DIYHiFi.org

For the sake of audio
It is currently Sun Dec 21, 2014 3:17 am

All times are UTC




Post new topic Reply to topic  [ 28 posts ]  Go to page 1, 2  Next
Author Message
PostPosted: Tue May 22, 2012 3:40 pm 
Offline
Muriel
User avatar

Joined: Thu Jul 26, 2007 5:45 pm
Posts: 868
Folks,

I did originally intend to post this over at the pub.

But instead of getting me some beer to get me pissed they pissed me off royally instead, French Croation Squid to them.

Since it's inception in the mid 1990's intended strictly for the mainly UK based "Analogue Addicts E-Mail List" and later publication by Gary Markowitz at Deadwax Caffee this phono preamp has been popping up every now and then and has enjoyed a modest level of popularity.

This popularity is not because it is particularly outstanding in terms of measured performance. There is no single parameter where this circuit cannot be exceeded by more complex and involved circuitry. Nor is it because of outstandingsubjective performance. There are many phono stage circuits that can provide improvements in sound quality over this circuit, though such improvements are rarely "night and day".

The reason this circuit has remained popular is that it is simple, quite suited to be realised DIY in dead-bug circuitry or via veroboard and that the actual performance is solid, credible and in many cases "good enough", if care is taken to follow the component recommendations.

It is worth reading the original article, which in it's origin goes back to 96 if memory does not fail me, this more polished up version was published in 97.

http://www.deadwaxcafe.com/vzone/phonopre.asp

I will not repeat what has been said in this article and still stand by pretty much all that I wrote there (give or take a little).

The reason for this new round of this "oldie but goldie" is simply to update it for the parts available today and to incorporate "lessons learned" in the over decade and a halve since it first appeared as ASCII Art in an e-mail on the Analog Addicts e-mail list. At the core the Analogue Addicts (or AA) Phono is tres primitive. It is really electronic crayons levels.

Circuitry like it has existed since the halcyon days of audio DIY when LP's where still Mono, Speakers where tres grande, voluptueuse et dynamique and amplifiers where tres petite and tres simple et a la recherche industrielle and the 16 Watt Williamson Amplifier was considered tres puissante ridiculement.

If you look at the Quad 22 Mono Preamp or the Marantz "Consolette" Mono Preamp you find circuitry of which the AA Phono is a spiritual heir. A single active device (Pentode in Quad 22, dual triode in Marantz and Op-Amp in AA-Phono) and active, feedback equalisation. Modest open loop gain compared to the closed loop gain also features, as does a modest open loop bandwidth.

There have always been those (myself included) who have felt that greater elaboration than such simplicity can bring greater performance and this indeed has been born out on diverse occasions, however as often have I found more elaborate and expensive circuitry to be sorely lacking in subjective qualities. I find my building another example for some reason or other every few years, be it as reality check, or for friends. The results are always convincing.

When the AA Phono was originally designed every Maplin store in the UK could get you Philips Tinfoil & Polystyrene 1% tolerance capacitors, 0.1% tlerance metal film resistors that where cheap and only very slightly magnetic, sealed lead-calcium batteries with suitable chargers and Burr Brown (not Ti) OPA637 in metal cans. And I still used only MM Pickups in those days (the cheapest MC pickups worth having where more or less "cloud cookoo land" pricing - the Denon DL-103 had to yet stage it's comeback). So the AA Phono was MM first with an MC Pre-Pre (courtesy of l'audiophile). It used the best parts I could get. It sounded very good and did not cost more than a decent a MM Cartridge.

But as Bob Dylan once wryly remarked, "The times, they are a'changing".

So without much further ado, here the new version.

[img=http://img189.imageshack.us/img189/5151/aap2k1opa827mm40dbschem.jpg]


Top
 Profile  
 
PostPosted: Tue May 22, 2012 5:13 pm 
Offline
Muriel
User avatar

Joined: Thu Jul 26, 2007 5:45 pm
Posts: 868
Dang, this was the wrong button. Only part posted. Let's try again...


