| nickthevoice |
Hello I look to buy GainClone with LM4780 (para) 1x 120w but many people said LM chip not great bass or no bass, blabla.......
what's the modifications to make to have BEST AMPLIFIER ?
What's the best +/- volt it's 30v or 35 v (for 120w 4 ohm load)
This amp have very little power supply Capacitor !
(no power reserve Capacitor for punch bass)
Do you add TANTALUM CAP for more great sound ?
WHAT CHANGES YOU HAVE MADE ??? (with good result only ;) !
Thanks !!!
Nick |
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| kuldeepsingh |
| add a good bass filter or bass boost circuit and see the bass quality output. |
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| pinkmouse |
| On my last active system with 4780s, I used 1000uF on the highs, 2200uF on the mids and 10 000uF on the bass. |
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| jackinnj |
| quote: | Originally posted by pinkmouse
On my last active system with 4780s, I used 1000uF on the highs, 2200uF on the mids and 10 000uF on the bass. |
I would say at least 10,000 uF on the bass.
The other thing, of course, is the input coupling capacitor and associated circuitry -- you can use a pair of electrolytics bypassed with a small polypropylene cap for this. |
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| I_Forgot |
Put BIG caps on the power rails. Bypass them with smaller caps.
I_F |
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| Leolabs |
| 10,000uF+3.3uF+0.1uF |
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| youyoung21147 |
The only way to get good bass is to have big PSU caps. It's mathematical.
I'd suggest you to use 1000 or 2200 µF on the chips + 2*10 000µF on the PSU board.
You can calculate the needed capacity with this formula :
P is the power you need
R is the impedance of the load
U is the RMS voltage at the terminal of the load
P= U²/R
Once you've got U, you calculate the equivalent voltage Ur of the supply rails :
Ur = U*root(2).
I'd suggest you to use the highest possible rail voltage.
Then you calculate C :
Uc is the voltage at the terminals of the cap
t is the period of the discharge cycle (time during which the capacitor is discharging)
Uc = Ur-Ur*exp(-t/(R*C))
With 50Hz mains, you have t = 1/100
Then you can calculate for a given C and a given Ur the real voltage Uc at then end of the cap's discharge cycle.
So you deduce the real uncompressed power you can get from your PSU :
Preal = Uc²/R
From these formulas, you can see that your maximum output power is limited by the rail voltage and the caps of the PSU.
Don't forget that the amp also takes juice and has a voltage dropout, so increase the capacitance value by a 1,5 or 2 factor.
I have LM4780 amps in bridged mode and they work very well. |
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| AndrewT |
Hi You,
I would like to compare the numbers predicted by your formulae with other recommendations.
How does this work?| quote: | | Uc = Ur-Ur*exp(-t/(R*C)) |
I can do the (-t/(R*C)) for 8r and 10mF =-0.125 but what operator is exp applied to Vr? |
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| AndrewT |
Hi all,
I queried the recommendation of using <=+-2.2mF on the chipamp as the sole smoothing/decoupling cap for a wideband amplifier in another thread.
All to a man/woman insisted that these wideband amps sounded best when the caps are kept small even suggesting that +-1mF was optimum.
It appears our thread starters has been following this advice.
Now I see the completely opposite recomendation if one requires bass rather than the more onerous wideband response.
What goes?
Are there two camps in the Forum, [big smoothing+decoupling] and [big decoupling]? |
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| owen |
I'd avoid a large 'lytic... and rack up 20 or so 1000uF, with a little extra bypass.
I'd also include some small chokes (high amp, low DCR, inductance doesnt need to be colossal - you're using it to hammer RF grunge) in all 3 rails (+, - and Ground) - make the star earth point after the chokes.
I would also adopt a 'Pass' trick - run some of the capacitance across between the + and - rail.
Local bypassing of the chip is useful if you have marginal stability, or RF grunge present on the rails, to stop anything that might excite oscillations.
Have fun!
Owen |
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| youyoung21147 |
AndrewT :
NOTE : i have made an error in the previous formulas. They applied to the charge cycle of the cap, which doesn't interests us.
