#nelson pass

[audio-luddite]

Take a Pass.

I like to explore things and so that is what I was doing. I looked up the person behind Threshold Stasis Amps and the design of my Naka-san amp, Mr Nelson Pass.

He has a company called Pass Labs that makes hi-fi stuff. He is rather unique in that he really understands what is going on in electronic audio stuff, and is very good and open about discussing it. He also has spent his entire career with solid state and has no romantic illusions about the vacuum. (I do have such)

I read a couple of articles he wrote discussing things golden ears wring their hands over. He has an intriguing thing about speaker cables, and hooked up test instruments to several samples. (Heavy is better unless its not.) He also goes into detail about power supplies.

The one I really enjoyed was about feedback and distortion.

Audio distortion and feedback - Pass Labs

Audiophiles seem to revel in minor controversies – vinyl vs CD’s, tubes versus solid state, capacitor, wires, magic dots… and negative feedb

FN brilliant this is. Clear and relatively easy to understand even without an electrical engineering degree. Basically it describes the decision matrix a designer must use to make something. Key is the sound versus the test results. I think this puts Nelson firmly in the what it sounds like club. No surprise.

I think this also helps me understand why different amplifiers sound different. My old Franken-amp is old school feedback is good, and it will pass excellent square waves. It has vanishing low distortion that humans should not hear if they were like test instruments. It has excellent detail. Naka-san is a Nelson Pass scheme that uses as little feedback as possible which is only to compensate for the non-linearities of some of the transistors. The result is less of the high order distortion he knows would be there. That is where the even better clarity comes from.

It also helps with understanding how the ARC Tube amp can sound so nice, but does not have the clarity and detail of the solid state. The fuzz and mud and lovely texture is distortion. NP mentioned some people liking even order distortion, others odd, and others still liking one or the other depending. I am obviously in that last group.

Golden ears throw thousands of words around these things, and simply do not understand or care apparently. The Audio Science Review club are solidly testing people, and more feedback is best types. Keep those numbers low.

The really cool thing here is what is actually the truth?

[audio-luddite]

Good Morning Audio people.

I did my usual perusal of the local equipment ads today. I noticed a relatively low priced super amp in there. It was a SUMO Andromeda. Big and black and it looked really heavy.

It was about 1/2 to 3/4 of the usual price for this type of thing, so interested I became. It reviewed well in the 90's, and gained favor in several magazines. I looked further into it. SUMO was another incarnation of James Bongiorno's businesses.

His name is either Good Morning in Italian or a homonym (or is it homophone) of that. So good morning!

He started at Marantz in the golden NY era. Then moved to New Jersey with Dynaco. Then California with SAE and then GAS, and eventually SUMO. Each step was further down the road of his quest for electronic perfection. Each stop produced notable products. A quest does not have to be linear or even successful.

I must remind you that JB was one of the three big golden age designers who gained respect even fans among the audiophile world. The other two being Nelson Pass, and Bob Carver.

Anyway back to the SUMO. The documents for this Amp, an Andromeda II, were interesting. They talked about separate power supplies and robust hardware. It was also one of the Early big FET amps. Stereophile sorta liked it in certain systems. When it was good it was very good. Both good and FET. It was priced about what I could get for my Franken-amp if I found a buyer. Wheels started to turn.

So I dig further. As per usual I looked up the circuit schematic. Holy shit! This was an electronic maze. I imagined service techs throwing themselves off of tall buildings if this showed up. It looked like each channel was made from two complete amplifiers bridged to act as one amplifier. That apparently is exactly what it was.

In the normal application many stereo amps can be bridged to act as one monophonic amp at about double the power. Good things usually happen. So why not, they thought, do that right in the box with four amps to make 2 bigger ones. Twice as many parts!

In my opinion one benefit of bridging amps is you have two completely separate devices so there is no cross talk. It is physically impossible. Putting two already bridged amps in a box would be fine if they had their own power supply like Harmon Kardon and others do. SUMO didn't do that.

