X250.5 amp vs the X350.5

thedudeabides

Well-Known Member
Jan 16, 2011
2,127
651
1,200
Alto, NM
Anyone have any experience comparing the two models?
 

thedudeabides

Well-Known Member
Jan 16, 2011
2,127
651
1,200
Alto, NM
Update. I returned the 350.5 after a week of auditioning. Much prefer the 250.5 in my system.

Very surprising indeed. Was not expecting that outcome.
 

thedudeabides

Well-Known Member
Jan 16, 2011
2,127
651
1,200
Alto, NM
Hi Doc,

Simply stated, the 250 sounds much more musical than the 350. Liquid, relaxed, excellent mid bass / low bass foundation versus clinical, incisive, and uninvolving emotionally.

I thought the Pass Labs amps had a similar, family sound. Based on my experience, seems not to be true. But who knows, maybe the 250 was the perfect "synergy" amp for my system

I suppose that's fine but it does give me pause regarding purchasing another Pass amp.

Thanks for asking.
 

valkyrie

Well-Known Member
Sep 12, 2011
65
10
315
I have noticed that with some amplifier gear (whether tube or solid state) high power outputs, that are typically developed using a large number of gain cells (tubes, FETs, Transistors) in parallel seem to sometimes lose their magic when the number of devices gets too high.

With transistors the culprit seems to be something called "diode hogging". Sure a diode becomes forward biased at 0.7vdc - but it is NEVER exactly 0.7 vdc, instead being somewhere in the range of that number. Which means in any parallel set of transistors (bipolar) one device will switch "on" slightly sooner than the other devices. First encountered this at Texas Instruments in the early '80s where I was working as an engineer. Later noticed in it "motor controllers" where large numbers of parallel solid state devices were being used to control a motor. In both instances I saw diodes (and a transistor does use diode action to become forward biased) begin to burn up - first one (the early switcher that would attempt to pass ALL THE CURRENT), then eventually the others as they now had to carry more current than they were designed to do.

Same applies with tubes - the change from anode to cathode is not exactly the same with every grid. I am not sure that FETs do the same thing - but I suspect so.

The net result from a sonic aspect is that with a large number of parallel gain cells you "may" begin to get a slightly "rougher" sound. This may be an aspect of why single gain cell devices have such a purity of tone - only ONE device (gain cell) is being turned "on" at any point in the amplification process.

I do know that Wayne Coburn, the Pass preamp designer, used an X150.5 as a personal amp - and he could have had ANY DEVICE in the line. Perhaps he heard the same effect? (just guessing on this).

I also know that Pass as a company and as a design imperative, takes extraordinary care in choosing the devices that are being paralleled so that they "match" as exactly as possible. I also know that Pass equipment is incredibly long lived. So please, this is NOT an attack on Pass - I too use a Pass amplifier and am lusting after a Pass preamp and a phono amp.

But perhaps this is what the "dude" heard.
 

DAG

Well-Known Member
Jan 7, 2017
6
0
128
UK
I couldn't disagree more. I have had the opposite experience. The 350.5 has much more authority,detail,far larger sound stage, more body and weight- exactly how my dealer described it.

Regards







X350.5.xp10,Bryston bdp-2,BDA-2,DH labs cables,Dynaudio C4
 
Last edited:

thedudeabides

Well-Known Member
Jan 16, 2011
2,127
651
1,200
Alto, NM
It's all about synergy and personal preferences.

I had the same expectations you did.

Glad you like the 350.5.
 

murphys33

Well-Known Member
Sep 28, 2011
112
10
258
Update. I returned the 350.5 after a week of auditioning. Much prefer the 250.5 in my system.

Very surprising indeed. Was not expecting that outcome.
I preferred the X250 to X350 but in the .5 series preferred x350.5 over the rest.
 

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