| demogorgon |
Now, i have been looking through the forums for an answer to this a for a long time, but to no availe, so i figure i'd just open a new thread.
the question is simple, how will the lm3886 respond to 50V rails?
I recon one of three things will happen:
1: the chip's protection sircut will shut the chip down.
2: The thing will pop instantly
3: the chip wil work, but very hot, and not very happy with low impedans loads.
i have a 300w 30V dual secondaries from the time norway had 220V power distrobution, and i dont wanna just keep it ideling around, so i figure using it sounds nice.
alas, when i power it up i read 35.4V pr. secondary. this should mount to DC voltages close to, if not over 50V pr. rail, so..
eagery awaiting your reply.
-Marius |
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| neutron7 |
| you could use LM338 regulator circuit and bring the voltage down to more reasonable level like say 35 volts. regulator max in>out difference is 40 volts so you could try various voltages if you wanted. |
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| leadbelly |
| quote: | Originally posted by demogorgon
i have a 300w 30V dual secondaries from the time norway had 220V power distrobution, and i dont wanna just keep it ideling around, so i figure using it sounds nice. |
I know everybody in this forum just regurgitates the same gainclone voltage guidelines over and over again ad nauseum, so I thought I would make a point just for fun. :) Sitting a couple of feet away from me is a commercial PCB set for a Line6 guitar amp that powers the LM3886TF with a 60VCT transformer. So go ahead. :) |
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| planet10 |
30-0-30 puts you right at the official limit about 42V... BrianGT has a bud running one at something like 46V.
You can try it... you'll likely find out pretty quick if the smoke stays in.
I like stable into low/complex impedances so i'd regulate or maybe try a CRC (or even CLC) to drop a bit of V.
dave |
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| pinkmouse |
| Use much bigger heatsinks, and give up the idea of driving low impedance/ difficult loads, and you can get by on 45v rails. That's as high as I got... |
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| carlosfm |
| quote: | Originally posted by demogorgon
i have a 300w 30V dual secondaries from the time norway had 220V power distrobution, and i dont wanna just keep it ideling around, so i figure using it sounds nice.
alas, when i power it up i read 35.4V pr. secondary. this should mount to DC voltages close to, if not over 50V pr. rail, so.. |
Marius, more important than if it will work is: will it sound decent?
A guitar amp doesn't need to amplify low frequencies, and the chip may work at it's max. voltage.
But you are not making a guitar amp, and you are passing the max. voltage.
Instead of fiddling with the whole bazooka making it play and stopping it's protection from kickin' in, I can't think of an easier route than unwinding some turns of wire from the trafo's secondaries.:idea:
| quote: | Originally posted by demogorgon
eagery awaiting your reply. |
Done.:D |
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| demogorgon |
| quote: | Originally posted by neutron7
you could use LM338 regulator circuit and bring the voltage down to more reasonable level like say 35 volts. regulator max in>out difference is 40 volts so you could try various voltages if you wanted. |
nah, to much work, and besides, they cost like 12dollars a piece here up north. thats almost as much as the rest of the amp cost me..
| quote: | Originally posted by leadbelly
I know everybody in this forum just regurgitates the same gainclone voltage guidelines over and over again ad nauseum, so I thought I would make a point just for fun. :) Sitting a couple of feet away from me is a commercial PCB set for a Line6 guitar amp that powers the LM3886TF with a 60VCT transformer. So go ahead. :) |
I just might do that :D
| quote: | Originally posted by planet10
30-0-30 puts you right at the official limit about 42V... BrianGT has a bud running one at something like 46V.
You can try it... you'll likely find out pretty quick if the smoke stays in.
I like stable into low/complex impedances so i'd regulate or maybe try a CRC (or even CLC) to drop a bit of V.
dave |
well, i hooked the xformer to the psu board, and measured 48.5V rails, so.. if i'm not mistaking, isn't the max voltage suply for the lm3886 96V unloaded?
time to test..
| quote: | Originally posted by pinkmouse
Use much bigger heatsinks, and give up the idea of driving low impedance/ difficult loads, and you can get by on 45v rails. That's as high as I got... |
my heatsink is fairly beefy, so i figure.. wait, you got to 45V, then what? :eek:
| quote: | Originally posted by carlosfm
Marius, more important than if it will work is: will it sound decent?
A guitar amp doesn't need to amplify low frequencies, and the chip may work at it's max. voltage.
But you are not making a guitar amp, and you are passing the max. voltage.
