DIY Moving Coil Phono Stage

[Hypnotoad]

I have been looking around for a high quality, easy to build moving coil phono stage, I got some PCB's a while ago and never did anything with them.

I have been etching PCB's at home for a while and it's easy to do so I decided to simplify the project. I don't even have a LOMC cart yet and hoped that since it will "only" work with moving coil carts, it would also work with high output moving coil carts like my Benz Micro Ace since they have similar coil structures to the low output ones.

Being obsessed at the moment with battery power I decided to see if it will run properly on them as most of the design is on a very low noise PSU. I just wanted the part that makes music.:)

This simplified the process no end so I designed a PCB and etched it earlier this week. I got the parts and using the suggested OPA27GP op amps, which are very cheap, and stacked plastic caps with metal film resistors to see if it would work. Very few parts, very cheap to build with very tight RIAA tolerance.

I used a gain calculator to give me the values of the gain resistors.

It worked first time, I was struck by how low the noise is, I have reduced the gain a lot but if this is any indication it should be extremely quiet with LOMC carts. I added a 0.1uf poly cap to each of the 8 x 100uf filtering caps, they certainly didn't hurt anything. To give you an idea it's much quieter than my modded 640P's and they are very quiet. With battery power you don't have to worry about hum for a start.

Right out of the blocks I knew this is going to be good VERY good, it bowled me over with the definition and smoothness on the first track which was Because by The Beatles off the Love album. I could easily hear the fly buzzing back and forth. The bass response and separation was second to none, Elanor Rigby sounded better than I have ever heard.

I kept thinking this thing is not even broken in yet, it can't be this good, those op amps are cheap as well. I called my wife she couldn't believe it either. It has a slightly warm yet very detailed and open sound, the music just flows out. If it has faults none of them stand out at the moment, it just sounds like vinyl should.

It's the best I have heard and is very easy to build, I am using 4 x 6v lantern batteries to give me +12v, 0, -12v I have guesstimated over a years use as it only draws around 15mv's.

Here's some pics, not as professional as some but it makes up for it in sound quality. By all accounts it really sings with the Denon DL-103 series.

http://i729.photobucket.com/albums/ww297/Hypnotoady_photos/Inside.jpg

http://i729.photobucket.com/albums/ww297/Hypnotoady_photos/Front.jpg

http://i729.photobucket.com/albums/ww297/Hypnotoady_photos/Back.jpg

[rusty bearing]

'not as professional as some'
:stalks:
Looks pretty damn good to me....
What batteries does it run off ?

[howlindawg]

Very nice.
What's the total build cost?

[Hypnotoad]

'not as professional as some'
:stalks:
Looks pretty damn good to me....
What batteries does it run off ?

I got 4 of those 6volt lantern batteries and have them in series with a center tap for the ground. But it will run on just two 9volts and get around 40 hours on those.

http://images.pricecanada.com/images/products/606/l606603.jpg

[Hypnotoad]

Very nice.
What's the total build cost?

$80.00usd whatever that is in sterling.

The circuit is named the phonoclone 3, it supposed to be a similar design as the 47labs phono cube which retails at over $2500.00usd without PSU. All I can say is it beats all my other phono stages by a mile, there is no comparison. I am hearing things I have never heard before and it's not even broken in yet.

It's such a simple design and is basically a transimpedance/transresistance amp where the cartridge is a current generator.

I can post a schematic if anyone wants to build one, you have to calculate the values of the first two resistors to suit your cart but that's easy to do. For a Denon DL-103 for example R1 is 40 ohms and the gain resistor R2 is 1.33k ohms. I cheat as I have a gain calculator from the guy who designed the circuit.:eyebrows:

[howlindawg]

The circuit is named the phonoclone 3

Is this the same circuit (minus the PSU circuit) that Peter Daniels uses in his audiosector kits?

[Hypnotoad]

Nothing like it as far as I know.

[sq225917]

They are based on the same design, but the layouts and implementation appear to differ wildly. The Audiosector kits look superb.

[DSJR]

I wonder what circuit the well received and inexpensive Angle Audio stage uses? Any chance of someone lifting the lid on theirs and taking a pic or three?

[Hypnotoad]

They are based on the same design, but the layouts and implementation appear to differ wildly. The Audiosector kits look superb.

