Mpp

[Joachim Gerhard]

the heat goes up, i like that but not the LT1115´s !
First again to Onvinyl : I could not do this topology with the INA163 (for example) subtituting the three opamps. As you see the first stage is inverted and i would not have a choice of feedback resistors. The internal resistors in the INA163 are set to 3kOhm and it is not ment to be driven inverted.
To Allen: R11 and R12 set the gain of the input stage to 26dB so i tried not to put the full gain at the colectors to use. The ground referenced cascode is a bit unusual and this is my first atempt to mate that with a shunt feedback stage no wonder i do not understand that circuit in all it´s details yet. Using the compensating capacitor from Pin2 to Pin6 of the LT1115 should help to lower oszilation tendency. You have to look at the LT1115 as part of the whole feedback chain and not in isolation. Circuits like that have proven to work. Syn08, i know that i am stupid. In earliers posts i told everybody that i have not mastered modern circuit simultion yet. I was formally trained in the late 70th at the University of Padeborn in telecomunications. That is also the home of Nixdorf/Wincor computers. My main task was to calculate 9 dimensional matrixes by hand. No calculator allowed. In the 90th i worked with Prof.Hawksford in Essex but training there was informal, inbetween the lines, so to say. I have a basic understanding of feedback systems and stability margins but whould not say that i am an expert on feedback theory like you. i use gobs of feedback in my commercial designs but they all use finished building blocks like intergrated Operational amplifiers that of cause behave much more predictable then an atempt to visionary discreet design.
I simply could call up a friend and he whould put the circuit through it´s paces in no time. I have a lot of friends that are professional engineers that master that art perfectly well so i never have seen a need to look more into that myself. In fact i have founded world wide operating companies like Audio Physic on a beer felt. Well that time is come now and i should look for a circuit simulator that would fit my purpose. Any sugestion ? Microcap?
To blueskynis: R7C11, R8C12 and C13,C14 belong to a high frequency compensation that rolls of the open loop gain at a certain frequency in the quest for stability after feedback has been set. In my case the circuit is still oscilating. In the words of Syn08 i whould say "it´s not good enough". In my words "it´s not ready yet". That sounds better to my stupid but wise ears.
P.S. originally i wanted to post new adventures with the High Z MPP but now i need a Tequila beer.

[Joachim Gerhard]

The MPP High Z Headamp is ready ! I inserted the Fet current source back and now offset is stable to + - 3mV after trimming without DC servo. I run the Leds now on 4mA. No other changes. The circuits sounds to my satisfaction and performs well in the lab. It is fast ( -3dB at 5 MHz), low noise ( 0.5nV/qHz) and low distortion (-100dB at 2V out). This is the best i can do without global feedback and better then most commercial stages on the marked especially in noise performance. 1nV/qHz is advertised as very low noise and is a knind of industry standart. This circuit is 6dB better. In my system ( low sensitivity speakers and 0.5mV cartridge, the noise, both hum and hiss is unaudible at the listening position at insane volume and i hear loud ( over 100dB peak). The sound combines elements of raw energy with elegant handling of tonality. The output is current so transimpedance RIAAs are posible, even all in one go but i did not try that out. If you plan to win the next noise contest use 4 Jfets on each side. The drain resistors have to be lowered and the cascode transistors have to be doubled or replaced by something like 2N4401/4403 in that case just like in the Ultra Low Noise Low Z MPP. Any better performance is only posibe with global feedback or error cancelation and the second circuit gives an example of a posible topology. HF compensation has to be added and a DC servo can be used to trim the offset of that very high open loop gain design. Maybe i will try that variation too but momentaryly i am working on stabilizing the Discreet Intrumentation Amp.
Today i got Z foil resistors from Sigurt in sweden. Many thanks to suporting my effort !
I will now design a PVCB bord that will alow you to try that circuit if you wish. I will also look now more closely into the shunt regulators that Salas designed in the backround. Sorry Salas that i am not ready yet. I build parts of the circuit but i have to order more parts. This thread is not my only ocupation as you might gess.
Thanks for contributing to all. It´s an enyoyable and exiting ride.
P.S. I will try the DC and distortion trim on the Low Z MPP too.

[john curl]

Joachim, could you contact me by direct e-mail. The system will not work for me either coming or going, and I do not have your direct e-mail address. Thanks. By the way, I got 4 'recommended products' in the latest TAS. Saw the Lyra in there as well. Any others?

[Sigurd Ruschkow]

Microcap is indeed a superb simulator with easy-to-use GUI! Highly recommended.
Spectrum software also has a very helpful support. Micropcap is
developed continiously and bugs are fixed quickly.

You can DL it here: Micro-Cap Evaluation Program From Request

If yo need any help with Microcap, I am willing to help out as much as I can.
I have designed a few RIAA amplifier with it.



Sigurd

Originally Posted by Joachim Gerhard

the heat goes up, i like that but not the LT1115´s !
master that art perfectly well so i never have seen a need to look more into that myself. In fact i have founded world wide operating companies like Audio Physic on a beer felt. Well that time is come now and i should look for a circuit simulator that would fit my purpose. Any sugestion ? Microcap?

[Joachim Gerhard]

Hi John! My e-mail is : xxxxx@xxxxx.com
send me a mail and i respond.
Hi Sigurd, thanks for the link.

Edited out after enough time so to have been seen by the interested party, due to spam security reasons. Salas.

[Bas Horneman]

Hi John! My e-mail is : xxx@xxx.com

Hi Joachim. It is better to not do that. There are email spiders that crawl through websites harvesting emails like this and then sending that to spambots.

[Joachim Gerhard]

My e-mail is already on the Linkwitz side and i have a good manual spam filter but thank you for warning me.

[Joachim Gerhard]

Today i tried the 1kOhm loading resistors. I compared the nonmagnetic Tantal (my reference) to the Texas Components Z Foil. First the resistive element looks eyactly like in the Charcroft but the resistor is put on something that looks like aluminim oxide. whereas the charcroft has a kind of bakalite material. I measured both resistors, one cold and the other still hot from soldering. They both measured exactly 1kOhm so the tolerance is better then 0.1% and the temperature coefficient seems to be very low.
Soundwise they are the sons of the Tantals. Again i could hear a slight improvement in microdetail but not with the light sound of the Caddock MK132. Something other was wrong and i found that the current through the Leds of the High Z MPP had quite a drastic effect to the sound. I had reduced the current in the Leds to 4mA but that seems to be to low for best sound. I adjusted the Fet back to 8-9mA and changed the base resistors back to 235 Ohm from 1kOhm. Now the sound gained a lot in size, power and presence. I like that better and this change makes a much bigger effect then swapping the resistors i must admit. I did the resistor comparison again and heard the same tendency. The Tantal with a very elegant vintage sound without much loos of information and the Z Foil with a more open and clear presentation. Ultimately i think the Z foil is more honest but i could happy life with both of them. So when you can grab an NOS Tantal for a good price, buy it. The Z foil is a fantastic modern replacement. It´s awaillable in small quantities with no problem. It´s expensive so one of my projects is to find an afordable resistor that sounds well too.
See the latest circuit diagram where i have replaced the fixed resistor on the Fet with a potmeter if you want to experiment. I used a value of 220 Ohm in the end.

[Joachim Gerhard]

Thanks Salas. I just tried to delete that e-mail adress myself or ask a moderator for help.

[Salas]

Nothing much, cheers.
So the source impedance and noise of your jfet ccs'ed led shunt cascode's base Vref is audible indeed. Most leds are at their best between 5-10mA for noise and stiffness in my experience BTW.