I decided to start spinning some vinyl again and am going to rebuild a Pas 3 I have lying around for a phono section. I would like to do to it what the 3X does, in that the tone controls are defeated when set in neutral. Is it a matter of pots or an extra piece or 3 that I can add when I recap and clean this thing up?
At this point I would rather leave the abilty to adjust the tone if I want an option, so I don't want to just bipass that section. This might have been brought up before but the search engine will not let me use 3X, or 3 or X.
At this point I would rather leave the abilty to adjust the tone if I want an option, so I don't want to just bipass that section. This might have been brought up before but the search engine will not let me use 3X, or 3 or X.
hi
here's a few links
overview:
http://home.indy.net/~gregdunn/dynaco/schneider.html
some details:
http://home.netcarrier.com/~rstevens/pas.html
more rebuilding than you're possibly in the mood for:
http://www.normankoren.com/Audio/Spice_preamp.html
otoh, if it ain't broke - don't fix it! i have 2 of the the PAS-3X's one which is reasonably stock (only the power transformer has been replaced by an off-board beefy UTC unit and some AC filtering + Selenium stack replacement + scratchy volume knob replaced with rat-shack pot), and the other one rebuilt so much that it is barely recognizable as a PAS-3X (most of the modifications in the 3'rd link above have been implemented).
although they do sound a tiny bit different, i *still* can't decide which one i prefer more! i believe that the PAS-3X is one of those classic designs, where the merits of the design means that choice and quality of passive components makes only marginal difference to the sound.
to summarize, i would recommend only
- safety upgrades (i.e. a fuse + IEC power cord + selenium rectifier replacement),
- a beefier transformer to extend the tube life (the original PA-211 is very noisy and leaves the tubes current starved)
- possibly faulty components like scratchy pots replaced etc.
also the original telefunken 12AX7's *ARE* an integral part of the PAS-3X's sound so i'd recommend hanging on to those. i've tried many other tubes but the original telefunken's are simply the best by far. NOS 5751's are also nice (much lower noise, useful in the phono stage) but have distinctly different dynamics.
sorry for the long rambling post....
-pradeep
ps: also curcio audio , van alstine etc sell most of the replacement/upgrade parts and a lot of their mods are downloadable off their web-site.
here's a few links
overview:
http://home.indy.net/~gregdunn/dynaco/schneider.html
some details:
http://home.netcarrier.com/~rstevens/pas.html
more rebuilding than you're possibly in the mood for:
http://www.normankoren.com/Audio/Spice_preamp.html
otoh, if it ain't broke - don't fix it! i have 2 of the the PAS-3X's one which is reasonably stock (only the power transformer has been replaced by an off-board beefy UTC unit and some AC filtering + Selenium stack replacement + scratchy volume knob replaced with rat-shack pot), and the other one rebuilt so much that it is barely recognizable as a PAS-3X (most of the modifications in the 3'rd link above have been implemented).
although they do sound a tiny bit different, i *still* can't decide which one i prefer more! i believe that the PAS-3X is one of those classic designs, where the merits of the design means that choice and quality of passive components makes only marginal difference to the sound.
to summarize, i would recommend only
- safety upgrades (i.e. a fuse + IEC power cord + selenium rectifier replacement),
- a beefier transformer to extend the tube life (the original PA-211 is very noisy and leaves the tubes current starved)
- possibly faulty components like scratchy pots replaced etc.
also the original telefunken 12AX7's *ARE* an integral part of the PAS-3X's sound so i'd recommend hanging on to those. i've tried many other tubes but the original telefunken's are simply the best by far. NOS 5751's are also nice (much lower noise, useful in the phono stage) but have distinctly different dynamics.
sorry for the long rambling post....
-pradeep
ps: also curcio audio , van alstine etc sell most of the replacement/upgrade parts and a lot of their mods are downloadable off their web-site.
Thanks for the info, I was basically going to replace and beef up the electrolits or if I have enough room cause there is only the electrolitics and the rectifier in that quarter if I remember correctly is maybe add some good high voltage oils and a choke. Maybe slap some Wimas on the boards. But if the X is because of special pots, I'll just have to make do with the pots that are on it. I have a ziplock full of Tele smooths and a few ridge plates. Guess I'll trade a couple with good labels for some black plate 5751s for the preamp section and stick with the AXs in the phono. I'll get the gain there and quiet it down in front.
Thanks again,
Thanks again,
hey now
in case you're looking to swap - i have a bunch of extra RCA NOS 5751's which i wouldn't mind swapping for telefunken 12AX7's. let me know offline by email if you're interested.
-pradeep
(i'm in cambridge, MA and my email address is sarin@mit.edu)
in case you're looking to swap - i have a bunch of extra RCA NOS 5751's which i wouldn't mind swapping for telefunken 12AX7's. let me know offline by email if you're interested.
-pradeep
(i'm in cambridge, MA and my email address is sarin@mit.edu)
hey now
in case you're looking to swap - i have a bunch of extra RCA NOS 5751's which i wouldn't mind swapping for telefunken 12AX7's. let me know offline by email if you're interested.
-pradeep
(i'm in cambridge, MA and my email address is sarin@mit.edu)
in case you're looking to swap - i have a bunch of extra RCA NOS 5751's which i wouldn't mind swapping for telefunken 12AX7's. let me know offline by email if you're interested.
