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Old 15th January 2013, 06:50 PM   #531
Gopher is offline Gopher  United Kingdom
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I think ur wrong owen. Noise adds in RMS fashion. The LTC application note demonstrates this.
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Old 15th January 2013, 07:01 PM   #532
opc is offline opc  Canada
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That depends... what is your dominant source of noise in the overall circuit?

In the case of these buffers, they are nested within the feedback loop of another op-amp, which is the dominant source of the noise in the circuit. You can parallel to your heart's content, and there will not be any additional noise benefit.

What there will be is longer traces and a less ideal layout, both of which result in more noise.

It all depends on what you're doing, and what the circuit looks like. In the case of the example in the Linear datasheet, the answer is yes, noise will be reduced. It won't be quite as ideal as stated, and I would imagine that given a low enough noise op-amp you will probably do more harm than good by adding several in parallel.

Again, there's theoretical, and there's the real world. I can build you a differential SPICE circuit that has absolutely no second order harmonic distortion, but if you build it, you'll see that's not the case.

Cheers,
Owen
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Old 15th January 2013, 09:43 PM   #533
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So the recommended transformer, L01-6363 is OOS at Digikey, and not due for 1.5 months.

The lower voltage L01-6362 is also OOS, but is due in a few days.

Since I don't the full 18VDC rails, I plan to use the 6362, and will live with around 15VDC rails.

From what I read here, that will also reduce the heatsinking requirement, and make it more likely that I can just used the BOM heatsink, with maybe a RAM heatsink thrown in.

Randy
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Old 15th January 2013, 11:01 PM   #534
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Quote:
Originally Posted by opc View Post
Therein lies the problem...

It's very difficult to have it both ways. Your average consumer, who has no interest in putting anything together should evidently expect to pay more for a completely finished and tested product. The problem is with the first part of your statement, which unfortunately is quite true. The BOM does not include development costs, or the costs of the expertise required to make a finished product. I think everyone here could draw up a basic schematic based on what I've said above, but going from that to a very good performing amplifier is not trivial. It's also not something that should be expected for free.

It think to successfully have it both ways, you need to tread a fine line similar to what Nelson does. He has Pass Labs, which offers excellent products at upper-market prices, and essentially gives people almost unlimited access to his expertise here on diyAudio. You'll notice, however, that he does not offer his Pass Labs products in kit form at cost, as that would surely impact finished product sales, and setup an unfair pricing structure.

Anyhow... I've been struggling with all of this, trying to come up with a fair compromise, but it's not a simple issue and it doesn't have a simple solution.

Cheers,
Owen

Owen,

I have actually been thinking about this for a while independently of this topic coming up here. I think if someone wants to de-value design work to the cost of a pcb manufactured in a short run, then let them buy second class ebay designed pcbs and let them enjoy their delusion, they're not in it for performance but just the need to say they built something.

Do people think that the Orion speaker is only worth as much as the cost of the drivers and some timber? Do people think that Geddes' Abbey is only worth the manufacturing cost of his custom CPLD baffle+waveguide? Why is it any different for a circuit board?

In DIY I actually am only aiming to get the best combination of equipment to minimise/control the number of compromises in my system. If that means outsourcing some menial soldering work and paying a guy who has designed an amp that is better than normal, I'm not going to lose a moment's sleep.


Quote:
Originally Posted by randytsuch View Post
So the recommended transformer, L01-6363 is OOS at Digikey, and not due for 1.5 months.

The lower voltage L01-6362 is also OOS, but is due in a few days.

Since I don't the full 18VDC rails, I plan to use the 6362, and will live with around 15VDC rails.

From what I read here, that will also reduce the heatsinking requirement, and make it more likely that I can just used the BOM heatsink, with maybe a RAM heatsink thrown in.

Randy

Randy,

I am not so sure that you don't want higher rails, depends on your target output I guess but off top of my head I'd have though that keeping the rails high would help in driving your high impedance load.


In terms of heatsinking, it depends a lot on where you're using it. If ambient temps are low then really these amps don't need much heatsinking. I know that my amps may get left on and that we get ambient temps here pushing 35-38degC most summers so when these are inside a case with class ab amps, the temp inside the amp enclosure will be ... quite warm, so that's why I went to extra effort. With normal temps without extra heat dumped from nearby gear I think the BOM heatsink is plenty though probably limited by the thermal conductivity of the LME49600 chip cases which is why I went under the pcb as the heat will come through the pcb more freely than the plastic chip cases. The opamps have only ever been reported to be a bit toasty by feel, in reality they are rated to run pretty warm and probably aren't an issue at all. I was going to leave them alone, but I ended up with them being covered by the alu that is taking heat off the buffers, then I worried about airflow in the 3mm gap and decided to put the 1.6mm bar to the opamps and a few 'speed holes' for extra ventilation. I decided the diodes would benefit from a bit more ventilation so overcompensated a touch with the hole under them!


Quote:
Originally Posted by opc View Post
Crikey! Those are some pimped out heatsinks!

Speed holes and all

You'll definitely have the happiest buffers of the group.

Overall it's a very elegant solution to the heatsinking problem, which was something that took a lot of effort with the "production" version.

