Considering one of three cartridges. Opinions?

[jackfish]

At that price there is not much of anything which is conical.
Dynavector 10X5 - Elliptical
Ortofon 2M Bronze - Nude Fine Line (Elliptical)
Ortofon Super OM 40 - Nude FG 70 (Elliptical)

Obs: "Fine Line" and "FG70" are not elliptical shapes.

I stand corrected. Thanks!

viewtopic.php?t=22894

[GlassWolf]

Hi GlassWolf,
I noticed that you built your valve phono stage and it has MC capability. There has been a bit of discussion lately on the challenges of using valves for MC stages.

Any chance that you could post a schemo and a description of your phono stage?

http://diyaudioprojects.com/Tubes/RIAA-Phono-Preamp/

This is the basic layout for the pre-amp I'm building, I just modified it a bit with the help of the author of the article, to be switchable between MM and MC by adding a switch to the design to flip over to a pair of Lundhal transformers for the low-voltage MC cartridges. Just need a little more room in the cabinet you choose for the project.
gofar99 on this forum is the designer of the pre-amp I'm working on, so he would be the guy to ask if you decide to give a try to building one. He's a great guy.

[Coffee Phil]

Hi GlassWolf,

Thanks for the link. It looks like a sound design. He is claiming no negative feedback. Well that is partially true. The voltage gain stages are triodes with active loads therefore the voltage gain is set by the amplification factor of the bottom tubes. The active loads however are cathode followers with the first stage driving the passive RIAA network. Cathode followers are unity gain voltage followers with a whole lot of feedback. The second stage is similar with the active load / follower driving yet another follower.

This of course is not bad but for a no feedback claim is treading carelessness with the truth. It is fair however to say no overall feedback or that the RIAA network is not embedded in a feedback loop.

The MC ability is accomplished with a transformer which of course is fine and probably the only practical approach with vacuum tubes.

It is hard to get the low noise performance required at the extremely low impedance of MCs with tubes.

I was wondering if the designer had some "secret sauce" or was going over the top by putting hundreds of high performance tubes like 6DJ8s in parallel to get there.

Phil

Hi GlassWolf,
I noticed that you built your valve phono stage and it has MC capability. There has been a bit of discussion lately on the challenges of using valves for MC stages.

Any chance that you could post a schemo and a description of your phono stage?

http://diyaudioprojects.com/Tubes/RIAA-Phono-Preamp/

This is the basic layout for the pre-amp I'm building, I just modified it a bit with the help of the author of the article, to be switchable between MM and MC by adding a switch to the design to flip over to a pair of Lundhal transformers for the low-voltage MC cartridges. Just need a little more room in the cabinet you choose for the project.
gofar99 on this forum is the designer of the pre-amp I'm working on, so he would be the guy to ask if you decide to give a try to building one. He's a great guy.

[GlassWolf]

When I inquired about making the MM pre-amp MC compatible with a low-voltage drive circuit, this was the response I received:

"Hi, Yes ... I would (budget considering) build the MM one and allow a about 6 square inches of board space for the transformers to be added at a later date. Allow room for the switch as well. I was rather hesitant to use transformers at first as I figured they would mess up a good thing. But the more research I did the more premium preamps I discovered that were actually doing that. The only phono preamps that I discovered that were in any reasonable price range to compare to (under 2500) that were as quiet and didn't use transformers were IC based. The Moon LP3 I have is one such unit. Really quiet... but also has a huge amount of negative feedback. I generally avoid NFB in my designs when possible and use it in very small amounts in some (the power amps) to insure stability and not to make them quiet or fix sonic problems. So the phono preamp uses no NFB and the equalization is fully passive. The advantage to that is you can (like I did in my main unit) make plug in cards for the equalization and if needed swap them in and out. So in a round about way, I settled on input transformers for low output MC cartridges. It kept the preamp quiet and didn't really harm the sound. BTW there are several brands of transformers and they come in several price ranges. I used Lundhals because they were available and reasonable in cost."

as per the designer of the pre-amp, which incidentally will be marketed shortly by Oddwatt as a commercial product available in either an MM or MC version.

I just wanted an affordable, quality pre-amp design I could build myself without dumping thousands of dollars on a pre-made commercial unit. Being disabled, money is tight. Having an E.E. degree, I'm able to tinker with building some of this myself as time and money and health permit.

[Coffee Phil]

Hi GlassWolf,

Congratulations on building yourself what looks like a very nice phono stage.

