Mpp - Page 806

as-audio · 11th December 2012, 04:18 PM

Quote:

Originally Posted by Joachim Gerhard

as, was that really single ended or parallel symmetric ?
I showed one stage folded cascodes a long time ago that had enough gain.

If you call a cascode single ended a folded cascode is single ended also, isn't it?

Quote:

Originally Posted by Joachim Gerhard

With single ended you have the problem that the high current in the folded cascode gives much too much DC over the transimpedance bass resistor. 50mA over 100kOhm is a lot.

Since the output of the folded cascode is at or near zero DCV I don't see the point here.
I don't choose a higher current in a folded casc. than I would in a regular one (of course
as seen for a single transistor).

Joachim Gerhard · 11th December 2012, 05:09 PM

Input cascoded plus folded cacode or only folded cascode ?

Joachim Gerhard · 11th December 2012, 05:13 PM

Ok, color me stupid. We can set the DC voltage out of the folded cascode to a low value with the biasing arrangement.

Joachim Gerhard · 11th December 2012, 05:30 PM

I still do not understand. Even when we set the current low in the folded cascode, say 1mA, we still have the problem by Ohms law that too much DC voltage develops over the RIAA. This way ......

as-audio · 11th December 2012, 05:38 PM

Quote:

Originally Posted by Joachim Gerhard

I still do not understand. Even when we set the current low in the folded cascode, say 1mA, we still have the problem by Ohms law that too much DC voltage develops over the RIAA. This way ......

No, the collector current of the pnp transistor in your drawing has to be sinked
to the negative side in a current source (gain is too low without).

Joachim Gerhard · 11th December 2012, 06:00 PM

Ok, then we have a plus-minus supply. I did not think about this.
Somehow my brain can not connect single ended to a bipolar supply but why not ?

as-audio · 11th December 2012, 06:05 PM

You should always work with split supplies in order to avoid coupling caps where possible.

Joachim Gerhard · 11th December 2012, 06:17 PM

OHH, JEE, one coupling cap less - one supply more, anyway it´s cool.

Joachim Gerhard · 11th December 2012, 06:20 PM

Do you remember FS´s phono i build him ? There you substituted a split supply with a single supply and it worked to my horror nevertheless.
That was the hat trick the other way around. The dove mutated into a cylinder.

as-audio · 11th December 2012, 06:43 PM

Quote:

Originally Posted by Joachim Gerhard

OHH, JEE, one coupling cap less - one supply more, anyway it´s cool.

At least two caps for stereo, and you need a negative supply for your opamp anyway?

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11th December 2012, 05:09 PM	#8052
Joachim Gerhard diyAudio Member Join Date: Mar 2009	Input cascoded plus folded cacode or only folded cascode ?

11th December 2012, 05:13 PM	#8053
Joachim Gerhard diyAudio Member Join Date: Mar 2009	Ok, color me stupid. We can set the DC voltage out of the folded cascode to a low value with the biasing arrangement.

11th December 2012, 06:00 PM	#8056
Joachim Gerhard diyAudio Member Join Date: Mar 2009	Ok, then we have a plus-minus supply. I did not think about this. Somehow my brain can not connect single ended to a bipolar supply but why not ?

11th December 2012, 06:05 PM	#8057
as-audio diyAudio Member Join Date: May 2008	You should always work with split supplies in order to avoid coupling caps where possible.

11th December 2012, 06:17 PM	#8058
Joachim Gerhard diyAudio Member Join Date: Mar 2009	OHH, JEE, one coupling cap less - one supply more, anyway it´s cool.

11th December 2012, 06:20 PM	#8059
Joachim Gerhard diyAudio Member Join Date: Mar 2009	Do you remember FS´s phono i build him ? There you substituted a split supply with a single supply and it worked to my horror nevertheless. That was the hat trick the other way around. The dove mutated into a cylinder.