Job 225

[ozarktom]

Thanks - I just bought one..... trying to resist the temptation to buy another, as I would REALLY like to use two of them. The PDF above is helpful and implies potential.

Although it may have been in jest, what do y'all think about using one-channel alone in each of two units; I mean I've heard of vertical and horizontal biamping but could we get more than the rated power per channel if used in this manner, or is it "unused?" I'm afraid I don't know enough about the amplifier....

I asked Antonio this last week and this is his comments.

"The Job 225 is a stereo analogue amplifier which has two isolated amplifiers for the two channels, in a stereo system we recommend to use one stereo amplifier or two mono amplifier, your solution is not a standard configuration that we apply in our audio system.

I can not tell you if it will be better or not for the simply reason that we do not test or make this type of system."

 

[untangle]

what do y'all think about using one-channel alone in each of two units; I mean I've heard of vertical and horizontal biamping but could we get more than the rated power per channel if used in this manner, or is it "unused?" I'm afraid I don't know enough about the amplifier....

I believe you would get minimal benefit from this configuration (other than having a spare amp).

Bob

 

[Ric Schultz]

If you paralleled the secondaries on the transformer then you indeed would have more umph from the transformer running mono this way. The difference would still not be that much. However, running a pair as balanced bridged monos is another story. Probably way better.....of course, you would need a balanced pre/source for full benefit and would have to make custom cables to go in. A friend emailed Job and they said they have never tried balanced bridged. I am going to offer mods on the amp (very simple and relatively inexpensive) and also try balanced bridged to see if it works and make sure it is stable into all loads. The mods I will be doing include (a better fuse, removing the steel plate and screw from the power transformer and gluing the transformer on a piece of plywood, damping all the rectifier diodes, removing the LED, damping the main heatsink and putting WA quantum stickers on various things. Also there will be three options for output connector (one is to just remove them and hang the wires outside and clamp or solder to your speaker wires, another is to drill a couple of holes in the chassis next to the binding posts and run the speaker wires outside the amp and wrap them around the outside of the binding post making the binding post a clamp only and the last and worse sounding option is to change the jacks to some Cardas jacks). I will have pricing on my website soon. The first person getting the mod will get 20% off. All of the above things all make a sonic improvement. I have been modding and manufacturing high end gear since 1978. End of ad...now back to your normal programming. he he.

 

[mep]

I believe you would get minimal benefit from this configuration (other than having a spare amp).

Bob

Bob-I disagree. If you have one channel shorted out with an RCA plug, that means the entire PS should be devoted to one channel. So instead of having two channels competing for power from the same power supply, you have effectively configured each amp to be a mono amp and the power supply is only feeding one channel instead of two. It should make a positive difference.

 

[Ric Schultz]

The benefit would be noticeable but not very significant because the power supply is already completely dual mono except for the transformer (notice the Golmund amp uses the same single board but just adds another transformer). There are separate rectifiers and power supply caps on each channel and they are running off separate secondaries on the single transformer. Dual transformers would only be slightly better. You would get slightly better bass, dynamics and high power clarity. If the power supply was common to both channels (as in a lot of stereo amps) then the difference would be major. The original Job amp had one power supply with a couple of really small power supply caps feeding both channels.....now that amp would have sounded way, way better running dual mono (I added 20,000uf to each rail with 4uf bypasses to good effect on that amp). It would be cheaper to get a couple of 500+ watt transformers and replace the whole chassis. This would have better sound than two Job amps. But better yet.....balanced bridged monos!!!!!!

 

[mep]

The benefit would be noticeable but not very significant because the power supply is already completely dual mono except for the transformer (notice the Golmund amp uses the same single board but just adds another transformer). There are separate rectifiers and power supply caps on each channel and they are running off separate secondaries on the single transformer. Dual transformers would only be slightly better. You would get slightly better bass, dynamics and high power clarity. If the power supply was common to both channels (as in a lot of stereo amps) then the difference would be major. The original Job amp had one power supply with a couple of really small power supply caps feeding both channels.....now that amp would have sounded way, way better running dual mono (I added 20,000uf to each rail with 4uf bypasses to good effect on that amp). It would be cheaper to get a couple of 500+ watt transformers and replace the whole chassis. This would have better sound than two Job amps. But better yet.....balanced bridged monos!!!!!!

