Dynaco PAS3 Preamp troubleshooting and volume mods 

Not mine. Client bought it in this modified state for a reason.

It is a 50k pot, 5k roughly. I put a 6.8 and 10k in parallel which brings is a little bit lower but sounding much better now. A logarithmic pot swap would do better but now it is acceptable. Initially it was 0 to full after 1/4 turn.

I don't know the history and I doubt anyone does because this thing has probably changed hands a dozen times in its lifetime.

Yup any pot can be tamed down a bit by adding resistor between the wiper and the ground side.

Depending where the volume pot is in the circuit, changing it's value can effect impedance which in turn could effect the frequency response of the amplifier. If, say a 100k pot is specified, it's for a reason changing the value will probably effect performance.

@@MichaelBeeny The pot is 50k. I believe what he is referring to is ro change from a linear to audio taper type.

Agreed I have no idea what the deal is here. 4 tubes on a pas phono preamp board is something I've never seen.

Yes and it was going high but adding an extra load and use actually restored the pot. This had been sitting unused for awhile . I have since removed these resistors because the control started working correctly again and it sounds wonderful now.

Anything tubes sounds fantastic. That is why they are gaining popularity again because people are rediscovering what guitar players have known all along. Tubes sound awesome. That is all I listen to at home. A nice little 40 watt el34 amp into a pair of sb7000a speakers.

No copyright issues. They are fradulant claims that get resolved as soon as I dispute them.

@@12voltvids Right. I knew that much from watching your YT video on it. It seemed as though the "artist" was pursuing you though. Fraud? Sounds like there are four videos that you've removed because YT will not pay you for the views. Seems shady on their part.

@@djscott9207 That has nothing to do with copyright. Those were reviews of "Android boxes" and I mentioned "ko_di" and that is now a no no because people can use it to pirate tv shows and movies. That was why they pulled the advertising and seized the funds they had already paid. That is why those videos came down. It had nothjng to do with any copyright claims. I reedited those videos removing all references to any 3rd party software and they are making money but don't have 300k views. I won't accept any android boxes for reviews now.

@@12voltvids Ok, well, the video I referenced in my post above is a recent one from late Oct. regarding the song intro in your videos. You went into some detail showing stats and that YT put a stop on compensation, so you decided to take them down. Your thinking was if you weren't being compensated, there was little point in keeping them up for viewership. I appreciate what you've done here and agree you deserve compensation. You're claim was the song is not in violation and commenters agreed. It sounded like the person who claimed copyright infringement was either in error or possibly engaging in fraud. My concern is if YT doesn't have your back then you may not continue uploading. That would suck.

@@djscott9207 The recent one was nothing to do with copyright. It was referencing another video that had a bogus claim against it and was just me going on a rant taking a few shots at RU-vid regarding their algorithms that keep flagging old videos over and over and have to be appealed multiple times. What happened was the video on the repair of my teac 3340, royalty free content was hit almost instantly when I posted. I pulled it and appealed. Copyright claim released so I put visor back public. A few months later some other 3rd party made a claim. So I appealed again and claim released. A few months later another claim by another different 3rd party. 3 different people had used the same music bakery bed and either used it as spoken word background music or put some lyrics and sang. I was being critical of RU-vid for allowing it to happen and even though I did not swear or curse I used the words "farking bull ship' and " morons, and retards", directed at RU-vid for the way they allow this to happen over and over on videos that had previously been disputed and claims released. Obviously someone at RU-vid couldn't handle a little criticism, because when they flagged it as unsuitable I appealed and was ruled against by one of the snowflakes that watched it and took offense. I wasn't directing my frustrations at anyone in general just RU-vid in general.

4 are used in the phono side, and the other 2 are output. So with a line level only 2 are used, and all 6 in phono mode. I belliebe 4 if it is a MM cartridge and all 6 for MC.

@@12voltvids okay I'm going jump into the tube preamp market. Have a chance to get the PAS model here in Canada for 300. But the guy took all the telefunken tubes out because there worth alot of money and put USA tubes in.

@@billwaplington8700 It is crazy what people will pay for old tubes. I run electroharmonix myself and am pretty happy with the sound. Preamps add the warmth to the sound, but myself I run full tubes, preamp and power.

Does sound like it. Never left the factory like that for sure.

