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Anyone have/ordered the Job 225?

There's almost no consumer impressions of this amp on the internet... but the 6moons review is intriguing.
girlsgeneration
devilboy
1,176 posts
 
???
What's the output impedance of your source?
Do you have any music that starts off VERY quiet and then SLOWLY increases in volume? I think it's Arthur Salvatore who calls it the "Bolero test". He connects a source directly into his amplifier and plays Bolero to see if a system can support a passive preamp.
*****BE CAREFUL!!! *****
Obviously volume is wide open here so make sure you stop the music before you do some damage.
I'm guessing your tube preamp and Job don't like each other.
grannyring's avatar
grannyring
6,479 posts
 
I am sure my rig is passive friendly, but I really want to keep my self designed and built tube preamp. The output impedance of my preamp varies with the volume setting. I use a shunt style stepped attenuator made by Khozmo. I measured the output impedance over the volume range I listen to and it changes from 360 ohms to 1k ohms. According to George this may be to high for proper matching with the Rothwell attenuators. 
georgehifi's avatar
georgehifi
10,312 posts
 

Lightspeed is around 10kohm Grannyring, it mimics similar parameters as a 10kohm logarithmic potentiometer. So sources feeding it should be less than <1kohm, as I believe in the >10-1 ratio rule.

And as for a tube amp and the Job not liking each other, it's not that they don't like each other it's the fact that there is too much gain, massive in fact, as Devilboy said way back about the Job "IMO, the 225's specs SCREAM passive"  You be nutz to put a preamp with it that has gain.

Remember what Nelson Pass said, (and he designs and sells active
preamps.)


Nelson Pass,

We’ve got lots of gain in our electronics. More gain than some of us need or want. At least 10 db more.

Think of it this way: If you are running your volume control down around 9 o’clock, you are actually throwing away signal level so that a subsequent gain stage can make it back up.

Routinely DIYers opt to make themselves a “passive preamp” - just an input selector and a volume control.

What could be better? Hardly any noise or distortion added by these simple passive parts. No feedback, no worrying about what type of capacitors – just musical perfection.

And yet there are guys out there who don’t care for the result. “It sucks the life out of the music”, is a commonly heard refrain (really - I’m being serious here!). Maybe they are reacting psychologically to the need to turn the volume control up compared to an active preamp.

  



Cheers George   

grannyring's avatar
grannyring
6,479 posts
 
George read my post above yours and give me your thoughts on the Rothwell. Hard to part with my preamp as it was a three month DIY project. They sound fantastic together. I do want to reduce the hiss and think you are absolutely right about too much gain.

I can also  reduce the gain in my preamp by changing out the plate resistor value I suppose.
devilboy
1,176 posts
 
Yes George, that's precisely what I meant about the "not liking each other"comment. Too much gain.
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