Solid state phono preamp design philosophy - Page 5 - 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 9th May 2008, 06:18 AM   #41
jam is offline jam  United States
diyAudio Member
 
jam's Avatar
 
Join Date: May 2001
Location: Auburn, CA, USA
Has anyone considered a combination of an active and passive eq. which might have some advantages.

Jam
  Reply With Quote
Old 9th May 2008, 07:38 AM   #42
Electrons are yellow and more is better!
diyAudio Member
 
peranders's Avatar
 
Join Date: Apr 2002
Location: Göteborg, Sweden
Blog Entries: 4
Quote:
Originally posted by Bonsai
Talking about the topology, I do have a predilection for the active a approach due to headroom requirements on the passive approach and possibly higher overall noise.
Is headroom really an important issue if the supply voltage is at least +-15 volts and if a totally passive correction is chosen. I have never measured how much a click in the LP will generate. All my RIAA amps so far have been the active variant.
__________________
/Per-Anders (my first name) or P-A as my friends call me
  Reply With Quote
Old 10th May 2008, 02:22 AM   #43
Bonsai is offline Bonsai  Taiwan
diyAudio Member
 
Bonsai's Avatar
 
Join Date: Jul 2003
Location: Taipei, Taiwan
On a MM I guess 3mV output at 1Khz. Assume at 20Khz 20dB above this (yes, I agree there is not much musical energy at 20Khz but as you point out there's clicks and pops which probably do have quite a bit of high audio frequency content). That takes us to c. 300mV. Then add some overload margin - take your pick here - at 1Khz a lot of people look for around 26dB - lets call it 6dB at 20kHz - now we are at 600mV. If you need an out put of 300mV midband, that means a typical gain of 100 . . . . so now we are at 30V output at 20Khz

Of course I've over simplified a bit to illustrate the point. If you use a passive approach, the first stage gain will have to be limited to overcome this problem, and you will generally need a second stage of gain. However, this will mean you have to accept more noise, since ideally you want to put as much gain up front for lowest noise.

So, maybe this is why passive topology is a better fit for tubes where you can get the headroom.

BTW, John Atkinson did a review of a phono stage about a year back that used the passive approach (solid state I have to say) and remarked that it had a great sound, but overload capability was only 6dB.
__________________
bonsai
Amplifier Design and Construction for MUSIC! http://hifisonix.com/
  Reply With Quote
Old 10th May 2008, 04:55 AM   #44
jcx is offline jcx  United States
diyAudio Member
 
Join Date: Feb 2003
Location: ..
my suggestion is to use a cfa op amp as the output buffer/additional loop gain stage in a composite op amp with the active riaa feedback enclosing both op amps

for mc the input op amp could be one of the "short list" AD797, LT1028/1115, LME49710, AD743/5 of suitably low noise (at low frequency - many fast opamps have 1KHz+ 1/f corner frequency) op amps

these op amps all have low open loop gain corner frequencies so implementing at least one riaa roll-off time constant as active feedback is ideal even by "feedback critic" Otala's criteria - the feedback factor remains nearly constant over the entire audio frequency range with active riaa and high gain/low corner frequency dominant pole compensated op amps
  Reply With Quote
Old 11th May 2008, 09:22 PM   #45
diyAudio Member
 
Onvinyl's Avatar
 
Join Date: Aug 2002
Location: Germany
Is there any alternative to a diff-amp when making a balanced input stage in this world (that has reasonable cmrr)?

Rüdiger
__________________
"I can feel what's going on inside a piece of electronic equipment. I have a sense that I know what's going on inside the transistors." Robert Moog
  Reply With Quote
Old 12th May 2008, 04:34 AM   #46
maney is offline maney  United States
diyAudio Member
 
Join Date: Sep 2005
Send a message via AIM to maney Send a message via MSN to maney Send a message via Yahoo to maney
Quote:
Originally posted by Onvinyl
Is there any alternative to a diff-amp when making a balanced input stage in this world (that has reasonable cmrr)?

