redrawing TridentCB9146

[richiyobs]

Hi folks... I tried to redraw CB9146
i d like to know if R2 & R6 in the attached schematic can be lowered ... or is it better to remove the input buffer i added and leave as it is?
I have read old post but useful links are gone
can you also please advice me a modern replacement for 2n5458? i ve simulated different jfet but no good results cause of distortion
and still confused about meter driver, changed values to get 100uA, the one i own at the moment

thanx for your attention
best
richi

 

[Bo Deadly]

I wouldn't add anything especially since it's wrong. U3B has no bias. That amp output is going to drift. I don't know this circuit but from what I can see you can just drop C17, U3B and R2.

 

[pucho812]

I wouldn't add anything especially since it's wrong. U3B has no bias. That amp output is going to drift. I don't know this circuit but from what I can see you can just drop C17, U3B and R2.

Circuit is a 1 RU trident rack mount compressor. It's duel channel with stereo link IIRC. He who's name shall not be mentioned unless you want him to show up lays claim to this circuit and a lot of other trident circuits.
The official schematic has been posted here before and is IIRC is in the tech docs section.

 

[abbey road d enfer]

As Bo pointed, U3Bdoesn't work. Also U1a and U2b are superfluous, as well as associated components.
In the original schemo, IC6 is the input buffer (unbalanced); you have added a balanced buffer to an unbalanced one.
Regarding the GR meter, it relies on the two diodes different threshold, one is SI, the other is Ge. It's a trick circuit, and may not be lending itself to tweaking.
In the original schemo, I fail to understand what R28 is doing.

 

[richiyobs]

Thanks for you reply....
yes i tried to go balanced, leaving IC6 as per the original schematic.
so, is it possible to mod IC6 to get balanced line?
i can only learn doing errors and bad simulation
R28 in the original one really don t know , not so expert.... but it was quoted in older post without going deeper
also thanks for explanation about meter driver, was confused cause i can t see it moving in simulation, only the right amperage, unlike other than I ve done

best

 

[richiyobs]

On LTspice removing R28 nothing changed....

 

[abbey road d enfer]

i can t see it moving in simulation, only the right amperage, unlike other than I ve done

What sim software are you using? What models have you used for the two different diodes?

 

[abbey road d enfer]

On LTspice removing R28 nothing changed....

Of course...

 

[richiyobs]

What sim software are you using? What models have you used for the two different diodes?

Default model for diode... Have to change them to verify

 

[richiyobs]

running 1n34 in place of OA47... seems to move
what is the role of R28, can be omitted? ... sorry for my dummy question ... just curious

best

 

[abbey road d enfer]

running 1n34 in place of OA47... seems to move

My question was where do you get the model for the Ge diode.

what is the role of R28, can be omitted? ... sorry for my dummy question ... just curious

As it is, it serves nothing, only to load unduly the oamp it is connected to. I surmise it's a remnant of an earlier version where there was a resistor between the output and the negative input, so as to provide some gain.

 

[richiyobs]

Found a model on Lt wiki or a similar link... No OA47... So choose 1n34

 

[peterc]

Small Bear has the 2n5458
https://smallbear-electronics.mybigcommerce.com/transistor-fet-2n5458/

 

[richiyobs]

Thanks for link... I ll check....
Found old post with useful updates by Bo Hansen:
R28 removed
Ne5534 in place of IC 6 & 9
Balanced input
And a opa buffer to the meter driver

I just finished pcb file with tl074 to start a proto
I d like to understand where to place the meter buffer and in which configuration, should be fine a simple non inverting follower?
Still have half tl072 for that
Thanks for your attention
Best

 

[richiyobs]

is this a good way for terminating half of TL072 and get meter buffer?

 

[abbey road d enfer]

is this a good way for terminating half of TL072 and get meter buffer?

U2b could be dispensed with; it buffers a buffered output...
Now changed one resistor a hundredfold and another tenfold does not seem reasonable to me.

 

[richiyobs]

Ok so Tl071 is a choice
is the null trim important for that part?
thanks in advance for your support

 

[abbey road d enfer]

is the null trim important for that part?

Fuggedaboudit...

 

[abbey road d enfer]

Ok so Tl071 is a choice

My comment was to point your attention to a design point. Now it's generally not a good decision to have a mix of single and duals of the same style, the reason being that it takes one more item in the inventory, and it introduces a risk of interverting one with the other, since they are both DIL8.
The original plan of having only duals is still valid (or only singles). Now you have a choice, you do what seems right for you.
It is quite usual to use only duals and leave one of them using only one half. In that case, it should be connected as a voltage follower and it non-inverting input connected to ground.
With duals, you won't have the dilemma about offset adjust.

 

[richiyobs]

In tech doc found a D&R mono compressor.... Similar design to Trident ... Except it has a mirror Jfet at vca...
Is it used to better bias the first one and distortion cancelation?