@grannyring...
what is the sensitivity of your speakers and the gain of the preamp you are using? this matters much with the job's 35db of gain and 0.75V sensitivity. i found that i also had a hiss with my 94db speakers and modwright preamp until i bled off quite a bit of gain at the inputs to the job. after doing so, the noise floor was back to where i expected - ie, no noise whatsoever.
that said, my amp gets warm, but never too hot to rest my hand upon, even after several hours of use, so it's possible there may be more going on with your amp. |
How did you bleed off gain at the inputs? Speakers are 84db effecient and my tube preamp I am not sure about. It is not high gain however.
The top cover is warm, however I am talking about the heat sinks on the back of the amp only. These sinks get very, very hot. |
0.75V sensitivity for full output! With all this gain and 94dB speaker why use a active preamp with gain?? Most sources give out more than 2v these days, even phono stages, and the Job I believe is 100kohm input impedance, all this is a perfect match for a passive pre such as the $49 Schitt Sys http://schiit.com/products/sys Then you will not have any hum or noise problems and as a bonus zero colourations that all actives have. Cheers George |
Granny, I agree with George in that the 225 is very "passive friendly" as long as output impedance of source isn't too high. However, its input impedance is 51K.....not 100K. Also, most every source has at least 2V output.
What concerns me is the tube preamp. I'm pretty sure Srajean at 6moons said to be very cautious pairing the 225 with a tube preamp. The 225 has no DC protection so any DC leakage goes straight to the speakers! Not good.
IMO, the 225's specs SCREAM passive. I'm not going to get into the passive vs active debate hear. That's another topic for another thread.
What puzzles me is at 84db, your speakers are not efficient. I would think you would hear LESS hiss and hum beacause of that.
That said, I think your active preamp is putting out too much gain for your extremely sensitive, 35db job.
Like I said, im FAR from an expert with this here. Just my 2 cents. |
I read one if your other posts again. In it, you say the heatsinks get much hotter the louder you go. I'm wondering if the Job might not like seeing an 84db speaker. I find this hard to believe, though. I've read that the 225 puts out more power than its 125 w/ch spec says.
Again, I doubt it. I'm just trying to think of any possible scenario here.
|
George knows I have owned, modified, and built LDR passive units so I know them well. I also know they would be a great match with this amp. Problem is I a/b'd my DIY preamp against a Tortuga LDR and my active was just more pleasing. I love George's LDR also. However, this was with a different amp and speakers. It may be time to try that comparison again as things have changed.
My preamp does not send out a spec of DC as I measured one, twice, and even a third time over a span of time.
I have written Goldmund and hope to fix the issue myself. |
With my volume control at 9 the music is at 80db at 10:30-11 the music plays at 90db or so average weighted C scale. No real noise to speak of until I get to 11AM and then it starts be become loud. If I play my music under 85-90db all is well. If I turn the volume up to 2 or 3 the noise is quite loud through the speakers with no music playing obviously. I hear a moderate buzz combined with loud hissing. The hissing sounds like tube rush, but I hear none of this with all other amps I have paired with my DIY preamp.
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George, my speaker is 84db and the input impedance on the Job amp is 51k. Amazing sounding amp. I have read that older units had a grounding issue that caused the noises I am having. |
@grannyring...i use an LDR preamp effectively as an attenuator at the Job inputs. the LDR piece is set at a specific level and simply left there. input switching and system gain adjustments in use are still handled by my Modwright preamp. rick schultz made this suggestion when i contacted him to build me a set of his evs ultimate attenuators. works perfectly - DRAMATICALLY reduced the noise floor of my system and enabled me to dial in the system gain such that the VC in my preamp now offers very fine control of overall system gain.
i agree that the 225 is a fantastic sounding amp, but does require some care in implementation for the gain and sensitivity. once worked out, it's truly excellent. |
Thank you very much srosenberg as this is a mighty fine idea. I was thinking of just using Rothwell attenuators, but they may degrade the sound? I have not used the Rothwells before. I love this little amp. Best value in high end along with the Lightspeed attenuator. |
Seems the Rothwells do change the sound in some not so great ways. Great LSA idea. |
It’s not that the Rothwell’s themselves can "change the sound in not such a great way" But what the Rothwell’s can do is change the perceived impedance as seen by the previous stage, as then not to have a good impedance match. This can mainly happen with a tube or passive preamps, most solid state preamps should not have this problem Cheers George |
@grannyring
i haven't used the Rothwells personally but have heard that they aren't the last word in transparency. I can say that the LDR pre in my application was completely transparent, and enabled me to perfectly dial in the amount of attenuation needed, unlike the fixed in line units, such as the Rothwell. |
I’m sure if you used two of my or any passive pre’s in series the sound would be crap as well without using the Rothwell’s. I'm sure the Rothwell will be fine on the input of a high input impedance (>47kohm?) poweramp, if the pre before it had a low output impedance of below say <50 or a 100ohms.