They did a weird thing in having two tiers of power supply one for the low level Class A front end and a second (smaller one!) for the big output transistors. Well he was in California, he may have been smoking something. If these power supplies could be cleaved apart for each channel and the big outputs given more umph capacitors things could look good.

Hey I am not an electronic engineer. BUT things were screaming at me why did they do that!

The only cool thing they did was to have the power stages biased so that they acted as Class A up to a couple dozen Watts. 95% of your listening is at very low Wattage. So a Class A Bias is generally a good thing though it makes it run kinda warm. Cool to be warm.

It looks like he went down a "lets try this" rabbit hole. Yes MOSFETs were involved but dear me. Interesting the Mr Pass went the route of simplicity. He also moved to a mountain forest.

All these things have a voice. The Stereophile review discussed how it sounded really good with some speakers and less so with others. Interesting that made such a difference. Obviously it was reacting to the speakers impedance function. Why else would it sound different? You shove a big electrical signal down the throat of any speaker it should just put out sound. But sometimes they argue. Sometimes the amplifier does not like arguments. Maybe if the power stage had more umph behind it?

So after being intrigued I thought give it a miss. I am sure someone will buy it and like it, until it breaks.

[audio-luddite]

Reading stuff

I read an interesting set of articles.  None were equipment reviews.  They were about or by a brilliant audio designer.  His name Nelson Pass.

He is associated with some big names in audiophilia you can look them up if you want.  His career has been in designing and building very good amplifiers.   He is an iconoclast and really a guru of electronic circuits.  One of his guiding principles is to make things simple.

I know enough about electronics to be dangerous. I know where I can poke. 

I had been checking out amplifiers as an orientation in the event my big black amp goes up in smoke.  It is my oldest electronic thing.  I just bought a full set of repair parts in case it dies, but even if I do most of it myself I will be off line for some time.

So I went down the following rabbit hole.

One strong candidate is an ADCOM GFA 555.  It is a 200 Watt stereo amp of roughly the same vintage but a robust reputation. I can get restored versions for reasonable money. In this age I can get photos of the inside and I see that it had a split power supply with rectifiers and capacitors for each  channel.  Hey just like I do!  I looked up a circuit diagram and saw that it had remarkably simple topology.  That included a small resistor on each output transistor to protect them from shorts.  Very clever. Digging further it seems to have been designed by or under the direction of Mr Pass.

I looked him up as now you can do.

I knew that he had done or suggested numerous modifications to older factory amps. He was an audio hot rodder. So I looked up more stuff.  He has a couple of businesses and things still on the burn and sometimes people head up to the mountain top to tap his wisdom. One thing he bases his work on is the sound of an amplifier depends on many things of which he seems to have a particular grasp. A design that sounds great may not measure great and visa versa.  He likes to design things that sound great.

A particular thing he said was he designed a simple small amplifier with an adjustment that caused a particular type of distortion in certain settings.  At one setting there was almost none. At another there was one kind and degree of imperfect sound. At yet another range there was another.  The idea was to let people set the knob to what they liked.

What they liked was a noticeable particular type of phase and harmonic distortion.  That created a sense of depth and volume to the image.  Well aint that interesting.  Is the depth and volume illusion actually a type of distortion?  Are we looking for something that is wrong objectively?

I think that is so cool.

[rotor25]

Nelson Pass on learning his craft, then starting Threshold, Pass Labs, F...

[ncdweller]

I couldn't find the heat gun to shrink up the heat shrink. It's around here somewhere.

The build instructions are wonderfully illustrated, yet still missing a few things, and the photos don't follow the order of assembly, so that's fun. It pays to read ahead.

All of this to correct my great audio misstep of buying an AV receiver. Those are great for watching movies and YouTube stuff, but awful for music. It's like having cotton in my ears. Not a lot of cotton, not a cotton ball, just a thin layer. It's been driving me crazy, as I know my records sounded better with my old Adcom amp, that I gave to my brother this summer. He is very happy with it.

