Mpp

[pdul]

I now have matching trannies for both channels at hfe 430 2% and for the inputs closer to 1%

[Stefanoo]

Originally Posted by Joachim Gerhard

You can find the latest schematic in post 13 of the thread " Paradise Builders".
There is also now a trimmer at the input where you can optimize DC offset at input and output. You may not know that Stefanoo.
I can not tell why the Paradise is noisy with the input shorted. Actually i never tried it.
Nevertheless you get a low noise result and very good sound in practice.
That is what counts to me.

yep I agree with you. I mean noise is really, really low and soundwise (with modification I have made let's not open this can of warm up) is really STUNNING!!!


I will however post a picture when I get a chance of the residual noise with and without input shorted.

[Stefanoo]

Regarding, the offset, I have installed it without the local feedback.

I measured an offset on my dummy modifieded DL-103R (I use this to test new design and when I am confident I plug the ZYX4D on, which it is going to happen tonight) is about 2mV.
The cartridge I think is 40ohm static impedance, while the ZYX is 4ohm which should then bring the offset down to 200uV, am I right?
Anyhow, I have no problem with that offset, however I will install the local feedback for the more expensive ZYX, connect at the input a resistor with the equivalent impedance of the cartridge, power up regulate the trimmer and then substitute it with two fixed resistors and then put the ZYX back on and power everything up.

[Salas]

The current through the two carts coils won't change. You can even short it and measure nothing in mV but the ib currents diff will be still circulating.

[RCruz]

Originally Posted by Stefanoo

yep I agree with you. I mean noise is really, really low and soundwise (with modification I have made let's not open this can of warm up) is really STUNNING!!!

What modification are you refering to Stefanoo ?

[Stefanoo]

Originally Posted by RCruz

What modification are you refering to Stefanoo ?

not the moment now to talk about this

Let's just wait a little and we can discuss about this eventually.

[Stefanoo]

Originally Posted by Salas

The current through the two carts coils won't change. You can even short it and measure nothing in mV but the ib currents diff will be still circulating.

I don't think you understand what I was saying or I mis-interpret what you are trying to say.
Anyhow, the goal is to cancel out the idle current from positive and negative side.
This only happens if you have 0V at the input (kirchoff's law docet).

for the nature of the BJTs and the circuit, with input changes on impedance and not perfect matching of input stage, you will get different offset values.
So the idea is to match voltage input based on the impedance of your cartridge since it is impossible to get such a perfect match on input stage to guarantee you an input offset below 50uV or so for any input value.
You could even adjust the offset while your cartridge is connected but you will have the following downsides:

1) playing with the circuit while cartridge is connected can lead you to short the BJTs at the input which could cause them to burn (less risky since shunt is adopted here but still a possibility to consider) and then cause a big DC offset at the input thus burning the coil.

2) you will have to connect your meter at the input and my concern with doing that and having a low impedance cartidge, is that if you don't have a dedicated low voltage meter, usually a regular one puts out 3.3V or more, you could easily damage the cartirdge's coil. I did that with the Denon since the impedance is higher but it wasn't probably a smart move.

So your best bet would be to connect the resistance equaivalent to the static impedance do the adjustments and then re-connect everything back.

Hope this helps explaining also for those who will connect the phono to their precious expensive cartridge!!
Please pay attention as this is not a JFETs input stage and depending on your build it can have significant input offset enough to cause an irrevarsable damage.

[Joachim Gerhard]

We have talked about the DC offset procedure before and yes it is correct to make a dummy resistor with the DC value of the cartridge then adjust the trimmer and then connect the cartridge. This thread is long so some will have missed that discussion. I will make sure that this procedure is described in the building instructions.
Yes, Salas the product of U x I is always the same, U goes down and I goes up. That is the reason i included the offset trimmer. In my Paradise build though the U x I product was very low. One way to get good initial offset cancelation is to select the NPN and PNP side not only for hfe but also for Ube. I may have had luck but my transistors matched very well in Ube too.

[hesener]

Originally Posted by Joachim Gerhard

We have talked about the DC offset procedure before and yes it is correct to make a dummy resistor with the DC value of the cartridge then adjust the trimmer and then connect the cartridge. This thread is long so some will have missed that discussion. I will make sure that this procedure is described in the building instructions.
.....

That's included on page 6, albeit very short. Joachim you may want to check or suggest a better wording

[hesener]

Originally Posted by RCruz

Hi MiiB

Can you quantify jfet buffer permanent offset ?

It's -1.5V on mine but I used J107 as output JFET