Dynaco PAT-4 preamplifier Manufacturer's Comment

Manufacturer's Comment

"...but you can't please all of the people all of the time." We'll admit we've had some complaints on the spring-loaded monitor switch—and some of the language has been a bit colorful—but if that's our most grievous error in 14 years, we don't feel too badly. For normal tape listening, of course, the selector switch rather than the monitor switch selects the same back-panel tape inputs. (This facility is not provided on other preamps that have a tape monitor switch.) We feel the arrangement on the PAT-4 is a logical one for most users, who play tapes more often than they record them. For those to whom the monitor function is important. we can supply the non-spring-loaded switch, as the Stereophile mentions.

The PAT-4 does incorporate a below-20Hz rolloff on the phono input to reduce potential rumble and acoustic feedback problems with solid-state amplifiers capable of delivering high powers at subsonic frequencies, and to eliminate transistor "flicker noise." It is one of the prices of "solid state progress" which was unnecessary in the days of tubes, but we do not see how this sub-bass rolloff could be audible, since there is probably no musical content below 30 Hz on any phono graph recordings. One reason why the PAS-3x is still available is because, in some subtle way, it does sound different, but we have no test data that would account for this difference.

As to the tone control action, we feel the advantages of this design outweigh its disadvantages. The tone control action is actually no different from that of the PAS-3x, but since it is concentrated in a smaller arc of rotation, it may seem more abrupt. The newer control system (as used in the PAS-3x and PAT-4) is, as the reviewer appreciates, flat in the center position, and it makes the unit independent of its load so that it will function equally well feeding either a tube or transistor amplifier.

As the PAT-4 manual states, if the high-level phono input is ever needed, Dynaco will supply information and parts for a minor change to assure optimum equalization (at the expense of altering the low-level input). So far, we have had only 3 or 4 such requests. The excessive noise level noted by the reviewer is most likely caused by a noisy front-end transistor, which should be replaced, though the noise will necessarily be more apparent on the high-level phono input because of the higher-impedance circuitry there. As the reviewer mentions, there are no currently made phono cartridges that can overload the low-level input, so there is practically no need for the high-level input anyway. It is included solely in the event that any future cartridges will require it.

Sound quality, though, is what makes "high fidelity," if not The Ultimate preamp. That's why the PAT-4 has succeeded in pleasing most of the people all of the time and all of the people most of the time.

Dynaco/Radial Engineering, Ltd.

dc_bruce's picture

The successor -- the PAT5 -- was Dyna's first effort to use an integrated circuit. The original IC resulted in a not very musical sound; a replacement was offered that sounded much nicer. Interestingly, the PAT5 did away with the spring loaded monitor switch.

My PAS3X was probably a bit more "musical" but seemed more noisy. That could have been from the tubes (which used an AC filament supply) or it could have been from the fact that all of the wiring was point-to-point, increasing the potential for cold solder joints or suboptimally routed wires.

jmsent's picture

...was DC not AC. The PAT-4 was crap, plain and simple. It didn't have a regulated power supply, so anytime someone switched on a high wattage appliance, you'd get a big dc level shift at the output of the preamp. The whole circuit was only 4 transistors/channel, basically, a transistorized version of a PAS 3X. But the reality was, the sound quality wasn't near as good.. The PAT5 did use a "second generation" op amp in the line stage and a 2 transistor phono stage. And at least they.used a regulated supply. The Bi-Fet versions were a small improvement. Still, by this time, Dynaco stuff was no longer the great sounding audiophile bargains that they were famous for in the vacuum tube era.

Michael Fremer's picture

I agree! I had a PAS-3X and a stereo 120 combo. I loved it. The 120 was kind of hard but the PAS-3X was a perfect compliment. As soon as the PAT-4 came out I bought and built one. I hated it! So much so that I called Dynaco to ask if something might be wrong...... the whole thing was wrong....

dc_bruce's picture

If memory serves, now that I think about it, the B+ was supplied by a tube rectifier and a selenium diode handled the filaments supplies. I had the PAS-3x paired with a Stereo 70, which sounded quite nice until the output tubes aged a bit. I sold them as a pair, got an integrated; and sometime later got the PAT-5 (with a Stereo 400). By that time, I had changed speakers several times and really couldn't compare it with the PAS-3x.

Jack L's picture


For sure transistors never sound as good as triode tubes, IMO.

Why? Transistor, or technically a bipolar junction device is NOT as linear as triode tubes, used in PAS2 & 3, which get a full set of linear signal transfer curves vs all bipolar junction devices get nonlinear transfer curves which are each bent down by a kink or 'knee' ! This is physics.

That's why all my design/built photostated/linestages & power amps only installed with triodes, period. 'Cause they are MUSICALLY friendly.

My question is: what was the problem of using only 4 transistors for the PAS-4 ?? Circuit design simplicity is MUSICALLY correct though it may not be so "polically correct" to many in marketing & sales of the products.

J Gordon Holt already commented PAT-4 was one of the best sounding preamp with minimum tonal coloration vs a straight line bypass. I wholeheartedly agree to his comment !! He knew what he was talking.

PAS-4 was built of 4 transistors per channel consuming so little power. Voltage regulation was indeed not necessary considering it was it was low power era half a century ago.

To many designers who design audio amps with op-amps being considered high-tech & 'fashionable'. I would never like their sound let alone installing them in my audio amps.

An op-amp is built up with many bipolar junction devices, e.g. transistors, & FETs with tons of global loop feedbacks.
Yes, they may be measured great great, but IMO, are not musically correct at all as the music complex harmonics got to pass through the many many capacitive bi-polar junctions & feedback loops. It is 'pain' for music signal to go through. This is physics.

Listening is believing

Jack L

RH's picture

Interesting read.

I've always liked reading Gordon Holt's old reviews. He's a very good writer: very crisp, and never holds any punches. In contrast audio reviews these days seem to do a tip-toe dance around negatives about a piece of gear. It's usually "wonderful, wonderful, wonderful..and then saved for the end 'well there's this teeny little negative thing, but I don't think it will bother most people.."

Holt just jumps in and I never get that feeling of reticence or holding back on criticism.

Jack L's picture


Yup. So many commercial journals bank on their sponsors & advertisers & do not want to publish anything deemed offending.

That's why Gordon earned my profound respect in holding himself accountable to his readers in his audio reviews - honest & straightforward !!

He might be deemed 'politically incorrect', but so what ? Apparentlly he did not give a rat ass.

Jack L

a.wayne's picture

They work best in homes with more than 2 breakers .. :)

Jack L's picture

.............. when reproducing phono inputs" quoted J Gordon Holt.


The bass boost was intended so in the PAS-3x phonostage circuitry design.

When you read carefully the schematic of the phonestage, there was a 47KR resistor bridging the cathodes of first stage (1/2 12AX7) & 2nd stage (1/2 12AX7), forming a POSITIVE loop feedback as both cathodes were IN phase.

I have not yet seen similar positive feedback design in tube phonostage ever since till todate. I recall reading this bass boost design for PAS-2 & -3 phonostage published in some journals.

Jack L