Designing a phono stage - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

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 28th April 2001, 05:47 PM   #1
diyAudio Member
 
Join Date: Apr 2001
Location: UK
Hi,

I would like to say many thanks for such an important site. Very informative, but I've got a question. I would like to build a phono amp that is able to accept MM and MC.
I have some practical experience and would eventually like to build a power amplifier. Like most of the people on this forum I would like good / excellent sound, but I am reluctant to pay the massive sums on the UK high street. Are there any such circuits that I could be referred to?

I would appreciate any help that could get me started.

Thanks.
  Reply With Quote
Old 28th April 2001, 09:20 PM   #2
Geoff is offline Geoff  United Kingdom
diyAudio Member
 
Join Date: Apr 2001
Location: UK
Have a look at the projects at the ESP Audio Pages:

http://www.sound.au.com/projects.htm

There are several pre-amp designs there, including an mc version.
  Reply With Quote
Old 29th April 2001, 01:04 AM   #3
diyAudio Member
 
Join Date: Feb 2001
Location: Columbia, SC
You might consider whether you want passive RIAA or active (generally construed as being EQ'ed via a feedback loop). You can also have a combination of both in the same circuit. Passive is better.
Also decide whether you want solid state or tube.
If you choose tube, I'd recommend staying away from circuits which split passive EQ into two or three sections. It makes the filtering easier on the initial go-round, but when you change tubes down the road, you may find that your replacement tube has a dB or two different gain, which would wreak havoc on a carefully tuned +-.1 dB EQ curve. Go for the all-in-one passive EQ, and you're guaranteed to be in good shape.
Off the top of my head:
Solid state--
http://www.passlabs.com Nelson was kind enough to post the service manual for his Aleph Ono (nice aural pun, there...)
http://www.metaxas.com They've got a passive EQ circuit as a DIY
Tube--
http://www.tubecad.com (or maybe http://www.glassware.com, I don't remember which; both sites are the same guy) has a passive RIAA circuit--two of them, actually
You might also try the Bonavolt site and others off the Links section, here.
There are schematics for various Conrad-Johnson, et. al. pieces floating about here and there, but you don't want to trust them blindly; I know for sure that there's a spurious MV-75 schematic that ain't the real thing. I believe I saw a PV-5 schematic that looked right. Caveat emptor.

Grey
  Reply With Quote
Old 29th April 2001, 06:12 PM   #4
diyAudio Member
 
Join Date: Apr 2001
Location: UK
Passive RIAA?
How much in the dark have I really been? (Don't answer that, it would be too embarrasing for me). I am more interested in Solid State at the moment, but this information will prove to be very helpful. Thanks GRollins and Geoff.

  Reply With Quote
Old 30th April 2001, 04:40 AM   #5
diyAudio Member
 
Join Date: Oct 2000
Location: Sunnyvale, CA
Cool Passive v. Not Passive RIAA

Brownlow

If I am understanding the term "passive" as used here, passive would be a single gain stage with all the RIAA filter stuff in the feedback loop.

Not "passive", or "active" here would have a few gain stages taking care of the different stages of the RIAA curve.

Multiple filter stages come from the idea the the RIAA curve is made up of three filter sections, more or less.

To take a more official look at it than this reply, check out http://www-s.ti.com/sc/psheets/slyt0...%3CIN%3E+A%29&

Looking at that URL, I'm not betting it will work, so go to ww.ti.com and search riaa. The first technical doc you get should be the one you want. You could also right click on that address and use "save target as." That might work better.

The article talks about designing single supply RIAA filters, but that doesn't change things much.

Hope this helps,
Erik
  Reply With Quote
Old 30th April 2001, 07:11 AM   #6
diyAudio Member
 
Join Date: Dec 2000
Location: Önnarp, Söderslätt
An informative application note can be obtained at National Semiconductor's homepage: http://www.nsc.com
Look for AN-346.
Partly based on this, Norman Thagard has constructed a Phone stage described in the magazine Electronics World, april and may issues.
Mr. Thagard's name may be familiar to some of you, just look at the article about the A-75, from mr. Pass.

