Mpp - Page 293

Joachim Gerhard · 28th October 2011, 04:44 PM

Holger Barskes website.

Joachim Gerhard · 28th October 2011, 04:45 PM

Analog Forum 2011

RCruz · 28th October 2011, 05:45 PM

Thank you so much. I am glad to see the weather was also favorable this year. Great show

Joachim Gerhard · 28th October 2011, 06:06 PM

We have phantastic weather at the moment but at night it is rather cold. Yes, Krefeld reminds me of the old Frankfurt show. Very relaxed and friendly, lots of socializing.

sampler · 28th October 2011, 08:45 PM

Hi Joachim,
I was quite intrigued with your starless circuit and decided to give it a go. So in real life, good matching of input cascade jfet's gives offset in uV range, so nothing to worry about. With current mirrors it was another case. Even with matched bjt's, 0.1% low ppm resistors and good thermal tracking, output wonders -+100mv, so yep, no chance of going DC coupled even with substantial efforts without involving servos. Did some quick fft to see if everything is as expected and thd (with 1Vpp output) was as close to sim'ed as it gets. Only 2d dominant, and that 3d is my ancient SB artifact.
Now the fun part. I suspected that operating my DL103 with it's high'ish impedance (45Ohm) to basically virtual ground, would be problematic, and I would need all the gain I could get, so I omitted that parallel resistor and opted with different riaa values (based on mirrors output impedance) that gave me couple extra dB. The sad part is that I'm stuck there (at some 0.7 Vpp output). Cant think of anything else to bump gain more or increase input impedance without hurting performance too much, maybe I'm missing something ?
Other than that, it performs excellent. I don't want to get carried with my subjective listening experience, but level of micro details is just staggering. It makes me wonder how DL103 can pull it off and why I didn't tried transimpedance input earlier

Joachim Gerhard · 28th October 2011, 09:28 PM

Many build my Nobrainer that has a transimpedance circuit too. Also in this case the DL103 works very well. I even tried a 20 year old Audio Technica High Output MC and even that worked satisfactory. The only thing that can happen is that you get some treble loss when the inductance of the cartridge is too high. Could you please post your actual schematic and then i can help you.

Joachim Gerhard · 28th October 2011, 09:35 PM

The distortion spectrum looks really good and i like the way you build it. How is noise ?

Joachim Gerhard · 28th October 2011, 09:58 PM

Sampler, the loss in gain comes from the rather high 45 Ohm impedance of your DL103.
That works like current feedback. My Titan i with 6 Ohm would give over 12dB more gain.
I can show you a way to stabilize offset and get more gain.

sampler · 28th October 2011, 11:24 PM

It's dead quiet Joachim, only broadband noise (2mV/div in foto). Yes, you are right, in my case resulting gain is ~52dB. With 6Ohm cart. that would be way much more. I attached circuit as build and some sims, any tricks and tips would be appreciated. I really like it, I'm even considering upgrading my preamp for more gain if that's the last resort.
I see you started new thread for nobrainer. That looks elegant/interesting too, I may give it a try, just were did I put those low noise 2sc/2sa...

Joachim Gerhard · 29th October 2011, 12:03 AM

Ok, you left out the parallel resistor and let the mirror do it´s work. Clever simplification.
Noise looks really low and does not have a particular spectrum. That is very good.
First you could add the helper transistors. That makes the matching of the mirror less critical and reduces distortion. Do you remember that twist or should i look it up for you ?
You could increase the emitter resistors in the mirror. When you double them output impedance doubles too. You can then raise the value of R8 by two and lessen the value of C1, C2 by half. That gives you 6dB more gain. The new emitter resistors drop some voltage. You could compensate that by raising the PSU voltage. When you take the PSU as is you loose some overload margin but it still will be fine. All other modification are more drastic. You could substitute the Fet output buffer with an Opamp with gain plus servo. That gives you DC coupling. I do that too because i found that ones the voltage is high enough the Opamp does no harm to the sound any more. That is the reason i prefer discrete inputs but have no objection to use Opamps in the following chain. I do that even in my 30.000,-€ Opus Magnum. It could be something like the second stage in the Nobrainer Servo but without the bass EQ components. The best Opamps i found are
OPA1611, LME49990 and OPA1641. An NE5534A will do for experimenting. I use OPA134 for servo most of the time. Another drastic measure would be to build another mirror with better bias stability. I have shown here the mirror with cascode that has excellent stablity. Again it was published here earlier. If you can not find it i can search it for you.
That may allow DC coupling. You could use my "strange" servo with the circuit you have.
Also published before. Anyway, i do not think that a 10nF cap does much harm or you would not experience the excellent result other then doing a soft subsonic filter. You could raise the value of the 10nF a bit. Maybe you like that better. I am very happy that it works so well.

