Mpp - Page 63 - 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 1st January 2010, 02:22 PM   #621
MRupp is offline MRupp  Germany
diyAudio Member
 
MRupp's Avatar
 
Join Date: Dec 2003
Location: Frankfurt area
Talking about noise and avalanche breakdown, there is a chapter “AVALANCHE BREAKDOWN AND NOISE” in Motchenbacher/Connelly that gives the following warning that may be of interest:

Quote:
Caution! … routine tests or adjustments can inadvertently ruin a perfectly good low-noise, high-gain transistor. This can happen when the base-emitter junction of a BJT is reverse-biased beyond its avalanche knee. The low-frequency noise of the device can be increased by 10 times because of a circuit turn-on transient, an overload signal transient, or the testing of V EBO. …
So far so good, but I just ordered a automatic component tester – Peak Atlas DCA 55 – that lets you “connect your component any way round and press the test button”, i.e. it searches for the correct terminals of the device. Now, the peak test voltage is supposedly 5.1 Volts, which is exactly where the EB breakdown of a transistor occurs according to the datasheets. I am just beginning to wonder how safe it is to use this type of tester. But again, I may be worrying to much (though I would not want to "tune" the noise performance of my transistors)
__________________
Martin Rupp
  Reply With Quote
Old 1st January 2010, 03:31 PM   #622
syn08 is offline syn08  Canada
Account disabled at member's request
 
Join Date: Aug 2005
Location: Toronto
Quote:
Originally Posted by Allen Wright View Post
I'm interested in your suggestions on how to improve my RTP3 circuit - but it needs to be a practical sonic improvement, not just measured.
This is what usually leaves me in a dazed state and also where the communication breaks down: In a MC pre, you say 1nV/rtHz noise is not an issue 'cause most people will live with it; you say open loop is fine, 'cause distortions are anyway not audible; and then you praise non-magnetic resistors, and other such, for their superior sound.

I (and I dare to say, anyone of my EE breed, not involved in the audio industry) would tell you that there are 1001 reasons, some of them many orders of magnitude larger, impacting the sound in your designs, before you can talk about (non)-magnetic resistors.

Under these circumstances, I doubt I can myself suggest anything for your designs, that you would consider as a "sonic improvement". All I can do is to wonder and to query your design decisions, in an attempt to find correlations (if any) with your "sonic results".
  Reply With Quote
Old 1st January 2010, 04:06 PM   #623
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
Quote:
you say open loop is fine, 'cause distortions are anyway not audible
Not a well-taken argument- the distortion figures that Allen achieves are quite low. And there's a good argument to be made that open-loop (especially with tubes) can have better overload recovery.
__________________
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 1st January 2010, 04:49 PM   #624
diyAudio Member
 
scott wurcer's Avatar
 
Join Date: Jan 2004
Location: cambridge ma
Quote:
Originally Posted by MRupp View Post
Talking about noise and avalanche breakdown, there is a chapter “AVALANCHE BREAKDOWN AND NOISE” in Motchenbacher/Connelly that gives the following warning that may be of interest:



So far so good, but I just ordered a automatic component tester – Peak Atlas DCA 55 – that lets you “connect your component any way round and press the test button”, i.e. it searches for the correct terminals of the device. Now, the peak test voltage is supposedly 5.1 Volts, which is exactly where the EB breakdown of a transistor occurs according to the datasheets. I am just beginning to wonder how safe it is to use this type of tester. But again, I may be worrying to much (though I would not want to "tune" the noise performance of my transistors)
Different avalanche than collector "weak" avalanche which is probably what is refered too previously. Increased noise due to this is complex and device dependent. A few days with the literature and some bench work could yield a useful list of devices that look good at high Vcb, but are no longer low noise. Some might keep this a trade secret even.

Avalanching a Veb generates hot carriers that can and do permanently or semi-permanently damage the junction making it (more not less) noisey.

Equipment in general would not survive the temperatures needed to anneal this damage.
__________________
Silence is so accurate.

Last edited by scott wurcer; 1st January 2010 at 04:55 PM.
  Reply With Quote
Old 1st January 2010, 06:37 PM   #625
syn08 is offline syn08  Canada
Account disabled at member's request
 
Join Date: Aug 2005
Location: Toronto
Quote:
Originally Posted by SY View Post
Not a well-taken argument- the distortion figures that Allen achieves are quite low. And there's a good argument to be made that open-loop (especially with tubes) can have better overload recovery.
I guess you know what I meant, but this seems to be the devil's advocate year?
  Reply With Quote
Old 1st January 2010, 06:56 PM   #626
diyAudio Member
 
