Class IX PP1 Vacuum Tube Phono Preamp

This circuit is based on the famous Marantz 7C vacuum tube audiophile preamp's phono section. This is not your average phono preamp circuit. Extensive development and reliable product support go into each one I produce. Isn't it about time you owned the best?

Simple connections. Add 285VDC and 245VDC, 6.3V heater voltage, input and output jacks and you're in business. High retention ceramic tube sockets prevent tubes from accidentally shaking loose from their sockets. RIAA equalization and the superb build quality of this assembly allow you to fully enjoy your vinyl collection in a way you have never heard it before. Amazing detail, ultra smooth response and the classic sound of vacuum tubes. Who could ask for more.

This circuit is closely based on the Marantz 7C phono circuit. Of course the physical size of components available to Marantz in the '50's and '60's wouldn't have allowed them to build such a compact assembly. The circuit board measures only 2" X 6" and can be mounted on the horizontal or vertical plane. Tubes required are 2X 12AX7 and 1X 12AU7 (or use 3X 12AX7 just like the original circuit). You can run the heaters on DC or AC. You'll get less hum with DC of course. In fact, the special front end shielding plate mounted on the solder side of the circuit board (not shown) coupled with full ground plane on the component side of the board will reduce EMI to a practical non-existent state.

NOTE - Vacuum tubes are not included with this circuit assembly and are shown only as examples in these photos.

The circuit board is constructed of double sided 1oz foil hot air leveled FR4 glass. All connections are plated both sides for exceptional component retention regardless of heat or vibration considerations. Easy impedance adjustment is accomplished by moving the selector shunts to the required impedance position. You have a choice of 22KOhm, 47KOhm and 100KOhm input impedance positions to match your preamp to virtually any moving magnet (MM) cartridge. All components have been specially selected for stability, tight tolerance and low noise. This is a premium quality circuit ready to give you the ultimate experience in phono listening enjoyment for many years to come!

Input impedance is easily set to 22KOhm, 47KOhm or 100KOhm by moving jumpers to the desired setting

Consider picking one of these up. Availability is very limited. The build quality is outstanding and the hookup is simple, especially if you have any experience with vacuum tube circuitry. This is a fully assembled unit and all you need add is power, tubes, and input and output connections. Makes a perfect companion to any DIY tube line amp stage. Start listening to your vinyl and enjoy it once again!

The ideal RIAA equalization curve must be adhered to as close as possible in order to ensure a high performance moving magnet phono preamplifier. Many solid state equipment manufacturers employ complicated circuit designs to comply with the RIAA standard. Designs range from relatively simple transistorized circuits to complex digital signal processing, yet the good old 7C design from way back in the '50's keeps it simple yet accurate. This design had it right in the first place, but engineers and audiophiles alike insist on re-inventing the wheel and have done so since the 1950's. Does it make any sense at all? I'm a follower of the "If it ain't broke, don't fix it" school of thought.

The diagram below represents the ideal RIAA (Recording Industry Association of America) phono equalization curve. The chart following the diagram outlines the frequency points and gain characteristics for the ideal RIAA response and actual readings taken from a typical PP1 preamp module outfitted with three 12AX7 vacuum tubes as measured on a Hewlett Packard 3582A FFT spectrum analyzer. Note the slight variances in gain between the ideal equalization curve and actual readings. In fact, the larger differences, or errors if you wish, are attributable to variances between voltage samples taken by the spectrum analyzer. The input voltage to the PP1 is random white noise flat across the audio spectrum. The analyzer is set to display RMS readings with Hanning filter response.

FREQUENCY (Hz)	IDEAL AMPLITUDE (dB)	MEASURED AMPLITUDE (dB)	FREQUENCY (Hz)	IDEAL AMPLITUDE (dB)	MEASURED AMPLITUDE (dB)
20	19.3	19.5	800	0.7	1.3
30	18.6	18.8	1000 ref set	0.0	0.0
40	17.8	17.9	1500	-1.4	-1.5
50	17.0	17.3	2000	-2.6	-2.8
60	16.1	16.7	3000	-4.8	-5.3
80	14.5	15.1	4000	-6.6	-6.7
100	13.1	13.2	5000	-8.2	-8.5
150	10.3	10.1	6000	-9.6	-9.8
200	8.2	8.1	8000	-11.9	-11.3
300	5.5	5.3	10000	-13.7	-13.8
400	3.8	4.0	15000	-17.2	-17.6
500	2.6	3.4	20000	-19.6	-19.6

This is a sample of what the white noise output signal looks like. The screen was captured on a Tektronix 7D20 digitizer. The PP1 was designed using top shelf test gear from Tektronix and Hewlett Packard. No detail was taken for granted in order that I would be able to provide you with the highest reliability product at a price that compares with cheap imports. I know you'll be pleased with the construction, performance, and ease of installation of the PP1 phono input preamp module. The hard work was done ahead of time so that you wouldn't have to do it. Simply mount the circuit, connect to your power supply, add tubes, then use the time you've saved to enjoy your music!

The Hewlett Packard 3582A screen is displaying measured frequency response of a PP1 phono preamp module. Random white noise is applied to the input of the preamp. The spectrum analyzer display settings are 10dB per vertical division and 2.5KHz per horizontal division. Frequency bandwidth displayed is 0Hz to 25KHz. Total overall amplitude differential is just under 40dB with the 0dB reference at 1KHz as indicated by the marker. Note that this display looks somewhat different than the ideal RIAA curve above. The ideal equalization diagram is based on a logarithmic horizontal scale whereas the spectrum analyzer display is a linear scale.

"Ken, I hooked everything up yesterday and success!! The measurements at load (after the supply has been running a half hour): heater is 6.32, the 245v tap is 248 and the 285v tap is at 278. The pre amp with the tubes installed was connected to my stereo at the time, and WOW. Fired right up. I played several "quality recordings" LPs I'm very familiar with and your board passed the acid test - huge, deep sound field and I was hearing details I'd never heard before. And like the best audio equipment, as it's burning in the output quality is getting even better.

Thanks so much for your help and letting me add a killer phono stage for pennies compared to what a comparative pre-built version of this quality would run. Several months ago, Stereophile magazine ran a review of a phono stage that like yours "was closely based on the Marantz 7C" and uses the same tubes. Like the version I built it also comes with a separate, stand-alone power supply. All at a price of almost $4,000 USD!! "

Yes, you'll be able to have a peek at how serious audio hobbyists around the world are packaging their PP1 preamps as well as getting some construction ideas and tips. Stay tuned!