Job 250 vs. LM4780 Chip Amp

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tortugaranger

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Job 250 vs. LM4780 Chip Amp
« on: 9 Jul 2015, 07:08 pm »
I just had an surprising experience with a new set of Job 250 mono amps that arrived yesterday. They are made by Goldmund in Switzerland for Job which I believe is a US based company. I've read quite a lot of good things about the Job stereo/mono amp and was looking forward to being wowed. I swapped out the LM4780 based chip amps I've been using lately and installed the Job's.

After listening last night and a couple of times today, I went ahead and put the LM4780's back in just to see if I was imagining what I was hearing. Nope. The LM4780 chip amps sounded clearly better than the Jobs. Warmer, more analog like. The Jobs were clearly very articulate and plenty powerful but were too bright and the sound stage wasn't as coherent. The listening experience simply wasn't as enjoyable with the Job monos.

The LM4780 amps I'm using are prototype designs that have been rattling around inside Tortuga Audio for a few years. They are dual mono amps as well each with a huge 400 VA toroidal transformer and top shelf components. As configured they are putting out somewhere in the 60-80 watt range which is considerably below the max rating of the LM4780s.

We have several customers with Job 225's who had great things to say about them so this really surprised me. I'm curious if anyone out there has tried the Job amp and if so how they compared to what you were using before.

RDavidson

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Re: Job 250 vs. LM4780 Chip Amp
« Reply #1 on: 9 Jul 2015, 08:27 pm »
I don't have experience with the Job amps, but I'm not really surprised. I bet the Job 225 would be better suited. The reason...

In my experience, most (not all) class A/B amps (particularly with about 100 wpc+) don't sound best when they're not being pushed a bit. It's almost like having a powerful automotive engine, but just idling along not even close to getting into its power band (cranking out torque ; Where the fun really happens). Conversely, I've found most (not all) class A and class D amps to sound consistent whether they are pushing .5 watts or in the upper territory of their non-clipping range. Class D might be the best in this regard overall, IME.

My question is, what speakers are you using? If they're pretty efficient (I imagine they might be as you're certainly using a Tortuga passive), then the Jobs are likely just loafing vs operating in their sweet spot. I think some of the good amp manufacturers around actually design amps with the assumption your speakers will use the power (and thus operate as they are best intended).

I think what you're realizing is that speaker : amp pairing may require more thought (for your listening preferences) as a synergistic system vs the more simplistic idea of "buy as many watts as you can afford, even if the speakers and room don't need it." Nothing wrong with the latter, if it makes you happy. I'm certain this works quite well in some cases....but, maybe not yours. :thumb:

tortugaranger

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Re: Job 250 vs. LM4780 Chip Amp
« Reply #2 on: 9 Jul 2015, 08:39 pm »
I don't have experience with the Job amps, but I'm not really surprised. I bet the Job 225 would be better suited. The reason...

In my experience, most (not all) class A/B amps (particularly with about 100 wpc+) don't sound best when they're not being pushed a bit. Conversely, I've found most (not all) class A and class D amps to sound consistent whether they are pushing .5 watts or in the upper territory of their non-clipping range.

My question is, what speakers are you using? If they're pretty efficient (I imagine they might be as you're certainly using a Tortuga passive), then the Jobs are likely just loafing vs operating in their sweet spot. I think some of the good amp manufacturers around actually design amps with the assumption your speakers will use the power (and thus operate as they are best intended).

I think what you're realizing is that speaker : amp pairing may require more thought (for your listening preferences) as a synergistic system vs the more simplistic idea of "buy as many watts as you can afford, even if the speakers and room don't need it." Nothing wrong with the latter, if it makes you happy. I'm certain this works quite well in some cases....but, maybe not yours. :thumb:

The 250 W Jobs are definitely loafing. The speakers are 90 dB efficient using single full range driver. Plenty of SPL to fill even the high ceiling great room they're located in when driven by the 60W LM4780s.

RDavidson

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Re: Job 250 vs. LM4780 Chip Amp
« Reply #3 on: 9 Jul 2015, 08:49 pm »
Yup. This has been repeated many times. If the first watt isn't pleasing, then why would you want more of them?

I'd be surprised if you pushed more than a constant 10 wpc most of the time (which would be very loud in your case). That's 4% of the Jobs' unclipped power. This isn't a "rule" but it seems to me that largish A/B amps sound best when using at least a constant 10% of their unclipped power. I think this may also account for the reason that smaller amps made by the same manufacturer can sound better in some cases/systems than their TOTL big boys. There was a discussion over in the Music Reference circle at one time on the topic and Roger Modjeski was in agreement with this general assessment and of course had some technical explanation. Having headroom on tap is great, but it has drawbacks that are system dependent and thus not always understood. Much has to do with the amp's design and how it reacts to various loads (both easy and difficult) too. It's a complex issue.
« Last Edit: 10 Jul 2015, 12:34 am by RDavidson »

33na3rd

Re: Job 250 vs. LM4780 Chip Amp
« Reply #4 on: 12 Jul 2015, 07:28 pm »
A Tortuga Audio Chip Amp might be a very interesting product!

tortugaranger

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Re: Job 250 vs. LM4780 Chip Amp
« Reply #5 on: 12 Jul 2015, 07:36 pm »
A Tortuga Audio Chip Amp might be a very interesting product!


