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Groovewatt - tube RIAA phono preamp
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Author:  gofar99 [ 01 Nov 2011, 23:43 ]
Post subject:  Groovewatt - tube RIAA phono preamp

This is the update and support thread for the Groovewatt - Tube RIAA Phono Preamp project. Feel free to ask questions and post comments about the Groovewatt in this thread.

PROJECT LINK - Groovewatt: DIY Tube RIAA Phono Preamp project.

Author:  Les [ 02 Nov 2011, 11:58 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

Ok. My mouth is watering now.... :mrgreen:

This may be my next build.... :smoking:

Author:  gofar99 [ 03 Nov 2011, 18:38 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

Hi, For an average diyer this should not be a really difficult build. Some things are quite important though. First grounding and shielding are critical to low noise performance. -90 dbv does not come easy. Second the power supply has to be clean. Third and a real problem is getting quiet tubes. Not all venders are really knowledgeable about the tubes they sell. I sent back a whole batch of name brand tubes that the dealer said were quiet. They were even listed on his site as such. Not so as they were over 3 db each noisier than the ones I finally used. I won't say they are the best...... but the JJ Gold Pin ECC83S tubes work for me. Get matched quads as well. I tried some cryogenic ones and they were not any better. All in all a challenging and rewarding project. :)

Good listening

Author:  Les [ 03 Nov 2011, 21:40 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

Thanks for the tips, Bruce. I had not considered matched quads. I was considering matched pair as well as matching triodes on the 12AT7. A low noise PS will be a little challenge. LV PS I can do in my sleep. I haven't attempted a HV PS as yet. I am confident that if I follow your design, it should be just as quiet as yours. It's taking longer than expected for me to get started on my first real tube build (the modified FireFly amp). Money issues keep getting in my way. Just when you think you've found a way to free up some capital, something else breaks / needs repair and there we are again. It destroys my project budget, but at least I am not creating new debt now. Kinda feels nice to not have to put things on credit card. Oooops, I wandered off topic a bit. ;-) Anyway, the point is that it won't be a quick build.

I have to say, your builds look really nice. I really like the recessed tube version.

Author:  CrazzyAbtTubes [ 06 Nov 2011, 16:32 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

Wow Bruce! That is a good looking circuit, it seems some what familiar to me?...... hmmmmm..... I'm thinking it reminds me of the Precision Fidelity phono stage circuits, like the C7, or the one I'm most familiar with, the C8, like the SRPP input stage, and the C7 has something like three, basically one stage after the other. I know this would totally ruin the fact that it is an all tube design, but have you ever thought of using a transistor at the output? I have no idea if it would be any performance gain to actually use one, but it worked for the Precision Fidelity circuits. ;)

But without a doubt you have put a quite some time and effort into the design, and I agree with Les, I have not started constructing my all out tube preamp yet, I have been waiting to put some moneys aside :2c: Tuition isn't cheap to pay these days, even for a trades course.

But your circuit will be easier to work with in my opinion than the Precision C8 design I was thinking of using originally, and from what I have read, it is likely more tamed too, I like it! :D

Are there any octal type tubes that will work in place of that 12AT7 at the output? I all ready have the whole cut in the chassis for an octal type tube.... I don't think I can size that whole back to a 9 pin miniature :P

Author:  gofar99 [ 06 Nov 2011, 18:10 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

Hi, Funny thing, I've never seen the Precision Fidelity circuit. I deliberately avoided looking at other folks designs. I did study how RIAA worked and various ways it might be implemented. The rest was just trying to figure out how to make it happen. If PF uses an odd number of gain stages then it may have a problem. Each gain stage will invert the signal 180 degrees. This is OK if you invert something else upstream. But if it is the only thing that inverts then it is a constant pain in the you know where. :? I didn't consider a transistor output but a high voltage FET ought to work. It just as simple or even simpler to direct couple a cathode follower there.

