Tube Phono Equaliser

“Scratch”

Page 1, Pre-Work

Tube Prepre

As explained on our hifi page: We prefer turntables over cdplayers when it comes to playing our favorite music. I did not yet count all my records, since we still have a lot of records that need cleaning. But I think we have more than 500 albums in house.

Because we do not especially like today’s music in the top-50 charts, we are happy with all music of the early 80’s being available on vinyl. And all the records are available for prices that are significantly lower than those for CDs.  And as I recently modified and tweaked my old Thorens TD-166mk1 turntable and built my own tube UL40-S2 amplifier, I decided that I needed a tube based phono equaliser to keep the analog feeling alive.

Commercially available tube pre-amps range in price from Euro 800 to Euro 1250 for a Unison Research “Simply Phono”. The last one is high on my wish list, and maybe this equaliser till will some day amplify my clearaudio turntable with DV17 cartridge. But at this moment, the Unison Research is just “simply expensive” and since it is meant for the study and not the living room so I decided to go for a more affordable alternative. Keeping both criteria, musicality and costs, in mind I decided that I may have to build my own phono equaliser.

Attack Plan

There are a few thinks to keep in mind, I learned, when building tube amplifiers yourself:

• When building without a Printed Circuit Board, one needs to have an idea about the final 3-dimensional construction in the air. This is my weak spot: I do have very little experience with building tube amps, and my first was the UL40-S” project based on a PCB.  I decided to prepare myself for this challenge by reviewing some projects of others paying special attention to this type of construction.
• All components, resistors, capacitors, tubes need to be of top quality. Humm or noise is easily introduced, especially when building a phono preamp. Fortunately, high quality new parts or new-old-stock parts are still available.
• There is not one supplier stocking all components needed, so it may take a while before all ordered items are delivered.  
• It pays to check Ebay and garage sales for components. It may save you lots of money.

Because my experience with building tube amplifiers is so limited, I decided to rebuild an existing project of someone else. I may choose other components, different tubes of another housing, but this gives the project my personal touch. On the other hand, I know at least that the thing “works” since someone has done it before.

scratch?

On the internet there are several projects listed that deal with building your own phono pre-amplifier. To mention a few:

• The phono prepre project of Fred Nachbaur
• Bob’s Vacuum Tube Phono Preamp
• Aleksander Kitic’s RIAA amplifier
• Thorsten Loesch’ Phono Amp “Toccata”
• The Phono and Line Pre-Amp of Erwin Wiesbaur
• Triode Dick ™ recently updated his scratch project.

The other day I had a chance to listen to Dick’s Scratch on his own Mitchell turntable and his SET amplifiers. Anyway, I liked the sound so much that I decided to build my own phonoamplifier from Scratch.

Just before I started my project, Dick has reworked his scratch a little and as a result it can be built with a tube rectified circuit in the power supply. I decided that this was the way to go … hopefully …

Links

• Tube formulas and spreadsheet; calculate output impedance, miller capacity, gain of tubes
• RIAA cookbook; how to build your RIAA filter even without SPICE tooling. With on the 4th page an analysis of Scratch' filter

© Maarten&Annemarie, November 2001

last modified on December 27, 2001