-pradeep
(i'm in cambridge, MA and my email address is sarin@mit.edu)
Hi David,Thatch_Ear said:
Dig up some copies of the early 80's Audio Amatuer and get the POOGE articles for it by Walt Jung for both the PAS and the Marantz 7C. They were pretty extensive for their time, and kept the basic topology, but did all the standard mods like passives and regulators etc. The PAS was more radical than the 7C. If you can't find the articles and you're interested in the, I can arrange to photocopy them and mail them to you.
The other option would be to rebuild the phono stage as per Allen Wright's circuits in the TPCB, or even an FVP5 stage. The PAS is a really average, old fashioned 'tubey' sounding circuit, even with premium tubes like TFKs in it, and unless you're going to just give it a basic tidy up, I would think your time might be better spent on rebuilding it completely with a better circuit, utilising as many of the original PAS parts as possible to keep the cost down.
In the tone stages, clean and lube all the pots (replace if neccesary) and upgrade all the passives. I'm not sure how much gain the stage has in the centre position for the controls, but you might have enough to be able to put a bypass switch in.
Cheers
I found a great article co-written by Jung called Pick A Cap. Good reading and have posted it at a couple of other sites.
<http://www.capacitors.com/pickcap/pickcap.htm>
Thanks again everyone. I am kind of rethinking this PAS thing, but since I need to go through it to sell it I will get it back up to specs if not bettter and use it till I get or make something better.
<http://www.capacitors.com/pickcap/pickcap.htm>
Thanks again everyone. I am kind of rethinking this PAS thing, but since I need to go through it to sell it I will get it back up to specs if not bettter and use it till I get or make something better.
I simmed the Amer and Vorhis RIAA mods -- haven't actually checked them out but one should be done tomorrow:
An externally hosted image should be here but it was not working when we last tested it.
As long as your power transformer is operating, I wouldn't worry too much about replacing it for now. Most of the PAS units used the 211 transformer, which was a little weak, but the late production units used another number which I can't think of right now, (but I think it's 511--I know the 522 is the 120/240 volt trans.) that was somewhat more robust. The mod. that can overstress the transformer is adding more tubes to the filament supply, such as copying the ARC SP-3/6, by adding cathode followers. If you decide to go this route, you can lighten the load some by replacing the power indicator lamp with an LED.
I installed the "Vorhis" mod when I first built my new PAS in 1979 and compared it to a number of stock preamps, and found the improvements to be considerable. Although I've done other upgrades over the years, such as adding a stepped attenuator, filament, PS and component upgrades, it's the unit that's the heart of my system to this day! The circuit that I chose, however, was his second offering in TAA, not the "Last PAS" that I found to be a little too radical for my needs. Because my PAS is an "X", I also chose to retain the tone controls.
If you are unable to find back issues of "The Audio Amateur", a talented gentleman, H. L Eisenson, published a volume in the same time period titled "TU-BE or NOT TU-BE" that has both technical descriptions and some actual "how do do it--step by step" instructions to improve the PAS. This is an excellent publication that I see offered for sale on a fairly regular basis on eBay.
I installed the "Vorhis" mod when I first built my new PAS in 1979 and compared it to a number of stock preamps, and found the improvements to be considerable. Although I've done other upgrades over the years, such as adding a stepped attenuator, filament, PS and component upgrades, it's the unit that's the heart of my system to this day! The circuit that I chose, however, was his second offering in TAA, not the "Last PAS" that I found to be a little too radical for my needs. Because my PAS is an "X", I also chose to retain the tone controls.
If you are unable to find back issues of "The Audio Amateur", a talented gentleman, H. L Eisenson, published a volume in the same time period titled "TU-BE or NOT TU-BE" that has both technical descriptions and some actual "how do do it--step by step" instructions to improve the PAS. This is an excellent publication that I see offered for sale on a fairly regular basis on eBay.
I am working on a PAS I found in a dumpster -- it worked -- in some respects -- the selector switch was shot which was probably the reason it got the heave ho -- had the original Dynaco tubes etc., etc.
I purchased a new selector switch from Curcio and modded the RIAA network per above.
One suggestion I would have prior to modding is to give the printed circuit board a bath in MEK (observing the appropriate cautions) followed by a rinse in hot water.
I don't know if Curcio uses a 6922 or 12A*7 for the line driver.
I purchased a new selector switch from Curcio and modded the RIAA network per above.
One suggestion I would have prior to modding is to give the printed circuit board a bath in MEK (observing the appropriate cautions) followed by a rinse in hot water.
I don't know if Curcio uses a 6922 or 12A*7 for the line driver.
Well, I wasn't too happy with the Vorhis RIAA modification -- the gain of the first stage of the ECC83/12AX7 is too low with his selection of feedback resistors. He indicated in the article that R9 + R10 of 1Meg + 475k = 1.475M in parallel with C4 of 3330pF, and R11//R12 100k 330k = 76.4k in parallel with C5 of 1,000pF
The new R9 R10 are 2.2 meg + 901k
Vorhis PAS mod is magenta, the new resistors are blue, not a lot of cutting and pasting -- the new values can be trimmed for an even better fit, etc., etc:
The new R9 R10 are 2.2 meg + 901k
Vorhis PAS mod is magenta, the new resistors are blue, not a lot of cutting and pasting -- the new values can be trimmed for an even better fit, etc., etc:
An externally hosted image should be here but it was not working when we last tested it.
Here's a snapshot --
An externally hosted image should be here but it was not working when we last tested it.
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