I assume the input load network with 2 C1s, R1,R2,&R3 are stuffed or not to conform to the load requirements of your cartridge.

I do have one little nit to pick with Bruce on his decision to not regulate the power supply. The circuity of the amp does not inherently have good power supply rejection. In most cases it won't make a difference but I have had an experience where it did. I had a bi-amped system with an ElectroVoice 30W. With my Harmon Kardon Citation IV every time the fridge would come on it would drive the sub nuts and invoke the protection in my sub-woofer amp. I went a bit nut-so in my protection since as you would expect I'm paranoid of anything happening to my ElectroVoice Sub.
I had to add a series pass regulator to the power supply of the Citation IV to protect the sub from the fridge.

Bruce has much larger power supply caps than were practical in the day when the Citation was designed so he may get by. In any case I don't see a downside in regulating at the point before the supply filter splits to the two channels.

Here is a shot of the monster sub of which I speak:

[img][/img]

That is looking at the celing of my stereo room. It is infinately baffled to the attic. The diameter of the driver is 30".

Phil

When I inquired about making the MM pre-amp MC compatible with a low-voltage drive circuit, this was the response I received:

"Hi, Yes ... I would (budget considering) build the MM one and allow a about 6 square inches of board space for the transformers to be added at a later date. Allow room for the switch as well. I was rather hesitant to use transformers at first as I figured they would mess up a good thing. But the more research I did the more premium preamps I discovered that were actually doing that. The only phono preamps that I discovered that were in any reasonable price range to compare to (under 2500) that were as quiet and didn't use transformers were IC based. The Moon LP3 I have is one such unit. Really quiet... but also has a huge amount of negative feedback. I generally avoid NFB in my designs when possible and use it in very small amounts in some (the power amps) to insure stability and not to make them quiet or fix sonic problems. So the phono preamp uses no NFB and the equalization is fully passive. The advantage to that is you can (like I did in my main unit) make plug in cards for the equalization and if needed swap them in and out. So in a round about way, I settled on input transformers for low output MC cartridges. It kept the preamp quiet and didn't really harm the sound. BTW there are several brands of transformers and they come in several price ranges. I used Lundhals because they were available and reasonable in cost."

as per the designer of the pre-amp, which incidentally will be marketed shortly by Oddwatt as a commercial product available in either an MM or MC version.

I just wanted an affordable, quality pre-amp design I could build myself without dumping thousands of dollars on a pre-made commercial unit. Being disabled, money is tight. Having an E.E. degree, I'm able to tinker with building some of this myself as time and money and health permit.

[GlassWolf]

I actually probably will use a regulated power supply. It's not like it'd add that much to the complexity or cost of the project to do so.

[Coffee Phil]

Hi GlassWolf,

In most cases it probably does not make a big difference, however if for any reason you can't tolerate sub audio crud coming out of the preamp the regulator will be a very good thing.

If you are interested, I can scan my hand drawn schemo for the regulator in my Citation IV. You will have to scale the feedback resistors to get the output voltage which you need but the topology should be very similar.

Phil

I actually probably will use a regulated power supply. It's not like it'd add that much to the complexity or cost of the project to do so.

[GlassWolf]

That'd be swell, actually. Thank you. It may be a bit before I get this project finished, though. Money is a little tight just now, so I may have to put off finishing this up for a month or two till things calm down a bit.

[Coffee Phil]

Hi GlassWolf,

My printer / scanner went south but we got a new one. Hopefully tomorrow I'll get it set up and scan the schematic. I'll also scan the OEM schematic of the Citation IV so you can see what I did. My regulator requires ~ 12 volts @ ~15 ma referenced to ground. I have an idea how you can get that without an additional transformer. I'll sketch that as well.

Phil

That'd be swell, actually. Thank you. It may be a bit before I get this project finished, though. Money is a little tight just now, so I may have to put off finishing this up for a month or two till things calm down a bit.

[GlassWolf]

Great. Whenever you get the time. I sent you a PM with my e-mail, which may be easier to send the files.

