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Groovewatt - tube RIAA phono preamp
http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=3545
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Author:  gofar99 [ 23 Dec 2011, 10:49 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

Hi, Only the one on the upper anode. The lower one would shunt all the signal to the ground.

Good listening
Bruce

Author:  mazzas [ 23 Dec 2011, 11:12 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

Showing you everything I know about audio circuit design... :blush:

So just on pin 6... I've changed the image (above) so that nobody mistakenly implements my bad advice.

Also, this is all OT and should maybe be moved to the Forewatt thread?

Author:  gofar99 [ 23 Dec 2011, 11:28 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

Hi, A little OT, but since it relates, probably no harm in leaving it here. The basic thought is regarding the use of remotely located power supplies on audio gear and really applies to pretty much any project.

Good listening
Bruce

Author:  Elithraldor [ 08 Jan 2012, 14:31 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

I have just ordered most of the parts for this build (Edcor transformer should take 1-2 months to get to Denmark :( ). Since this is my first build, I decided to go for the JJ ECC83S and ECC81 (not the Gold plated, super stuff) just to save the money should I burn them somehow. Then I can upgrade them when (if) it all works, and if I see fit.

It is going to be running on a Beogram 4000 turntable with a SP15 / Soundsmith MMC20EN pickup (http://www.sound-smith.com/cartridges/bosmmc20en.html). The input resistance should be >47k and capacitance >400pF - I might include some switching in order to be able to change this and figure out what sounds the best. Anyone has some preferences?

The "audio-grade" capacitors I have ordered so far, is some SCR / Solen Fast (5%). However I want some more precise for the RIAA filter - anyone knows a good brand and place to get them in Europe?

Author:  Soundbrigade [ 08 Jan 2012, 16:04 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

Among the VERY best caps for analoge filters ever made are RIFA's PFE225 (I think they were called). They were housed in small white plastic boxes (http://www.wellgainelectronics.com/rifa ... 100v2.aspx) and were originalled developed ofr Ericsons analogue telephone exchange systems.
They may be very hard to find but are extremely precise and stable, much more than so called "audio grade" caps are. (Don't expect an "audio grade" cap to be anything more than a standard cap with golden print och the can and an exclusive price tag).

Author:  gofar99 [ 08 Jan 2012, 17:29 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

Hi, I checked the specs on the cartridge and it appears to be a low output moving coil. The Groovewatt has more gain than most at 45 db, but it is designed for high output moving coil and MM cartridges. You may have enough gain in your preamp to get it up to the level you need. Hard to say.

Good listening
Bruce

Author:  Elithraldor [ 09 Jan 2012, 01:23 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

My current RIAA is the Cambridge 640P (set to MM) and the pickup is the original SP15, this works just fine. According to the Cambridge datasheet the nominal sensitivity is 3.35 mV, so it will work with the SP15. The question is then if the Soundsmith is "the same" as the SP15.

Edit: The SP15 renamed the MMC4000 (and later renamed MMC20EN) is specified to have Output mV/cm/sec.: 0,6mV/47kOhms - which is equivalent to the SMMC20EN. Also the gain of the Cambridge (MM) is 39dB. so everything looks like it is in the clear.

Author:  mwhouston [ 09 Jan 2012, 01:59 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

If you don't get sufficient gain try the Le Pacific MC preamp. Adjust the input impedance resistor to suit the cartridge. But after building three they simply appear to do a good job.
http://www.diyaudioprojects.com/Forum/viewtopic.php?f=10&t=3046#p22908

Author:  gofar99 [ 10 Jan 2012, 11:15 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

Hi, If it works with the Cambridge with its gain, then there should be no issues. :)

If I recall correctly...not all cartridges are measured / spec'ed the same way and some use output (millivolts/cm) at different groove modulation levels. This could well be such an instance.

Good listening
Bruce

Author:  gofar99 [ 24 Jan 2012, 22:04 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

Hi Everyone, An update and some info on what comes next. I incorporated a Groove and Forewatt into one chassis with a digital wireless remote (that part is not my design and is modular and could be replaced with an Alps 100K). The results are excellent and and I will post a project on it in the not too distant future. Now for some details, I used all Jantzen Silver Z coupling caps (both electrically and physically large) to replace the Auricaps and PIOs in the photos. Auricaps are very very nice, IMHO the Zs are better. I have to "break them in" a bit yet before I can do any measurements but the sound is really special now. The next step is .... (fanfare) making it able to do low output moving coil cartridges. Initial tests are that a simple mod will achieve this and still retain nearly all of the 90 dbv S/N. With a 1.6mv output MC it will easily drive my Oddblocks directly to full output in the passive preamp mode. I suspect that the extra 5 db I can get easily will make it just fine with low (0.5mv) cartridges. Stay tuned for further progress.
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Pre In system.jpg

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Pre inisde with covers2.jpg

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Pre inside no covers view 2.jpg

Good listening
Bruce

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