Folks,

I did originally intend to post this over at the pub.

But instead of getting me some beer to get me pissed they pissed me off royally instead, French Croation Squid to them.

Since it's inception in the mid 1990's intended strictly for the mainly UK based "Analogue Addicts E-Mail List" and later publication by Gary Markowitz at Deadwax Caffee this phono preamp has been popping up every now and then and has enjoyed a modest level of popularity.

This popularity is not because it is particularly outstanding in terms of measured performance. There is no single parameter where this circuit cannot be exceeded by more complex and involved circuitry. Nor is it because of outstandingsubjective performance. There are many phono stage circuits that can provide improvements in sound quality over this circuit, though such improvements are rarely "night and day".

The reason this circuit has remained popular is that it is simple, quite suited to be realised DIY in dead-bug circuitry or via veroboard and that the actual performance is solid, credible and in many cases "good enough", if care is taken to follow the component recommendations.

It is worth reading the original article, which in it's origin goes back to 96 if memory does not fail me, this more polished up version was published in 97.

http://www.deadwaxcafe.com/vzone/phonopre.asp

I will not repeat what has been said in this article and still stand by pretty much all that I wrote there (give or take a little).

The reason for this new round of this "oldie but goldie" is simply to update it for the parts available today and to incorporate "lessons learned" in the over decade and a halve since it first appeared as ASCII Art in an e-mail on the Analog Addicts e-mail list. At the core the Analogue Addicts (or AA) Phono is tres primitive. It is really electronic crayons levels.

Circuitry like it has existed since the halcyon days of audio DIY when LP's where still Mono, Speakers where tres grande, voluptueuse et dynamique and amplifiers where tres petite and tres simple et a la recherche industrielle and the 16 Watt Williamson Amplifier was considered tres puissante ridiculement.

If you look at the Quad 22 Mono Preamp or the Marantz "Consolette" Mono Preamp you find circuitry of which the AA Phono is a spiritual heir. A single active device (Pentode in Quad 22, dual triode in Marantz and Op-Amp in AA-Phono) and active, feedback equalisation. Modest open loop gain compared to the closed loop gain also features, as does a modest open loop bandwidth.

There have always been those (myself included) who have felt that greater elaboration than such simplicity can bring greater performance and this indeed has been born out on diverse occasions, however as often have I found more elaborate and expensive circuitry to be sorely lacking in subjective qualities. I find my building another example for some reason or other every few years, be it as reality check, or for friends. The results are always convincing.

When the AA Phono was originally designed every Maplin store in the UK could get you Philips Tinfoil & Polystyrene 1% tolerance capacitors, 0.1% tlerance metal film resistors that where cheap and only very slightly magnetic, sealed lead-calcium batteries with suitable chargers and Burr Brown (not Ti) OPA637 in metal cans. And I still used only MM Pickups in those days (the cheapest MC pickups worth having where more or less "cloud cookoo land" pricing - the Denon DL-103 had to yet stage it's comeback).

MC capable Op-Amp's where either one know as a bit of bitchy prima-ballerina, that was next to impossible to get to behave and which was awesome if you got everything "just so" but totally awful if you did not and the only other viable option was not available in England. So the AA Phono was MM first with an MC Pre-Pre (courtesy of l'audiophile). It used the best parts I could get. It sounded very good and did not cost more than a decent a MM Cartridge.

But as Bob Dylan once wryly remarked, "The times, they are a'changing".

Much has changed. The old favourite op-amp's and MC Pre-Pre J-Fets are but fond memories, as are the Philips Tinfoil & Polystyrene Cap's (ROHS and market changes did them all in), batteries have improved but are harder to use and I have learned to make better AC powered powersupplies than I did in 96.

So without much further ado, here the new version.

Image

First, now there are two distinct ways of building this Phono.