28th October 2011, 05:45 PM	#2923
RCruz diyAudio Member Join Date: Sep 2006 Location: Saxon Blog Entries: 1	Thank you so much. I am glad to see the weather was also favorable this year. Great show __________________ RC

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28th October 2011, 04:44 PM	#2921
Joachim Gerhard diyAudio Member Join Date: Mar 2009	Holger Barskes website.

28th October 2011, 04:45 PM	#2922
Joachim Gerhard diyAudio Member Join Date: Mar 2009	Analog Forum 2011

28th October 2011, 06:06 PM	#2924
Joachim Gerhard diyAudio Member Join Date: Mar 2009	We have phantastic weather at the moment but at night it is rather cold. Yes, Krefeld reminds me of the old Frankfurt show. Very relaxed and friendly, lots of socializing.

28th October 2011, 09:28 PM	#2926
Joachim Gerhard diyAudio Member Join Date: Mar 2009	Many build my Nobrainer that has a transimpedance circuit too. Also in this case the DL103 works very well. I even tried a 20 year old Audio Technica High Output MC and even that worked satisfactory. The only thing that can happen is that you get some treble loss when the inductance of the cartridge is too high. Could you please post your actual schematic and then i can help you.

28th October 2011, 09:35 PM	#2927
Joachim Gerhard diyAudio Member Join Date: Mar 2009	The distortion spectrum looks really good and i like the way you build it. How is noise ?

28th October 2011, 09:58 PM	#2928
Joachim Gerhard diyAudio Member Join Date: Mar 2009	Sampler, the loss in gain comes from the rather high 45 Ohm impedance of your DL103. That works like current feedback. My Titan i with 6 Ohm would give over 12dB more gain. I can show you a way to stabilize offset and get more gain.

29th October 2011, 12:03 AM	#2930
Joachim Gerhard diyAudio Member Join Date: Mar 2009	Ok, you left out the parallel resistor and let the mirror do it´s work. Clever simplification. Noise looks really low and does not have a particular spectrum. That is very good. First you could add the helper transistors. That makes the matching of the mirror less critical and reduces distortion. Do you remember that twist or should i look it up for you ? You could increase the emitter resistors in the mirror. When you double them output impedance doubles too. You can then raise the value of R8 by two and lessen the value of C1, C2 by half. That gives you 6dB more gain. The new emitter resistors drop some voltage. You could compensate that by raising the PSU voltage. When you take the PSU as is you loose some overload margin but it still will be fine. All other modification are more drastic. You could substitute the Fet output buffer with an Opamp with gain plus servo. That gives you DC coupling. I do that too because i found that ones the voltage is high enough the Opamp does no harm to the sound any more. That is the reason i prefer discrete inputs but have no objection to use Opamps in the following chain. I do that even in my 30.000,-€ Opus Magnum. It could be something like the second stage in the Nobrainer Servo but without the bass EQ components. The best Opamps i found are OPA1611, LME49990 and OPA1641. An NE5534A will do for experimenting. I use OPA134 for servo most of the time. Another drastic measure would be to build another mirror with better bias stability. I have shown here the mirror with cascode that has excellent stablity. Again it was published here earlier. If you can not find it i can search it for you. That may allow DC coupling. You could use my "strange" servo with the circuit you have. Also published before. Anyway, i do not think that a 10nF cap does much harm or you would not experience the excellent result other then doing a soft subsonic filter. You could raise the value of the 10nF a bit. Maybe you like that better. I am very happy that it works so well.