Referencing Figure 1, we note the function of various components. Resistors R7, R8, R9, and R10 serve to slightly isolate the inputs and outputs from the transistor pins, preventing parasitic and other types of oscillation. The values for these resistors can range from 100 to 475 ohms, and 221 ohms is about the best value.

In regards to R18 & R19:
If you have elected not to use input protection Zener diodes Z1-4, then you will want to be quite careful when you plug sources into the inputs. Generally this means touching the ground of the interconnect cable to the ground of the female connector or to the chassis before inserting the plug. The input Gates of the MOSFETs can take 20 volt peaks. I have seen them withstand 80 volt transients, but not reliably. If you don't use the Zener diodes, but do use P1 and P2, then you can always turn the potentiometers to 0 (counter clockwise) during connection.
Also note that if you do not use Zener diodes for input protection, you will not need R18 and R19, and they may be replaced by wire. Their function is to ensure stability for the circuit driving the input, since directly looking at a Zener diode can drive some circuits into oscillation. This is also why we use R7 and R8, and R9 and R10.

So it looks like R18 & R19 prevent oscillations from the INPUT sources, not the output like the ACA's. What kind of inputs don't like "directly looking at a Zener diode"?

I don't know, I'm not an Electrical Engineer, my last electronic class was in 1975.
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Old 4th April 2019, 09:43 PM   #52
elwood625 is offline elwood625  United States
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Also, I never connect or disconnect any interconnect unless EVERYTHING is turned off. Maybe I don't need R18 & R19 and the Zener diodes. Unless I have a "senior moment" I should be OK.

What do you think?
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Old 4th April 2019, 10:05 PM   #53
zygibajt is offline zygibajt  Poland
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Originally Posted by Zen Mod View Post
check with ohmmeter are they Shorting or not

precisely , with buzzer on your DMM
Even shorting Elma switches (DACT uses Elma) make pops in practice use. Looking close at them the wiper should be wider to clearly cover both neighbour steps pins to make a clear contact between them. I guess even high quality Swiss products are not that perfect. Shallco are suppose to be better but never tried those so can’t say but have been very disappointed with Elma. Also with the fact that the never used one stored few years all the contacts from gold became cherry almost brown colour )

Last edited by zygibajt; 4th April 2019 at 10:08 PM.
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Old 4th April 2019, 10:50 PM   #54
elwood625 is offline elwood625  United States
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Cheap electro gold plating discolors from the alloys mixed with the gold to make it "stick". Dipped gold plating, think auto airbag connectors, never corrode and discolor, at least from the gold side.
I've seen far to many gold plated connections where the gold was the only thing left, no base metal of wire connection. Just green....
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Old 8th April 2019, 06:19 PM   #55
PH104 is offline PH104  United States
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Balanced Zen Line Stage Preamp
elwood625 -- Received my board today. Thanks very much!

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Old 29th April 2019, 05:49 PM   #56
JMacII is offline JMacII
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I completed my first DIY project, an ACA, in December. I've been reading your work, and am blown away by your finished product. I want to build a second ACA and run balanced mono as well, and will look for your boards in the swap section. Not sure when I will have the time to kick this off, but it should be fun!
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Old 13th May 2019, 12:59 AM   #57
elwood625 is offline elwood625  United States
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I finally had a chance to listen and evaluate my BZLS with 2 mono block ACA v1.6 amps. I finished the BZLS a few weeks ago and found the volume control (P1 & 2) which was a four ganged 24 step vishay resistor pot, was not to my liking. So I found another, this time linear, huge difference. During the time I was listening to the BZLS, I had P3-4 at full CW, 0 ohms. I wasn't thrilled, however I wanted to fix the volume control first.