One is pure MM, the other is pure MC.

Each version uses one of a number of Op-Amp's most suitable to the task. I do not suggest they are all made equal and I have build and tested this design using the OPA637 and the LT1028 and the LT1115 only, however I have all reason to believe that the other listed options will also perform well.

As MM Pickups do not brook any significant DC current too well, one requirement for the MM version is to use a Fet input Op-Amp. Many nowadays exist. We prefer 5nV|/Hz or less noise. However even a 20nV|/Hz Op-Amp will allow acceptable noise performance with around -67dB noise (unweighted) referenced to a 5mV input, the OPA827 will give us -79dB. If we apply A-Weighting (everyone does) we get around 10dB improvement, so for MM and the "preferred part" OPA637 or OPA827 we get around -89dB SNR re 5mV, not class leading, but by no means shabby.

Please do not use TL072 or related, if you want to hear what I heard with the OPA637, but hey, it's your phonostage.

MC's are much less concerned about some DC flowing in their coils, so we can use Bipolar Op-Amp's that give us under 2nV|/Hz input noise. With a 1.1nV Ein for the OPA1611 we will get around -69dB noise (unweighted) referenced to a 0.5mV input. If we do a bit of A-Weighting we get -79dB, again not class leading, but non too shabby. I used LT1028/1115.

Please do not use 5532/34 in the circuit for MC, just because you someone else do it. Only monkeys imitate other monkeys.

The use of four 10nF capacitors in the EQ has it's reason again in availability. You can still get 1% tolerance Polystyrene Capacitors made by LCR in the UK from a range of source, including Mouser, Digikey, Farnell, Newark Electronics and RS Components, all of which stock also suitable Op-Amp's and other parts, even at reasonable cost, but being more "business customer" focused they will usually not sell you one or two small parts, but at least ten. The EQ and bypassing for the output cap take care using up such a ten-pack.

The output coupling cap (the 2.2uF) should be the best you can get, definitely film. The 2.2uF value allows the use of as low a load as 10kOhm. If your load is much higher you may wish to scale the value lower, smaller capacitors usually "sound better" and cost less. Personally I always use Tinfoil & Polypropylene or Tinfoil & Polystyrene types, others exist.

Resistors use E12 standard values. My most recent builds all used Rhopoint "Squareristor" non inductive copper alloy wirewound resistors. They are expensive but take this design to a new level. Honest.

Other options exist, Takman Metalfilm are resistors I liked okay in recent times, as are Shinkoh and other Tantalum types. Ordinary Dale or Welwyn RC55 grade types also work okay. I never liked vishay or caddock foil resistors, but some do. Pick your poison.

Here the EQ response for "zero tolerance" in MM (10K + 1nF IHF load - simulated):

Image

This is better than +/- 0.1dB 20Hz - 20KHz. In practice the use of multiple tight tolerance capacitors should keep things to better than 0.5dB.

For MC the high gain needed starts rolling off the treble a trifle. The slight overall slope is likely not a bad thing for MC's:

Image

Overall still better than +/-0.2dB ideal and still better than +/-0.5dB with 1% tolerance capacitors and 0.1% tolerance resistors for the worst case.

There are many 1uF Film capacitors in small form factors available, I still use WIMA items with 5mm lead spacing, but I suspect some of the more recent SMD options would be better for decoupling. Layout is critical, the 1uF capacitor between the PSU pins needs especially close mounting and short leads. The use of star grounding should be obvious.

I have not sim'ed for Harmonic Distortion, as I suspect the models in tina-Ti are not very good for that, a quick look at the datasheets suggest however for MM around 0.004% at 1KHz and at 3V output, we can expect 0.04% THD for MC (same conditions), not ground breaking and clearly horrendously awful to members of the low church of meter readers and double blinders, but perfectaly acceptable in my book, especially accounting for the distortion in Speakers and cartridges... More crucially, due to the falling gain the typical rise of HD (and IMD) towards higher frequencies we normally see with Op-Amp circuitry is substantially negated.

