You shouldn't pay more than $200 for a Pas 2 or Pas 3 preamp in excellent condition. The Pas 3x is a little different. When the tone controls are in the center position the tone control circuit is defeated. These are entry level tube preamps at their best and sound their best with the Dynaco tubes which were actually relabeled Telefunkens. The sound is soft and lacking in dynamics compared to modern tube preamps. Many people have modified these preamps in the past usually by beefing up the power supply to improve dynamics and bass. The Dynaco was a very cheaply built product designed for a price point. For a little more money you can get a real preamp like Cary, CJ, Audible Illusions, VTL, Counterpoint or Music Reference. Stay away from the early Audio Research preamps. They usually have problems and it costs a fortune to have them repaired. I speak from experience. Good luck and happy listening.
To answer your question, the PAS2 and PAS3 are exactly the same preamp with different face plates and knobs. The 3X has different tone controls, which, if you are actually going to listen to the thing, rather than being a collector, is probably moot, as you would want to bypass them anyway. There was a running change where the output coupling cap in the line stage was increased in value. Again moot, as you would want to increase the value and use a modern film or oil cap. This is a great piece, if you want to learn to work on electronics and hack on gear. There are many inexpensive mods on the internet as well as completely re engineered circit boards by AVA and Curcio. Figure on $150.00-200.00 for the preamp and $100.00 to $500.00 for full mods.
You have been very helpful.
I run a Dynaco PAS-3X in my 'second' system (McIntosh 250 / Dynaco PAS / Dynaco AF-6 tuner / KEF Q60 speakers / Panasonic linear turntable and Pioneer CD player). The PAS is a very pleasant preamplifier and with a SDS Power Supply board, new coupling capacitors and tone control bypass it does a competent job. As mentioned above, it isn't exactly the most detailed or revealing preamplifer, but it is very musical. Perfect for less-than-stellar recordings and less than perfect audio systems.
They do have a high output impedance and work better with an amplifier of higher input impedance.
Again, there is no need to bypass the tone controls on the Pas 3x because the tone controls are bypassed when set to the neutral position. The Pas2 and Pas 3 do not have this tone defeat circuit, so you may want to bypass tone controls on those units.
I would respectfully differ on that point based on personal experience. If you jumper the PC-5 circut board, you will avoid all of the crap wire, and solder joints, running to the tone controls themselves. Trace the board and you will see that the signal runs from the board, to the tone controls and then back to the board. The tone controls can effectively take their wipers out of the circuit, but they can't take the wire running back and forth to the board out. Try it. I did on my PAS 3X, and was quite surprised. Not the difference made my bypassing the blend and balance controls, but good none the less.
I've been doing mods on the PAS preamps for 30 years. There is **plenty** of reason to bypass the tone controls! Even if set flat, the stock line stage lacks bandwidth and resolution. However the line stage circuit can be seriously upgraded such that the unit will easily keep up with many modern high end preamps.
The phono section is only good for high output MM cartridges, but it too responds readily to upgrade. If you have no plans of using it for tape, the EQ components can be moved to the PCB and the middle wafer on the input selector swich can be eliminated. There are also improved EQ values, and one of the coupling caps at the output of the phono can be easily eliminated too.
They are, IOW, great preamps if you plan to tinker or update. In stock form they are OK but nothing special. The 3 and 3x look a little nicer and that is the only reason to pay any more for them. The filter caps, both high voltage and filament, should be replaced regardless of your plans. I usually replace the filament rectifiers as well- the old selinium units are nasty.
I just picked up a Pas 2 that looks just like a Pas 3 so I assume it is a later production model. IMHO bypassing the tone controls is a instant upgrade.It eliminated a lot of noise and it is so easy to do anyone with any soldering skills can do it in no time at all.The benefits are huge!
I plan on doing many upgrades to mine,but first will be the potentiometer and the power supply.The power supply upgrade is very inexpensive and makes it a much safer piece,not to mention (from what I understand having not done it yet) a sonic improvement.
