Dear Jarthel,
I dont mean that 16 V/V is ideal for you... Just have a quick resulting;
If you already have a 8x gain preamp... And if you want 200mV input sensivity; then to get 44W RMS into 8ohm load with 1% THD you will need 16V/V. You dont need a special data to calculate that. Just mulitplying.
However I made a mistake while giving the values in gain meaning. So in fact my calculation gives you a exact result.
If you want to have 200mV input sensivity, you must give 16V/V gain to your amp. But if you use it with a CD Player which has 2v RMS output level, YOU DONT NEED ANY PREAMP.. It will be enough to get full power on output with 16 or 20 gain...
I dont mean that 16 V/V is ideal for you... Just have a quick resulting;
If you already have a 8x gain preamp... And if you want 200mV input sensivity; then to get 44W RMS into 8ohm load with 1% THD you will need 16V/V. You dont need a special data to calculate that. Just mulitplying.
However I made a mistake while giving the values in gain meaning. So in fact my calculation gives you a exact result.
If you want to have 200mV input sensivity, you must give 16V/V gain to your amp. But if you use it with a CD Player which has 2v RMS output level, YOU DONT NEED ANY PREAMP.. It will be enough to get full power on output with 16 or 20 gain...
jarthel said:
I didn't read it. Like I explained earlier, this label is misleading.
The figure in this box relates to the figure in the "Max Pd at POUT" box. Input sensitivity and gain determine whether an amp clips at it's maximum power level. Maximum power is dictated by rail voltage.
Dxvideo said:
Exactly.
MJL21193 said:
Sorry, wrong box. The "input for 1% output" box is related to the "1% THD output" box.
If you're more confused, I don't blame you. Most of this stuff is not straightforward.
Take my word for it when I say that figure is the above mentioned box is the maximum input voltage.
Last thing you want to do is to drive this amp to clipping.
When they say "input for 1% output", they mean, the input level to produce an output level where the amp starts to produce 1% distortion, which just at/before the threshold where clipping begins. This is explained in the document on how to use the Overture design spreadsheet. You've read that right?
Hi,
the maximum output from the 3886 is about 60W into 8ohms.
Let's convert this to voltage and amps.
Vrms=Vac=21.91Vac=30.98Vpk. Ipk=3.87Apk into 8r0, or about 11Apk into real 8ohm speakers.
The minimum gain of the 3886 MUST be >=10times (>=+20db)
The input voltage required to drive the chipamp with 10times gain will be 30.98/10=3.1Vpk=2.1Vac.
This almost exactly is what most CD players and many other digital sources send to the receiver. This is fortunate for those that want to avoid the extra complication of using an active pre-amp.
If you have a pre-amp with 8times gain (=+18db) then the input to the preamp to drive the chipamp to maximum power is 2.1/8=274mVac. This is approximately the level from many of the low level outputs from analogue sources.
However, do not forget that most pre-amps are fitted with an attenuator to control the volume.
This usually has a working range from 0db (maximum volume) to -80db (almost silent).
It is not unusual for the attenuator to be set at -40db to -60db.
Do add that into any calculations you do for "normal" listening levels rather than maximum levels which are only approached with peak transient signals.
the maximum output from the 3886 is about 60W into 8ohms.
Let's convert this to voltage and amps.
Vrms=Vac=21.91Vac=30.98Vpk. Ipk=3.87Apk into 8r0, or about 11Apk into real 8ohm speakers.
The minimum gain of the 3886 MUST be >=10times (>=+20db)
The input voltage required to drive the chipamp with 10times gain will be 30.98/10=3.1Vpk=2.1Vac.
This almost exactly is what most CD players and many other digital sources send to the receiver. This is fortunate for those that want to avoid the extra complication of using an active pre-amp.
If you have a pre-amp with 8times gain (=+18db) then the input to the preamp to drive the chipamp to maximum power is 2.1/8=274mVac. This is approximately the level from many of the low level outputs from analogue sources.
However, do not forget that most pre-amps are fitted with an attenuator to control the volume.
This usually has a working range from 0db (maximum volume) to -80db (almost silent).
It is not unusual for the attenuator to be set at -40db to -60db.
Do add that into any calculations you do for "normal" listening levels rather than maximum levels which are only approached with peak transient signals.