Now for the AC supply. Simple, straightforward. Please note the diodes shown have too low a voltage rating. Use at least 60V rated schottky diodes, mine are 11DQ10 (100V/1.1A).

Image

A few small details.

The voltage setting network for the 317 (I would suggest using LT1083/84/85 though) is arranged to draw 100mA. This extra current creates a lower output impedance for the regulator and allows better dynamic behaviour, as the regulator in effect can sink up to 90mA current without loosing control.

The RC filtering after the schottky rectifiers has around 7Hz turnover frequency, so attenuation at 100Hz is not massive (a touch over 20dB - still helps the 3-Pin regulator out though) But higher frequency noise (>1KHz), that the 3-Pin regulators are not good at catching, is well attenuated. Using LT1085 we should get ~ 100dB suppression of ripple and rectifier noise up to around 100KHz, where the common electrolytic capacitors fail us.

The filters after the regulator are intended to comply eliminate the REGULATORS OWN NOISE, with an 0.5Hz turnover and 2nd order effective filtering any remaining noise from the regulator is squashed flat. With 0.5Hz turnover they offset the lack of power supply rejection ratio we incur as penalty for cranking the gain way up.

The 3,300uF Capacitors should be good "low impedance" types, prefereably genuine Nichicon, made in Japan. If you like, Elna Silmic 2 3,300uF/50V make a good (if expensive) upgrade. The resistors, I just use 2W metal or carbon film.

The final 1,000uF should be Elna Silmic 2, absolute values etc. are not supercritical, I use 1,000uF/50V as these are in wide use where I work. I cannot personally from my testing any other "premium audio grade" electrolytic capacitor. But again, it's your Phonostage. Just don't use Black Gates, unless you joined the cult. The last filter cap's belong close to the Op-Amp they supply, the rest is not very critical. You may wish to experiment with snubbers on the supply lines, however as it stands the single set of bypassing only creates one single resonance and that at a fairly high frequency (>> 100KHz).

Going full dual mono and adding mains side RF filtering, as well as using split bobbin transformersand LL ir double C-Core types all can help to aid performance. Bigger transformers are often better, but I see little point going past (say) 30...50VA per channel, but you never know. Resistors in the PSU lines may be replaced by suitable chokes, but leave the final filter (330R/1,000uF) an RC one.

That's it. Decently low noise, decently flat EQ, decently low (T)HD, decent sound. Add Carlos's AD815 Linestage (elsewhere here) for full function Preamp. What more do you want from a simple Op-Amp circuit?

Ciao T

PS, embellishments such as class A biasing of the output or extra buffers may be employed, but they detract from the circuits simplicity and are not reliable means of improving performance, concentrate on layout, powersupplies and passive parts first.


Top
 Profile  
 
PostPosted: Tue May 22, 2012 6:21 pm 
Offline
Sheep

Joined: Fri Feb 25, 2005 2:26 am
Posts: 49
Location: il
T;
thanks for sharing. would you confirm the desired values for R10/R22 (330 ohms) and R12/R23 (100 ohms) ?
they seem a bit large to me ...

mlloyd1


Top
 Profile  
 
PostPosted: Tue May 22, 2012 7:28 pm 
Offline
Muriel
User avatar

Joined: Thu Jul 26, 2007 5:45 pm
Posts: 868
Hi,

mlloyd1 wrote:
would you confirm the desired values for R10/R22 (330 ohms) and R12/R23 (100 ohms) ?
they seem a bit large to me ...


Yes, these are my choices. They filter a lot.

If you look at normal signal levels the Op-Amp (including output) operates in Class A.

Stuff at very high frequencies is dealt with by 2 * 1,000uF (or more) next to each chip.

