Mpp - Page 61 - diyAudio
Go Back   Home > Forums > Source & Line > Analogue Source

Analogue Source Turntables, Tonearms, Cartridges, Phono Stages, Tuners, Tape Recorders, etc.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 31st December 2009, 08:32 PM   #601
diyAudio Member
 
Joachim Gerhard's Avatar
 
Join Date: Mar 2009
Default New Year

I was still not totally satisfied with the sound of the Inductive Shelve RIAA.
In my attept to DC couple i had lowered the series resistor from the servo to 900 Ohm. I found out that this influenced the Inductive part too much. At higher frequencies this resistor is in parallel to the coil and that was the last reason for the somewhat sharp sound. I put in a 100kOm, wraped it only around the Inductive stage because there was some instability when i included the output stage, AC coupled the MPP and suddenly everything clicked into place. You have to use a precission opamp in the output to do that. I use a LT1468 and offset was under 0.5mV.
Sound is now extremely neutral and stiil the transparency and quick timing is there. I got quite a shock on Petruschka on Athena with Ernest Ansermet. Mag Selma with the Art Enseble of Chicago was a showcase of resolution, space, dynamics and detail. I can now listen to slighly bright recordings without fatique. I will post the current circuit here. It works very well and i recommend it without ceveat.
What come next ?
I react well on critisism usually so i will try to improve the ECHO to a point where even critical people will be happy with the measured performance i hope. So i post here the ECHO Extrem. It has 4.5dB less voltage noise and the lower bias on each transistor should lower the current noise too. Noise resistance is around 13 Ohm now. Equivalent input voltage noise is 0.6nVQhz under this conditions. I will use Fet current sources and an anhanced current mirror for better stabilty, PSRR and protection of the cartridge coils in case there goes something wrong in the powersupply. Anyway i never had a fried cartridge with DC couple bipolar input stages and i build some really weard ones over the years ! Happy New Year ! I wish you all the best and may this website prosper.
Attached Files
File Type: pdf Phonostage New Year.TSC - TINA.pdf (81.0 KB, 151 views)
File Type: pdf ECHO Extrem.TSC - TINA.pdf (58.2 KB, 135 views)
  Reply With Quote
Old 31st December 2009, 08:34 PM   #602
diyAudio Member
 
Joachim Gerhard's Avatar
 
Join Date: Mar 2009
Thank you Scott. I hope you will still contribute here.
  Reply With Quote
Old 31st December 2009, 08:48 PM   #603
diyAudio Member
 
Join Date: Jun 2009
Send a message via Yahoo to kannan_s
Joachim
that is the spirit - allowing others to use your design posted here as well provide your own layout containing PCB' with components you feel that works the best as an alternative. And as Scott points out - I do not feel anybody would object to your offerings. This forum is great as it has many international contributors and members except some are **** how to say? - I wonder why on earth an experienced Engineers feel offended by questions from non engineering DIY audio enthusiasts or feel bad about subjective observations or preferences? No two human beings hear same sound similarly which is known scientific truth. I can always defer somebody else' view in a gentle manner.
I will try some of your circuits very soon as I do not have any MC cartridges on my turntable yet.
kannan
  Reply With Quote
Old 31st December 2009, 09:00 PM   #604
diyAudio Member
 
Joachim Gerhard's Avatar
 
Join Date: Mar 2009
Kannan i will be exited to hear the results !
One last thing before i celebrate New Years.
I found the reson of the anoying cracking noise in one channel that i had contributed to flicker noise. I was a half loose cable in the Inductor docks. I had used solid core there and had put the dock on and off many times. I resoldered that connection and now everything is fine. White noise on both channels.
Another scoop: i am working with a well respected maker of transformers and inductors for the audio industry on a mu metal shielded version of the inductor. Unfortunately this will not be cheep. I still recommend my ferrite inductor. I use it and it sounds just fine, is has to be shielded though and put away from tranformers.
I have an idea to use that inductor in a hum bcking arangement of four. I will tell you more tomorrow.
  Reply With Quote
Old 31st December 2009, 09:21 PM   #605
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
Quote:
I wonder why on earth an experienced Engineers feel offended by questions from non engineering DIY audio enthusiasts
Most don't, fortunately. We are fortunate to have some of the best electronics designers in the world on this forum, and most of them are incredibly nice people who are glad to help us non-engineering types.