I will consider these states in my explanation :
t0 is the moment at which the voltage at the capacitor's terminals is maximal (fully charged)
t is the time elapsed from t0
t1 is the time elapsed during one discharge cycle of the cap, that we will consider being equal to the time elapsed between two voltage peaks (pessimistic, and simpler)
Ur is the maximal voltage from one rail to the ground. It is the rail voltage as we would like it to be in a perfect world with infinite caps.
Uc is the voltage at the cap's terminals, which is the real voltage of the rails during the discharge cycle
Uc = Ur*exp(-t/(R*C))
exp is the exponential function. exp(x) = 2.72^X
At the end of the discharge cycle, with 50Hz mains and a full wave rectifier,
t1 = 1/(50*2) ) = 1/100
So finally we have :
Uc = Ur*2.72^(-0.01/(R*C))
For example :
I have a 25-0-25V trafo
with infinite caps, I get Ur = 25*root(2) = 35V
with 2*10000µF caps
4 ohms speaker
50Hz mains
fullwave rectifier
I get, using the formula above :
Uc = 35*2.72^(-0.01/(4*0,02)) = 31V
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| youyoung21147 |
So, we now know the minimal supply rail voltage.
If we are in bridged mode (which I don't recommend you with 4 ohms), we add the voltage of both rails and get 60V p-p
The equivalent RMS voltage is 60/root(2) = 42V R.M.S
So in 4 ohms, you obtain :
42²/4 = 450W
What you can see is that 4 ohms bridged is totally impossible with one chip. As you want to do, we can parallel the two amps in the LM4780, or use an 8 ohms driver.
Using an 8ohms driver :
P = 42²/8 = 225W
Paralleling the amps (or using only one, that's the same). This is the safest solution, and the less heating :
P = (31/root(2))²/4 = 110W
Keep in mind this is theoretical. The amps have a voltage dropout, and you will always need extra margin for transcients.
Note that it is very interesting to increase the supply rail to their maximum voltage.
E is the energy stored in a cap
C is the capacitance of the cap
Uc is the voltage at its terminals
E = C*Uc²
You can see that the energy is proportional to the square of the voltage !
More juice for no cost (or little if you need to increase the cap's rating)
Hope it helps,
cheers ! |
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| burnedfingers |
My tech-diy LM4780 gainclown has very poor bass. It has power supply caps of (4) 10,000 mfd bypassed with 1000's, 330's and 10's.
It is without a doubt a total loss of both time and material and is headed to the garbage can. |
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| burnedfingers |
| In all fairness I must state that the tech-diy board is a very nice board. It is made quite well and the layout is very good. I believe the problem lies with the chip. I don't quite understand it because the LM3886 boards have very good bass response. |
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| jackinnj |
Is this the one to which you refer?
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| burnedfingers |
| quote: | | Is this the one to which you refer? |
Yes it is. Thank you but I already have page 8 from the 11 page set of information. It still suffers from a lack of bass and it was assembled from the part worksheet which is from the engineering specifications and or circuit that is recommended by the manufacturer. |
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| jackinnj |
| quote: | Originally posted by burnedfingers
Yes it is. Thank you but I already have page 8 from the 11 page set of information. It still suffers from a lack of bass and it was assembled from the part worksheet which is from the engineering specifications and or circuit that is recommended by the manufacturer. |
OK, you run a similar graph and let's see what you get. |
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| burnedfingers |
| quote: | | OK, you run a similar graph and let's see what you get. |
Yes, I could run a similar test but on this one I can clearly hear what I'm not getting. I generally use a warble generator and calibrated microphone with my speaker in a controlled setting to perform my response test.
The LM3886 performs well and has good bass response. The 4780 clearly sounds like you took it to the Vet for an operation.
Like I mentioned....your board is very nice and I clearly don't have a problem with it. I am questioning the 4780 chip. Maybe I need a bank of 100,000 mfd caps and dual 650 va transformers to wake it up. Maybe there is a problem with the chips. Heck I don't know.
It would seem the chips are working correctly as I have DC offset of 3.7mv one channel and 5.7mv on the other. I get a clean sine wave on both channels.
At this point in time I surely wouldn't recommend it to anyone. I especially wouldn't try to use it for a subwoofer amplifier. |
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| pinkmouse |
| I'm sitting listening to a 4780 driven sub at the moment, and it's fine. The 4780 chip is actually two 3866s on one die, so I suspect your implementation is at fault. |
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| janneman |
| quote: | Originally posted by burnedfingers
Yes, I could run a similar test but on this one I can clearly hear what I'm not getting. I generally use a warble generator and calibrated microphone with my speaker in a controlled setting to perform my response test.