This is my first tube component in over 30 years of solid state sterility. So far it is nothing but fun to hack on and sounds amazing.Old and funky?sure, but it is cheap and fun for hacking and the sound is way better than any SS preamp I have ever heard.
btw Viridian and Ralph Atmos are very experienced and are guys to listen to.
Emorrisiv, here are some tips if you are interested:
try to retain the rectifier tube. Replace all the filter capacitors. Replace the selenium filament rectifiers with 3A low voltage silicon devices.
Tape has become more popular, but usually the tape machines have their own playback EQ. So its a nice trick to move all the EQ components for the phono off of the switch and onto the bottom of the board. You can also wire the phono input directly to the phono board as a result. This eliminates the need for the middle wafer on the selector switch.
I've made 24-position stepped volume controls for the PAS that have worked out quite well! If everything is done right this preamp can challenge a lot of modern preamps, but it will not do LOMC without a stepup device.
Ralph here is my progress and plans.
I have bypassed the tone controls. All the caps have been replaced.(orange drops from the looks of them)
I replaced the funky bad balance volume pot and disconnected the loudness feature.
I added a couple of 47k resistors to the volume pot to help the taper.(much better)
I have a stepped attenuator coming.
I have a power supply upgrade board coming to get rid of the rectifier, but keeping the tube.
I would like to eventually get rid of the blend switch and the tape eq for more inputs, but that is low on the priority list. I only listen to LP,CD,FM and I have enough inputs for those already.
I have my SUT connected but I had to go back to the 15:1 ratio because there was too much gain. No problem.
It sounds so good. I am in tube heaven. Those old Telefunkens are sweet.
I feel like I have never really known what "inner detail' meant. This has inner detail in spades. Not to mention timbre and presence the likes of which I have never known.
I have to mention that I got a lot of help from George Regenesis. He offers Dynaco upgrade boards and was a big help to me so he deserves a shameless plug here. He also has some of the best prices too.
Ralph, would this mate up with the Atmosphere's MA-1?
I really want to hear those amps.Of course I would need some Zero transformers too.
I can't wait to go back to work and making a living.
Emorrisiv, the PAS can drive our amps just fine!
There is a way to eliminate one coupling cap in the phono circuit. I usually build a new line stage as well- one that has no feedback. I usually retain the original power transformer (if the mods don't fit in the original chassis then you might as well start from scratch...). We also have a tiny high voltage regulator that does amazing things for the sound.
There are very few preamps that will sound better than a PAS if it is properly modified. Its kinda fun to have a giant-killer in the PAS guise :)
Ralph, that sounds like it could be beyond my beginner abilities unless I had directions.I think that the impedance values are kind of weird, but I can live with it for now.Very sensitive volume pot.
I saw that there is a guy that offers new "Spice" designed boards that incorporate 3 tubes on each board. Interesting!
Regenesis and Dynaco Doctor both offer new boards.
Are these updated circuits/caps or are they just replacements?
Emorrisiv, some are replacements, others are updates of one sort or another.
Since I don't like the unit to grow into multiple chassis, I keep the original power transformer and supply. That means that the line stage I have for it has to not draw more power than the original, which is important due to the limitations of the transformer.
If I were you I would start with simple mods and see how things sound. The nice thing about the PAS used to be that they are very simple, inexpensive and there were a lot of them. Nowdays they have gotten more rare, but they are still very easy to modify and I'm pretty sure its the most-upgraded/most-updated preamp ever made.
Just to chime in, if you disconnect the light bulb that serves as a pilot lamp, you will take a lot of current draw off of the power transformer, which is operating pretty hard as it is. Just remove it from the socket. If having no indicator bothers you, you can replace it with an LED. Directions are in one of Frank Van Alstine's bulletins. The time to do this would be when you replace the power supply as you will have easy access to the take off points.
For my money, those orange drop caps sound terrible, hard and splashy. For a few bucks you can crap can them and replace with Russian paper-in-oils or polyprop and tin foil. The difference will not be subtle, IMHO.
The Curcio boards are a complete reengineering of the circuit. I think the others are just new parts in the same circuit.