So there is no issue having such RC filtering, you see it's equivalent in tube circuitry all the time. BTW, LFD's Phono's use 75R/2,200uF after 78XX/79XX regulators... :grin:

If you are REALLY worried, I would add a buffer to the output using a TO220 BJT (say 2SC4793) using an LM317 as CCS at around 30mA (this allows the use without heatsinks). The supplies for this extra follower would be directly from the 317 before the RC filter chain. Then the current modulation from the output is cut 100 fold and should stay within class A under all conditions.

Ciao T


Top
 Profile  
 
PostPosted: Wed May 23, 2012 4:07 am 
Offline
Sheep

Joined: Fri Feb 25, 2005 2:26 am
Posts: 49
Location: il
T:

ok, thx!

mlloyd1


Top
 Profile  
 
PostPosted: Thu May 24, 2012 6:53 pm 
Offline
Sheep
User avatar

Joined: Wed Jan 19, 2005 6:12 am
Posts: 51
Nice!

What about AD797 for MC? I know, sometime it´s a beast. It´s better to simulate this first.

Kuei Yang Wang wrote:
Please note the diodes shown have too low a voltage rating.

You know, this schematic will be spread over the www in nullkommanix. Better change it now, before you risk to ruin your reputation.

Carsten


Top
 Profile  
 
PostPosted: Thu May 24, 2012 6:56 pm 
Offline
Board jester
User avatar

Joined: Mon Dec 13, 2004 3:08 pm
Posts: 2006
carawu wrote:
Nice!

What about AD797 for MC? I know, sometime it´s a beast. It´s better to simulate this first.

Kuei Yang Wang wrote:
Please note the diodes shown have too low a voltage rating.

You know, this schematic will be spread over the www in nullkommanix. Better change it now, before you risk to ruin your reputation.

Carsten

Huh? It's only an opamp...
And I don't like the OPA827

_________________
Elso


Top
 Profile  
 
PostPosted: Sun May 27, 2012 3:14 am 
Offline
Muriel
User avatar

Joined: Thu Jul 26, 2007 5:45 pm
Posts: 868
Carsten,

carawu wrote:
Nice!


Well, nothing ground breaking, just a rehash of things long standing. But easy.

carawu wrote:
What about AD797 for MC? I know, sometime it´s a beast. It´s better to simulate this first.


I tried it and could not get it to work in my build. Having many other options I took the smart way and used them.

Personally I have been using LT1028 with MC (DL-103) and OPA637 plus MC Stepup Transformer. I preferred the LT1028, FWIW, but not by a lot.

carawu wrote:
You know, this schematic will be spread over the www in nullkommanix. Better change it now, before you risk to ruin your reputation.


I have decided to always leave one or two such things in my schematics. As the chinese kopy kats (CKK) usually lack even enough electronic knowledge to spot and fix such a simple item I consider Kopy Protektion.

:D

Ciao T


Top
 Profile  
 
PostPosted: Sun May 27, 2012 3:19 am 
Offline
Muriel
User avatar

Joined: Thu Jul 26, 2007 5:45 pm
Posts: 868
Elso,

Elso Kwak wrote:
Huh? It's only an opamp...


True. Consider it a warm-up. I'll post something a little more interesting another time. It should be obvious that the basic EQ can be applied to a variety of Phono Stages. Need to locate some readily available j-Fet's with decent MM noise behaviour for the more interesting stuff...

Elso Kwak wrote:
And I don't like the OPA827


In the best style of Apple's late Steve Jobs: "Then don't use the OPA827!"

There is a wide range that will do fine, pick your favourite. See text.

Ciao T


Top
 Profile  
 
PostPosted: Sun May 27, 2012 6:15 am 
Offline
Benjamin
User avatar

Joined: Mon Dec 13, 2004 3:29 pm
Posts: 4187
Location: Tralfamadore
Kuei Yang Wang wrote:
carawu wrote:
You know, this schematic will be spread over the www in nullkommanix. Better change it now, before you risk to ruin your reputation.


