Hi
it seems that this forum is one of thew main contact point for chipamp freaks, maybee u can help me here.
I've just built a3886 based Amp for a friend and it worked pretty well.
Now i'd like to build one of these for my computer.
I have very big speakers, with 12inch woofers, 4Ohm, and I want to use a 2x22V Transformer.
This seems to be a little hard for a single 3886.
Now im thinking about paralleling two LM3886 or one 4780 will give more reserves.
Is this going to destroy the sound of the gainclone?
Yes, there are hundreds of threads, but I found no answer for this point...
it seems that this forum is one of thew main contact point for chipamp freaks, maybee u can help me here.
I've just built a3886 based Amp for a friend and it worked pretty well.
Now i'd like to build one of these for my computer.
I have very big speakers, with 12inch woofers, 4Ohm, and I want to use a 2x22V Transformer.
This seems to be a little hard for a single 3886.
Now im thinking about paralleling two LM3886 or one 4780 will give more reserves.
Is this going to destroy the sound of the gainclone?
Yes, there are hundreds of threads, but I found no answer for this point...
I was actually using bridged LM3875 chips with 22V AC PS and 4 ohm speakers (effective load 2 ohm per chip) for approx 6 months and I didn't experience any major problems.
When driven hard, the heatsink got pretty hot (60 deg C or so) but the protection never kicked in. On some tracks, with deep bass, clipping occured, but that's about all. The drivers (FAL) were 95 dB efficient.
Regarding sound quality when paralleling chips, it may be perceived as slight losses in immediacy, fine detail and bass control, but depending on a system and listener experience it may not be noticable as anything serious.
LM3886 has more current output than LM3875 so maybe 4ohm woofer will not be such a burden, it also depends on listening habits and how loud you like to play it.
When driven hard, the heatsink got pretty hot (60 deg C or so) but the protection never kicked in. On some tracks, with deep bass, clipping occured, but that's about all. The drivers (FAL) were 95 dB efficient.
Regarding sound quality when paralleling chips, it may be perceived as slight losses in immediacy, fine detail and bass control, but depending on a system and listener experience it may not be noticable as anything serious.
LM3886 has more current output than LM3875 so maybe 4ohm woofer will not be such a burden, it also depends on listening habits and how loud you like to play it.
AndrewT said:
Hi Andrew,
Clearly you're not familiar with the LM3886. Mine has been happily driving my 4ohm speakers for a year or so just fine. The chip is rated at 68w RMS into a 4ohm load. Paralleling it's obviously good for nearly double the power and current at half the impedance. My transformers are 25vac - a touch high.
It's not really possible to kill a 3886. I can play as loud as I like within reason. All that happens is the sound softens up a bit at very high levels.
Simon
LM3886 Cannot drive 4ohm speakers!!!
I suspect sometimes ago what Andrew said may not 100% correct, he said the same thing in a no. of posts on this site, I did not say anything as I do not have any direct experience.
Now that P. Daniel & SimonY have come out and dispute him, who would rather believe P.D and SimonY or Andrew?
I believe accurate technical issues should always prevail. Thanks to P.D and SimonY for responding...
I suspect sometimes ago what Andrew said may not 100% correct, he said the same thing in a no. of posts on this site, I did not say anything as I do not have any direct experience.
Now that P. Daniel & SimonY have come out and dispute him, who would rather believe P.D and SimonY or Andrew?
I believe accurate technical issues should always prevail. Thanks to P.D and SimonY for responding...
Hi,
Follow the manufacturer's design process in the data sheet and 22Vac with a reactive 4ohm load and one finds that this combination is taking a chipamp too close to it's limits, particularly with regard to case temperature.
The saving is that music is often played at average levels around 10 to 30db below the peak level. That low average level keeps the chip cool.
Peter,
is your example using a regulated supply or on PSU using near +-1mF of smoothing?
I feel inclined to ask just how low the supply voltage at the chip pins fell when clipping was heard?
agreed.
Follow the manufacturer's design process in the data sheet and 22Vac with a reactive 4ohm load and one finds that this combination is taking a chipamp too close to it's limits, particularly with regard to case temperature.
note, I placed a condition that seems appropriate to Arnop's proposed use for a bass only driver.
The saving is that music is often played at average levels around 10 to 30db below the peak level. That low average level keeps the chip cool.
Peter,
is your example using a regulated supply or on PSU using near +-1mF of smoothing?
you have been very fair to also quote the conditions that you found successful. But driven hard into 95db/W speakers (presumably widebandwidth) is possibly a sutble warning that may go straight over the head of a newbie.
I feel inclined to ask just how low the supply voltage at the chip pins fell when clipping was heard?
Arnop,
With some additional details we can probably tell you if you'll be ok with just the single LM3886 or not.
How loud do you tend to listen? What efficiency are your speakers? Do you intend to use it for long, loud party sessions?