Joachim, a question that I've never been able to get a satisfactory answer to (you're not the only person who does this)- why inductive? Even top quality inductors are much less ideal than even moderate quality caps.
__________________
You might be screaming "No, no, no" and all they hear is "Who wants cake?" Let me tell you something: They all do. They all want cake.- Wilford Brimley
  Reply With Quote
Old 31st December 2009, 10:18 PM   #606
syn08 is offline syn08  Canada
Account disabled at member's request
 
Join Date: Aug 2005
Location: Toronto
Quote:
Originally Posted by Joachim Gerhard View Post
I react well on critisism usually so i will try to improve the ECHO to a point where even critical people will be happy with the measured performance i hope. So i post here the ECHO Extrem. It has 4.5dB less voltage noise and the lower bias on each transistor should lower the current noise too. Noise resistance is around 13 Ohm now. Equivalent input voltage noise is 0.6nVQhz under this conditions.
Good

Now, simply paralleling more bipolars while lowering the bias won't help much. Voltage noise goes up with decreasing the bias, and goes down with paralleling devices ('cause the equivalent Rbb' decreases), however, the current noise goes up with paralleling more devices, as it is proportional to sqrt(Ib).

In this mess, there is an optimum (or compromise) where the bias is Ic=Vt*sqrt(Beta)/Rsource, where Vt=0.026V, and Rsource is the source impedance (the MM cartridge). E.g. for Beta=100 and Rs=10ohm, Ic=26mA (not coincidentally, the HPS 4.1 bias value). For these values, the total noise (voltage noise plus noise current*Rsource) are at a minimum. You can of course split this bias over several paralleled devices, to benefit from the reduced Rbb' (and therefore a lower voltage noise).

About the input bias current, in an asymetrical configuration, I don't think there's much to do; you have to live with it, at least during transients. Never connect the cartridge before powering up, and provide a DC path for the input cap. Some input bias current cancelling methods (servos) can be used, but none of them comes without a noise penalty.

BTW, a BC550 has at best 2.2pA/rtHz noise. Nine of them paralleled have 20pA/rtHz, which is already huge. A 10ohm MC adds 0.2nV/rtHz at low frequencies, and at 1KHz could be, due to the cartridge inductance, over 1nV/rtHz. There goes your nice 0.6nV/rtHz equivalent input voltage noise

Noise budgets are perverse
  Reply With Quote
Old 31st December 2009, 10:22 PM   #607
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
Quote:
Nine of them paralleled have 20pA/rtHz, which is already huge.
Is that correct? I would think their noise currents would be uncorrelated so you'd have power addition.
__________________
You might be screaming "No, no, no" and all they hear is "Who wants cake?" Let me tell you something: They all do. They all want cake.- Wilford Brimley
  Reply With Quote
Old 31st December 2009, 11:32 PM   #608
syn08 is offline syn08  Canada
Account disabled at member's request
 
Join Date: Aug 2005
Location: Toronto
Quote:
Originally Posted by SY View Post
Is that correct? I would think their noise currents would be uncorrelated so you'd have power addition.
Oops! You are of course right. Didn't I say noise budgets are perverse?
  Reply With Quote
Old 31st December 2009, 11:35 PM   #609
diyAudio Member
 
scott wurcer's Avatar
 
Join Date: Jan 2004
Location: cambridge ma
Quote:
Originally Posted by SY View Post
Is that correct? I would think their noise currents would be uncorrelated so you'd have power addition.
That is right, but I have found recently the source impedances of exotic phono front ends make things more complicated than one might expect. Mainly the virual ground inputs are not always the best choice for very low Rs (real part of souce impedance) carts.
__________________
Silence is so accurate.

Last edited by scott wurcer; 31st December 2009 at 11:38 PM.
  Reply With Quote
Old 31st December 2009, 11:50 PM   #610
diyAudio Member
 
Holger Barske's Avatar
 
Join Date: Jan 2001
Location: Ruhrgebiet
May anyone point me to the mistake(s) I must have made? The results I get are not very promising:
Click the image to open in full size.
__________________
Best regards: Holger
www.holgerbarske.com - Deutschsprachiges Paradise-Support-Forum
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



New To Site? Need Help?

All times are GMT. The time now is 05:53 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2