Instead of fiddling with the whole bazooka making it play and stopping it's protection from kickin' in, I can't think of an easier route than unwinding some turns of wire from the trafo's secondaries.:idea:
Done.:D |
ooohh... that actually sounds like a good plan..
I'l try it if the amp blows on me. :hot: |
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| tonitze |
Carlos,
How successful can a person unwind trafo secondaries to your opinion. Is there any chances that you might screwed up the trafo because overlapping of sec. winding? I mean stuck halfway..
Toni |
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| I_Forgot |
If the transformer is a toroid you can lower the voltage by ADDING a few turns of wire around the core, but wound in the opposite direction as the existing windings. No need to take the transformer apart...
I_F |
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| carlosfm |
| quote: | Originally posted by I_Forgot
If the transformer is a toroid you can lower the voltage by ADDING a few turns of wire around the core, but wound in the opposite direction as the existing windings. No need to take the transformer apart...
I_F |
Yes, that's one of the options.
Guys, a toroid is not so complicated inside...
If you don't feel like doing it, wind in the opposite direction. |
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| demogorgon |
just to kill the thread, it worked well, at leat for some time, then i managed to make a fool of myself and short something while unplugging a phono plug, and pow, the magic smoke escaped from one of the lm3886.
god thing i have a couple in reserve then.
thanks for all your input.
marius |
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| peranders |
| quote: | Originally posted by demogorgon
Now, i have been looking through the forums for an answer to this a for a long time, but to no availe, so i figure i'd just open a new thread.
the question is simple, how will the lm3886 respond to 50V rails?
I recon one of three things will happen:
1: the chip's protection sircut will shut the chip down.
2: The thing will pop instantly
3: the chip wil work, but very hot, and not very happy with low impedans loads.
i have a 300w 30V dual secondaries from the time norway had 220V power distrobution, and i dont wanna just keep it ideling around, so i figure using it sounds nice.
alas, when i power it up i read 35.4V pr. secondary. this should mount to DC voltages close to, if not over 50V pr. rail, so..
eagery awaiting your reply.
-Marius |
Why don't you build an amp which actually can take +- 50 volts?
You could also add two windings (approx. 0.3 volt/turn) and let them counteract. (-x+ +x-) Try to loose 3-4 volts => 10-13 turns |
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| XELB |
| quote: | Originally posted by demogorgon
well, i hooked the xformer to the psu board, and measured 48.5V rails, so.. if i'm not mistaking, isn't the max voltage suply for the lm3886 96V unloaded?
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A friend of mine have tested the LM3886 at ~50V(35V trafo), now is going to 60V :eek:
Is using a massive heatsink :bigeyes:
Is testing the chip in different conditions and comparing the sound quality.
Ps: At 50V he said that it plays very well ;) |
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| carlosfm |
The job won't be done until you test 4 ohm speakers, playin' "Burning down the house" by Talking Heads LOUD, at +/-60v.
Also, try a pair of B&W 602 S3, they are 8 (in the treble) ohms.
You guys are crazy.:crazy: |
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| Stocker |
| Not so crazy. Also, not so brokenhearted to let the smoke out. |
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| planet10 |
| quote: | Originally posted by carlosfm
You guys are crazy.:crazy |
crazy like a Fox... keep testing the limits guys :)
dave |
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| XELB |
He's testing the chip to know is behavior in different conditions.
Since he have free :bawling: LM3886 chips, burning is not a problem for him :p
I will follow is work with attention, than, I will post some data ;)
At this moment, I think my amp will run at 30V(based in the new Carlos regulated PSU).
Do you guys use big heatsinks at this voltage ? |
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| macboy |
| quote: | | just to kill the thread, it worked well, at leat for some time, then i managed to make a fool of myself and short something while unplugging a phono plug, and pow, the magic smoke escaped from one of the lm3886. |
I would guess that you didn't 'short something' while unplugging the RCA. Your amp was very likely unstable (or only stable under certain conditions if you prefer), and disconnecting the input source was enough to send it into oscillations. That, combined with the ungodly power supply voltage, promptly destroyed the chip. |
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| I_Forgot |
If you run an amplifier at voltage higher than its design limit, what will you learn? What knowledge is to be gained besides "gee, if I run it at 2X the maximum rated voltage it blows up". You can learn that by looking at the data sheet. Even if you know nothing about electronics and all those other numbers don't mean anything to you, ANYONE can understand what ABSOLUTE MAXIMUM RATINGS means.