Just for sake of example, my speakers dip slightly under 4ohms, are about 91db efficient and I play fairly loud, sometimes very loud (to near the limit of the speakers). My voltage rails are + and - 35vdc unloaded. My transformers are 100va @ 25vac, one per side. I have never heard clipping. I have reasonable heatsinks only and run the amp in a nearly sealed plywood chassis. It gets warm, I expect it's exceeded 60 degrees C. This could be a problem for parties etc. if caution is not excercised.
I think clipping is hard to achieve because of the high voltage rails and low va transformers, I simply run out of current at high levels (I guess, not really sure what happens).
I actually have some interest in paralleling these chips myself as this amp was only built as a test to see if it could stack up against my Roksan Caspian. It did and it's been in use for many months since! I may actively bi-amp and add an extra bass section to my speakers, which could be powered by a paralleled LM3886 (would be 2ohm load).
Simon
With some additional details we can probably tell you if you'll be ok with just the single LM3886 or not.
How loud do you tend to listen? What efficiency are your speakers? Do you intend to use it for long, loud party sessions?
Just for sake of example, my speakers dip slightly under 4ohms, are about 91db efficient and I play fairly loud, sometimes very loud (to near the limit of the speakers). My voltage rails are + and - 35vdc unloaded. My transformers are 100va @ 25vac, one per side. I have never heard clipping. I have reasonable heatsinks only and run the amp in a nearly sealed plywood chassis. It gets warm, I expect it's exceeded 60 degrees C. This could be a problem for parties etc. if caution is not excercised.
I think clipping is hard to achieve because of the high voltage rails and low va transformers, I simply run out of current at high levels (I guess, not really sure what happens).
I actually have some interest in paralleling these chips myself as this amp was only built as a test to see if it could stack up against my Roksan Caspian. It did and it's been in use for many months since! I may actively bi-amp and add an extra bass section to my speakers, which could be powered by a paralleled LM3886 (would be 2ohm load).
Simon
AndrewT said:
It is unregulated supply with 100uF capacitors directly at the chip and 1000uF at the rectifiers (2ft umbilical).
I didn't had a chance to measure the supply fluctuation when clipping. It was basically occuring only on Burmester CDIII, track 10 and Patricia Barber's Companion, track 4.
Hi
thanks for your answers.
The manual gives two pairs of variates:
SPL 86dB (3m distance) at 5,8W and
SPL 80dB (3m distance) at 1,45W
Losses in fine detail and immediacy... Well i am no HIFI expert and I dont want to say anything heretic, but maybe your single chip has just a bad bass responce, an thus you experience more emphased high and middle frequencies?
I have read somewhere that a parallel chipamp had a "deeper" sound.
But why losses in bass control?
When i compare the diagramms in the national semiconductor data sheets, i can't se any difference in distortion between 3886 at 4Ohm with 28V and the parallel circuit at 35V 4Ohm.
I don't want to create any sound, thats not how i understand HIFI.
I want no sound at all, it should be neutral. Just amplify the input
thanks for your answers.
No, you misunderstood. It's a 3 way speaker with 30cm Woofers. Old Canton GLE Series.
I dont know
The manual gives two pairs of variates:
SPL 86dB (3m distance) at 5,8W and
SPL 80dB (3m distance) at 1,45W
Losses in bass control?
Losses in fine detail and immediacy... Well i am no HIFI expert and I dont want to say anything heretic, but maybe your single chip has just a bad bass responce, an thus you experience more emphased high and middle frequencies?
I have read somewhere that a parallel chipamp had a "deeper" sound.
But why losses in bass control?
When i compare the diagramms in the national semiconductor data sheets, i can't se any difference in distortion between 3886 at 4Ohm with 28V and the parallel circuit at 35V 4Ohm.
I don't want to create any sound, thats not how i understand HIFI.
I want no sound at all, it should be neutral. Just amplify the input
AndrewT see inside
Andrew,
look up this site you will find the LM3886 can drive 4.7ohm up to 90% full power using square wave.
http://dogbreath.de/Chipamps/GainCardCopy/GainCardCopy.html
any more questions you should ask the author.
Andrew,
look up this site you will find the LM3886 can drive 4.7ohm up to 90% full power using square wave.
http://dogbreath.de/Chipamps/GainCardCopy/GainCardCopy.html
any more questions you should ask the author.
Hi,
I have many questions, but that is not the point.
The poster asked for advice, admittedly about sound quality, into low impedance loads from a highish voltage supply.
I simply pointed out that some caution is needed when using high voltage transformers (22Vac) and 4ohm loading.
BTW,
that site reference showed the author used 18Vac and 4r7. How he got 90% of output voltage into an 11W resistor is beyond me.
Arnop,
the 86db/5.8W @ 3m indicates a maximum SPL of about 96db on musical peaks. Allowing the usual -20db below maximum for average music power when turned up to the max then the average SPL will be about 76db. This is a loud conversation.
