MPP

Jump to Latest
#10,501
MiiB said:
Well it is a phono-stage, so you have plenty gain at low frequencies, in input cap is to protect the cartridge from DC current.

The paradise servo is injected into the current source driving the circuit, so it works by skewing the currents, rather than injecting DC into the signal like the marantz does.
Click to expand...

Skewing the currents ?

Would you explain it please ?
 
#10,502
The servo in The Paradise works by altering the voltage over the current setting resistors in the driving 4 transistor CcS. This changes (skews) the currents in the top and button part of the circuit, this moves the operation points of the gain transistors to a point where they reach a balance
 
#10,503
Please let me remark that changing dc current conditions or
"injecting DC (voltage) into the signal" is the same thing in
different words as long as the ac operation of the amplifier
is not affected (and this is the sole purpose of a dc servo).
In fact an important point in making use of a servo or other
form of dc feedback is to find a point in the circuit where it
can be applied properly.
 
#10,504
MiiB said:
I think in caps are only there for safety and not because they are needed. Maybe during startup there can be some offset.
Click to expand...

Again I don't completely agree. Even at startup or turnoff any input offset in a BJT
base input is that of a base current difference only (sub microamp region).

I have even used mc phono emitter inputs for years (since 1992), that means an input
offset is the difference of the base emitter voltages of pnp and npn. Unadjusted it may
be some millivolts. I had never problems with that even with turnon and off.
 
#10,505
Off course you are right in therms of not getting DC out, both ways works the same. But I can assure you they don't sound the same, the skewing of currents is much to be preferred, at least in the paradise where you have no feedback to correct the signal

I really can't explain why they put the cap there, we both agree on that its not needed, do you have an idea..?

Still I can't really make my mind up what is best for a phono stage, servo or DC cap(s) in the middle of the circuit
 
Last edited:
#10,516
Hi Joachim,

This is great news and clearly shows you are on the mend. Relax with your loved ones. Experiences like this get ones priorities calibrated... The rest is low priority although we love talking phonostages and the world always needs another 🙂

Take care,
Mogens
 
#10,517
Welcome back Joachim it was getting rather quiet without you.😉

Here is is something else from Marantz.

Trick gain stage..................

Jam
 

Attachments

  • Snap 2015-04-23 at 18.00.40.png
    Snap 2015-04-23 at 18.00.40.png
    258.8 KB · Views: 380
#10,518
jam said:
Welcome back Joachim it was getting rather quiet without you.😉

Here is is something else from Marantz.

Trick gain stage..................

Jam
Click to expand...

And where is the tricky part. The output stage is driven from the supply current of the opamp? that's it? IMHO this is really bad, please don't (do this at home), take this as a bad example!! Even Marantz seems to make mistakes.
 
#10,520
jam said:
I did not say it was good but but I have never seen this topology implemented in a line level product let a lone a phono stage .........I wonder what it measures like?:scratch2:
Click to expand...

It is a 'relatively' normal circuit and old also, but not tricky at all.

The thing is, here we talk about Joachim's circuits (and related (even remotely)) not Marantz. So where is the reference to any of Joachim's circuits?
 
You must log in or register to reply here.
Top Bottom