You can run an IC at its maximum rated voltage, but its reliability will decrease. A blown up amplifier definitely won't drive your speakers very well, but I guess that won't matter much if the amp takes your speakers with it to "the other side"...
Good luck!
I_F |
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| demogorgon |
| quote: | Originally posted by macboy
I would guess that you didn't 'short something' while unplugging the RCA. Your amp was very likely unstable (or only stable under certain conditions if you prefer), and disconnecting the input source was enough to send it into oscillations. That, combined with the ungodly power supply voltage, promptly destroyed the chip. |
That sounds like a probable case scenario, i couldn't under stand what i could possibly have shorted.
well, i guess i'l have to think of something to hinder oscilliations at the input, maby a lowpass filter..
nothing is impossible, it just takes a while longer.
| quote: | Originally posted by I_Forgot
If you run an amplifier at voltage higher than its design limit, what will you learn? What knowledge is to be gained besides "gee, if I run it at 2X the maximum rated voltage it blows up". You can learn that by looking at the data sheet. Even if you know nothing about electronics and all those other numbers don't mean anything to you, ANYONE can understand what ABSOLUTE MAXIMUM RATINGS means.
You can run an IC at its maximum rated voltage, but its reliability will decrease. A blown up amplifier definitely won't drive your speakers very well, but I guess that won't matter much if the amp takes your speakers with it to "the other side"...
Good luck!
I_F |
Well, anyone can read a datasheet as you say, at least the maks voltage input part, but I wasn't looking for a datasheet answer, i wanted real life resoults, of which i got, so i'm satesfied. (and 10bucks poorer..)
I gained the knowledge that if the lm3886 is to be used outside it's maks ratings, some precautions have to be taken.
-Marius |
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| carlosfm |
| quote: | Originally posted by demogorgon
I gained the knowledge that if the lm3886 is to be used outside it's maks ratings, some precautions have to be taken.
-Marius |
Like respecting the max. ratings.:D
I think some of you guys don't love your speakers.:bawling:
Or you need an excuse to make (or buy) another pair.
Ops... |
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| WorkingAtHome |
How do you think they come up with those Max Ratings anyway? They set up an amp and crank up the voltage until the thing becomes completely unstable and/or blows. It's not really a theoretical thing that they worked out on paper (though I'm sure they did that as well).
Just be sure you don't grab the mains lines to be test whether the warning labels about electricution are accurate. ;) |
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| Yoghourt |
Foy your info...
In France, we are a bunch of guys who are using BPA200 schematics with +/- 42V rails when no load on supply. In other words, amplifier theoritical max supply voltage is exactly at LM3886 absolute maximum rating.
French line is specified at 230V with some tolerance, and we did not take that into account. Result is that supply rails can get a bit over 42V. So, some of us had the bad surprise to see some of their LM3886 smoke while turning amp on or off.
They are more valuable (electronic) games than playing off-limits. |
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| carlosfm |
Mains voltage is 230v here too, "standardized" as it is across Europe.
Sometimes I measure as low as ~220v, sometimes almost 240v.
So, an unregulated PSU may produce a certain voltage one day, and more or less the other day.
If it's already on the limits of the chip at 230v mains, when it's higher (as it is very often) then...:hot:
Also one important point:
I still see trafos on dealers' shelves with 220v primaries.
Avoid them. They are old stock and not apropriate for today's mains voltage. Consider them only if they are very cheap.
These will produce higher voltage on the secondaries than specified, and will sometimes get hot and vibrate when the mains voltage gets much higher.
The other day I measured 236V, and I have already measured as high as 239v:att'n: |
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| I_Forgot |
| quote: | Originally posted by WorkingAtHome
How do you think they come up with those Max Ratings anyway? They set up an amp and crank up the voltage until the thing becomes completely unstable and/or blows. It's not really a theoretical thing that they worked out on paper (though I'm sure they did that as well).
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Semiconductors are manufactured to work reliably in millions of consumer products. If parts start failing, the IC manufacturer can lose million of dollars when the consumer product maker switches to a competitive IC vendor. The semiconductor manufacturers treat each part as a potential multimillion dollar income or loss generator. They work EVERYTHING out on paper several times, before committing time and money to a mask set ($500k-$1M are not unusual) and all the follow-on testing.
The absolute maximum ratings numbers are formulated as a combination of the physical characteristics imparted to the semiconductor material and metalization layers by the manufacturing process, characteristics of package used, and accelerated life testing (thats the part where they hook them up and try them out).