I like how small this thing is. About half of the case volume is heat sink material, to deal with the heat from the class A operation.

[ncdweller]

ACA 1.6

Amp Camp Amp. The case arrived yesterday, as did the backordered caps (with the red tops). I also swapped out the 3,300uf caps for 4,700uf Nichicons.

Tonight I plan to wire these to the RCAs and switches and give it a smoke test.

Those keratherm pads under the transistors are awesome. Much nicer than messing with the white goop.

[ncdweller]

Just adding the ACA to the world of Tumblr tags.

That is all.

[hasafraker]

Nelson Pass Amp Camp Amp, full Class-A Monoblocks. 6 Watts never sounded to good!

Ok, first, this kit won't break the bank and you can build it in a day. It is available over at DIYAudio.com I was very excited to get this kit and even more excited to hear it. What I wasn't ready for was how much better than my normal amp these sound. These little amps sound really really good, they remind me of my Decware SET amp, and that amp only makes 2.5 watts. The ACA monoblocks make 6 watts. Here is a link to the original article by Nelson ACA project

I can only assume these little babies will need some break in time as just about everything else has from 8hrs to a few days or so, but if they keep getting better as they get older... I'm not going to know what to do with myself. I need to get them upstairs so I can hear them with the Tekton 8.1's. I need to figure out a way to get my sub back into the mix. My PSB's don't quite have the bottom end without the sub to fill it in. 

So anyhow, this is a very straight forward build. I used my work bench pc to pull up both of the build walkthroughs so I could see different examples of how to build these little guys. I am never in a hurry when I build something. I like to take my time, make sure everything is right and my work is neat and tidy.

lay out all the parts, identify everything, make sure I know where everything is and what it is. done. Stuff the boards starting with the small stuff, all components included in these kits are top notch. The only thing budding audiophools might complain about are the switch mode power supplies that Nelson picked out, and to quote Nelson, "Get over it – they work fine." So there you have it. Now I'm sure you could design your own power supply and spend half again the cost of the kit on a sweet external power supply but from where I'm sitting I think you'd be hard pressed to make audible improvements over the included units.

So after getting the boards all done, adding the special tweak 2.21k ohm resistor off the leg at Q3, I'm ready to attach the boards to the heat sinks. The 2.21k resistor squeezes and additional 1watt of power and actually lowers the distortion according to Nelson Pass. He worked to optimize the amp after the original designs were done and found the addition of the resistor made a number of improvements. On a low wattage power amp a 1 watt increase is nothing to laugh at.

Oh! LOL I almost forgot, LED's will NOT light up worth a damn if you install them backwards lmao. Yup... guilty... shh, don't tell! At least I figured out what I'd done and flipped it round and woo shiney! Hah! I seriously had to laugh at myself, the first channel I fired up the LED didn't come on and I was like what the hell!? Got my meter out and was like ok what the heck is going on?! I figured it out pretty quick.

So the only other thing I had to do was redrill the hole for the RCA input jacks. The nylon washer has a step in it and the pre-drilled hole was just not big enough and I've installed enough RCA jacks in my time that I KNOW if that washer is used and the hole isn't big enough eventually the nut holding the jack in place will work lose and then you have a huge pita trying to get it all tight again and it will eventually work itself lose again. I drilled the holes out, now the step washer fits properly and all is well. Beyond that fit and finish is excellent!

After getting both fired up, I ran them for the instructed 30minute and then checked and re set the bias back to 10vdc. All done. screwed everything down, packed it all upstairs and tucked it into my main system. I noticed after about an hour these amps really are quite amazing. VERY detailed, nice open sound stage, they are definitely better sounding than my normal amp. I'm not sure what I'm going to do now... ARRGH! Oh well I'll get over it LOL

I am extremely pleased with the results from this kit. Nelson you are my hero.