__________________
Regards
Hoffmeyer ;0)
  Reply With Quote
Old 30th April 2001, 04:10 PM   #7
diyAudio Member
 
Join Date: Feb 2001
Location: Columbia, SC
Hmmm...
Didn't realize that this was a tough concept. Sorry. I would have been more explicit, had I known.
RIAA equalization can be handled either 'passively' thus:

GAIN-->EQ-->GAIN

Or it can be handled via a feedback loop, thus:

GAIN-->GAIN
***|--EQ--|

Or by a combination of the two, thus:

GAIN-->EQ-->GAIN
****|-----EQ----|

(Ignore the *'s, as the forum appears to scan out white space characters in excess of one space, and the diagrams collapse without them. They're just there to space things out.)

Passive (the top one) is considered better because you don't have the time/phase delays through the feedback loop. Any of the three topologies will work. Good examples of phono stages have been constructed of each kind. Passive EQ simply reduces the number of things that can go wrong.
Important to note is that the RIAA EQ curve (the classic one, there was a later variation that didn't get widely adopted) is not one curve, but three overlapping ones; one at 50Hz, one at 500Hz, and one a little over 2kHz. Each is a simple 6dB/oct filter section. This leads to the temptation to arrange the circuit thus:

GAIN-->EQ-->GAIN-->EQ-->GAIN-->EQ-->GAIN

with each gain stage buffering and providing gain to offset the insertion loss in the intervening EQ section. (This is what led me to comment on the [non-] advisability of using this method with tubes, above.)
The total gain needed will vary somewhat, depending on whether you plan to use a moving magnet or moving coil cartridge--from 40dB (pretty much standard for average moving magnet cartridges) to 70-80dB for the really low output moving coils. An average gain for moving coils will be on the order of 65dB. This is measured at 1kHz, as (by definition) the RIAA section is a filter and does not have flat response. Insertion loss for a typical (passive) RIAA EQ will be, say, 20-25dB and this must also be added to the overall gain required from the phono stage.
Viewed as three 6dB/oct filters, it's not that bad, conceptually, but proper execution can be tricky.
Historical note, for those who may be tempted to think that passive RIAA EQ is some new tweak developed by the high-end folks...it ain't. Go dig up an ancient RCA manual and you'll find a nice little number in there using the two halves of a 7025 (the industrial version of a 12AX7) with...you guessed it...passive EQ.

Grey
  Reply With Quote
Old 1st May 2001, 08:19 AM   #8
Alex M is offline Alex M  United Kingdom
diyAudio Member
 
Join Date: Apr 2001
Location: Hampshire, UK
I've just been looking at an old article in Electronics
Today from 1993 where John Linsley Hood discusses the
various possibilities in phono stage design, and then
gives a practical circuit. The latter is the same as
the one sold by Hart Electronics, and discussed here:

http://users.classicfm.net/williamshart/phono.htm

If you give me your address I can send you a photocopy
of the article.

Alex
  Reply With Quote
Old 1st May 2001, 09:12 AM   #9
diyAudio Member
 
Join Date: Apr 2001
Location: UK
Hmm,

it does seem that my understanding with Passive and Active are not quite compatible here. I would certainly say that a Passive phono is beyond me currently. Anyway, I'll say thanks again to all for sharing advice.

On a final note, Alex M does the JLH phono stage sound good? What would you compare it to?
  Reply With Quote
Old 1st May 2001, 09:54 AM   #10
Alex M is offline Alex M  United Kingdom
diyAudio Member
 
Join Date: Apr 2001
Location: Hampshire, UK
Default JLH phono stage

I haven't put together the complete circuit, but I did
build a hybrid of the RIAA part of the JLH circuit with a
different input stage (taken from another of JLH's ETI
articles, but specifically designed for low noise).

I used this in my preamp for several years; it sounded very
good, if not quite as clear and open as the Audio Synthesis
ADEQ I use now.

I have several very positive reviews of the Hart kit, one in
HFNRR (I think) comparing it favourably with a Naim preamp
at three times the price.

There is an online review here, for instance:

http://www.digitaltheater.com/reviews/seperate12.html

Alex
  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 phono to replace roksan phono stage seroxatmad Analog Line Level 6 14th December 2008 05:46 PM
new phono stage or old preamp with phono? flohmann Analog Line Level 2 2nd October 2008 09:51 PM
Designing a phono pre. #1: high gain block Onvinyl Analog Line Level 11 6th November 2007 07:16 AM
Help designing Input and Vas stage's DoomPixie Solid State 28 13th January 2006 09:28 PM
Should I replace Scott 222C phono stage with Claret phono stage? Bing Yang Analogue Source 0 22nd August 2005 06:41 AM


New To Site? Need Help?

All times are GMT. The time now is 11:13 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