[gofar99]

Hi, Your thoughts are noted and always welcome. Yes I would agree on a technical level about the no NFB. No global would be a better description. Passive equalization was a goal as I tried versions with the RIAA equalization in a NFB loop and felt it compromised the sound. I did try lots of tubes in the circuit and finally settled on the JJ ECC83S gold pins as they provided the low noise level I was after. Most others that were supposed to be quiet were worse, sometimes much worse. Builder beware. I actually did use a regulated supply in one prototype (with LR8s) and the difference was so slight (under 0.5db) that it didn't merit using it. The project was conceived as a diy one and I deliberately tried not to over complicate it for that reason. The actual power supply evolved over several iterations in a 24 month period to be a "best value" one and while simple in appearance is quite effective. In this project the layout and grounding are the things to watch out for. The have a major influence on the noise level. Using input transformers was really the only way to keep complexity down and maintain the low noise levels. I tried several other approaches and all added either more noise or a lot of components. I used Lundhal transformers, but others are certainly fine. They all have what I would call a flavor and if you build one of these preamps you should use ones you like. In operation the preamp is very quiet. One is presently in use at a high end audio dealer to demo turntables. His first comment to me was that he thought it was not functioning when he first turnrd it on as there was no noise. Putting the stylus to the vinyl changed that thought quickly. The preamp is suitable for most of the high output MC cartridges without a transformer and has more than average gain (about 45dbv). I normally use a Dynavector 10X5 (on the MM input) and have used others with as little as 1.5mv output. I use a Benz on the MC inputs.

I thank everyone for their input and in a few cases inspiration for designing this preamp. I nearly gave up a year ago when I couldn't get it as quiet as I felt necessary.

[Coffee Phil]

Hi Bruce,

Your phono stage looks like a very nice one to me. I don't want to come off like I'm dissing your lack of power supply regulation. The time constant of your power supply filter looks much longer than the one in my Citation IV so it could be it may have been fine against the fridge and crappy aluminum wiring which I had in my old house. I lived with out the regulator for years and it was fine with a transformer-less amp driving my sub. or at least I didn't notice it. It could be the 30W didn't think much of it. When the amp crapped out and put DC on my sub I had to get it re-coned. I developed a paranoia of transformer-less amps feeding the woofer. I designed a MOSFET transformer coupled amp using a massive old TV power transformer as the output transformer. The former 117 volt input winding is now the secondary driving the sub. It works fine and can deliver full power (~45 Watts) from ~18 Hz to ~300 Hz. Subsonic stuff into it would cause the transformer core to saturate and pop its internal fuse. Regulating the PS. of the Citation IV stopped that aggravation. It did not add much complexity. I used a TL431, an opto-isolator, and a MOSFET pass transistor. The MOSFET replaced the first resistor in the existing PS filter. Replacing the 1 /2 wave selenium rectifier with a silicon bridge gave me a bit more headroom for the regulator.

Phil

Hi, Your thoughts are noted and always welcome. Yes I would agree on a technical level about the no NFB. No global would be a better description. Passive equalization was a goal as I tried versions with the RIAA equalization in a NFB loop and felt it compromised the sound. I did try lots of tubes in the circuit and finally settled on the JJ ECC83S gold pins as they provided the low noise level I was after. Most others that were supposed to be quiet were worse, sometimes much worse. Builder beware. I actually did use a regulated supply in one prototype (with LR8s) and the difference was so slight (under 0.5db) that it didn't merit using it. The project was conceived as a diy one and I deliberately tried not to over complicate it for that reason. The actual power supply evolved over several iterations in a 24 month period to be a "best value" one and while simple in appearance is quite effective. In this project the layout and grounding are the things to watch out for. The have a major influence on the noise level. Using input transformers was really the only way to keep complexity down and maintain the low noise levels. I tried several other approaches and all added either more noise or a lot of components. I used Lundhal transformers, but others are certainly fine. They all have what I would call a flavor and if you build one of these preamps you should use ones you like. In operation the preamp is very quiet. One is presently in use at a high end audio dealer to demo turntables. His first comment to me was that he thought it was not functioning when he first turnrd it on as there was no noise. Putting the stylus to the vinyl changed that thought quickly. The preamp is suitable for most of the high output MC cartridges without a transformer and has more than average gain (about 45dbv). I normally use a Dynavector 10X5 (on the MM input) and have used others with as little as 1.5mv output. I use a Benz on the MC inputs.

I thank everyone for their input and in a few cases inspiration for designing this preamp. I nearly gave up a year ago when I couldn't get it as quiet as I felt necessary.

[GlassWolf]

Hi Bruce,

Thank you for not giving up, and for offering to help those of us trying to build the project now, and for joining the discussion.
Interestingly enough, the dynavector 10X5 is the same cart I'm going to be running in the Pro-Ject, so things should go well, since you have direct experience with the same cart.