The LM3886 performs well and has good bass response. The 4780 clearly sounds like you took it to the Vet for an operation.
Like I mentioned....your board is very nice and I clearly don't have a problem with it. I am questioning the 4780 chip. Maybe I need a bank of 100,000 mfd caps and dual 650 va transformers to wake it up. Maybe there is a problem with the chips. Heck I don't know.
It would seem the chips are working correctly as I have DC offset of 3.7mv one channel and 5.7mv on the other. I get a clean sine wave on both channels.
At this point in time I surely wouldn't recommend it to anyone. I especially wouldn't try to use it for a subwoofer amplifier. |
It is very, very uncommon that a bass problem has ANYTHING to do with supply caps. Even with 1000uF people have reported good bass. The fundamental mistake here is to relate the cap discharge of the supply caps to bass response. The only relation is to max output power at bass frequencies, but that's not the issue. The issue (if indeed you have lack of bass) is that the 'gain' at bass frequencies is lower than that at mid/high frequencies. This is a freq response problem.
Possible culprits: input coupling capacitor, feedback decoupling cap, etc.
Without a schematic diagram with values this is impossible to troubleshoot. Give us the circuit!
Jan Didden |
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| burnedfingers |
| quote: | | I'm sitting listening to a 4780 driven sub at the moment, and it's fine. The 4780 chip is actually two 3866s on one die, so I suspect your implementation is at fault. |
Mr Pinkmouse
I understand that the 4780 has two LM3886's in it:D
If I followed the schematic that I put a link to would my implementation still be at fault?:eek:
Somehow I just don't think so..:clown: |
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| janneman |
| quote: | Originally posted by burnedfingers
The circuit can be found here:
http://www.tech-diy.com/LM4780_bridgedamp.htm
I followed it except that I used my existing power supply.
All the values I used for the amplifier are per the schematic. |
The circuit looks OK. The high-pass frequencies from the input coupling and feedback are down to a few Hz, so that cannot explain the bass problem.
How do you know you have a bass problem? If you indeed have one, how do you know it is in the amp, and not in the speaker or the room? Is the problem in both channels? Did you measure the frequency response, or maybe the gain at some spot frequencies?
Jan Didden |
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| AndrewT |
Hi Burned,
you have bridged two 50W into 4ohm amps to give 100W into 8ohm.
The supply is just 4 * 10mF.
That is equivalent to just +-10mF per 4ohm amplifier.
For good bass, I would recommend +-40mF/amp to +-50mF/amp, yes that's 16 to 20*10mF.
Seems like you will need to spend some money on more caps before you trash it.
Do you realise that if you had built a normal 100W into 8ohm amp the smoothing requirement would have been +-20mF/amp to +-25mF/amp? |
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| Netlist |
Are both speakers connected in-phase?
/Hugo |
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| burnedfingers |
| quote: | | The circuit looks OK. The high-pass frequencies from the input coupling and feedback are down to a few Hz, so that cannot explain the bass problem. |
| quote: | | How do you know you have a bass problem? If you indeed have one, how do you know it is in the amp, and not in the speaker or the room? Is the problem in both channels? Did you measure the frequency response, or maybe the gain at some spot frequencies? |
How do I know that I have a bass problem. In my field I am required to be able to spot any and all problems associated with any given audio system very large or small.
You have very good questions and certainly the same that I would ask of someone.
Given the same placement of the speakers in the room the same source gear and the same signal in this case the same CD with the same track I tested 3 different amplifiers. There was clearly no lack of bass from the LM3886 chip amp, the Quicksilver mono block 8417's, or an Altec 9444.
Now, I could go further and hookup a warble generator and calibrated microphone and plot a frequency response graph like I did. I tried to send the graph but it is too big. |
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| burnedfingers |
| quote: | | Are both speakers connected in-phase? |
First thing I checked....Yes |
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| Netlist |
I'll gladly make the graph fit the forum's format if you send it to hugorx and hot mail.
/Hugo |
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| AndrewT |
Hi,
I think the lack of understanding of the current requirements of a bridged pair of amplifiers has led to the poor bass.