Cheers George |
I wonder what the input impedance of the Rothwell devices are as George makes a good point. I believe the input impedance of the LSA is 20k and that is not a good match for the output impedance of my tube preamp. |
???
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. |
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.
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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 |
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. |
Yes George, that's precisely what I meant about the "not liking each other"comment. Too much gain. |
Yes grannyring your output impedance of your pre at up to 1kohm, (which by the way is not far off a 10kohm passive for drivability) should be fine for any poweramp with say 33kohm or higher input impedance. But you probably have gain in it also, it would be nice if you could configure it to have unity gain, if it stays stable, some opamps can be used as output buffers and are unity gain stable as well as being very low output impedance like 10-20ohms. eg OPA627.
Cheers George |
Joeinid
Did you fancy the EAR 890? |
Joeinid
Did you fancy the EAR 890? Hi Glory, Yes, I did. It's a great tube amp. When I bought mine there was a pinched wire that would cut out one channel. Once I got that straightened out, sound was warm (but not too warm) and wonderful, sweet and airy. A friend had to have it so I sold it to him. With the right speaker load (not to tough), it was a wonderful performer. I even had the 868 (?) preamp and that was a nice piece too. |
But is as good as the Positive Feedback Leavy guy says it is? Got one coming on Monday. Running 96db speakers |
glory1,274 posts10-02-2016 2:59pmBut is as good as the Positive Feedback Leavy guy says it is? Got one coming on Monday. Running 96db speakers Congratulations! You'll love it. Please start a new thread when you get it set up. |
Attention GEORGELOFI I noticed your post...
"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.)"
Are you able to confirm exactly which tubed preamp that you were using, that ultimately did not provide a usable gain-match with the JOB 225 please?
Importantly, I'd like to understand how much gain that particular tubed preamp had, as I am seriously considering a JOB 225 to use with my own tubed preamp with 12dB of gain. Appreciated.
(I use 4-8 ohm dynamic speakers of around 90dB sensitivity...)
To my ears, I have found that all systems benefit from having tubes in the circuit, somewhere in the chain. Of course, this assumes all other factors - such as impedance and gain matching are well and good.
I look forward to your thoughts...
|
I would want to try the Decware CSP3 preamp with the Job. It has an adjustment for incoming voltage and a volume control for out. Read about it on the Decware website. You can adjust voltage to sound the best or as a Steve Deckert calls it "riding the gain" |
It's been a bit since anyone has commented in here, but I was wondering if people still have their 225's, and if so, are they still in love with them?
I have a Firstwatt F7, and am thinking about getting the Job to take me closer to neutrality. But (unless someone's willing to send me their 225 to evaluate 😀) I'd have to sell or trade my F7 to get it.
So how is everyone feeling about their 225's?
Thanks guys! |
Most have moved on from the job,I don't think it would be that much more neutral than a F7,could be system dependent though.
You got to remember that the job is a very high gain Amp,10db higher than the average of 26db for most solid state amps.The job pairs best with a passive or low gain preamp.
The benchmark AHB2 is probably a lot more closer to neutral than any other I can think of but is twice the price.
It can of course be system dependent and you didn't list the rest of your system.The F7 is probably the most neutral of all the first watt offerings that I have heard though.
Best of luck to you,
Kenny.
|
Kenny is right about the Job being system dependent. The LTA MZ2 did not work well with it, the Decware CSP3 did work well because of the input adjustment. The Job also can occasionally make a big pop sound when it decides to pass a little DC to your speakers.
|
Anyone compared the Job225 to the Benchmark Ahb2 amp? |
It's been a bit since anyone has commented in here, but I was wondering if people still have their 225's, and if so, are they still in love with them?
Got my Job 225 and Pre2 in September and loving them. I think folks are still holding on to their Job, hard to find in the used market back when I was looking. |
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For all the high end qualifiers thrown its way, for me its a music lover amp. It is not ultimate high end amp. It runs hotter into 4 ohm, I currently use with 8 ohm. I also found it ran a little hotter with a passive versus active. Overall I prefer with active. A keeper, amazing solid state sound. |