I actually just found his thread on DiyAudio and it is a very similar design, I see he added a cap across R1 to avoid oscillation of higher bandwidth op amps which wasn't a problem with the ones I used. His RIAA stage is completely different and it has no DC blocking cap with accompanying drain resistor in the output stage. The RIAA deviation on the one I built is 0.01 dB

The main problems with these designs is in the power supply and with batteries those problems are removed, and it simplifies the circuit no end.

I think both designs would sound very similar depending on the components used, no wonder people are excited. I am only using the cheap recommended OPA27GP op amps and it sounds fantastic. I see Peter recommends OPA627/OPA637's that cost up to ten times as much. Other AD797's might be really good but would definitely need that bypass cap to prevent instability.

I really only built this thing to see if it would work and was shocked by the performance, it's totally stunning.

[howlindawg]

I'd love to see your schematic if you fancy posting it Phillip.
I intend building a phonostage as my next project and it was the AudioSector variation I was favouring... but a simplified option is extremely tempting.

Very neat work BTW, that PCB is as clean as a whistle.

[Hypnotoad]

I'd love to see your schematic if you fancy posting it Phillip.
I intend building a phonostage as my next project and it was the AudioSector variation I was favouring... but a simplified option is extremely tempting.

Very neat work BTW, that PCB is as clean as a whistle.

No problem Martin, it would be good to have another opinion of the sound.

The only difference is I added a 0.1uf poly cap to each of the 100uf filtering caps, not sure if it did anything big but the noise is very low. On the schematic you will see the value of R7 is 75k and it has since been changed to 68k.

The RIAA caps are all 1nf, the closer you can get the better, I bought a dozen and measured each one choosing the nearest ones, which were within 1%. The DC blocking cap on the output is 2.2uf, I tried Panasonic polyesters, they give super detail, you can hear every breath and the fingers on the strings while sounding a little sterile IMO. I then tried some Panasonic Polypropylene's I had laying around, it makes it more mellow, with a little less of the detail I didn't really want. It's a trade off I really like.

The opamps are these:

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=OPA27GP-ND

Oh and RJM posts this freely and doesn't mind others using it.;)

http://i729.photobucket.com/albums/ww297/Hypnotoady_photos/pc35b-schematic.jpg

[howlindawg]

Thanks Phillip.

[Hypnotoad]

Thanks Phillip.

Martin I see you have a Benz Micro Ace SL, I love Benz carts, here is the values of R1 and R2 to suit for the correct gain:

R1 = 12 ohms

R2 = 300 ohms

[howlindawg]

here is the values of R1 and R2 to suit

:lol:

You anticipated my next question!

:cool:Cheers!

[Hypnotoad]

After finding this phono stage gets even better with time I built another one when I acquired a lightly used Benz Ace SM.

It's without a doubt the best phono stage I have heard by a mile, the music is so natural it's eerie, it's like having a whole new record collection.

There is no noise at all from this thing, you can crank the volume right up before the needle drops and hear nothing at all, you only hear whats on the record.

[Reid Malenfant]

Aha, i see why it is quiet ;) What you have there are two op-amps with shunt feedback around each one. This is usually much quieter than series feedback, the output signal is also absolute phase as both op-amps invert the signal..

Shunt feedback tends to have a much reduced noise in the upper frequencies, any noise generated is more of a rustling sound rather than hissing :)

Quite neat :cool:

[Thing Fish]

I have never used a dedicated phono stage. I currently use my Adikt with a Naim 62/90 hicap. Would I really hear the benefit of a dedicated phono stage?

How much would I roughly have to spend on fleabay to benefit?

A bit vague I know but hey ho...

[kor952]

I actually just found his thread on DiyAudio and it is a very similar design, I see he added a cap across R1 to avoid oscillation of higher bandwidth op amps which wasn't a problem with the ones I used. His RIAA stage is completely different and it has no DC blocking cap with accompanying drain resistor in the output stage. The RIAA deviation on the one I built is 0.01 dB

The main problems with these designs is in the power supply and with batteries those problems are removed, and it simplifies the circuit no end.

I think both designs would sound very similar depending on the components used, no wonder people are excited. I am only using the cheap recommended OPA27GP op amps and it sounds fantastic. I see Peter recommends OPA627/OPA637's that cost up to ten times as much. Other AD797's might be really good but would definitely need that bypass cap to prevent instability.

I really only built this thing to see if it would work and was shocked by the performance, it's totally stunning.

I also experimented with the Phonoclone 3 lately. I ordered a second pair of boards/kits and changed the phono part into the Peter Daniel's 'The Phono Stage'. It's rather simple to do.

A few note's.