I've been very impressed with the 3886/4780(dual 3886) amp chips and have had various versions running for several years. Well executed these really perform wonderfully.

33na3rd

Re: Job 250 vs. LM4780 Chip Amp
« Reply #6 on: 12 Jul 2015, 07:42 pm »

I've been very impressed with the 3886/4780(dual 3886) amp chips and have had various versions running for several years. Well executed these really perform wonderfully.

I am interested in trying a Chip Amp, but worry that they might not have enough juice for my speakers that dip down to 3.5 Ohms in the mid bass. Perhaps my fears are unfounded, similar to those folks who fear that a Passive can't drive their amp!  :D

Folsom

Re: Job 250 vs. LM4780 Chip Amp
« Reply #7 on: 12 Jul 2015, 08:05 pm »
Jeff Rowland uses the 3886 in an amplifier. Actually I think it's 3x per channel. I'll let you ponder that.

wisnon

Re: Job 250 vs. LM4780 Chip Amp
« Reply #8 on: 12 Jul 2015, 09:36 pm »
I had the Job 225 and the 250s for a month and they were excellent. Not a hint of brightness and I used both a passive preamp and the Aum acoustics LDR preamp (which was even better). The 225 and the 250s had the same sound signature and with my 91 db speakers, both were "overkill".

Mind you, I fronted them with an Onkyo CD player as well as a Big 7 Lampizator tube Dac.

Job is coming out with an Integrated amp soon, It will also have a built in Dac that plays PCM 384 and DSD. No specs or prices listed on their web site yet.

tortugaranger

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Re: Job 250 vs. LM4780 Chip Amp
« Reply #9 on: 12 Jul 2015, 09:53 pm »
I had the Job 225 and the 250s for a month and they were excellent. Not a hint of brightness and I used both a passive preamp and the Aum acoustics LDR preamp (which was even better).


The Aum LDR preamp is a Tortuga Audio preamp in all but name insofar as it uses the core Tortuga LDR3x preamp controller board.  :thumb:

RPM123

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Re: Job 250 vs. LM4780 Chip Amp
« Reply #10 on: 12 Jul 2015, 10:37 pm »
I used to own a JOB 225 and found it to be very cable dependent, including power cords. It is a high band-with amp, so it may accentuate unruly highs, especially on CDs. Overall though, I did not find it to be bright. Also, I would give it more time to break-in, e.g., 100 hours or so and then give it another serious listen. I have since switched to an all tube based system to better mate with my new speakers.

bos3812

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Re: Job 250 vs. LM4780 Chip Amp
« Reply #11 on: 6 Aug 2015, 04:20 pm »
I own a Job 225 and can tell you that this little amp has become very special to me. I bought it a half year ago. When I unpacked it and connected it I was very curious because of the rave reviews. When I listened to the first songs my first reaction was a little disappointment. The sound was a little thick and veiled. But as time passed the amp became better and better. And now, a half year later it's my reference. The Job has something special I never heard with other amps I owned. It has a real live factor. It does not only have a nice sound like many other amplifiers but it plays real music that makes you smile or cry of emotion if you want. This amp really needs time to unfold itself. And it is correct that the Job is very cable sensitive.

Eric, the Netherlands

DaveC113

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Re: Job 250 vs. LM4780 Chip Amp
« Reply #12 on: 6 Aug 2015, 04:50 pm »
The Crown XLS amps do really well with single drivers and have built-in 24 dB/Oct L-R filters so you have a very transparent dsp based xo solution built right in. My Omegas sound much better at higher volumes with a 50 Hz highpass filter engaged. You can get the previous gen amps for VERY cheap right now. Pomona binding posts fit right in and are an almost necessary upgrade.

I do think you should make integrated amps and active or buffered preamps using the LDR to add to your line...  :green:

roymail

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Re: Job 250 vs. LM4780 Chip Amp
« Reply #13 on: 6 Aug 2015, 08:23 pm »
Tortugaranger, what is the input impedance of your LM4780?  It must be compatible with an LDR, like 47K or so.  Bet that does sound awesome.  So many integrateds used an Alps VC or something of even lesser quality.  I once had a 3886 chip amp with a Goldpoint stepped attenuator that sounded very nice.  Like so many others have done, I moved on when I should have kept it.  But I will say, that LDR volume controls are the best I've ever heard.

tortugaranger

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Re: Job 250 vs. LM4780 Chip Amp
« Reply #14 on: 6 Aug 2015, 08:35 pm »
Tortugaranger, what is the input impedance of your LM4780?  It must be compatible with an LDR, like 47K or so.  Bet that does sound awesome.  So many integrateds used an Alps VC or something of even lesser quality.  I once had a 3886 chip amp with a Goldpoint stepped attenuator that sounded very nice.  Like so many others have done, I moved on when I should have kept it.  But I will say, that LDR volume controls are the best I've ever heard.

Running the 4780 in parallel mode with a 47k input impedance. Great match with the LDR preamp any source with 1k or less output impedance - which covers most but not every source out there. Even though the 4780's in parallel are rated for a nominal 120 watts I've found that these chips run way too hot at the voltage needed for that output and prefer to limit output to somewhere around 60-80 watt to avoid excessive heat and big sinks. Plenty of boom boom for most speakers but a bit low for the most inefficient.