This in turn has prompted the poor implementation.
Burned,
go back and review what you did and why.
Then imagine starting again with a 50W into 8ohm amplifier and instead of using 4*10mF for smoothing you substitute 4*2500uF.
Would you expect a change in the bass delivered?
It's down to that factor of four increase in current that the bridged amplifier needs. |
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| janneman |
| quote: | Originally posted by AndrewT
Hi Burned,
you have bridged two 50W into 4ohm amps to give 100W into 8ohm.
The supply is just 4 * 10mF.
That is equivalent to just +-10mF per 4ohm amplifier.
For good bass, I would recommend +-40mF/amp to +-50mF/amp, yes that's 16 to 20*10mF.
Seems like you will need to spend some money on more caps before you trash it.
Do you realise that if you had built a normal 100W into 8ohm amp the smoothing requirement would have been +-20mF/amp to +-25mF/amp? |
Andrew,
As I noted, the supply caps have nothing to do with the bass response except in the limiting case of constant full power output. This is clearly a freq response problem.
I also noted that apparently everybody here likes to chase ghosts about supply caps without really being interested in WHY the bass lacks.
Anyway, I wish you all a lot of fun chasing those ghosts (and possibly trashing a perfectly good amp).
Jan Didden |
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| jackinnj |
Most likely it is the input coupling -- in the bridged board I left space for a variety of coupling caps -- and in the article showed an alternate arrangement whereby two 100uF electrolytics could be back-to-backed with a polypropylene or other. The parallel board shows 1uF which has a much different f3 point. This is OK, but remember that the phase is shifting all the way out to a few hundred hertz with a 1uF input capacitor !!!
It would be helpful if you had a power vs frequency chart for your setup, and some more info on the general application. In the absence of that we are left to wonder whether there isn't something lacking in the completion of the board. The pic below shows gain and phase plots with two different coupling caps.
 |
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| AndrewT |
Hi,
the two input filters are at 0.6Hz (260mS) and 3.4Hz (47mS).
I can't see where 5.4Hz comes from.
Could the phase difference between 260mS & 47mS be part of the problem?
I suppose it would be fairly easy to set both filters to about 100mS and listen. Change C4 from 1uF to 4.7uF and the combination of C5//Cb2&3 from 54.7uF to 22uF.
Janneman,
I don't agree. |
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| jackinnj |
Andrew -- sorry -- I ran that for the parallel board, not the bridged ones.
Burnedfingers -- send the board back to me and I will check it out. |
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| janneman |
| quote: | Originally posted by AndrewT
[snip]
Janneman,
I don't agree. |
Hey Andrew,
That's OK. It would be boring indeed if everyone did!;)
Jan Didden |
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| janneman |
Andrew,
Maybe some additional reasoning:
Suppose we have an amp with +/- 40V supplies, with 50.000uF capacitance. Suppose this amp is delivering 50W into 8 ohms at, say 20Hz. That's 28V peak output signal.
Now change the supply caps to 10.000uF. What will happen to the output signal level? Hint: nothing! Therefore, IF this amp gives less bass, the problem is freq response, also hinted at by Jack above.
Jan Didden |
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| burnedfingers |
It seems that everyone or just about everyone except for me feels that adding mega capacitors in the power supply is going to up the bass. Sorry, but I feel a need to cry BS on this one. Unless someone proves me completely nutty I am going to assume that 20,000 mfd should be more than enough to run the pair of bridge amps. Hell, a 9440 Altec amp doesn't have over 20,000 total capacitance in the power supply to deliver over 800 watts in mono bridge mode and it will take your head off with the low end capability.
Jack,
I will look over the board again. I have already used (2) 47uf caps in the ca2,ca3 position bypassed by ca1. I have changed this to (1) 47uf poly cap bypassed by a .1
I will yank these out and try a single 4.7 uf cap. I will yank out my 1.0uf cap in the C4 position and measure it.