Needs something like a 500K ALPS pot

Factory was a 250K log pot with a tap at 47K to enable a loudness switch (louder bass at lower volumes) that in disabled position shorts a .1 mfd cap and puts a 4.7K resistor in parallel - you can easily find the schematic online and there’s even a really in depth pdf explaining in detail how the whole circuit works. From the video it looks like PO replaced the loudness switch with another pot, wonder what happens when you turn that. Another thing to note is that the combination of volume pot, balance pot, and loudness circuitry is carefully engineered to put the right load on the preceding circuitry. If you change the load on that prior circuitry you also change its frequency response so tread carefully. There is a character on eBay who sells a modern manufactured replacement part including the loudness tap for $90 but if you don’t care about the loudness switch you can get away with a modern 250K log pot bridged with a 1M resistor to bring its overall resistance to 200K as the original pot was with a 4.7K resistor bridging the lower 47K of the pot.

No bias issues. No DC on the outputs. This has been modded expensively. Pair of tubes before the volume and pair on output. This gives it loads of gain.

They are not quite as bad as the wax paper caps, but yes they do go bad. The wax jobs fail in much higher numbers especially when they have been in a hot chassis which makes the wax soft and it drips out. Air gets in and oxidizes the paper making it conductive.

Capacitors that are 50 years old need to be replaced period... doesnt matter if they were sealed good or not...lolol...

@@mrrobot6757 The paper caps fail in very high numbers. The epoxy ones are not as bad but they do go bad. The wax ones are by far the worst and electrolytic.

@@12voltvids yes i know all about paper caps... and epoxy ones are just as bad... and in a tube pre... anything capacitor needs to be replaced... expecially if its over 50 years old... lolol...

@@mrrobot6757 These are mylar caps in the old shape, they are just as reliable as the more modern mylar caps. The difference can been visually identified, if there is a little nub at one end where the outside foil was soldered to the lead, it is an old paper in oil cap. These appear to be the mylar ones, no good reason to change them.

This unit has been modded so many times since it was first built. Power supply external, 2 additional tubes in the phono preamp.

Can't beat tubes for sound.

That's the metal inside turning

Yes I know it has been modified. From what I have been told it was one of the dynaco partners that started his own gig modifying equipment. Again I have no history of it. My client buys all this stuff on Ebay and brings it to me to check over.

Looks like the orange caps in the preamp section are new

The guy that modded this unit went on to work for Acoustic Research.

Yes and I got hit with a bullshit copyright claim on it. Royalty free music used. A crop of shit if you ask me.

This is SO RIDICULOUS! Third time in the last few days I’ve heard of copyright claims on royalty free music or, get this, original music! Bastards!

@@budandbean1 Once I dispute it, the claim gets released. The music bed was used by a guy named Rick hart. He used the background track, and wrote some lyrics to it and recorded that. So his record company makes a claim. I file a dispute with the link to the music bakery track along with my purchase receipt and the claim gets released. Still a pain in the ass as they come back time and time again. I think they are hoping that someone that used the track will not dispute (perhaps if they did not purchase it for example) and they will just go with the revenue sharing. Since I purchased a full library years ago I have the standard release files for each track that I just submit. Problem solved.

Yeah, I understand but you shouldn’t have to... that’s really my point. You are still the guy who has to jump through the hoops. Their bot is what caught this. Actually, this is the first time I’ve heard this one about guy gets royalty free music and writes words to it and then copyrights it. I could have sworn most royalty free music has specific exclusions against this.

Rick Hart has done this with a number of tracks from Musicbakery. I have to dispute each and every one. It used to be worse.

This is exactly why the best, and some of the most expensive amps you can find use a pair of preamp tubes to add in even order harmonic distortion that is lost in digital recording. Digital is far superior in every respect, however the warm analog sound of tubes sound better to the ear, and when you are paying big bucks for an amp, you want the one that sounds best to your ears. It doesn't matter what it says on paper your ears are only what matters, after all it is your ears that are the input to tour brain. The best sounding amp I own is my Luxman hybrid amp, and I am going to have to service it as it has developed a little issue. I use it in my studio, but for editing I work exclusively with cans and I can plug them in directly into my yeti digital microphone. By digital, I mean it has the A/D and D/A plus a headphone amp built in.

I would have kept the pre amp stock as well... your right about the loudness control...

Most dynaco products were kits. You could buy them assembled where for an extra charge someone at the factory would hand build them but dynaco and haffler were mostly sold in kit form. Fyi dynaco and haffler dmr company, David haffler. Today the brands both owned by radial engineering. Very high end, built in coquitlam bc.