I had P3-4 at 3 o clock, the 5K is log, couldn't find a linear version, so adjustment is limited to 3 o clock to 6 o clock. Using balanced input for my Music Hall 25.3 dac, and balanced output for the ACA's I played Adios by Glenn Cambell, CD. Uninspiring to say the least, sound stage was flat, subdued and lacking the wow factor of the ACA's. So I decided it was time to play with P1-2 and P3-4. I turned P3-4 a couple of clicks toward 6 o clock, what a difference.
First, gain increased so I decreased p1-2 to match the level I was listening to and found the sound stage gained depth and width, the highs were brighter and the bass was pronounced, good start. So as any good american thinks, if a little is good, a lot is better. So I adjusted p3-4 to 0 ohms, 6 o clock, sound stage moved to the ends of the width and the depth did not change. The sound was brilliant with an excess of highs, with p1-2 adjusted to reduce the volume to the same listening level. when I did that, the sound stage started to move toward the center, not far, but enough where if I turned p1-2 back and forth, you could hear the sound stage move.

My wife was listening also and provided her opinion so that we were able to discuss the changes.
With every new song, I would make changes to p3-4 and p1-2 together and was able to "dial" in a sound far superior to anything we had heard with the ACA's. This is no ordinary line stage, it requires adjustment of both p1-2 and p3-4 to achieve incredible sound.
I then changed input to RCA input for my 12AX7a phono stage and Thorens TD125 with a Shure V15 v4 with a JICO SAS needle. A slight change of p3-4 allowed me to dial in the phono just like the CD. AWESOME!

Now for the bad, the selector switch I'm using "pops" every time I make a change and then p1-2 starts to pop every time I adjust after the input is changed. Wait a couple of minutes and p1-2 stops making any noise during adjustment. The input select switch must disrupt the circuit and requires a minute or two before p1-2 is quiet. I need to fix that!
Not since the old days when Bob Carver (sonic hologram preamp) and Tom Holman (APT/Holman) have I found a preamp adjustment which will change sound stage and sound quality like the BZLS. Only the BZLS is doing it without manipulating the circuit in such a complex method, p3-4 just changes output impedance. I struggled understanding the why and how of p3-4, now I get it. Second bad thing, I can't find a 5K four ganged 24 step LINEAR pot. So I bought a blank and will buy the resistors necessary to build my own. I'm thinking the increased adjustment going from LOG to LINEAR will be worth the trouble of soldering all those resistors, considering how much improvement to the sound is achieved adjusting p1-2 and p3-4.
The best thing about this preamp, I wired it for RCA outputs so I can drive the ACA's in Balanced, Bridged or Parallel. I'm in the process of building an F5t v3 mono blocks, I've read that the sound of the F5 is not to every ones liking. I'm hoping the BZLS will tame the sound and allow me to dial in a great sound either with XLR or RCA outputs.
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Old 14th May 2019, 07:51 PM   #58
Nelson Pass is offline Nelson Pass  United States
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Balanced Zen Line Stage Preamp
Originally Posted by elwood625 View Post
Here are the Gerber files for the PC Boards, already made PC boards are available at the SWAP section under Balanced Zen Line Stage PC boards.
I recently update this artwork for double sided and Gerbers very
compatible with China PCB Prototype & Fabrication Manufacturer - PCB Prototype the Easy Way

PL45A IS 8.0" X 4.6" and PL45B is 4.5" x 4.6"

Attached Files
File Type: zip PL45BR0.ZIP (27.1 KB, 16 views)
File Type: zip PL45AR0.ZIP (31.9 KB, 7 views)
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Old 16th May 2019, 06:27 PM   #59
cubicincher is online now cubicincher  Germany
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When I was reading this I put out my BZLS with added CCS and was hanging
it onto my M2X today (sure running se). Very nice! Old but gold!

I am listening now for more than 2 hours. And it sounds really good.

But that 'baby' should get a nice warm house - ah, I meant a metal case.
It looks so lost on the piece of wood for the last 2 years.
And it has high railvoltage!

Attached Images
File Type: jpg BZLS playing with M2X pic2.jpg (118.0 KB, 97 views)
File Type: jpg BZLS playing with M2X.jpg (104.7 KB, 96 views)
File Type: jpg BZLS closeup.jpg (101.5 KB, 99 views)
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