The consumer product maker demands to see all the simulation and test data (and statistics on the manufacturing process) before buying an IC for one of their products. They don't want to risk their reputation putting out products that fail because some IC manufacturer screwed them over with unreliable parts.
This all means that the Absolute Maximum Ratings data is skewed toward the conservative side for the garage hobbyist. Most parts will probably work for a while at or above the absolute maximum supply voltage rating, but once you cross that line, you're asking for trouble. Why try to squeeze a couple more watts out of an amp chip when another chip, costing about $0.50 more, will deliver 30 watts more and be well within its maximum ratings?
How do these parts fail? Do they short one of the rails to the output? Are you going to connect expensive commercial speakers (or speakers in which you have invested a lot of time and energy building) to a chip that is operating beyond its maximum ratings to find out?
What's next, testing 1/2 Watt resistors at 3/4 or 1 Watt?
I_F |
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| demogorgon |
| quote: | Originally posted by I_Forgot
Semiconductors are manufactured to work reliably in millions of consumer products. If parts start failing, the IC manufacturer can lose million of dollars when the consumer product maker switches to a competitive IC vendor. The semiconductor manufacturers treat each part as a potential multimillion dollar income or loss generator. They work EVERYTHING out on paper several times, before committing time and money to a mask set ($500k-$1M are not unusual) and all the follow-on testing.
The absolute maximum ratings numbers are formulated as a combination of the physical characteristics imparted to the semiconductor material and metalization layers by the manufacturing process, characteristics of package used, and accelerated life testing (thats the part where they hook them up and try them out).
The consumer product maker demands to see all the simulation and test data (and statistics on the manufacturing process) before buying an IC for one of their products. They don't want to risk their reputation putting out products that fail because some IC manufacturer screwed them over with unreliable parts.
This all means that the Absolute Maximum Ratings data is skewed toward the conservative side for the garage hobbyist. Most parts will probably work for a while at or above the absolute maximum supply voltage rating, but once you cross that line, you're asking for trouble. Why try to squeeze a couple more watts out of an amp chip when another chip, costing about $0.50 more, will deliver 30 watts more and be well within its maximum ratings?
How do these parts fail? Do they short one of the rails to the output? Are you going to connect expensive commercial speakers (or speakers in which you have invested a lot of time and energy building) to a chip that is operating beyond its maximum ratings to find out?
I_F |
thanks for explaining. one learns something new every day.
| quote: | Originally posted by I_Forgot
What's next, testing 1/2 Watt resistors at 3/4 or 1 Watt?
I_F |
Or running computer cpu's above specs or something else stupid.
There is headroom everywhere, and thats something one can take advantage of.
I'v always pushed limits, thats the way progress is made and maby one learns something new in the process too.
what i do with my chips is my own risk, no need to go overboard.
This was something that i just had to test.
got the answer, there isn't sufficient headroom i the lm3886 maxs ratings. leson learned.
I'l be investing in a pair of lm318\338 as soon as i can afford them. |
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| I_Forgot |
| quote: | Originally posted by demogorgon
I'v always pushed limits, thats the way progress is made and maby one learns something new in the process too.
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I have always thought that progress is made not by pushing known limits, but rather by pushing the limits of what is known.
That's what the guys with the PHds in semiconductor physics did to get their PHds, and that's why we have chip amps and all the other semiconductors to play with.
I_F |
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| carlosfm |
| quote: | Originally posted by demogorgon
Or running computer cpu's above specs or something else stupid. |
I do that since 1986, when I had an IBM PC/XT at home.
That's an 8088 CPU at 4.77 Mhz.:cool:
I even changed the Intel 8088 by a Nec V20 (compatible), an absurd idea at the time, nobody did those things.
You can't compare different things, though.
The CPU doesn't need to drive a pair of speakers.:D |
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| planet10 |
| quote: | Originally posted by carlosfm
even changed the Intel 8088 by a Nec V20 (compatible), an absurd idea at the time, nobody did those things. |
Did that in 1985... still not fast enuff, so we got one of the very 1st 286 boards.
dave |
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| carlosfm |
| quote: | Originally posted by planet10
Did that in 1985... still not fast enuff, so we got one of the very 1st 286 boards.
dave |
At 6 Mhz?
Cool.:cool: |
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| demogorgon |
| quote: | Originally posted by I_Forgot
I have always thought that progress is made not by pushing known limits, but rather by pushing the limits of what is known.
That's what the guys with the PHds in semiconductor physics did to get their PHds, and that's why we have chip amps and all the other semiconductors to play with.
