Simple Symetrical Amplifier - Page 20

Joachim Gerhard · 14th August 2011, 01:39 PM

Nico, could you please post the schematic that you are using right now ? That is the version i like most by intuition.

Salas · 14th August 2011, 01:56 PM

Also some info on the bias current used, test rails potential, and the power it achieved for 0.1% THD on 8 & 4 Ohm, will be welcome.

Bigun · 14th August 2011, 02:32 PM

Quote:

Originally Posted by Lazy Cat

Offset trimmer was missing, now output DC OK.

I like it in BJT-only form, this has every chance to be a popular circuit.

I find the way you have drawn the schematic adds to the interest for me, not sure I can explain, but it looks nice

Lazy Cat · 14th August 2011, 03:35 PM

It will be even more popular with values given.

So now in this configuration we have 4,3mA input BJT's collector current, 15,9mA driver's current and an output BJT's quiescent current adjustable from 0 to 1,8A.

Lazy Cat · 14th August 2011, 04:28 PM

These values are of course discussable, cause now I see that the second stage (driver) voltage gain should be significantly higher, so substantial reduction of 22 ohm emitter resistance must be done. Recalculation in progress ...

wahab · 14th August 2011, 04:39 PM

Quote:

Originally Posted by Lazy Cat

These values are of course discussable, cause now I see that the second stage (driver) voltage gain should be significantly higher, so substantial reduction of 22 ohm emitter resistance must be done. Recalculation in progress ...

A good option would be to simply implement a double EF
as output stage , reducing THD efficently , as displayed
in the following graph.

IQ is about 0.42A in both cases.

Lazy Cat · 14th August 2011, 04:57 PM

Quote:

Originally Posted by wahab

A good option would be to simply implement a double EF
as output stage , reducing THD efficently , as displayed
in the following graph.

IQ is about 0.42A in both cases.

I know but than we are a little out of the concept.

Please recheck THD with these new values.

wahab · 14th August 2011, 05:08 PM

Quote:

Originally Posted by Lazy Cat

I know but than we are a little out of the concept.

Please recheck THD with these new values.

This is better but still more than 20db higher THD
than with a double EF final stage.
The VAS is really too much loaded and this ruin this circuit
capabilities wich are quite good given the schematic simplicity.

Good work , Lazycat , anyway...

Lazy Cat · 05:21 PM

It looks in this concept with 8 transistors, lateral MOSFET output's would give the best THD figures, loading the VAS less than other versions.

MOSFET driver is another option, maybe ... the best solution of this simple concept lies in the right driver/output configuration, as we have already discussed here.

Joachim Gerhard · 14th August 2011, 05:17 PM

How about a BJT - Lateral Mos Szikley compound ? I really would prefer that the mosfets drive the speaker from the drain but i am not a power amplifier specialist.

14th August 2011, 05:16 PM	#199
Lazy Cat diyAudio Member Join Date: Sep 2007	It looks in this concept with 8 transistors, lateral MOSFET output's would give the best THD figures, loading the VAS less than other versions. MOSFET driver is another option, maybe ... the best solution of this simple concept lies in the right driver/output configuration, as we have already discussed here. Last edited by Lazy Cat; 14th August 2011 at 05:21 PM.

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14th August 2011, 01:39 PM	#191
Joachim Gerhard diyAudio Member Join Date: Mar 2009	Nico, could you please post the schematic that you are using right now ? That is the version i like most by intuition.

14th August 2011, 01:56 PM	#192
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	Also some info on the bias current used, test rails potential, and the power it achieved for 0.1% THD on 8 & 4 Ohm, will be welcome.

14th August 2011, 04:28 PM	#195
Lazy Cat diyAudio Member Join Date: Sep 2007	These values are of course discussable, cause now I see that the second stage (driver) voltage gain should be significantly higher, so substantial reduction of 22 ohm emitter resistance must be done. Recalculation in progress ...

14th August 2011, 05:17 PM	#200
Joachim Gerhard diyAudio Member Join Date: Mar 2009	How about a BJT - Lateral Mos Szikley compound ? I really would prefer that the mosfets drive the speaker from the drain but i am not a power amplifier specialist.