Keep up the good work!

Thanks Owen, cannot wait to have them all up and running, that'll be a while yet. I am starting to think of this 4ch amp as 'Temple of Wire'. I really need to get back to the auto-bias pcb design for the LME amp soon but those little alu bars took a lot more time than I first expected. I only have a hacksaw, a hand drill and some sandpaper so making those was certainly doing it the hard way. Hope those buffers appreciate it!!



Cheers,
Chris
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Old 15th January 2013, 11:10 PM   #535
pos is offline pos  Europe
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Quote:
Originally Posted by opc View Post
I use a 103dB 1W/1m midbass, and a 116dB 1W/1m compression driver to listen for detectable noise.
Owen,
Have you tried current drive with your midbass driver? (or just using a series resistor to simulate it)
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Old 16th January 2013, 01:22 AM   #536
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Quote:
Originally Posted by hochopeper View Post

Randy,

I am not so sure that you don't want higher rails, depends on your target output I guess but off top of my head I'd have though that keeping the rails high would help in driving your high impedance load.


In terms of heatsinking, it depends a lot on where you're using it. If ambient temps are low then really these amps don't need much heatsinking. I know that my amps may get left on and that we get ambient temps here pushing 35-38degC most summers so when these are inside a case with class ab amps, the temp inside the amp enclosure will be ... quite warm, so that's why I went to extra effort. With normal temps without extra heat dumped from nearby gear I think the BOM heatsink is plenty though probably limited by the thermal conductivity of the LME49600 chip cases which is why I went under the pcb as the heat will come through the pcb more freely than the plastic chip cases. The opamps have only ever been reported to be a bit toasty by feel, in reality they are rated to run pretty warm and probably aren't an issue at all. I was going to leave them alone, but I ended up with them being covered by the alu that is taking heat off the buffers, then I worried about airflow in the 3mm gap and decided to put the 1.6mm bar to the opamps and a few 'speed holes' for extra ventilation. I decided the diodes would benefit from a bit more ventilation so overcompensated a touch with the hole under them!

Cheers,
Chris
35-38C? Over here, that would be 95-100F, little warm.
They have this new invention called AC, you might want to look into it

If I was about 10 miles further inland I would have the same temps, but I am lucky, and my summer temps are problably more like 30C, and it cools down at night when I usually listen to music.

I could buy an 18VAC TX now, but then I would have to drop at least 7V through the regs.

Maybe I just wait until mid March for the 15VAC tx's to come back into stock.
In the meantime, I could build them up, and between my Variac and the tranny's I have around, I could build and check them out.

Thanks for the input.

EDIT:
Or maybe I could use this instead
Another 15VAC torroid

Randy
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Last edited by randytsuch; 16th January 2013 at 01:36 AM. Reason: add alternate device
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Old 16th January 2013, 01:53 AM   #537
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Quote:
Originally Posted by randytsuch View Post
35-38C? Over here, that would be 95-100F, little warm.
They have this new invention called AC, you might want to look into it

If I was about 10 miles further inland I would have the same temps, but I am lucky, and my summer temps are problably more like 30C, and it cools down at night when I usually listen to music.
I wouldn't live without AC! I have probably spent too much time designing industrial stuff (control systems and power systems) where equipment designs are derated to allow for worst case thermal situation.

Plus I'm a bit realistic, I just know that there are times others use the system, don't turn the amps off, but DO turn the AC off then walk straight out the door (with the house still all closed up) ... so I almost feel like the 38degC example is underdone by 10 or 15degC by the time I look at temps inside the enclosure under those conditions. I know a guy who has left Class A amps on inside closed house accidentally while they were away for 2 weeks or so

Since I know LPUHP in its current form is essentially irreplaceable, I'm being a tad over-cautious with mine. Especially when I am next up going to be building external controllers to integrate all of my amps and have the whole system tv/source/dsp/amps power on/off from one button to allow for the above stupid times where the system is accidentally left on.

In the end I know I am spending a lot of time catering for the 1% situation and 99% of the time it will be overkill, but it is just such good fun!


Chris
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Old 22nd January 2013, 02:50 PM   #538
IanAS is offline IanAS  England
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Owen, how does the sound quality from the 50W version of this amplifier compare to your LM49830 with the Alfets?
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Old 22nd January 2013, 11:10 PM   #539
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We reached mid 40ís C twice last week and with no AC, so Iím all in favour of heat sink overkill even if it adds a few more dollars (and has no negative side effects)
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Old 30th March 2013, 12:08 AM   #540
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OK, so this is the best amp I've ever had. And I've had a few good ones. I'm learning to trust it too - It doesn't have a character as such - but is never the weak link. Can be so lively and extrovert. And does something rare in solid-state amps - there is a powerful focus that is different from 'over highlighted detail' - its more akin to Nickel-core SETs penetration. Very useful!

Now, I want to make another pair for my horn tweeters. They need a couple of watts max. So I'm thinking 2 devices per channel. They will always be used with a crossover cap too - so I'm thinking of breadboarding them with just single rail power supply. Can someone help me with the circuit for this? I only need unbalanced input.

Thanks in advance...
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