Tube Phono Equaliser

“Hounddog”

Page 1, Why another tube preamp?

Last modified: 10 November, 2006

Tube Prepre

After I finished the Scratch phono pre I had a critical look at the result and made a few remarks for myself:

• Although the Scratch amp had been easy to build and played at the first try, lots of effort went in modifications in order to get the amp silent without humm or hiss.
• I noticed that I spent my money on an enormous housing end expensive components. I wanted to be sure that without such expensive components I would finish a next project just as easily. After all, phono equalisers are difficult animals as they are very sensitive to noise.
• The scratch phono pre has a passive RIAA filter, which is probably the best on paper, but such a project requires expensive components, complex power supply and extra care with the layout.
• I needed to know whether the same results could be obtained another way with less money.
• in other words: I wanted to learn about tube amps...

And there is only one way to get there: Get your hands dirty and build another one. This page tells the story of the second phono equaliser I built, with a totally different design as Scratch.

The pictures on this page show clearly how lightweight the Houddog is compared to Scratch (which it is standing on).

Active RIAA filter

As mentioned earlier on the Scratch pages, several designs for phono amps can be found on the internet. In order to bring some structure in my process of comparing different designs I made a list of requirements for this project:

• I wanted to cut down in costs. This meant: Cheaper components, but also making compromises where necessary.
• In order to save weight and space: No tube rectifier but "cheap" diodes and voltage regulators.
• Active RIAA filter. This would mean making use of negative feedback. It would make the amplifier less sensitive to oscillation etc. But would I be able to hear the difference?
• I will without doubt encounter several (new) problems when building this amp and I want to solve these myself. therefore, things should not get too complex yet.
• Related to this last requirement, I will again build an existing design. Who knows I will buld my own design next, but this time I do not want to take too much risk.

After studying several designs on the internet and in books I found the site of Fred Nachbaur (unfortunately, Fred's site is not on-line most of the time). Looking for a name for this pre-amp I noticed the name of Fred's company: Dogstar Music. I decided to make the dog sing.

Looking back on the building process (when writing this translation, more than a year has passed) I learned a great deal. For example: Copying another design 1 on 1, especially for designs from the USA , is nearly impossible.

Fred Nachbaur not only publishes the schematics on his site but you will also find background information on RIAA etc. on his site.

And this is how my Hounddog looks after being 90% finished. I have placed the (temporary external) transformer out of sight. I prefer mounting the ECC83 tubes horizontally since I have small humans living in our home and therefore everything getting hot or running on mains power goes behind bars.

Of-course it's a matter of taste, but I do really like th looks of this amp. Something not shown on these pictures are the small neon bulbs which are used. Seen through the openings of the housing are small Xmas lights. On page 3 is a picture that shows these little lights.

© Maarten&Annemarie, November 2002, 2006