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Gyrator loaded Son of ZV9/F3
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Old 11th July 2015, 06:40 AM   #21
juma is offline juma  Germany
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Yes, the only one thete is - BF862 made by NXP ( ex Philips).

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Old 16th July 2015, 04:48 PM   #22
nr12 is offline nr12  Germany
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Originally Posted by juma View Post
A fellow member asked me if this preamp can be made with simple BJTs only so I gave it a try and it works lovely.
He is OK with max. 6V_RMS at the output so the rail voltage is down to 24V.
Since the use of a BJT at the input and single rail PSU imply the use of an input cap I introduced local Schade feedback (R10, R3) to control the gain (about 13dB). Z_out is a bit higher (150-200 R) , Z_in too (47k), some elements' values are changed, but it still sounds very good...
Hello Juma,

can you tell me where to put the volume pot in the schematic built with bjts?
Will a 10k pot be ok?

Thanks,

Ulf
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Old 16th July 2015, 06:06 PM   #23
juma is offline juma  Germany
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The pot should be at the input.
10k is great.
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Last edited by juma; 16th July 2015 at 06:10 PM.
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Old 22nd October 2015, 12:05 PM   #24
juma is offline juma  Germany
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I've been doing some more work on this circuit to improve further it's sound and characteristics.
Now the feedback loop is gone and the input impedance is much higher (about 680k) while the Zout is still low (less than 50 R). The gain is about 14 dB and it depends on R4 and R13. R4 degenerates the JFET and R13 loads the gain stage, so more load (lower value of R13) and/or more degeneration (higher value of R4) means less gain, and vice versa. Practical values would be 1k5/680R for about 6dB gain and 3k9/330R for about 20dB.
Power supply voltage is somewhat higher (40V). Max output is about 9V_rms at 10k load. Current consumption is about 11mA and it depends on BF862's Idss. If your BF862 has Idss higher than 16mA make R3=10 R or so. The input cap is introduced (I use WIMA MKC) because JFET's gate sits at about 6V but since it is of a small value it's not of a great importance.
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Old 23rd October 2015, 07:28 PM   #25
jvhb is offline jvhb  Europe
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Gyrator loaded Son of ZV9/F3
Hello juma, just want to say thanks for the update! I have been looking at this design for a while now, and plan/hope to build it during winter. Seems like a nice simple circuit for a novice like me

A question regarding power supply please: Should I even be thinking about a regulated supply for best performance, or is the PSRR so high that a simple CRC setup will be sufficient? (Is this where the Gyrator does its bit?..) - Do you still use the Smps based solution?

Edit: Perhaps I should rather ask if you use the capacitance multiplier mainly because of the Smps? Would you still use it with a regular toroidal transformer based power supply?

Your work and contributions is much appreciated

Last edited by jvhb; 23rd October 2015 at 07:41 PM. Reason: clarification
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Old 23rd October 2015, 09:24 PM   #26
juma is offline juma  Germany
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Hi jvhb,
I used an SMPS in previous version just because I had it handy and the voltage was suitable but I prefer a nice linear PSU, from reasons which I'll bring out if you open the separate thread about it.

For the circuit in post #24 I use 10VA 2 x 18V~ transformer with secondaries connected in series which gives about +50V after rectification. The simple regulator follows - same as usual MOSFET cap multiplier with a small addition: 3 x 15V zeners connected in series, from gate to ground and a 5mA CCS from drain to gate to feed the zeners. That gives about +41V at the source pin.