- The Phonoclone is not a real Phonocube clone but Richard Mudey's implementation of this kind of circuit.
- The phono part of Peter Daniel's 'The Phono Stage' is an exact copy of the 47Labs PhonoCube. However Peter uses extreme quality components and a Current Source / Shunt Supply instead of the simple supply (78xx/79xx) used in the PhonoCube.
- The cap parallel to R1 is not to avoid oscilation but is part of the RIAA network. With the PhonoCube / The Phono Stage the RIAA network is devided over the first and the second stage.
- Due to the low output offset of the second stage of the PhonoCube / the Phono Stage no output capacitor is needed.
- There is no need to adjust resistors with the PhonoCube/the Phono Stage, most MC carts are doing well with these preamps except for carts with rather high Ri and low ouput voltages such as Denon DL103 (40 ohm / 0.25 mV) because the gain may be to low for your system, but a DL103R will do fine (14 ohm / 0,25 mV).

I prefer the sound of the PhonoCube/the Phono Stage (the supply for both the Phonoclone and the Phono Stage was kept identical). When upgraded with OPA627/OPA637 the sound becomes way better. If you want to upgrade the Phonoclone with OPA627/OPA637 you have to use the OPA637 on the first stage certainly not on the second stage because gain will fall below unity for the high frequencies.
At the moment I am seriously considering ordering the PCB's from Peter Daniel because I want to know how good a Current Source / Shunt Supply will sound.

My two cents,

Ronald Koridon,
Amsterdam.

[kor952]

........... When upgraded with OPA627/OPA637 the sound becomes way better.....

I have to change my opinion...
After a few weeks I put the OPA27's in again and the sound is much smoother and harmonic, maybe in Peter Daniels' The Phono Clone the OPA627/637 will sound better NOT in a changed Phonoclone 3.

Ronald Koridon,
Amsterdam.

[Hypnotoad]

I have to change my opinion...
After a few weeks I put the OPA27's in again and the sound is much smoother and harmonic, maybe in Peter Daniels' The Phono Clone the OPA627/637 will sound better NOT in a changed Phonoclone 3.

Ronald Koridon,
Amsterdam.

Ronald,

Since building the Phonoclone 3 I have redesigned it after trying the Peter Daniels offering but not with his power supply. I use different op amps, different RIAA stage and different dc blocking cap setup. In fact there are only two parts the same in the whole thing.

To my old ears it's more detailed, smoother, with more space between the instruments and a wider, deeper soundstage and tighter bass, but then again I might me biased.:D

Using them on batteries is far superior to using a PSU IMO. YMMV

I call it the HTMCPS (HypnoToad Moving Coil Phono Stage)

http://i729.photobucket.com/albums/ww297/Hypnotoady_photos/HTMCPSPartStuffed-1.jpg

[howlindawg]

Well it took eighteen months for me to actually get around to starting but I eventually got around to building one.
I'm very glad that I did, it sounds wonderful with my Benz Glider SL.

http://imageshack.us/a/img827/6706/asphonosection.jpg

I even put it into a nice box.

http://imageshack.us/a/img534/2007/rearhx.jpg

[Bigman80]

This is a great thread !

[CornishPasty]

This is a great thread !


Have you looked at the date of the last post before yours? You might find some continuity over on the Diyaudio forum.

[Bigman80]

I have. Just displaying my enjoyment of the thread.

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[CornishPasty]

I have. Just displaying my enjoyment of the thread.

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No worries. Glad you're enjoying it :) This does seem an interesting phono stage but as a confirmed valve man I really shouldn't. However I always try to be open minded so some investigation is required.

[Bigman80]

No worries. Glad you're enjoying it :) This does seem an interesting phono stage but as a confirmed valve man I really shouldn't. However I always try to be open minded so some investigation is required.
[emoji1] it's something I'm looking into doing so it's been a good read. I'll obviously look around as much as possible but it's got a very good reputation on here so I've put it on the maybe list

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[CornishPasty]

[emoji1] it's something I'm looking into doing so it's been a good read. I'll obviously look around as much as possible but it's got a very good reputation on here so I've put it on the maybe list

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I'm going to have a read through this and see where it takes me.

http://audiokarma.org/forums/index.php?threads/ad797-phono-stage-build-and-help-desk-thread.501186/

[sachu888]

Since someone got interested. I want to update about new boards http://audiokarma.org/forums/index.php?threads/ad797-phono-stage-build-and-help-desk-thread.501186/page-51
Its called AD797 HQMC phonostage.

Regards
Sachin