Saying an amp is dual mono except for the power transformer is like saying someone is a man except they are a woman. The power supply is the heart and soul of any piece of electronics. Does the JOB use a single power transformer but have separate bridge rectifiers and capacitors for each channel or is it a single power transformer with a single rectifier and single B+ supply? You really can't be classified as dual mono with a single power transformer that is shared between channels.

 

[untangle]

Sigh. The amp's trafo has *dual secondaries*. So if you just short one set of inputs you will not be using the entire power supply for one channel. You will be using the entire primary but only half the secondary windings. If you parallel the secondaries (rewire) as Ric suggested, then you will have the entire power supply for one channel.

I would expect some benefit from this mod. I would not expect much benefit from simply shorting one set of inputs.

I have used Goldmund and Stellavox monoblocks with this circuit for 5 years. The Goldmund variant has a beefier power supply (and also much more mechanical isolation). The difference is audible but not earth-shattering.

Based on my experience, I therefore question the ROI of buying a second unit for this purpose.

Bob

 

[Elberoth]

Sigh. The amp's trafo has *dual secondaries*. So if you just short one set of inputs you will not be using the entire power supply for one channel. You will be using the entire primary but only half the secondary windings. If you parallel the secondaries (rewire) as Ric suggested, then you will have the entire power supply for one channel.

+++1

 

[LazyMan]

Wow, many thanks for the very educated replies.

Assessment: No-go on the solo shorting act.

However, perhaps a little cosmetic surgery could make this baby sing even better; however I would not want to detract from the strengths of the unit with regard to dual mono mods (first do no harm).
But I"ll be the first to volunteer

This may pair up nicely with the MMMicroOnes.... mucho quality / el cheapo. I will report back on this.

A decent 9 min video of Michel Reverchon of Goldmund giving a frank (read opinionated) discussion of his design philosophy: YouTube " Seminar On Goldmund Telos Amplifier "

 

[bhakti]

I just saw this on the Job website:

"Special Notice:
If you bought one of the first JOB225 delivered before June 25, 2013, we used in the product a ground configuration optimized for the dynamic range but which requires extreme care in selection of cables and cable path. We found out that most of our JOB friends may have difficulty installing the amplifier with the zero-noise that can be achieved. In most case the noise was not a disturbance. However with very high efficiency speakers or especially inappropriate cabling, it could become bothersome. So we proposed a modification that makes it much more buzz-immune. Note that all amplifiers delivered after June 25th are modified and all customers who want the amp to be modified can write to service@jobsys.com to be taken care of. To answer the most usual question, we consider the moification as having an effect on sound quality quite difficult to detect."

So it appears the "fix" does affect the sound of the amp, but apparently is quite difficult to detect.

I had neither inappropriate cabling nor high efficiency speakers and it was still bothersome.

Kind of interesting that a company with this kind of pedigree would drop the ball right on their foot! They pride themselves in engineering excellence and yet can't seem to get this right. I'm little suspect of this whole endeavor, but I will withhold further analysis. Perhaps they are just having a hard time getting started with this side of their business.

By the way, I returned my amp for a full refund. I would like to re-purchase, but I will wait for the bugs to be worked out.

Has anyone purchased one lately??

 

[ozarktom]

A friend of mine bought one and no hum. He likes it better than his Ncore 400's.

 

[joeinid]

I'll have to check the date on mine but I did not have a hum issue. I'm using it right now on my Sonus Faber Evolutions and it sounds wonderful. Articulate bass, big soundstage, amazing detail without being harsh. Awesome voices. It feels more than powerful enough.