I have decided to always leave one or two such things in my schematics. As the chinese kopy kats (CKK) usually lack even enough electronic knowledge to spot and fix such a simple item I consider Kopy Protektion.

:D

Ciao T


I've been known to take the even further. I have sold PCBs, with minor design flaws. I wait a few weeks, and tell the buyers about the minor mistake, and how it can easily be fixed. (Usually something silly like a bypass cap that doesn't bypass.) I ask the recipient to acknowledge they have received notice of the error.

The only ones who do not respond are in the part of the globe where they freely copy everything they get their hands on.

I guess they did not like the fact they already made copies, and now they were stuck with "defective" PCBs.

I love it when a plan starts to come together.


Top
 Profile  
 
PostPosted: Sun May 27, 2012 10:22 am 
Offline
Board jester
User avatar

Joined: Mon Dec 13, 2004 3:08 pm
Posts: 2006
Kuei Yang Wang wrote:
Elso,

Elso Kwak wrote:
Huh? It's only an opamp...


True. Consider it a warm-up. I'll post something a little more interesting another time. It should be obvious that the basic EQ can be applied to a variety of Phono Stages. Need to locate some readily available j-Fet's with decent MM noise behaviour for the more interesting stuff...

Elso Kwak wrote:
And I don't like the OPA827


In the best style of Apple's late Steve Jobs: "Then don't use the OPA827!"

There is a wide range that will do fine, pick your favourite. See text.

Ciao T

Real men do it discrete.....
;)

_________________
Elso


Top
 Profile  
 
PostPosted: Sun May 27, 2012 11:18 am 
Offline
Muriel
User avatar

Joined: Thu Jul 26, 2007 5:45 pm
Posts: 868
Elso,

Elso Kwak wrote:
Real men do it discrete.....
;)


Real men do it with Tubes, actually.

The AA Phono was designed to meet a few criteria:

1) Ease of obtaining parts (in the UK anyway)
2) Ease of build, including strip board, by less than experienced constructors
3) A performance that beats the phono stages integrated into most cheap gear and most affordable stand alone phonostages

For a lot of people this is what they need. There are enough other designs of mine that are discrete, tubes, extremist and so on.

Ciao T


Top
 Profile  
 
PostPosted: Sun May 27, 2012 4:07 pm 
Offline
Board jester
User avatar

Joined: Mon Dec 13, 2004 3:08 pm
Posts: 2006
Tubes in MC phono stage ????

_________________
Elso


Top
 Profile  
 
PostPosted: Sun May 27, 2012 5:43 pm 
Offline
Muriel
User avatar

Joined: Thu Jul 26, 2007 5:45 pm
Posts: 868
Elso,

Elso Kwak wrote:
Tubes in MC phono stage ????


:hello:

Image

Does need selected ECC88 and I never found chinese or russian 6N11/6N23 quiet enough, but yes. Gain select needs to be shorted to ground for MC...

These days I prefer an MC Stepup of really high quality:

Image

And then there is the diyhifisupply "Cole Max" with WE 396A Mu Follower driving LCR RIAA followed by a triode wired 6688, of course als MC step-up transformer.

On the other hand my recent "Stereophile Class A rated" (whatever that means or says about it) uses a hybrid circuit and RC EQ.

Many ways to make good phono stages. The AA Phono does not compete with any of the more serious designs, but it it's own right it is very good.

Ciao T


Top
 Profile  
 
PostPosted: Tue May 29, 2012 6:58 am 
Offline
Board jester
User avatar

Joined: Mon Dec 13, 2004 3:08 pm
Posts: 2006
Would be interesting comparing the noise of the E810F and a 2SK146 amplifying an Ortofon SPU.....
(Has 0.2mV output at 5cm/s)

_________________
Elso


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 28 posts ]  Go to page 1, 2  Next

All times are UTC


Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
cron
Powered by phpBB® Forum Software © phpBB Group