I have a signal generator that is capable of frequency changes as small as .1 HZ. I will try some caps that I have measured and see if the response changes. After thinking about this all day I am wondering about the quality of my 1.0uf cap. |
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| jackinnj |
| feel free to send it back -- i just looked at 3 bridged boards which I had assembled and they conform pretty much to what I showed --- you can get wonky response if the power supply isn't putting out much juice -- and you can get the chip to oscillate if the heat sink isn't adequate (it's a long story...) |
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| pinkmouse |
| quote: | Originally posted by jackinnj
...and you can get the chip to oscillate if the heat sink isn't adequate (it's a long story...) |
Yup, been there and smelled the smoke...:) |
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| jackinnj |
5 Hz to 500 Hz -- this is at very low level with an attenuator in the path:
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| sasmit |
| As far as I understand..the main purpose of having a mega capacitor on the supply rails is to prevent the rails from sagging when you need a sudden burst of current from the PSU...as long as they serve that purpose ..doesn't make any difference how big a capacitor u have on the rails...at least for me it didn't.. :) |
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| janneman |
| quote: | Originally posted by sasmit
As far as I understand..the main purpose of having a mega capacitor on the supply rails is to prevent the rails from sagging when you need a sudden burst of current from the PSU...as long as they serve that purpose ..doesn't make any difference how big a capacitor u have on the rails...at least for me it didn't.. :) |
Yes. But there can never be any burst more heavy than a full power continuous signal. If the rails hold up enough for, say, 100W at 20Hz (if that is the spec), with actual music the load will always be less, burst or no burst.
Jan Didden |
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| AndrewT |
| quote: | Originally posted by janneman
.....there can never be any burst more heavy than a full power continuous signal. If the rails hold up enough for, say, 100W at 20Hz (if that is the spec), with actual music the load will always be less, burst or no burst..... |
even transient signals can be worse than this. That's why bypassing at the main current consumers are so important.
Now change the specification to full power at 10Hz (within 0.2db of 1kHz), then try full power at 5Hz (within 1db of 1kHz).
| quote: | | doesn't make any difference how big a capacitor u have on the rails |
balderdash. Ripple voltage is directly proportional to load current changes. |
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| janneman |
| quote: | Originally posted by AndrewT
even transient signals can be worse than this. That's why bypassing at the main current consumers are so important.
[snip] |
This is nonsense. NO transient can be worse - in terms of discharging the supply caps, and THAT is what we are discuissing here - than a full power lf signal. The whole idea that smaller supply caps give weak bass is just plain wrong, EXCEPT in full power situations where lower supply caps cause earlier clipping so lower max output power. I gave the example of a 50W in 8 ohms continuous signal from a +/- 40V supply amp. There is absolutely NO change in signal level whether you have 10000, 20000 or 50000 uF cap. THINK!
| quote: | Originally posted by AndrewT
[snip] balderdash. Ripple voltage is directly proportional to load current changes. |
Yes, ripple voltage is directly proportional to load. Everybody knows that. But thats not the issue. Don't change the subject. The issue is whether the supply cap value can lead to 'weak bass'. And THAT is balderdash, my friend.
Jan Didden |
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| janneman |
| quote: | Originally posted by AndrewT
[snip]Now change the specification to full power at 10Hz (within 0.2db of 1kHz), then try full power at 5Hz (within 1db of 1kHz).[snip] |
More nonsense. Don't tell me the original poster experienced 'weak bass' because at 10Hz or 5Hz his response was down a few dB.
Jan Didden |
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| sasmit |
| quote: | Originally posted by janneman
This is nonsense. NO transient can be worse - in terms of discharging the supply caps, and THAT is what we are discuissing here - than a full power lf signal. The whole idea that smaller supply caps give weak bass is just plain wrong, EXCEPT in full power situations where lower supply caps cause earlier clipping so lower max output power. I gave the example of a 50W in 8 ohms continuous signal from a +/- 40V supply amp. There is absolutely NO change in signal level whether you have 10000, 20000 or 50000 uF cap. THINK!
Yes, ripple voltage is directly proportional to load. Everybody knows that. But thats not the issue. Don't change the subject. The issue is whether the supply cap value can lead to 'weak bass'. And THAT is balderdash, my friend.
Jan Didden |
exactly what I meant.... :) |
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| AndrewT |
I am going to let this thread cool down.
The two camps are never going to agree. |
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| burnedfingers |
| quote: | | Yes. But there can never be any burst more heavy than a full power continuous signal. If the rails hold up enough for, say, 100W at 20Hz (if that is the spec), with actual music the load will always be less, burst or no burst. |
I have to agree 100% with Jan.