Even a transistor amp fed with a tube preamp sounds fantastic. The preamp adds the even order harmonics. I have 3 tube amps, well 4 if I count my vintage Macintosh. 2 kit amps, and a commercial EL34B push pull. It is a yaquin chinese amp, but that really doesn't make a difference as they basically cloned an american amp. They wind their own iron, and they have a great sound. I plan to build another one as soon as I can get one. ELE has a new 40 watt push pull I would like to build, or perhaps a 300B amp. That one is pretty costly though.

@@12voltvids NICE - Thanks for the info, I'll need to try a tube pre-amp to see if it cleans up the harmonic distortion that I hear (with SOME amps) when playing combinations of high piano notes. Maybe it needs to be hunted down; it's not coming from the keyboard; might even be from my speakers. I started off with tubes (before transistors) and now, it's going back to tubes again for the quality! lol

Thats why there are so many tube amps on the market again. People are re-discovering the sound.

It is personal preference. If you were given a blind listen and not told what you were hearing, like 90% of listeners you would pick the tube gear. You actually do not hear even order harmonics. Odd order from solid state you can hear even the smallest distortions and they are very harsh. You can hear anything above 0.12% thd on the odd order harmonics. It takes about 12% with even order harmonics.

@@12voltvids I see. Thanks for the clarification. So distortion on solid state has more impact than on tube hardware. You never stop learning! So if both amps are of good quality with low distortion, it's hard to hear much difference.

@C17H25N FTW Provided you get a good solid state amp. Cheap crap with lots of distortion doesn't really help even if it has greater dynamic range. Since my Creative USB Sound Blaster X-Fi HD isn't supported anymore and the driver made problems, I was forced to use my on board audio of my ASUS ROG ZENITH EXTREME motherboard until I find a new audio interface. I was surprised how good it sounds, no need to even get a new sound interface for my PC!

Solid state produces odd order harmonics which are nasty and make the sound harsh. Tube gear produced even order harmonics. Even order harmonics are in phase, and 1 octave above the fundamental frequency. So if the musician was playing the note "A" the 2nd harmnic would also be an "A" but an octive up. The 4th would be "A" 2 octives up, the 6th 3 octives up. On a transistor amp, the 3rd harmonic of A would be an E. 5th harmonic would be a D. As you can imagine these do not ring in phase and thus beat with the original note and cause a very annoying nasty distortion that you can hear in very low levels. 0.12% for odd harmonics. Even harmonics do not become objectionable until you get to about 12%

Sure do but they don't have the tube sound. There is a reason that people spend the big bucks to get tube gear. They are after the sound, and it doesn't matter how good your SS amp is, it will never produce the warm sound of a tube amp. That is why they are still made. Call them overrated if you want call us audiophools if you want. We know what we like and WE HAVE THE MONEY to spend on these overrated and overpriced pieces of equipment. No one is forcing you to buy tube gear. We, and I am including myself in this as I run tube gear, like the sound of tube equipment. We have the money to buy it. We keep these small manufactures in business.

What's your point. There is no high voltage or high current on audio pots. Also there is no high current in a preamp. There may be 100 or so volts on the plates of the tubes but not on the controls. But then if you knew anything about electronics you would already know that. The signal level on the pots are in the microvolt range. They are not going to spark. Even though the spray is flammable I have never had contact cleaner light up unless I have intentionally sprayed it onto an open flame. Then you get a flame thrower. Even if you spray it onto a hot soldering iron you just get smoke. It takes something considerably hotter than that to ignite the lubricating oil it contains.

@@12voltvids So you are saying, as a tech…. That it is ok to spray liquids into powered up and operating electronics??? I am not as much worried about electrocution as I would be worried about frying a vintage tube amplifier… Just saying dude… you are teaching guys like me that actually do NOT have much knowledge in electronics, a very bad way of doing things…. Perhaps the same reason we see videos of guys hosing down amplifiers at the car wash…. You don’t need to get defensive about it. I’m just asking if that is the safe and correct way of doing things?

@@LittleTinyKittens you won't fry anything. The cleaner is not conductive. It would be incredibly hard to fry a tube amplifier. They can actually withstand the EMP from a nuclear blast. That's why the Russians continued to use them in aircraft radio and navigation systems. So if the Yanks fired icbm their way their fighters wouldn't fall out of the sky. The way to destroy a tube amplifier is very simple though. Turn it on and crank it up with no load on the speaker terminals. That will blow it up. Shorting the speaker wired however will not do any damage. Now for your next question, how is that possible?