So yes, a nice clean PSU is always beneficial. Since the current consumption is in this case low it would be easy to do some shunt reg or anything else that one likes...
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Old 30th October 2015, 09:42 AM   #27
jvhb is offline jvhb  Europe
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Thanks for the offer regarding seperate SMPS thread, but lets leave it for now: I am not interested in using SMPS, for the simple reason that I prefer to build with technologies/topologies that I more or less understand. And SMPS I will never really grasp, and much less be able to service or repair . So I will stick with linear PSU in any case

I have been reading up on capacitance multipliers (which I have not made or used before), and the principle seems quite clever and not too complicated. Made me wonder why I don't see them used more? I would imagine there is an ongoing debate on capacitance multiplier vs. very large capacitors - and which solution "sounds" better..
But I might start with a simple CRC(RC) layout, and then add/try out cap. multiplier and (shunt?)regulation at later stage. Or why not a Gyrator combined with cap. multi! (or is that not a good idea?). BTW: I am not really expecting answers to the above, as it would also be a topic for a another thread..

A philosophical sidebar: As many other novices in audio electronics, I probably tend to focus too much on the PSU, and not enough on the actual amplifier topology and design. I think the simple reason for this is that PSU design seem easier to understand. In the same manner, people with even less (or no) grasp of electronics, will often focus all their attention on (overpriced) cables and such.

What I would really like to hear your comments on, is how this latest design compares to the old version, and also how it is conceptually different from the BOZ preamp?
Is one better than the other, or are they just variations on the same principle? I have been comparing the schematics, but can't really follow or fully understand what is going on .

I saw another thread regarding the use of ZV9 layout as preamp, and Nelson responded by indicating that the use of a single JFET was not actually so good: Zv9 as preamp? (Read just the first two posts)
- What is your view on this?

And please don't say I should just build both BoZ, BoSoZ and Gyrator ZV9 based pre (and why not BA3-FE and Pumpkin also), and simply compare the sound! -I may eventually do just that, but all these things are very time consuming, and we can't always build or test all we would like to..

As you may have gathered by now, I am trying to learn this stuff (as much as possible anyhow), and not just blindly follow a recipe
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Old 30th October 2015, 10:51 AM   #28
juma is offline juma  Germany
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Quote:
Originally Posted by jvhb View Post
... I am not really expecting answers to the above, as it would also be a topic for a another thread...
Exactly

Quote:
Originally Posted by jvhb View Post
.... In the same manner, people with even less (or no) grasp of electronics, will often focus all their attention on (overpriced) cables and such.
Absolutely. And that is good so - everybody should have fun on the level they choose.

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Originally Posted by jvhb View Post
...Is one better than the other...
I don't publish stuff that doesn't sound better (to me) than known equivalents.

Quote:
Originally Posted by jvhb View Post
... Nelson responded by indicating that the use of a single JFET was not actually so good: Zv9 as preamp? (Read just the first two posts)
- What is your view on this?
I didn't read that. I read that differential cascoded JFETs sounded better to Mr Pass than single cascoded JFET. There is no schematic, no other data to make a sensible comparison, so I can't comment on that, except that there is a noticable difference in this circuit between BF862 and 2sk170. There is also a difference between CCS and gyrator, so there is no chance for apples to apples comparison...

Quote:
Originally Posted by jvhb View Post
... And please don't say I should just build...
That's exactly what I do. I like prototyping and testing/listening to diverse circuits, playing with them and changing them the way they sound better (to me). I don't have an agenda here, I sell nothing, not trying to prove anything, just doing what I like and sharing the results ....
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Old 30th October 2015, 11:44 AM   #29
jvhb is offline jvhb  Europe
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Alright fair enough.. I certainly didn't mean to imply that you had any sort of "agenda", I was simply interested to hear your views on these different variations of single ended preamp topologies

Have you had a chance to do any type of distortion measurements on your design?

I have actually had most of the parts for a BA3-FE sitting around for a while now (too long!). But it looks like your design may end up being built first, as I feel it should be simple to do on perf-board - and Reichelt.de has all the (cheap) components

So I might be able to do a comparison of those two during the winter (if all goes well..)

-Almost forgot: Wima MKC are not available. Do you think MKS-4 will work ok instead?
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Old 30th October 2015, 12:29 PM   #30
nr12 is offline nr12  Germany
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-Almost forgot: Wima MKC are not available. Do you think MKS-4 will work ok instead?
Have a look:
MKC4 0,047U 250V
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