Upgrading my Pass Aleph-X changed the character of the amplifier.

[slowikpl]

I had recently a upgrade done on my Monoblock Aleph-x because one of the amplifiers did not worked anymore. I asked an engineer-friend to do some research and he advised me that I could better go for another Aleph-X board. I did so. During this upgrade I have asked him if is possible to make upgrade from IRF9610 to JFet`s. So we did that. On another hand he said that my MOS-FET ( see picture) boards ware like crap soldered and he will make some of his own.
After that upgrade the Amplifier sound was very different from that I was familiar. Very transparent , fast and with no color , warm sound what was my best things in this Amplifer. So I thought maybe I have to burn the in. After 1 month the sound remain that bad. Just nothing special. We removed the JFETS and putted IRF9610 back in. No change in sound character.
I told him this , and he answered that I wanted to have some more speed on the sound so he have assembled it with other resistors war ware according to him better ones. I had this brown ones and now they are smaller blue ones.
The question is if is that important the resistors on the MOS-FET boards , and could have that influence on my sound reproduction? And if I go and change them wil I get my Pass back to the musical and warm machine?

 

[Zen Mod]

you didn't mention most important thing - what is a change (changes) vs. your previous iteration ?

you're asking something of which only you already have an answer

 

[slowikpl]

You are fast Zen

I`m just asking about the influence of the resistors on MOS-Fets PCB. Are those essential for the sound reproduction , because my friend says that it is not that important any that the new Head PCB is the main reason to this reproduction of this sound.

 

[Zen Mod]

NP is using MOX as source resistors , while you're using paralleled MF ones

dunno which type were your old ones , but there can't be any dramatic difference , sound wise , between any of them

problem certainly lies in difference between your old main pcb and new one ....... and I can bet that's difference in schematic/some part value(s)

 

[Eric]

My first reaction is that you changed the bias point of the mosfets with your new resistors on the output boards. What were your old values? What are your new values? I am thinking bias point will cause a bigger difference than the type of resistor that was used.

 

[Zen Mod]

well , his friend being an engineer ....... I'm sorta hoping he didn't change that much

 

[slowikpl]

I will ask him what are those values. And what is now the difference between the old one measurement.

 

[Zen Mod]

put your other amp and preamp in closet , while he's around

 

[slowikpl]

Thanks for the advice But they are heavy ones, so I will bring my Aleph X to his place

 

[Eric]

Not much need to ask. Power up the amp and measure the voltage drop across the source resistors for the original and the "new" amp. This will provide insight to the bias point.

 

[slowikpl]

Can somebody tell me what brand are those resistors?

 

[Zen Mod]

as I said in our private exchange , those are most probably 2W MOX

 

[slowikpl]

as I said in our private exchange , those are most probably 2W MOX

Ok , i did`t know that MOX was a brand

 

[Zen Mod]

no , MOX is Metal Oxide

brand is irrelevant , considering that only premium factories are making them

 

[Eric]

Brand is probably an irrelevant element here. If you are interested in replacing or replicating these resistors (mosfet source resistors?) in a new build, just choose any non-super-cheap resistor that can handle some power. They are used to bias the mosfet, no audio signal passes through them. In my AX build (~100w monoblocks, each with 12 mosfets), each mosfet has three 1-Ohm 1-watt 1% Dale resistors in parallel, thus forming a 0.33ohm 3w resistor. They don't get very warm at all.

 

[slowikpl]

Brand is probably an irrelevant element here. If you are interested in replacing or replicating these resistors (mosfet source resistors?) in a new build, just choose any non-super-cheap resistor that can handle some power. They are used to bias the mosfet, no audio signal passes through them. In my AX build (~100w monoblocks, each with 12 mosfets), each mosfet has three 1-Ohm 1-watt 1% Dale resistors in parallel, thus forming a 0.33ohm 3w resistor. They don't get very warm at all.

Thanks Eric. ZenMod had told me that those 600mW x 3 = is little too low for it. Normally this should be 3W. So I have to change those.

At my Gate the resistors are also different from the original. Unfortunately I don't have 1 of the old mos-fet pcb. So I have to change those with different ones. Many people have on those places the Panasonic ERX or ERG. Are those the best choice for my audio preferences?

 

[Zen Mod]

I would say that Panasonic 3W MOX are good choice

by memory , yes - ERG and ERX

Through Hole Resistors | Resistors | DigiKey

 

[oreo382]

Can somebody tell me what brand are those resistors?

Vishay BC components

 

[slowikpl]

Vishay BC components

Thank you !

 

[slowikpl]

I have now ordered 100 Vishay BC 2-Ohm 2W resistors for the mosfet and also 60 Vishay BC 1-Ohm 3W for the output


I wil comment if there are any differences in sound reproduction.

also i will rewire the unit with Western Electric Vintage cable.

Can someone tell me tell me is there any diffrences in Power Mos-Fet`s like IRFP240 vs Vishay. And where can i get matched 12 pcs IRFP240 on the net ?


http://www.ebay.com/itm/12-PIECES-O...hash=item5889d91b78:m:mTZhkbTF3GARZ4MvrbBdL6Q


Zen i image you will be first to post