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PostPosted: 25 Oct 2020, 16:49 
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Joined: 13 Jan 2018, 21:33
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Location: australia
Back to future, have blown my 6as7 amplifer power and output transformer cash and bought a Thorens TD160 turntable expected to arrive today. It is old so I may need to do some work on it. This is to play just a handful of the hundreds of LPs I couldn't bring myself to part with in the early 90s. I may have to shelve my power amp building ambitions for a bit but not forever.

Now none of the three transistor amps I have or my tube amp have a phono stage with RIAA. I have been looking at the phono stage projects on this site, but thought I would ask people's views on a good tube phone stage in case other ideas have emerged lately. Looks like I will have about 4mv output from the turntable--yet to measure-- I am looking to bring the output up to line level for my 6sn7/300b SE which operates loudly enough from my iPad or CD player with the 250k pot hardly past 12 o'clock.

A miniature tube or tubes would be nice. A question to ask along the way too is - are tubes the way to go for a phono stage? I see Mark has been building a variety of transistor phono/mc stages. In the past my Quad amp had a phono stage and I used battery powered Naim unit to boost the MC output. I thought this sounded rather neutral but had never listened to a tube phono stage at that time.

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PostPosted: 25 Oct 2020, 21:15 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
Hi, A worthy endeavor....however you will find the SS phono preamps are a lot cheaper to build than tube ones. I have several of each type. The ones Mark is using (he is a long time audio buddy of mine ..about 12 years now) are the ones in the project I posted a while back. Check the thread on it in the forums. Surprisingly nice sounding and really quiet. They can run on batteries (drain is about 10ma) but I prefer AC. That explains the well regulated supply. It adds about $25-30 to the cost but I hate batteries as they always seem dead at inconvenient times. A handful of AA or a pair of 9 volt ones will give a goodly number of hours though and is a cheap solution. High quality tube phono preamps run the gamut of prices. I personally have not seen any much below $1000US that are really any good. Most below that range are actually hybrid with most of the gain from an IC and the the tube is often just a buffer. The project I posted is all tube and quite excellent. It will cost significantly more to build and does require skill in layout, construction and wiring. I don't consider it a good project for a first time tube build. Done correctly it is a killer. Done less well and it is a debacle..with a lot of hum issues.

Your TD160 is a worthy turntable and if you want to know how to maintain it check out vinylengine.com. That forum is friendly has a huge following and lots of knowledge. Great reference section as well.

Good listening
Bruce

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PostPosted: 25 Oct 2020, 21:34 
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Thanks Bruce. Much appreciated. Will study up on the circuits.

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PostPosted: 04 Nov 2020, 17:10 
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I came across this circuit on page 542 of the RCA tube manual. It uses a single 12ax7 per channel I believe and includes components for the RIAA network. Are there any views on the relevance of the circuit today, the tubes used or alternative tubes that could be used such as 12AU7, subminiature or the RIAA network? I like the apparent simplicity of it and may be a better match for my abilities as long as it will sound good. I haven't thought too much on the power supply yet.


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PostPosted: 04 Nov 2020, 21:19 
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Hi, I thought this was about the 21st century not the 19th ( :D ). That circuit will certainly work. But not IMO all that great. They actually made small (4X4X5H inch ) preamps like that. They cost about $5 as I recall. Really cute little buggers. I suppose with really good power filtering they could be acceptable. The originals were pretty sad. S/N of around 40db and response from about 60HZ to 10K. I think any new $50 solid state preamp could easily out perform it. Back when the circuit was in vogue phonos were mostly mono and really not hi-fi as we understand it today. I expect the budget Crosleys now on the market would sound better than many did back then. I would search the web for more current preamps and when you find one or more post it and ask what we think about it. Folks on this forum are not all knowing, but we do have some expertise in such matters and will help guide you in a good direction.

Good listening
Bruce

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PostPosted: 05 Nov 2020, 03:11 
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Location: France
Tube/Valve phono stage ideas for the 21st century :

I plan to rebuilt a tube phono preamp... One of these days... I remember that the SRPP Anzaï worked fine.

In the SS departement, Realistic/Radio-Shack sold in the past a little box that was a phono adapter. In this box, there was nothing but the copy of the excellent Marantz receiver 2250B / 2275 phono RIAA circuit !

I still have them, rehoused with complete facilities :

Image

Cheers,

-tbln.

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PostPosted: 05 Nov 2020, 03:28 
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@gofar99 very true, the words RCA receiving tube manual and 21st Century probably don't go together in the same sentence. That circuit does roll off the accepted low and high frequencies a bit early. Listening to tube amplifiers is like holding on to the past. @tubelectron - I should look around some of the second hand stores. I might find an old amp having a phono stage at a reasonable price.

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PostPosted: 05 Nov 2020, 08:55 
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Hi, Cute little preamp. I actually own both a Marantz 2250 and a 2265B. Both are excellent performers but I like the sound of all tube gear. I currently use a pair of pre-production Groove (name not really determined yet) phono preamps, a passive line stage and a quad of mid size Oddblocks. I also use on a daily basis a Marantz 1060 integrated amp in my computer room/ shop. Nearly as nice with features like lots of inputs etc that get used as a test amp as well.

Good listening
Bruce

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PostPosted: 29 Nov 2020, 05:35 
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while googling tube phono and RIAA I came across the attached circuit. Bruce and others, I would value opinions on how this would perform with a Shure V15 III cartridge? I would prefer to keep it simple and tubes, but wiling to head down the opamp path if necessary. I think this is a Broske design according to the link which I will add when I can find it again. edit: http://www.beigebag.com/case_riaa_1.htm


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PostPosted: 30 Nov 2020, 02:32 
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I built this one a couple of years ago and it is my daily driver. Very quiet if you pay attention to your build techniques.

I put the power supply in a separate case and regulated the output with lr8 regulators/HV pass transistor. The heater current is dc as well.

I used 6n23p tubes as they have a screen between the two triodes that can be grounded to eliminate noise between the two. It can all be built on a relatively small piece of perf board, which is the method that I used and then placed it into a copper shielded cigar box. Worked like a charm.


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