In a room this will be termed medium level (teenagers will say too quiet). If monitoring at a computer (1 to 1.5m) then the levels will appear to be about 6db louder.
These are low sensitivity speakers that will demand big power for big volume. They require eight times the power that Peter Daniel's example needed for the same volume. Be careful.
I have many questions, but that is not the point.
The poster asked for advice, admittedly about sound quality, into low impedance loads from a highish voltage supply.
I simply pointed out that some caution is needed when using high voltage transformers (22Vac) and 4ohm loading.
BTW,
that site reference showed the author used 18Vac and 4r7. How he got 90% of output voltage into an 11W resistor is beyond me.
Arnop,
the 86db/5.8W @ 3m indicates a maximum SPL of about 96db on musical peaks. Allowing the usual -20db below maximum for average music power when turned up to the max then the average SPL will be about 76db. This is a loud conversation.
In a room this will be termed medium level (teenagers will say too quiet). If monitoring at a computer (1 to 1.5m) then the levels will appear to be about 6db louder.
These are low sensitivity speakers that will demand big power for big volume. They require eight times the power that Peter Daniel's example needed for the same volume. Be careful.
Yet another LM3886 driving a 5ohm load
Still another site to showing waveform on a CRO where a LM3886 driving 5 ohm load. Giving about 50V peak to peak at the verge of chipping, it works to be about 60 watts, using the data shown.
Not bad, if one has a pair of 90db speaker, operating at 60w the speakers will sound very loud indeed before it clips.
Still another site to showing waveform on a CRO where a LM3886 driving 5 ohm load. Giving about 50V peak to peak at the verge of chipping, it works to be about 60 watts, using the data shown.
Not bad, if one has a pair of 90db speaker, operating at 60w the speakers will sound very loud indeed before it clips.
@ Upupa Epops:
Have you ever tried this?
How was the sound?
I'm not sure about those SPL values...
I used these speakers for years with an old Blaupunkt Amp, with is based on the STK-082 and is rated 55W sine and 75W musik power.
And when i turn it up it's VERY load. Louder than I can bear for long.
Can anyone acknowledge this?
Especially the losses in bass control?
Have you ever tried this?
How was the sound?
I'm not sure about those SPL values...
I used these speakers for years with an old Blaupunkt Amp, with is based on the STK-082 and is rated 55W sine and 75W musik power.
And when i turn it up it's VERY load. Louder than I can bear for long.
Can anyone acknowledge this?
Especially the losses in bass control?
The beauty of Chipamp is all the active devices, ie transistors are embedded in the same substrate hence you get the devices that are well matched, ie parameters that are close to each other esp. when you get them to work in a push pull configuration.
This will give you a most coherence music output.
By paralleling output chipamp or output transistors you will lose this effect as the all the output transistors are not well matched so is the chipamp. I believe most people are using the same argument by comparing single ended with push pull configuration, that is why most people report single ended sounds better because you can never get push pull transistors or tubes that can match sufficiently close enough(except chipamp!!)
This is just a view...maybe some of you here may disagree, I am building an amp based on single op-amp driving fairly efficient speakers eg >= 90dB, hence no need for high powered amp.My system uses active x-over hence I need 6 channels each driving separate drivers. This configuration will give me a large sound stage and imagery.
This will give you a most coherence music output.
By paralleling output chipamp or output transistors you will lose this effect as the all the output transistors are not well matched so is the chipamp. I believe most people are using the same argument by comparing single ended with push pull configuration, that is why most people report single ended sounds better because you can never get push pull transistors or tubes that can match sufficiently close enough(except chipamp!!)
This is just a view...maybe some of you here may disagree, I am building an amp based on single op-amp driving fairly efficient speakers eg >= 90dB, hence no need for high powered amp.My system uses active x-over hence I need 6 channels each driving separate drivers. This configuration will give me a large sound stage and imagery.
To Answer the original question, does it change the sound? well all the designs I have seen with parallel amps shows that you need to put a small resistance on the output of each device to balance the current drive. the resistance is small, equivilant to less than 0.1 ohms. but this changes the electrical q of the loud speaker. so lets say 7.4 ohm speaker with QMS 3.5 and Qes 0.39. would normally give a total Qts of 0.350. with a 0.1 ohm resistor in series the Qes goes up. giving a QTS of around 0.355, thus probably not noticable, but it would change the alignment of a bass reflex enclosure, basically the enclosure would need to be bigger and tuned lower as Qts increases. Other wise you will get a slight dip in the bass responce. Also crossover is effected. Best way to simulate this is you can just put a 0.1 ohm resistor in series with your existing amp and see if it sounds different. I use MTM so the mids are 4 ohms and the tweeter is about 7 ohms, so yes I do notice the difference but particularly because of higher impedance of the tweeter, the already bright tweeter gets brighter.
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