Hi
I wonder the gain of this parallel lm3886 amp. Here is the scheme link:
http://i.ebayimg.com/images/g/QbgAAOSwqYBWmNEy/s-l1600.jpg
I wonder the gain of this parallel lm3886 amp. Here is the scheme link:
http://i.ebayimg.com/images/g/QbgAAOSwqYBWmNEy/s-l1600.jpg
Hi again,
I have the following board:
Assembled 120W 120W LM3886 Dual Parallel Pure Power HiFi Amplifier Board SN | eBay
and my sound card (asus xonar phoebus) has 2.2Vrms output. I think that i do not need any preamp but when i use the amp with a 25-0-25V 250VAC toroidal transformer and 6 ohm speaker, i think the output power is low. Are there any solution to increase the input gain of the board. What do you think about the input gain of the amp?
I have the following board:
Assembled 120W 120W LM3886 Dual Parallel Pure Power HiFi Amplifier Board SN | eBay
and my sound card (asus xonar phoebus) has 2.2Vrms output. I think that i do not need any preamp but when i use the amp with a 25-0-25V 250VAC toroidal transformer and 6 ohm speaker, i think the output power is low. Are there any solution to increase the input gain of the board. What do you think about the input gain of the amp?
Post26 shows 220k and 10k as the feedback resistances.
This gives a gain of -22times for the inverting amplifier.
The input impedance is 10k||10k = 5k
This is unusually low.
It is a PA100 style topology and should be built to the recommendations that National/Ti give for this.
I suspect it is not.
Don't waste your money.
This gives a gain of -22times for the inverting amplifier.
The input impedance is 10k||10k = 5k
This is unusually low.
It is a PA100 style topology and should be built to the recommendations that National/Ti give for this.
I suspect it is not.
Don't waste your money.
Not disagreeing with Andrew (my end conclusion is not too different) but trying to refine data a little:
1) you do not have that much power available to begin with, about 66W/ch at best ; "120W" is an "optimistic" over simplification created by Marketing dept
2) you are not measuring power output ; "i think the output power is low" is quite subjective, and depends a lot on speaker efficiency/sensitivity.
3) also: "my sound card has 2.2Vrms output" should be read as: "up to 2.2V RMS"
That depends a lot on program material ... recordings are usually made at an average level quite under maximum peak capability , and that is good, is made to keep good dynamic range without even approach clipping.
You don't mention clipping or sound muddying so I guess your amp is not being fully driven.
4) I hate parallel amp configurations, even if suggested by Factory (they love it because they double sales and can quote impressive power figures which aren't actually there
) ; and even more the cheesy/unforgiving way it has been applied here: each channel is made out of 2 fully independent amps in parallel (if anything, they should use one as a master, the other as a unity gain follower/slave, which conceptually improves tracking);
only way to avoid disaster is to have *perfect* matching of NFB network resistors.
As it's easy to imagine, if you change them to improve gain (say, halve R112/113/212/213) new resistors fit there must perfectly match too.
Personally, and as it seems to work as delivered, I wouldn't mess with it at all, and add an external 2X to 5X gain preamp.
Of course you may mount it inside your existing cabinet.
A simple TL072 , each half driving one channel, +IN grounded and NFB resistors 100k/22k would be:
* inverting (not bad, your power amp is already inverting)
* gain ~5X
* input impedance 22k (better than the 10k you have today)
you can build it on perfboard and get +/- 15V from existing power rails, with a couple 2k2 1W resistors, 2 15V 1W Zeners and 2 100uF x 25V caps.
Total cost around $5 and addresses your problems straight on.
4) anything more complex soon becomes not cost effective.
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Some chip amps have a minimum gain so be careful lowering it a lot.
I got caught out with the tda7294. I had a valve front end with gain of 8 so I lowered 7294 gain to compensate. The 7294 oscillated badly and got red hot.
I managed to bodge itr in the end by putting 1000pf across inverting and non-inverting inputs. I think the datasheet said it must have min 22 gain.
And it will also distort way more , since you are losing the error correcting feature of NFB, you will probably have way less response at very low and high frequencies, lose damping, etc.
All that for saving $5 (or less) from a single basic preamp, as I suggested above: a humble TL072 and a handful of cheap components.
You don´t need a case or connectors for this basic preamp, just build it on perfboard and fit it inside the LM3886 chassis.
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