Rüdiger
Sure. You can take a pair of CF opamps (AD844, say, since you don't want any long-tailed inputs). Apply balanced signals to the + inputs, tie the - inputs through a resistor to define the gm, add gain-setting resistors... oh, you wanted feedback? You can work it that way, too.

Or if you want the circuit unbalanced past the input, there's the classic use of a unity gain inverter, seen more often going the other way in eg. older Audio Research power amps, to drive the balanced gain stages from the SE input. SImple case, take two gain -1 amps, one of which has to have a summing node. One input goes through the other inverter then sums into the second along with the second input. Play with the gain structure to suit your needs. Implement the inverters with opamps (long tailed or not), SE transistor stages, tubes even.

Or, of course, you could use a transformer. :-)

-- Martin "fifty ways to love your lever" Maney
  Reply With Quote
Old 12th May 2008, 08:14 AM   #47
Bonsai is offline Bonsai  Taiwan
diyAudio Member
 
Bonsai's Avatar
 
Join Date: Jul 2003
Location: Taipei, Taiwan
lets see some circuits maney.

And leave your lever out of it.
__________________
bonsai
Amplifier Design and Construction for MUSIC! http://hifisonix.com/
  Reply With Quote
Old 12th May 2008, 06:12 PM   #48
maney is offline maney  United States
diyAudio Member
 
Join Date: Sep 2005
Send a message via AIM to maney Send a message via MSN to maney Send a message via Yahoo to maney
Quote:
Originally posted by Bonsai
lets see some circuits maney.

And leave your lever out of it.
Well, let's start with the various forms of differential amps described in the early pages of Evolution from Operational Amplifier to Data Amplifier , a late-sixties paper from Analog Devices. Although some of the circuits presented assume amps that almost have to have long-tailed input stages, a number of them would be amenable to other implementations. The righthand circuit in Fig 8 was what I was trying to handwave talking about inverters, but the other version could probably be built from single ended gain stages without much more effort. The pair of 844s would look very much like the circuit of Fig 9 (for the closed-loop version), with only some additional consideration of the effect of the feedback resistor's magnitude on the OL gains needed.

OTOH, there's room for disagreement that the cross-coupled complementary input stages of a pair of 844s isn't an odd variant of the normally long-tailed differential pair. If that doesn't immediately make sense, look for Grey's recent treatise on how the FET version of that sort of thing works in his GR-25 amplifier, which is what got me started thinking about it that way.

I don't need to draw a picture of using a transformer for this, right? :-)

-- Martin "haven't got an easy way to send you graphics right now anyway"
  Reply With Quote
Old 12th May 2008, 06:54 PM   #49
Electrons are yellow and more is better!
diyAudio Member
 
peranders's Avatar
 
Join Date: Apr 2002
Location: Göteborg, Sweden
Blog Entries: 4
Default Dennis Colin Audio Xpress - the LP797

Have you read Dennis Colin's article in aX 2007? Interesting statements and a good design no doubt.
__________________
/Per-Anders (my first name) or P-A as my friends call me
  Reply With Quote
Old 12th May 2008, 07:08 PM   #50
Electrons are yellow and more is better!
diyAudio Member
 
peranders's Avatar
 
Join Date: Apr 2002
Location: Göteborg, Sweden
Blog Entries: 4
http://www.audioxpress.com/magsdirx/.../colin2774.pdf
http://www.audioxpress.com/magsdirx/...ig2_correx.pdf
http://www.audioxpress.com/magsdirx/...ig3_correx.pdf
__________________
/Per-Anders (my first name) or P-A as my friends call me
  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


Similar Threads
Thread Thread Starter Forum Replies Last Post
Diy Solid State Preamp Pocoyo Solid State 21 17th July 2007 04:53 AM
Solid state preamp gchrist Solid State 4 7th April 2004 11:19 AM


New To Site? Need Help?

All times are GMT. The time now is 11:18 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