I too like the version with all the tubes inside. It was a bit of a challenge to make it work clean though. On top was also easier to fiddle with while working on variations. I lost count of how many there were. It was over 20 though. Funny thing is all of them worked, but none were quiet enough until the last ones (those in the write up). I could get into the low -80s for S/N easily, but just couldn't jump past it until I went to the twin SRPPs with passive equalization. I could actually get a little better with active equalization, but it seemed sensitive to tube types used and IMHO didn't sound as clean. This one sparkles. :) I was listening to some acoustic guitar music a few days ago (accompaniment of all things on an old Linda Ronstadt LP) the guitar was solo much of the time. You could easily hear the fingering and make out it was a six string dreadnought. I will grant it doesn't hurt to have a really excellent cartridge as well.

One thing I tried that had merit was make it a two chassis design with the PS remote by several feet. This was fine, but even though I love diy and do much of this for fun, there will be an Oddwatt Audio kit eventually and two chassis designs have lower acceptance and higher cost (BTW it will not be cheap anyhow with $125 worth of tubes alone).

Good listening

Author:  Les [ 07 Nov 2011, 13:36 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

Hey Bruce,
I was thinking of separating the power supply myself. Even with all the tinkering and the fact I used a shield between the PSU and pre-amp board of my K301, I still haven't ridden it of all hum. The downside is it requires two cases; the upside, the cases can be smaller. Another downside is the manufacture of a power cable to go between the PSU and the preamp. Lots of things to weigh and consider.. ;-)

Author:  gofar99 [ 08 Nov 2011, 13:39 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

Hi, I did it one version because the tubes would pick up the radiation from the transformer directly. There are a number of factors that play into this. One is the actual tube type and brand. Second and one you can do something about is the circuit impedance. I like to keep grid circuits at or below 100K. You lose a bit of gain doing this, but make them far less sensitive to noise and hum. Shielding is key as well. I find that shields work better connected to the chassis ground and not the signal ground (I always separate the two with a capacitor/resistor combination). Every time I used the signal ground for things like tube shields the hum and noise went up. It can be tricky to use the chassis as the connection when the tubes are inside it.

If I recall correctly the K301 uses mini tubes that have directly heated filaments and not cathodes. This by itself complicates the build. The heater supply must be at least as clean as the B+ and be properly implemented to avoid contamination by the rest of the circuit. This is one reason why I don't use DHTs. A second one is that I like the way SRPPs work and DHTs make it more complicated to separate the signal from the power.

All that said...if you follow the general build configuration in the third prototype you should be fine. A big this is to be sure that no AC carrying wires or parts are inside the signal area and that the B+ lines have two sections of filtering before there as well (all sections is best though).

Good listening

Author:  msmpe [ 24 Nov 2011, 01:10 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

Hi All:

Very nice project. I've filed it for consideration when the time (finally) comes to build my phono pre-amp. My first two thoughts skimming over the project description - the CF can be left out if phono, pre, and amp(s) are close enough together, and a separate power supply has distinct audio advantages. In my case, I will have a phono pre and a bi-amp active crossover - all tube, separate chassis, so a separate PS could power both. Wouldn't the connecting power cable only be four conductors: B+, B-, Htr S, Htr R - one cable for each pre-amp? The "secondary" filter string for each would go in the respective pre chassis starting with both R2. The xover would us the same type of filter string arrangement. What do you think?

Bruce, you mentioned trying a number of tube types. Did you try 6DJ8/6922? It is lower microphonics, but lower mu also, so lower gain? For the 12AX7, the 12DT7 is low noise, but might be pricey. Any other NOS worth considering?

How does the dip switch work?

What problems did you have looking for a suitable toroid PST? It seems to be a perfect application.

Thanks again for sharing your work. :up:

Mike 8>)

Author:  HT Performance [ 24 Nov 2011, 18:11 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

Bruce... I have just read your phono pre-amplifiers comparision (22Nov). You really work hard, looking for perfection. The results tell it.

And now I need to build a GrooveWatt tube phono preamp! I blame you! :P


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