I still do NOT see a need for mega sized caps in this design or any other. I have never seen where adding 2X or 4X the size of the caps has added to bass content. It primarily made it sound muddy and undefined. In addition, it made it necessary to add a soft start circuit and a different approach to turning it on to keep from frying the on/off switch.
Andrew,
Sorry guy but I just cannot buy what your saying about my lack of capacitance as the cause of a lack of bass here.
Please show me with a graph showing where adding additional capacitance will add to the low frequency responce and I will never challenge this again.
Jack,
The chip response is free of oscillation due to the large sized commercial piece of heatsinking. This was confirmed on my scope.
As posted earlier I will confirm the size of the 1.0 mfd cap on my tester. I have already re-confirmed the correct placement of my other caps. Note* I had done this prior to assembly by using my meter. There isn't a problem there. |
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| jackinnj |
| quote: | Originally posted by AndrewT
I am going to let this thread cool down.
The two camps are never going to agree. |
Yes, why do boys always fight in the sandbox?, better to play nicely with your dollies (and by the way, yesterday was Barbie's 50th birthday.) The message of Lysistrata was correct. |
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| burnedfingers |
I got bored and changed the input caps to 4.7 mfd. Yes, they are installed correctly. Amplifier still cannot come close in low frequency response to the LM3886 gain clown I put together.
Any more ideas?
Please don't tell me I need a bank of 100,000 mfd caps to get some low end out of this. |
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| youyoung21147 |
Oh, maybe your LM4780 are just bad ! (broken pin inside, bad thermal junction, ESD damage etc...)
Have you tried to replace them ? |
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| jackinnj |
| Tell us about the modulus of impedance with your speakers. |
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| AndrewT |
Hi,
Is 6weeks long enough?
Have you tried using each channel un-bridged?
Youyoung may have a point about one half of the chipamp mis-behaving. |
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| jackinnj |
| the other point is that if the impedance is very low (this is a bridged amp) you are going to thermally stress the amplifier -- this is the case of any bridged amp -- the LM4780, LM3886, LM3875 have wonderful thermal protection but if the heatsink is inadequate or the power supply differential is too large you get all sorts of thermally related problems. |
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| burnedfingers |
Gentlemen,
Please correct me if I am wrong here but if there was an internal problem wouldn't this show up on the scope with a sine wave input? Positive and negative wave forms being equal in my opinion would make me believe the amplifier is in fact behaving properly.
| quote: | | Is 6weeks long enough? |
Well, Andrew I had hoped that we might be able to discuss this without problems. Am I wrong? I hope not....
jackinnj
The impedance figures for my speakers are as follows:
4.5 ohms@ 100hz, 6.3 @ 330 hz, 8.4 @ 1k, 7.5 @ 10k
I apologize for not being able to go lower in frequency but the good impedance meter is at the shop. I believe the speaker dips to 4.0 ohms @ 63HZ if my memory is correct. The speakers were made by myself and Mr. DJK of whom I am sure you know from the contributions he has made over the years in the Solid State forum.
In addition....the 4780 has been tried with my old but true Altec model 9 speakers which present a 8 ohm load at low frequency.
The heat sinks are from two Altec 150 watt mixer amplifiers. Each channel has an identical heat sink. Under several hours of testing and run time the heat sink temperature rose about 4 degrees per my TPI model 371 infrared thermometer. |
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| jackinnj |
DJK, of Flaming Tiger fame?
We need a little more empirical data here -- please to borrow a Mitey-Mike, take the speaker and amp outside, with woofer down and measure the response with the bridged amp and a reference amp using something like True-Audio from 10 to 1kHz. |
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| burnedfingers |
| Ok, you got me...what the hell is a mitey-mite? |
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| AndrewT |
| quote: | | Well, Andrew I had hoped that we might be able to discuss this without problems. Am I wrong? I hope not.... |
it's six weeks since I bowed out and I was hoping that was long enough to let me come back in without being shouted at. :)
I do try to help. |
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| AndrewT |
Hi,
it looks as though you have built a 4 to 8ohm speaker.
Can you confirm that?
Is it a pair of 8ohm bass/mids in parallel or a 4ohm bass/mid with an 8ohm tweeter?
If the bridged amp is managing to drive the treble just fine and runs out of current into the lower impedances then bass will suffer.