 

[Ric Schultz]

Just got a Job in today and took a look inside. The transformer cannot be bigger than about 250 watt. So, you could never get more than 125 watts into any load (peaks, a little more). The amp runs on high voltage (about plus and minus 75V) so high power is possible. If you put this amp in a bigger chassis and used 400 watt transformers for each channel you could easily get 200 watts into 8 ohms and just about double that into 4. The amp is biased very low. Maybe 50 milliamps max per pair of mosfets. The heatsink is very small so that is why some say it runs very warm. There are four pairs of mosfets and at 50 milliamps at 150V you get 30 watts of dissipation. Don't think its even that high. I have not measured the idle current but based on the size of the heatsink and how hot it is I would say it is only putting out about 15 watts or so. So, this is a low bias class A/B amp. Imagine if you put the amp into a large chassis and put a serious monster heat sink on it.....and then turned up the bias!!!!! The only trouble with using large transformers and increasing the power is that you only have 2 pair of mosfets per channel.....so they will limit the current and be at risk for blowing at super high power. The size of the stock transformer keeps it in a good power dissipation mode for safety sake. The best way to make more power is to go balanced bridged. I will be testing it in this mode sometime in the next week. If stable, then using two of them could be super killer as balanced almost always sounds better than single ended and bridging usually sounds better than standard balanced....and of course mono-ing would improve the sound slightly too. You would have about 250 watts into all loads except under 4 ohms. I should have all mods tested in about 2-3 weeks.

 

[LazyMan]

Ric, thanks for the excellent initial observations. The DIYaudio site has many threads devoted to analysis of the circuit; I'm away from my home computer but among the interesting quotes was one mentioning that the power supply was made to be a "limp dick" on purpose - something in relationship to keeping the (? lateral) Mosfets from blowing up since their only weakness is HEAT. Thus the explanation for the rather delicate looking heatsinks, etc. Goldmund is not stupid, in other words. I find it rather interesting that since there are cloned PCB boards for the truly DIYers out there, Goldmund decided to join the bandwagon, sort of.

Not to go off topic, but could there be space for a high-quality volume control, to make it into a one-source integrated? However, someone would have to put a drill to that nice faceplate

Back to OT, I am praying to the audio gods that there is space for the bybee music rails..... please oh please.....

 

[untangle]

The Job circuit was originally designed to power computer speakers (really). So it was meant to run cool in that config.

However, audiophiles (and Goldmund) observed that the thing sounded sensational and audiophile implementations were born. (History resembles t-amp.) For whatever reason, the basic power delivery scheme was retained. Perhaps this was to ensure the "agility" of the sound remained intact. Perhaps for longevity.

I tried the Bybee PS mod and didn't get much out of it. I tried it after hearing the sensational improvement it provided to Class D amps. [Ric - I may have the parts lying around.]

As for hum/cables, I only had a problem with my Job monoblocks once. I was running six of them (tri-amped active xover). I solved it by making well-shielded cables with the shield *grounded at both ends*. Don't ask me why....

Bob

 

[Elberoth]

Ric Schultz - are you the person that worked for Virtual Dynamics ? Just curious as your nick name rings some bells in my head (still have a Power 3 PC - an excellent, entry level PC).

 

[LazyMan]

Rick (or Ricky) Schultz = designer and inventor, currently of High Fidelity Cables and Connectors, formerly of Virtual Dynamics

Ric Schultz = CEO of EVS (Electronic Visionary Systems) AKA tweakaudio


I know, I was getting the two confused initially. Would love to see what happens at CES time at reservation desks, etc.

 

[Elberoth]

Good to know, thanks !

 

[LazyMan]

Hi Bob, that's amazing..... SIX units employed. I have absolutely no experience with active X-overs other than Rockport going to that route with their big boys. My Voce VA-3s have 2 sets of rear binding posts but I will have to find out if they are really separated at the Xover; my goal if Ric's balanced-bridge setup works will be to use 4 Jobs in toto at about 500 W total per side.

 

[untangle]

I have absolutely no experience with active X-overs other than Rockport going to that route with their big boys. My Voce VA-3s have 2 sets of rear binding posts but I will have to find out if they are really separated at the Xover

Ric has a lot of experience with active xovers, so he can help you.

Your Voce's almost-certainly just decouple the high-pass and low-pass elements of their passive xover. Great for biamping, but not active crossovers. Usually simple, reversible mod to go active though.

Bob