I_F |
Yeah, ok, but still, thats how I can make progress.
dont do such a good job of beating my arguments. It's frustrating. ;) |
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| planet10 |
| quote: | Originally posted by carlosfm
At 6 Mhz?
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Something like that... i know it predated the "official" 286 standard and had a whole bunch of logic on it to make it look like an 8088/8086. We ran FORTH on it during the development of some OCR software.
dave |
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| officeboy |
| quote: | Originally posted by demogorgon
I'l be investing in a pair of lm318\338 as soon as i can afford them. |
Be watchful of this.| quote: | | Note 2: These specifications are applicable for power dissipations up to 50W for the TO-3 (K) package and 25W for the TO-220 (T) package. Power dissipation is guaranteed at these values up to 15V input-output differential. Above 15V differential, power dissipation will be limited by internal protection circuitry. All limits (i.e., the numbers in the Min. and Max. columns) are guaranteed to National’s AOQL (Average Outgoing Quality Level). |
Since you have the ability to draw 5A from your 150W per leg trafo and the LM3886 can use it all , you will have about 42.5 volts and you will really only be able to drop down to 37.5 volts after regulation (5A x 5V=25W) without overloading a different national product. :cannotbe:
And at 37.5V you are gonna have problems running a 4ohm load.
"Required heat sink is too large!" says overture design guide |
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| XELB |
| quote: | I think some of you guys don't love your speakers.
Or you need an excuse to make (or buy) another pair.
Ops...
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I think everyone tests first with a 8Ohm resistor instead of the speakers.
After bulding an amp, first I connect to resistors and then I turn it on to see what happens....
I don't like to spend money in speakers :dead:
Edit:
The LM3886 could not resist to 60V! LOL :D :clown:
50V is the top line and you must have a massive heatsink....
Now he is using the LM3886 at 35V ;) |
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| carlosfm |
| quote: | Originally posted by officeboy
Since you have the ability to draw 5A from your 150W per leg trafo and the LM3886 can use it all , you will have about 42.5 volts and you will really only be able to drop down to 37.5 volts after regulation (5A x 5V=25W) without overloading a different national product. :cannotbe: |
This is not a class-A amp and 5A continuous will never happen.
5v input-output differential is on the limits for a proper regulation when the amp needs more current. The unregulated PSU voltage will sag.
42.5 volts can be regulated to around 32V without any problem.
I have an amp with a PSU at around these values ~42v in / 32v out.
Of course, the heatsink to be used is not those small things you use with 78/79xx regs, but any medium-sized old CPU heatsink will do. |
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| carlosfm |
| quote: | Originally posted by XELB
I think everyone tests first with a 8Ohm resistor instead of the speakers.
After bulding an amp, first I connect to resistors and then I turn it on to see what happens....
I don't like to spend money in speakers :dead: |
I said that in a context.
How does you friend knows that at +/-50V the LM3886 sounds good?
I suppose he can't take final conclusions with cheap test speakers, no?
I still don't know of resistors that can output something listenable.:clown:
I do use resistors, test speakers, quite decent (bench) speakers, and then the final test in my main system.
Only on my main system I can give you a definitive impression of how it sounds.
And the speakers I have there are not for playing around. |
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| XELB |
Of course he tests in really good speakers!
I don't trust simulators, the best way for me is to test it in real life.
But he only tests when the "thing" is stable at 50V.... He doesn't like to take risks ;)
The main reason he makes these experiments is to compare with is won chip(amp). ;) |
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| carlosfm |
| quote: | Originally posted by XELB
But he only tests when the "thing" is stable at 50V.... He doesn't like to take risks ;) |
Please understand that "stable" at 50V doesn't mean it will be stable with his good speakers.:xeye:
I would't take the risk to crank up the volume with that amp and my beloved speakers. |
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| XELB |
| quote: | Please understand that "stable" at 50V doesn't mean it will be stable with his good speakers.
I would't take the risk to crank up the volume with that amp and my beloved speakers. |
Not even I ;)
But he only do this because it's his work :cool:
He doesn't do this at home! LOL :D
I was choked when he told me that is Jeff Rowland Concerto Integrated Amplifier uses LM chips inside :dead: |
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| carlosfm |
Yes, of course it does.
There are more chip amps out there than you think.
And some are very good amps. |
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| XELB |
The Concerto amp is very good!
This give us some strength to belive that we(DIYers) can do good and budget amps :cool:
If they use this chips it's because they are good! ( I hope so :dead: ) :D |
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