this new product has been under development, and kept secret, for about 3 months now.
This product isn't for the average consumer, this is for someone that wants the ultimate tube phono preamp,
but doesn't want to pay $2500 or more for an Audio Research PH6 or PH8.
The PH16 is our latest and best phono preamp design. It was developed through many hours of research, refinement, and computer optimization of circuit parameters and circuit layout.
Our phono circuit is similar to that of the PH15, but with a new AIKIDO style output buffer, and is powered by a newly developed power supply that utilizes 4 independent voltage regulators, plus a pair of Constant-Current-Sources (CCS).
The 1st gain stage is our proven super-low noise JFET current source driving a 6922 amplification stage with the 50Hz and 500Hz poles of the RIAA filter. This staqe has a gain of around 50db.
The 2nd gain stage has the CCS as a plate load on the 6922 amplification stage with the 2122Hz RIAA pole of the RIAA filter,
and has a gain of around 45db. The CCS acts to stabilize the impedance and thus insure more accurate RIAA EQ, as well as increase gain in this stage by a factor of 2.
Both of these stages are supplied with a regulated B+ voltage, one for each channel.
A passive RIAA network will have insertion loss that varies with frequency, with roughly 0 dB loss at 20 Hz, 20 dB at 1 KHz, and 40 dB at 20 KHz. ,
With the RIAA EQ, has a loss of around 40db, the overall gain at 1 KHz is now around 55 dB.
The 3rd and final stage is comprised of an AIKIDO style output buffer, with it’s build in PSRR circuitry,
and this is also supplied with a regulated B+ voltage, one for each channel.
This stage gives a low output impedance of around 330 ohms and isolates the phono amp from interconnects and further amplification.
This circuit design produces far less distortion than comparable circuits by using complementary, balancing load design. By loading a triode with the same triode, under the same cathode-to-plate voltage and idle current
and with the same cathode resistor - works well to flatten the transfer curve out of that triode. The circuit reduces power-supply noise from its output, by injecting the same amount of PS noise at the inputs of
the top and bottom tubes in the two-tube cathode-follower circuit. Since both of these signals are equal in amplitude and phase, they cancel each other out,
as each triode sees an identical increase in plate current. The improved PSRR advantage greatly unburdens the power-supply, and results in a better than -30dB PSRR figure.
The B+ regulators also reduce PSRR by about 60db, with near zero ripple current from the power supply
Overall, this design delivers the sonic goods. It offers high amplification, super accurate RIAA EQ, low distortion, low output impedance,
a great PSRR figure, and feedback-free amplification.
The secret to its superb performance— despite not using global feedback— lies in its internal symmetry,
and it’s channel to channel isolation resulting from using 4 independent B+ regulators.
This board has DIP switches to set the correct load for the input cartridge.
For use with MM (moving magnet) type cartridges, switch S1-B should be set to the ON position to give the correct 47K load.
All other switches should be in the OFF position.
If you want to experiment with loading, using S1-A (68K) will give a slight tilt up on the higher frequencies. Using S1-C (33K) will give a slight tilt up on the lower frequencies.
For use with MC (moving coil) type cartridges, refer to the manufacturers recommendation
for your specific cartridge. About 80% of MC cartridges are spec’ed to be used with a 100 ohm load on the input,
that would be S2-H set to the ON position, and all other switches OFF.
Depending on your cartridge and your phono interconnect cables, you may need to add resistance (switches S2-D thru H give a range of 100 ohms to 1000 ohms) and/or capacitance
(although this is rare) which would be using switches S3-X thru Z give a capacitance range of 33pF to 201pF.
The resistors are all in parallel with the input. Resistances combined in parallel give a lower value (100 and 221 in parallel give a load of 69 ohms).
The capacitors are also in parallel with the input. Capacitances combined in parallel give a higher value (68 and 100 in parallel are added together to give 168pF).
I have built and tested two of these, and have sent them to my partner Troy for some final tweaking and his independent objective review.
Since he has built many PH15s for me, and has his own PH14 as well as some other custom built preamps, he has the knowledge and experience,
and listening comparisons that no one else can do at this time.
This product is more suitable to buyers who have MC type cartridges, as the gain is 55db, way too much for MM type cartridges,
although it might be a good match if you want to directly source just MM and CD inputs as then the voltages to the amp will be similar.
Even better news, the price will be the same as the PH15, at least on these first two builds, $795 fully assembled and tested.
Below are a couple of preliminary photos (same chassis and appearance as PH15 & PH14) and one interior view.
Kit price is unknown at this time, as our chassis supplier had a major warehouse fire last month and we won't have more chassis until
at least mid-May. Also we may need to substitute the power transformer as those are from the same supplier, and out of stock.
I would though like to find out how many people might be interested in this product so I can plan on how many circuit boards to order.
Last edited by tubes4hifi on Tue Mar 19, 2013 2:13 pm; edited 1 time in total