Building a phono preamp

[trains are bad]

I'm thinking about building a phono preamp for a physics lab project. Possibly a tube amp, although I'm not sure about what kinds of tubes you need and how available they are...I don't want my costs to skyrocket.

I'm just wondering how difficult this would be and if anyone had any resources that might be helpful.

BTW I have access to scopes, fuction generators and the like. And we have an entire large drawer full of old vacuum tubes.

 

[nikongod]

bottlehead makes a sweet kit. it comes with the first pair of 6dj8 (not too rare, and available inexpensively for decent quality) tubes.

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^^that ^^ site also has some info, and what looks like good schematics if you want to use opamps.

click
^^that^^ site has some good info on the HISTORY of RIAA and how to calculate the newtork values (for a passive filter anyways)

 

[joe_cool]

If you want low noise, consider a JFET amp. It can sound very smooth like a triode and uses a lot less power. I can offer a schematic if needed.

 

[jiiteepee]

Hmm... maybe out of subject a bit but, did you try this already?

jiitee

 

[trains are bad]

Quote:

did you try this already?

It's not that I actually need a phono preamp. My amp has a phono input. It's just that I need a physics lab project, and thought a nice tube stage would be a good one. I can make the enclosure, design the circuit board etc.

Quote:

If you want low noise, consider a JFET amp. It can sound very smooth like a triode and uses a lot less power. I can offer a schematic if needed.

Yes that would be awesome. It will be more legit if it's a novel design or something...building a kit like the bottlehead is a bit weak if you know what I mean. I don't think I have to reinvent the phono stage, but building one from a schematic on my own board with my own components and such would be more likely to be approved.

 

[luvdunhill]

personally, I'd look at modding the Pass Pearl as there are a lot of areas that could benefit from some tweaking.

 

[Vertigo Acid]

http://www.dogstar.dantimax.dk/tubestuf/sapindex.htm
I'm building one right now. There are improvements to be made with regards to SQ (capacitors in the signal path, for example), but, overall it seems to be a solid design

 

[Uncle Erik]

You might want to buy a copy of this book:

http://www.transcendentsound.com/audioreality.htm

It has a nice all-tube phono preamp as well as plans for a tube preamp and three amps.

I've got all the parts for this phono preamp, however, time has been lacking. But soon. It's on my list as the next project. I think I've got about $200 into it so far.

 

[JWFokker]

I don't know if you want point to point, but you can get a PCB based DIY phono preamp from Hagerman Technology, the Bugle. It's $39 for the PCB, and I'd say $30 or so for the parts from Digikey. It's an excellent performer. A prebuilt Bugle goes for $400, to put it in perspective.

 

[joe_cool]

This circuit is copyright Rockford-Fosgate Corporation (Hafler 915 Preamp). Out of production for many years but noteworthy for several reasons.

The input stage avoids differential inputs to reduce the noise by 3db (this is basically a current-feedback design).

Each half of the complementary input stage is loaded by an FET connected as a "gyrator" to provide higher gain at low frequencies.

The second stage is also the output stage. Complementary (push-pull) class A.

The circuit will support moving-magnet and moving-coil phono cartridges.

Signal to noise ratio is rated at -87 db referenced to 6 mv rms input (MM at 1 kHz, gain = 38.4 db).

 

[luvdunhill]

Here is a schematic and design discussion on the Pass Labs Pearl:

http://www.passdiy.com/pdf/pearlphono.pdf

Also, the more complicated Pass Ono schematic is also out there, as it's another retired design that Nelson Pass has made available to the DIY community.