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Dynaco PAT 4 Pre-amp...Why is it bashed?

R

Rocky1313

Active Member
I just bought this Dynaco PAT 4 pre-amp.
Paired it with Emerald Physics Class D 100.2 SE Amp.
And SPEAKERS :
Mark Audio Full Range P12
I am puzzled why there are so many negative comments being posted
regarding this pre amp sounding harsh and bright.
It sounds good to me,...clear and detailed.
Any PAT 4 Users comments or input ?
No modifications to pre amp ...(In Stock Condition only)
Thank you
 
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Well, it is a solid state pre-amp and this is the tube Audio forum. I think you will get more meaningful responses in the Solid State Forum.
 
I owned one some years ago. Wasn't impressed by it. To my ears it imparted a more compressed, flat'ish sound. I think I sold it for around $75.
 
Rocky1313 said:
I just bought this Dynaco PAT 4 pre-amp.
Paired it with Emerald Physics Class D 100.2 SE Amp.
And SPEAKERS :
Mark Audio Full Range P12
I am puzzled why there are so many negative comments being posted
regarding this pre amp sounding harsh and bright.
It sounds good to me,...clear and detailed.
Any PAT 4 Users comments or input ?
No modifications to pre amp ...(In Stock Condition only)
Thank you
Click to expand...
It sounds and measures fairly well.
What could be done to reduce dist is replace the final transistor with a darlington
( forgot the type , mess me if you want to know )
I have nothing against it.
 
peterh said:
It sounds and measures fairly well.
What could be done to reduce dist is replace the final transistor with a darlington
( forgot the type , mess me if you want to know )
I have nothing against it.
Click to expand...
There is a thread somewhere about changing the transistor and a few other parts to make them sound better. There is or was even a small inexpensive kit to improve them including the phono stage. They aren't horrible, but can be made to sound a bit better. I had one for awhile that I played with.
 
The active circuitry in it is extremely simple and the transistors used in it are notoriously noisy. A little googlin' will turn up inexpensive ways to improve it substantiall.
"As is"... well... it looks nice. I have one which was given to me by a kind AK member a few years back.
The PAT-4 isn't as harsh sounding as the Crown IC-150.
 
The PAT-4 is really a PAS circuit with transistors substituted for the tubes and appropriate changes made to the feedback component values as required. In other words, no ICs -- just a two stage (i.e., two transistor) design for both the phono and high level sections just like the PAS. It even uses the exact same volume control as the PAS uses. True to the simplicity but excellent performance of the Dynaco brand, it was a rather ingenious way for the company to --easily enough -- jump from tubes to transistors -- a move that sank many other audio companies of that day. The transistors are (obviously) from the 60s and are no match for today's components, but can be changed out easily enough for much quieter operation, and with a darlington final, improved performance, too. I use one for grunt work and it does its job admirably enough. The biggest issue I have with them is the durability of the bass control. They fail easily enough and often enough such that every one I've ever seen would not reliably maintain a flat setting due to failure of that control. Cleaning didn't do any good -- the track just wears out quite easily. And of course, replacements are made of unobtainium. I was able to makeup a suitable conventional control that works quite well, but requires a slight loading adjustment on the output so that a flat setting produces a truly flat response.

Dave
 
I had major issues with the tone controls on mine. They seemed very peaky on either side of that "flat" centre position, and in that centre position mine was horrible sounding.

Once adjusted, I thought it was pretty good and had that classic Dyna vibe.
 
Here's something interesting, as was already mentioned the phono and line sections
have 2 transistors per channel. They operate in single ended class A, whereas most
OP amps are class AB and have a hard time driving low impedance loads. The
transistors were selected for low noise where important, yes you could do much
better today but not bad for the time. The output transistor runs hot as it should
for class A. There are a lot of cheap electrolytic caps in the signal path, that should
probably be replaced at this point.
I don't see anything wrong with the design, it also measured well.
It was designed before they discovered that the RIAA section should be accurate
within .25 dB of the spec so it is only about 1 dB to spec and there are a few values
to change to make it better.

I built a few of them as a young kid.
 
Lavane said:
There is a thread somewhere about changing the transistor and a few other parts to make them sound better. There is or was even a small inexpensive kit to improve them including the phono stage. They aren't horrible, but can be made to sound a bit better. I had one for awhile that I played with.
Click to expand...
I used BC517 as replacement for Q4.
 
I should add that there were many articles on improving and correcting the RIAA
curve back in the 70s-80s in SB and AA.
 
I built 2 Dyna PAT-4 s as a young kid, I also copied the design from scratch into
an amp that I was building and later worked on them for friends. I'd never seen a
review back in those days and stumbled onto this last night:
https://www.stereophile.com/content/dynaco-pat-4-preamplifier

I was shocked to read this by JGH:
"One extremely critical test of any preamplifier is the "bypass test," whereby the sound coming out of it is compared with the same sound fed directly from the signal source into the power amplifier. We have never yet found any preamp that did not add at least a subtle coloration—a little extra bass or a little added high-end roughness—to the sound, although the PAS-3x and the Marantz 7C (not the 7T) came as close to perfection as anything we had ever tested. Now, both of these have been bettered—sonically, at least.
With all of its tone controls and filters set to Flat, and feeding any high-level input, we were simply unable to tell whether we were listening to the original "raw" signal or the output from the PAT-4. In this respect, we cannot see how any preamp, present or future, could surpass the PAT-4."

Of course they had to backtrack in a follow-up because you can't have a cheap ($69)
preamp out performing the super expensive models.
This supports the claim that a properly designed solid state amp, operating in the linear
region has no sound of its own.
I have an A/B switch and have done this sort of experiment many times.
 
Pete B said:
Here's something interesting, as was already mentioned the phono and line sections
have 2 transistors per channel. They operate in single ended class A, whereas most
OP amps are class AB and have a hard time driving low impedance loads. The
transistors were selected for low noise where important, yes you could do much
better today but not bad for the time. The output transistor runs hot as it should
for class A. There are a lot of cheap electrolytic caps in the signal path, that should
probably be replaced at this point.
I don't see anything wrong with the design, it also measured well.
It was designed before they discovered that the RIAA section should be accurate
within .25 dB of the spec so it is only about 1 dB to spec and there are a few values
to change to make it better.

I built a few of them as a young kid.
Click to expand...

Looking at the phono stage, tone boards, first stage amplification, would there be a possible improvement expected by replacing resistors to modern design?
 
I believe that there were a few resistor value changes that would tighten up
the RIAA curve. Dyna did use metal film resistors in the locations where it
mattered. Best would be to make them all metal film 1% value if it matters
to you. But it is a lot of work for little if any difference in the sound other than
tighter RIAA.
 
Last edited:
Tom Bombadil said:
I owned one some years ago. Wasn't impressed by it. To my ears it imparted a more compressed, flat'ish sound. I think I sold it for around $75.
Click to expand...

Same here, moved on to way better stuff ages ago. Traded mine away along with the matching Stereo 120 power amp and don’t miss either of ‘em. I remember it sounding kind of lifeless and grainy, also a lot of loud popping through the amp when changing functions (especially when switching to/from phono position). I did try it with other power amps before I finally got rid of it, no real improvement. I do appreciate the historical significance of it though and with improvements mentioned above I’m sure it would be a great little preamp. If I still had one that’s probably what I would do with it.
 
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