Seems to be even more reason to temporarily hook up a single channel and listen to the resulting frequency balance. |
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| youyoung21147 |
Bridged in 4 ohms is really not recommended.
Try to build a parallel version of your amp using the same chips and see how it works. |
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| burnedfingers |
The impedance readings are not only dependant upon the drivers but also the crossover. There is a single 15'' woofer, horn midrange and horn tweeter. Its a clone of the Klipsch Cornwall speaker with the exception of better drivers and refined crossover.
The 4780 has been run with my Altec Model 9 speakers and they measure 8 ohms impedance @63 Hz. Still they lack the bass response.
As I mentioned earlier if there was a problem with the amplifiers/bridged pair of 3886's it would have to show up in sine wave response wouldn't it? Identical wave form would indicate proper performance in my humble opinion.
Maybe its not recommended to run the 4780 bridged into a 4 ohm load but at moderate levels with a large power supply there shouldn't be a problem. My experience with these amplifiers is they make a nasy noise when they clip. I wasn't close to clipping the amplifier. It should be capable of a few watts on peaks. Temperature monitoring would also indicate the amplifiers weren't pushed. A low impedance load with a healthy level would bring forth a temperature rise higher than I experienced.
Juke box manufacturers such as Rockola use dual 3886's in mono bridge config for their external channels. Their specifications show loading of two 8 ohm speakers or one 4 ohm speaker per external channel for 120 watts per bridged channel. They also show the capability to bridge the two external channels for a total of 240 watts to drive a 1 ohm load. Page C-9 Rock-ola Operation and service manual. |
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| youyoung21147 |
When you look at your scope, are the speakers plugged ?
Also, a good shape of the sinewave doesn't mean it has the good amplitude. |
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| jackinnj |
| quote: | Originally posted by burnedfingers
As I mentioned earlier if there was a problem with the amplifiers/bridged pair of 3886's it would have to show up in sine wave response wouldn't it? Identical wave form would indicate proper performance in my humble opinion. |
The contact surface area of 2 LM3886's is larger than that of on LM4780. If you keep the rail voltage less than or equal to 24V you shouldn't have a problem in this regard.
If you want, you can always dissemble the chip from the heat sink and send it back here and I'll take a look at it. |
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| burnedfingers |
| When I look at my scope the amplifier was connected to a 4 ohm load or 8 ohm load by the flip of a switch. If the wave form is equal doesn't it have even amplitude? |
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| burnedfingers |
jackinnj,
I appreciate the offer but I could purchase another chip at less cost than shipping this one across the country. Tell me... am I incorrect in thinking that if the wave form and amplitude are equal the amplifier is functioning correctly? |
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| youyoung21147 |
Isn't it a problem with your speakers (demagnetized woofer, broken solder or connexion lead...)
Also, you should look at the scope with the speakers connected, not a resistor which isn't a reactive load. Maybe the amp oscillates only when connected to speakers. |
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| AndrewT |
Hi,
a shelving bass response that is 3db down compared to the midband will sound as though someone has turned the bass way down.
Even -1db shelf is easily detectable within the passband of music. It's so easy for the ears to compare the various signal levels and frequencies that are present simultaneously.
Some commentators claim that errors as low as -0.1db are detectable, I would not try to substantiate that.
Where I'm coming to is that a frequency response that is just 90% of voltage in the bass band compared to full voltage in the mid and treble will sound quite bass light.
Your measuring system must be able to give results better than 2 or 3% to see that 90% reduction with some confidence.
Good technique and careful calibration will get you into the right ball park. You must be able to guarantee that you are using the same input signal when measuring the output signal AT VARIOUS frequencies.
Don't worry about reactive loads at the moment. Concentrate on 4ohm, 8ohm, & 100ohm and 20Hz, 100Hz, 1kHz, 10kHz at output levels of 1Vac and 10Vac
Are you able to confirm the impedance of that 15inch driver? Have you got a 4 to 8ohm speaker? |
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| burnedfingers |
I will try to get a warble generator plot to show up.
This should provide the necessary proof there isn't anything wrong with the speakers.
Plot using a calibrated flat microphone, warble generator and HP plotter. I went over it several times because the pen is getting hard to read. As you can see there is a 1db boost in the lower region. The speakers graph very good and sound even better. |
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