PAS preamp project

[ctjetta]

Long time, first time, as they say.

As a preface: I acquired a pair of AR 10pi's (were used with an 80's Denon receiver), realized they needed real power so picked up a HK Citation 16 for reasonable money. Now want a decent preamp of that era. Decided to go the tube route and the Dynaco PAS seemed the best alternative.

But have you seen what people are asking for them?! A good chunk of change AND THEN you gotta recap, replace the boards, and apparently some kinda mod to properly drive a SS amp. A tube amp down the road is always a possibility.

So let's start with a fresh chassis, a proper power supply, attenuators, etc . . . . But what about the actual circuits? Including phono. Bare boards, kits, fully assemble boards. Clones, Z-Mods, Curcio, Aikido. It's crazy, albeit in a good way. Would rather too many choices, after all.

So all that being said, I'm leaning towards the Z-Mod kits from Tube Nirvana, thinking kinda retro with proper upgrades. Anyone have experience with these circuits?

Can anyone suggest a reason (good or otherwise) why the Curcio, Aikido, or other version would be a wiser choice?

All opinions and suggestions are welcome/needed.

 

[peterh]

The best PAS is the original , in good shape of course.
Forget any addon ( except for a power board that replaces the Se rectifier and power cap), anythin else is a waste of time&resources.
If you want to spend more money i suggest that you start fresh, build a new preamp that fit's your taste.

 

[ctjetta]

The best PAS is the original , in good shape of course.
Forget any addon ( except for a power board that replaces the Se rectifier and power cap), anythin else is a waste of time&resources.
If you want to spend more money i suggest that you start fresh, build a new preamp that fit's your taste.

I'm sorry if I wasn't clear- I do tend to ramble on. I am starting with a fresh chassis (from Dynakits), et al . . . . Just need some guidance as to which line and phono circuits to place in my pristine, new, unmolested chassis. But I hear what you say- a "good" original would be nice. I would rather just build one to my liking rather than struggle to find one that's good and not outrageously priced.
Thanks!

 

[gadget73]

You don't have to replace the boards. They can be rebuilt most of the time, unless you want a different circuit or the originals are wasted. Used as intended and with properly working parts, the originals really aren't terrible.

Honestly if the plan is to put totally different guts in one, it doesn't make a lot of sense to buy an old one just to empty it and load it with all new parts. You may as well just buy a new chassis and start fresh. As to what to load it with, every product is better than every other product according to everyone

 

[peterh]

I'm sorry if I wasn't clear- I do tend to ramble on. I am starting with a fresh chassis (from Dynakits), et al . . . . Just need some guidance as to which line and phono circuits to place in my pristine, new, unmolested chassis. But I hear what you say- a "good" original would be nice. I would rather just build one to my liking rather than struggle to find one that's good and not outrageously priced.
Thanks!

Ok,
if you don't want a PAS then it's better starting with another chassies that has better place for power transformer etc. The weak point
with a PAS is the lack of excess power. There is no power to add more functions.

 

[ctjetta]

Ok,
if you don't want a PAS then it's better starting with another chassies that has better place for power transformer etc. The weak point
with a PAS is the lack of excess power. There is no power to add more functions.

Thanks, peterh.
Regulated PS's from Tube Nirvana or Dynaco Doctor are claimed to be good up to six tubes. I assumed either would be sufficient for the two line and two phono tube circuit. You may know better. I am considering- the Z-Mods from Tube Nirvana. I can still use a PAS chassis and follow the PAS architecture. I would like to stay close to the original intent of the circuit design. I will not be using tone controls however to simplify things. Nor loudness. And certainly not the stereo/mono function thingy. I know, it sounds less like a PAS the more I discuss it.
I am open to all suggestions regarding circuit choices.

 

[triode17]

ctjetta - "I will not be using tone controls however to simplify things." However, if you do, I can highly recommend using a circuit called "A Tone Control You Can Love" by Max Robinson. It's on the Funwithtubes.com website. This man knows his stuff. I hand built a tube preamp that has an analog selector, phono section, voltage amp, volume control, tone controls, mono/stereo switch finally followed by an Aikido cathode follower. It was built into a stripped Dynaco SS amp chassis similar to the PAS that I got on ebay for $35. Works so well that my PAS3x has been put into 'mothballs' for now.

