Pass Labs and Fuses

I continue to enjoy my Pass Labs Int-60 amplifier with my horn based system. My listening area has been intensively treated for acoustic - speaker interaction and it is always a joy for me to listen to a Dialed In system.

For my latest listening experiment I decided to evaluate the sonic differences using three fuses in the Pass amplifier. A brand new Bussman fuse, a Synergistic Research Blue fuse and a Synergistic Research Orange fuse. I keep this amp on 24/7 as suggested by the manufacturer. The Blue fuse has over a 1000 hours on it and the Orange had a 160 hours (continuous playing time) on it before any listening evaluations. The Bussman was listened to for the first time immediately out of the box.

The Bussman fuse did a fine job. But going from the Blue fuse which I had been using to the Bussman, there was a definite change. With the Bussman the sound was now more two dimensional. Instruments were not as full bodied. The depth of the soundstage was compressed front to back. I was more aware that I was listening to a recording versus being in the room with the musicians. The music was less emotionally involving. I did for completeness sake reverse the direction of the new Bussman fuse several times. It did consistently sound better installed in one direction, not huge but it is there.

Comparing the Synergistic Blue Fuse to Orange Fuse was similar to my past tube rolling experiences with my 300B tubed amplifier (but cheaper to carry out). Different tubes change the sound and these different fuses change the sound. Both of these fuses brought out more of the music that the Pass Labs amp was playing when compared to the Bussman fuse. Before any serious listening was undertaken, the fuses were evaluated for best sounding direction - and they both were directional.

The Orange fuse really is exceptional in it’s ability to let me enjoy the music and who is playing what. The detail of Willie Nelson’s nylon strings on his guitar had much better dynamics and richer texture than I have previously heard using the Blue fuse. His Stardust album continues to impress me.

When listening to music that has more musicians playing, such as on Sierra Una Noche, I can more easily distinguish each instrument and it’s contribution to the musical whole. Also in this live recording that uses only two mics, I get a better feel of each musician’s distance from the microphones and that they move toward and away from the microphones while playing. These factors allow me to forget I am listening to a recording of an event. With the Orange fuse, I feel I am at the event as it is playing.

This fuse experiment was fun to do and educational.
Feel free to call.

David Pritchard

I have used a Blue Fuse in my Pass XP-20 preamp. It was easy to choose direction and, when in the correct direction, contributed to superior performance versus the stock fuse (which was also checked for direction and removed and reinserted as a check).
How is it that one way it sounds better than the other-way??
When the AC (clue here "alternating current") is changing it direction 60 x a second?? You would have to be changing the fuse direction also 60 x a second to prove what you said that it "it sounds better one way than the other".
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On "You Tube there is a six part interview with Nelson Pass. I found it fascinating. He has been experimenting with solid state designs for over 40 years. But it is important to know he is not the only designer at Pass Labs.
First Watt 7 amp - Nelson Pass primary designer
Pass Labs INT-60 Wayne Colburn primary designer
Pass Labs HP-1 Jam Somasundram primary designer

I am fortunate to have an example of each designers work.
Wayne Colburn has been designing at Pass Labs for 31 years!

A few quotes from Nelson on why there is more than one product sold and why he has been doing this for 40+ years. "What interests me most about amplifiers are the differences in sound created by different topologies". He creates amplifiers that create a "sound which has a particular signature".

In a You Tube video from 2016 there are shots of many Pass Labs products with their sides and lids removed to show the inside layouts and parts used. On purpose there is a high commonality of parts used to decrease variables. Nelson collects and stockpiles different transistors for possible future products whether they be Pass Labs products, First Watt products, or as a diagram released to the DYI community. Showing just one parts bin, Nelson estimated he had 250,000 examples of that chip.

He will run out of time on Earth before he runs out of different chips to evaluate.

I have also admired audiophiles who post results of evaluating the sonic changes using different capacitors of the same value in a piece of equipment. Tedious, time consuming, and requires excellent soldering skills (which I do not have).

I have enjoyed tube rolling in amplifiers for years. I have a large collection of the same type of tube made by different companies, that vary in age from new to 70+ years old. I do not find the sound to be dramatically different except my emotional response can be dramatically different. With some tubes I get a "That's the sound I want ! " I find that moment exciting and worth the effort in time and money.

I have also experienced the same satisfaction trying different fuses in the same piece of equipment. I now have 11 different fuses of the same value that I have listened carefully to. It is very time consuming and tedious but I find it satisfying.

 I work hard at minimizing any variables. My house is kept at the same temperature, the humidity is kept exactly at 37%, listening is always done at the same time of day (8:00 to 10:00 pm ), a record is kept of how long the fuse has been in the equipment, which direction installed, and the same music is used for evaluation. Written notes are kept to refer as a record.

On occasion I have read people asking the question about possible sonic changes heard using different fuses. I try my best to report my experiences listening to different fuses so others may use them as a data point of reference.

 As in Vacuum Tube rolling or Capacitor swapping, others may not hear a difference between different fuses or may come to a different conclusion to the quality of the change in sound.

David Pritchard

Tubes and capacitors are not fuses, not even close, and tube swapping (I don't change capacitors unless some malfunction has occurred, or, as in the case of a 60 year old tube guitar amp, they leak) results in interesting and obvious tonal changes. Fuses do not, and claims that "improper" fuse direction will make a component sound out of phase or otherwise compromised is silly and not an actual thing regardless of how many amps one has owned or how carefully somebody keeps track of this silliness, or how much carefully worded hyperbole is generated to shill for SR.
"How is it that one way it sounds better than the other-way??...."


I agree with you that fuse direction loses all meaning in an alternating current (AC) application.