Joachim Gerhard's Avatar
 
Join Date: Mar 2009
Hello Syn08 !
When i use your formular with the 12 BC550 and my 5.5Ohm cartridge i end up with 117ma, 9.7mA for each transistor. That is a bit unpractical. On the other hand the Rbb of the BC550C does not change much with collector current. It has 170 Ohm at 0.1mA, 163 Ohm at 0.5mA, 160 Ohm at 1mA and 130 Ohm at 10mA. So something between 0.5 and 3mA could be a compromise. Anyway, i will not eleborate more on that circuit. I went to far. A row of 4 2N4401 or 2N4402 is a better idea i think for a cheap Headamp.
I will recalculate the values here and present a circuit that works. For the cautios: it presents a DC current to the cartridge at turn on and it works best with low impedance MCs. I praxis i have never burned a cartridge though.
  Reply With Quote
Old 1st January 2010, 07:17 PM   #627
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
Hello Syn08 !
When i use your formular with the 12 BC550 and my 5.5Ohm cartridge i end up with 117ma, 9.7mA for each transistor. That is a bit unpractical. On the other hand the Rbb of the BC550C does not change much with collector current. It has 170 Ohm at 0.1mA, 163 Ohm at 0.5mA, 160 Ohm at 1mA and 130 Ohm at 10mA. So something between 0.5 and 3mA could be a compromise. Anyway, i will not eleborate more on that circuit. I went to far. A row of 4 2N4401 or 2N4402 is a better idea i think for a cheap Headamp.
I will recalculate the values here and present a circuit that works. For the cautios: it presents a DC current to the cartridge at turn on and it works best with low impedance MCs. I praxis i have never burned a cartridge though.
It's not "my" formula, it's a classic but of course, that's to much. A good sign that you are using a very low impedance cartridge, therefore you may neglect the current noise - but you can't expect everybody to use a $5k Lyra Titan MC cartridge!

Actually, you got it pretty well - 2N5401 and 2N5551 are about the lowest noise TO92 devices currently in production in the USA, they are much better than BC550 and BC560. They have Rbb' around 100ohm. There's a table with measured Rbb's on my web site: Low Noise Design Schematics

Rbb' is barely supposed to vary with Ic.
  Reply With Quote
Old 1st January 2010, 07:27 PM   #628
syn08 is offline syn08  Canada
Account disabled at member's request
 
Join Date: Aug 2005
Location: Toronto
Quote:
Originally Posted by scott wurcer View Post
Different avalanche than collector "weak" avalanche which is probably what is refered too previously. Increased noise due to this is complex and device dependent.
Same thing, really. Impact ionisation mechanism in both cases, increases as McIntyre with k=0.2. The absolute cross sections, multiplication and threshold are very device and process dependent, but for common epitaxial devices it can be assumed the excess noise matters at Vce>0.5*Vcb0. Another good reason to close the loop, to keep Vce close to bias, can usually be about 5V.

Last edited by syn08; 1st January 2010 at 07:39 PM. Reason: Addition
  Reply With Quote
Old 1st January 2010, 08:00 PM   #629
diyAudio Member
 
Joachim Gerhard's Avatar
 
Join Date: Mar 2009
Default Echo simplife

Here is a circuit that should work. I choose the 2N4403. Adjust the fet with the trimmer until 4mA are flowing in the 750 Ohm resistor. A fet with Idss of around 8mA is fine. I found that the current that flows in the current mirror triples in the input transistors. This is because of the 100 Ohm resistor. T6 can be omitted. After adjusting the bias DC has to be cancelled with the trimmer to the positive supply. Higher Bias could be tried out, that needs some other resistor values. I use 1mA here because that is the value that Douglas Self uses for the 2N4403 and his circuit has a reputation for low noise.
Attached Files
File Type: pdf ECHO simplife.TSC - TINA.pdf (44.2 KB, 109 views)
  Reply With Quote
Old 1st January 2010, 08:21 PM   #630
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
Here is a circuit that should work. I choose the 2N4403. Adjust the fet with the trimmer until 4mA are flowing in the 750 Ohm resistor. A fet with Idss of around 8mA is fine. I found that the current that flows in the current mirror triples in the input transistors. This is because of the 100 Ohm resistor. T6 can be omitted. After adjusting the bias DC has to be cancelled with the trimmer to the positive supply. Higher Bias could be tried out, that needs some other resistor values. I use 1mA here because that is the value that Douglas Self uses for the 2N4403 and his circuit has a reputation for low noise.
Now you need to add local power supply regulators/buffers and a cascode. Otherwise, this thing has virtually zero PSRR. If you plan to feed via batteries, it's probably good as is. I would though suggest at least 5mA. and decrease the load resistor for the same gain.

Step back for a moment and look at your design. Do you like the caps in the signal path? Wait until M. Fremer will find out about
  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 09:27 AM.


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