 

[ctjetta]

You don't have to replace the boards. They can be rebuilt most of the time, unless you want a different circuit or the originals are wasted. Used as intended and with properly working parts, the originals really aren't terrible.

Honestly if the plan is to put totally different guts in one, it doesn't make a lot of sense to buy an old one just to empty it and load it with all new parts. You may as well just buy a new chassis and start fresh. As to what to load it with, every product is better than every other product according to everyone

gadget73, thanks for your input.
I am intending to use a new chassis from Dynakits. A regulated power supply, new I/O board, stepped attenuator volume and balance and pretty little red LED power indicator.
A "good" used PAS is not really doable due to cost and probable cap and PS needs. No point in rebuilding something that should be left alone. I don't want some Chinese thing.
I like the vintage nature of the PAS. I don't need the nth degree in whatever parameter you might strive for, be it detailing, spaciousness, inner nuance, et al. I'm just trying to take advantage of the circuit options available looking for opinions on those circuits anyone might have experience with.
Now that it's been said to go a different route entirely we can now avoid further similar comments and help me with my questions regarding the circuits available for the PAS preamp.

 

[Lavane]

I built one with a new pas chassis. But I wanted new. I used tube nervana dual power supply, ph10 phono board and Aikido line stage. On the front there is only an input selector, volume control and rotory power switch. It turned out nice. FM3 Zone had the face plate made as to what I wanted. It wasnt a cheap build, but im happy with it. Very quiet and clear sounding.

 

[airtime]

The best PAS is the original , in good shape of course.he Forget any addon ( except for a power board that replaces the Se rectifier and power cap), anythin else is a waste of time&resources.
If you want to spend more money i suggest that you start fresh, build a new preamp that fit's your taste.

Agreed !!!!!
The PAS is a great little preamp just as it is. All it needs is a good cleaning up and update that power supply.

Note: don't do the Curcio power supply board. There is a problem with the voltage regulator that I believe Joe never ironed out. Otherwise I would recommend anything else he has and he is a great guy as well.

 

[Lavane]

Agreed !!!!!
The PAS is a great little preamp just as it is. All it needs is a good cleaning up and update that power supply.

Note: don't do the Curcio power supply board. There is a problem with the voltage regulator that I believe Joe never ironed out. Otherwise I would recommend anything else he has and he is a great guy as well.

Do you know what the problem is? I bought the one with a thermistor and havnt had any problems so far. The reason I went with it is the Aikido has a higher current draw. The power supply for the Z-mod and other line stage boards wont work with the Aikido.

 

[ctjetta]

View attachment 851002 I built one with a new pas chassis. But I wanted new. I used tube nervana dual power supply, ph10 phono board and Aikido line stage. On the front there is only an input selector, volume control and rotory power switch. It turned out nice. FM3 Zone had the face plate made as to what I wanted. It wasnt a cheap build, but im happy with it. Very quiet and clear sounding.

Lavane,
That's more in the spirit of what I'm attempting. New chassis, I got a gold faceplate from an ebay seller (not the perfect layout, but I wanted gold). I guessing that the Aikido/ph10 is probably sonically superior to the Z-Mod boards but I'm thinking, could be wrong, that the Z-Mods might be warmer sounding while still providing an improved phono and lower impedance for a SS amp.
I could still be swayed toward other options, and you make a good argument.
Thanks.

 

[Lavane]

@ctjetta
The Aikido isnt what I would call, warm. But it is very clear and clean sounding. The PH10 phono board is the same as the PH10 that tubes4hifi sells, just a smaller package to fit the PAS chassis. The zmod power supply and line stage should go well with the PH10 board. Also as for the face plate, FM3 Zone will make one what ever color you want.

 

[daveg3588]

I know you want to build, but you have the Citation 16, the 2 finest preamps for this are the Citation 11/17. The phono sections are second to none!

