zen without feedback

[apassgear]

I stick with the zen design. So not the aleph ccs.



I am curious about effect of the feedback on the original zen.

Original Zen has an Aleph type ccs.

 

[apassgear]

Original Zen has an Aleph type ccs.

Sorry about my previous post, I was wrong

 

[eLarson]

A few revisions into the series, though, it did indeed morph into an Aleph-style current source.

Not that far off, in my book.

 

[apassgear]

A few revisions into the series, though, it did indeed morph into an Aleph-style current source.

Not that far off, in my book.

I agree.

The main difference is that the original ccs does not modulate.

 

[GRollins]

The Aleph current source counts as feedback since it derives a signal from the output.

Grey

 

[jh6you]

I have thought that it sits there to get the current boost, following the order of the output sensor. . . . not to get stability, distorsion correction, closed loop gain, or. . .

Regards
jH

 

[hacknet]

i was toying round the idea of a negative rail. i`m a newbie to mosfets and i`d love to learn more.

i was played around and this is what i came up with. its very crude and isn`t really stable. can anyone help me make the circuit work? whats wrong with it? i know i`m getting too much local feedback and thus the gain is rather low, is there anyway to solve this?

 

[Nelson Pass]

The Aleph current source counts as feedback since it derives a signal from the outputGrey

If you want to be picky, the CCS also has feedback
(locally). Me, I'm not that picky.

 

[Vix]

Hi

As I see, some of you are concerned about the CCS and its effects. I will not worry about it. I am planning to use a CCS like in ZEN v2, and perhaps even try a lightbulb...

However, what worries me (still didn't get an answer) is the input impedance of the circuit. Original zen has a low input impedance, but since it is used with Bride of Zen, it is fine. But, I plan to connect a transconductance ZEN "directly" to a CD player (via 47 K ohm pot). I'm really curious how CD player's output will cope with current Zen input impedance and mosfet capacitance...

Thanx

Vix

 

[planet10]

what worries me (still didn't get an answer) is the input impedance of the circuit.

Everytime i see that, i think valve buffer.

dave

 

[Nelson Pass]

what worries me (still didn't get an answer) is the input impedance of the circuit. Original zen has a low input impedance, but since it is used with Bride of Zen, it is fine. But, I plan to connect a transconductance ZEN "directly" to a CD player (via 47 K ohm pot). I'm really curious how CD player's output will cope with current Zen input impedance and mosfet capacitance...

Without an (audio frequency) feedback loop, the input impedance
can be quite high - whatever resistance you want to set it at.

The input capacitance is dependent on a number of things, but
a typical value is between 1 and 10 nF. As a practical matter
the source component would want an impedance at 600 ohms
or lower.

 

[Vix]

Thanks!

 

[steenoe]

Vix, any chance you could post the final schematic, resulting from this thread.

Steen

Edit, seems I had Vix mixed up with Lilmik

 

[steenoe]

I tried to collect the "breadcrumbs" and ended up with this result.
Is this schematic "pass"able, as a single-ended, non feedback, current source Zen amplifier? Any suggestions?

Steen.

 

[Vix]

Hi

Schematic seems fine, except one thing: R1. I would connect it directly to the Gate, as close as possible. Everything else would be connected after this resistor. This is my opinion, of course Nelson may have to "approve" it

I have written before about my concern for the imput impedance. As I understood, we can put , say, a 22 KOhm resistor in front of C1 and then this circuit would have 22 K input impedance?

Thanks a lot!

Vix

 

[apassgear]

I second Vix on R1,

I started to work also on a similar non fb amp. CCS will be as the original Zen and will have a regulator as shown on page 2 of Zen Variations part 3 (the simple one, not the Aleph sliding CCS or sliding regulator).

Rail will be something around 25 to 30V. Bias, whatever my fan asisted sink will allow, maybe 3 amps.

Will start with an output load of 15 Ohms as NP has on F2, he also mentioned a starting load of 22 Ohms, so watever works with my FE 164.

Hopfuly I will get those 5W, will see what happens.

 

[apassgear]

Vix, I don't think you will be able to lower the input impedance adding whatever series resistor. The impedance, as I remeber NP saying, is set by the biasing of the gate and the gate of the active component. Since we don't have effective FB that's it.

A shunt resistor before the input cap could help lowering the impedance as seen by the source. Me thinks.

 

[apassgear]

I tried to collect the "breadcrumbs" and ended up with this result.
Is this schematic "pass"able, as a single-ended, non feedback, current source Zen amplifier? Any suggestions?

Steen.

Traditionally Zen has not use the zener protection so you can do without it to keep the spirit. Though it’s a good idea to protect the gate.

As I remember NP does not use any resistor when using zeners as protection. If you use the zener remember that R1 should stand between the zener and the gate.

 

[steenoe]

Thanks for your replies

Schematic seems fine, except one thing: R1. I would connect it directly to the Gate, as close as possible. Everything else would be connected after this resistor. This is my opinion, of course Nelson may have to "approve" it

So you mean R1 should sit right after IN+, also maybe a higher value? I will drive this amp off from the BosoZ, so the low input impedance might be ok? I thought of 600ohm as NP said earlier on this thread.

CCS will be as the original Zen and will have a regulator as shown on page 2 of Zen Variations part 3 (the simple one, not the Aleph sliding CCS or sliding regulator).

I have the original Zen amp, and will modify it to preferably something close to the F2 I will use the P channel CCS. Maybe I will use the regulator too. I have used that reg. on several amps with good effect.

As I remember NP does not use any resistor when using zeners as protection

I believe to remember NP said he would never let a zener see the outside world, thats why I put the R in front of it. Parasitic oscillations might occur
I was forgetfull and didnt mail the .SCH file home I will redraw the schematic on monday, when I get to work again
In the meantime, any suggestions would be very much apprieciated Thanks again guys for your input.
BTW I intend to build a pair of single unit speakers for this amp

Steen

 

[apassgear]

I think Vix tryed to explain the same that I did regarding R1. The resistor should be as close as posible to the gate as the last element before signal enters the trany. This way the zener does not look directly to the gate. Yes I also remember NP saying that zeners should no look directly to the outside world. R5 could be at the top also hiding still more the zener. Anyway I dont think it will make much difference as long as R1 is on said position. Regarding value for R1 I would stick with what Nelson uses, 220R.

Yes Steen, thats the CCS that I will use, the P channel IRFP9240 to follow Nelson's tips.

I was thinking on the same line as you, updating my old original Zen and thats the way I started thinking to build this "F2" Clone. but after my initial intentions found out that the box for this is way to small for the components I have in mind. So I will mock up to test over a playwood and if all goes well I'll do a proper box.

My original Zen which I added a front end a la Z4...