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

A CdSe photocell (and other photocells) attentuator may require little power, but definitely not a passive device. It is an active device. It is a semiconductor. Light induces more available charge carriers. 
My apologies George.
I wrongly assumed there would be no mains voltage involved in a passive device.
Thank you for enlightening me.

Common mistake, if you can read a circuit diagram, you’ll see that the signal (green) from input to output of each channel only goes through one fixed passive "light dependent resistor" (LDR), that changes it’s resistive value via a chemical reaction, to the amount of light that is shone on it from a light emitting diode (LED).
The only active part is the LED’s and what powers and adjusts them, the rest where the signal travels, is totally passive

There are no active parts, no volume control, no resistive wiper contacts, no switch contacts in the signal path as active preamps all have.
The Title of this thread is Pass Labs Amplifiers and fuses, and so I will discuss at least some aspects of the title subject.

Yesterday Mother's new Pass Labs First Watt SIT-3 amplifier arrived from Reno HiFi. Enclosed was an informative manual.

"The amplifier requires about One hour of operation to reach full operating temperature. I personally do not see a reason to run the amplifier all the time, but you can do that if you want to. The power supply capacitors are likely to last 20 years or more, and while they will slowly dry out just sitting there, they will have a longer life if the amplifier is not run continuously. Practically speaking, it makes sense to shut the amplifier off if you are not planning to use it the rest of the day".

"I answer all questions, even if the answer is No.
and sometimes it takes a little while" - Nelson Pass

In the experiment I performed with the Pass Labs INT-60, I heard a distinct difference using three fuses. 

The newly acquired SIT amp is designed having a SET tube amplifier sound without using vacuum tubes or transformers. The goals of this amp are " to get transistors to sound like Triodes(vacuum tubes) and simplicity and minimalism of circuit design". I think this amplifier with a simple design will be a good test vehicle to further evaluate different fuse affects on sound. The amplifier will be left on 24/7 to minimize any "break in effects". This amp uses about 150 watts when on. And yes the Main circuit breaker is turned off when fuse rolling.
This amp is entirely designed by Nelson Pass and only 250 were manufactured. There are a few new units still for sale.

Out of the box with one hour warm up and the stock fuse, the sound is wonderful. For audiophiles with efficient speakers and wanting an amp that is sold state but sounds like a SET vacuum tube amp, this is a  compelling option.

I soon will also be posting the results of the interaction of fuses and the Pass Labs Headphone amp. 

I hope all readers will take some time to reflect that today is the date of the attack on Pearl Harbor.
David Pritchard
FYI for those interested: There is a purchase 2 get 3 Orange Fuse promo on offer for a short time period.

There is a purchase 2 get 3 Orange Fuse promo on offer for a short time period.

Of course there is, people are starting to wise up to this voodoo snake oil BS and they have an over supply, wonder what the next color will be.