 

[ctjetta]

[QUOTE="daveg3588, post: 10210483, member:controls]I know you want to build, but you have the Citation 16, the 2 finest preamps for this are the Citation 11/17. The phono sections are second to none![/QUOTE]
I have serious aversion slider style tone controls. I would love to havea Citation pramp. If I can find a 17 without them, I saw picture of one once, I would have that as well as the tube unit. It's important to hve options.

 

[ctjetta]

So, a few thoughts. Yes, we are fortunate to have a good number of choices available. But, if I correctly understand you to say that you want, in some manner, to stay close to the original intent of the [original] PAS circuit, then substituting a different circuit topology would seem inconsistent with this goal. Of course, it may depend on exactly what you have in mind when you say “close to the original intent.” Since you're building your PAS from scratch, please note that new copies of the original PC boards are available.

I wanted to stay close to the original design when I rebuilt my PAS. But, rather than substituting an altogether different circuit design, I kind of just “cleaned up” the original circuit to bring out more of its inherent sonic potential. More specifically, I took a minimalist, purist approach, e.g., removed the tone controls and other bells and whistles. Doing this removed the functional features but retained the basic original Dynaco circuit topology. I found the results quite good.

It is not hard to adjust the original Dynaco PAS circuit to drive a wider variety of power amplifiers than often thought. In fact, the “adjustment” to which I refer is simply an emulation of the original Dynaco PAS X-mod. I tried looking up the specifications for the Harman Kardon Citation 16. One copy of the manual I found specifies its input impedance at 10K ohms. According to the analysis done by Audio Regenesis, if the PAS tone controls are bypassed per their procedure, frequency response is down something like 1dB at 20Hz into a 20K load. I would not think this would be audible. It would be down a bit more into a 10K load, but, again, what’s the likelihood that it would be audible?

I’d suggest contacting Audio Regenesis to ask what they think about the PAS with the tone controls removed driving a 10K load. In fact, before making any decision, you might have a read through the recent Audio Regenesis studies of the PAS. IMO, these are the best, most constructive, unbiased and sensible studies available. They’re on the left hand side of the page http://www.audioregenesis.com/

petercapo, thanks for your thoughtful and informative reply.
I had read that at one time, but, not having a PAS in hand I didn't think about doing clone boards with the mod. I just assume I'd run with modded boards. Or if sufficiently persuaded an all new circuit. As you suggested I will reread that material and give it more consideration.

 

[kve777]

Here's something else to consider- a PAT-4 chassis. Lots cheaper than PAS chassis. Drill holes in the bottom cover for airflow and use brass standoffs to mount the boards. Simpler controls on the front. Better switches. Load the Power Switch with an LED. Another nice mod is to use the cover for an FM-3, for ventilation. You just need to trim the back, which only takes five or ten minutes. Runs way cooler so you get less value drift in caps and resistors.

 

[BinaryMike]

The PAS output impedance problem is easy to solve by adding sonically transparent SS buffer chips, at about six bucks each, and they can be powered conveniently from the heater supply. TI's LME49600 seems to be the current iteration of devices that I've used very successfully in the past for this job. It even has the grunt to drive headphone outputs if you like, and that certainly fits with the idea of using a PAT-4 chassis. BUF634 is available in DIP-8 and TO-220 packages and might be a little easier to work with, but I don't think it's been fully characterized for audio.

 

[daveg3588]

[QUOTE="daveg3588, post: 10210483, member:controls]I know you want to build, but you have the Citation 16, the 2 finest preamps for this are the Citation 11/17. The phono sections are second to none!

I have serious aversion slider style tone controls. I would love to havea Citation pramp. If I can find a 17 without them, I saw picture of one once, I would have that as well as the tube unit. It's important to hve options.[/QUOTE]
Its called a 17s, no tone control sliders.
https://www.hifiengine.com/manual_library/harman-kardon/citation-17s.shtml

 

[gadget73]

personally I just don't care for slide pots. They seem to get dirty easier than rotary ones.