| I got this schematic of a power amp, would like comments - Click HERE for Original Thread |
| pat allen |
I will not tell yet where it came from. I got all the parts to duplicate it, and wondering what expert think of this kind of design. The power supply is +37 0 -37.
I got an original working amp made out of this sch (factory, not homemade) and all i can say is that it gives a lot of power for what it is.
Comments please !! |
|
|
| Steven |
Simple amplifier, uses cheap (and relatively dirty) 4558 opamp as driver. The next stage with Q101, 103 and Q102, 104 is a 10x amp to get the required voltage swing that the opamp is not able to deliver. The output stage is underbiased and will generate crossover distortion. Biasing is via D105...D107 and the bias voltage it makes (only 3 diodes) is too little to create the required idle current in the darlington output stage. Probably done to save an adjustment resistor and adjustment time. On the other hand it will also not drift.
Q113, 114 is for overload protection.
I guess it is a musical instrument amplifier or car audio amplifier in the category "most bang for the buck".
Steven |
|
|
| pat allen |
Interesting comments. Yes, it is a car audio power amp, rated at an optimistic 250w max. It is bridgeable and can drive 2 ohm loads.
It is indeed a cheap amp, but delivers very high spl's on proper subwoofers.
My goal is to build such an amp to drive 2 TL for my home basement.
Maybe you have some suggestions to improve this design, i would like yo delete the op amps, and use some back to back fets or regulat transistors. I hate op amps :smash:
I also have a schematic from a Randal musical instrument amplifier, and is rated as much as 700w at 1ohm load. The circuit is incredibely simple and uses 2n3773 for the outputs. But the voltage rail is too high for now, i only have a toroidal transformer that can deliver 2x 30v ac.
The speakers i have for this project are 4 ohm car subwoofers that can take a lot.
thanks for the inputs.
Pat Allen |
|
|
| Steven |
If you want to use these amplifiers and not start from scratch, I would just make very small changes on the original PCB, otherwise you could just as well start designing or building a completely different amplifier (even with the same components, well, at least the expensive components).
Replace the opamp with a better quality one and add a bias adjustment to the output stage by replacing the three series connected diodes by a Vbe multiplier, thermally coupled to the heatsink.
Changing the opamp may result in the necessity to change the frequency compensation (C114, C115), though. You will need a scope to check stability. The easiest is by applying a (small signal) square wave and looking at overshoots.
Steven |
|
|
| destroyer X |
One of our big brains.
Just to inform, in the possibility you have not this information.
For me, low knowledge guy, everything this man say is a law...well .... each one is each one, you can be another big brain too.
regards,
Carlos |
|
|
| destroyer X |
So, as you have luck, i will be searching you, to have chance to hear what he say too.
regards,
Carlos |
|
|
| burnedfingers |
Altec Lansing and EV use a more simplified version of this in their 9444B, (EV2600), 9446.(EV3200). The power output of the 9444 and 2600 is 200 WPC@8 ohms and 300 a channel at 4 ohms. The 9446 and 3200 put out 600 wpc at 8 ohms. I forgot the 4 ohm rating. The 9446 and 3200 will mono bridge at 1200 watts.
These can be purchased very cheaply on ebay with the going rate at about $100 an amp. I should note that these amps are commercial and will take a balanced or unbalanced input. They are also fan cooled and feature metal case T0-3 case outputs.
I think I could post a schematic since the original company went out of business. I think you would enjoy the simplicity of the design. |
|
|
| Eva |
Inside a car, cabin gain boosts LF efficiency by 20 to 30dB. Mid frequencies are also boosted by 3 to 9dB due to corner gain or wall gain depending on driver placement. Also the cabin load effect at LF reduces the cone excursion requirements for a given SPL up to 1/10th in comparison with outdoors
So almost everything sounds loud inside a car [and manufacturers take good care of this fact :dead:], but car audio gear produces frustrating results outside the car [sometimes also inside it...]
This amplifier only produces about 60W at 8 ohms with a standard unregulated supply. This power applied to a small 6" or 8" driver placed in a medium or large room is not going to sound loud at all, even TL loaded. With more power the cone excursion limit of the drivers will be easily reached. Typical 'Car-audio-loudness' is not so easy to obtain in rooms and it's quite hard outdoors... |
|
|
| burnedfingers |
| EVA has brought out some very good points here. Another point to consider is the power output of a car amplifier. I spent a lot of time on the bench in the 90's and one memory comes back to me when I think of car power amps. Even with a bank of batteries they don't deliver the advertized rating. My point is...why bother with the thought of designing or building a power amp when the models I have mentioned can be purchased for peanuts and sound good. |
|
|
| pat allen |
Have to know that i already use this exact same power amp outside of a car, in bridged mode with a 2 ohm load (two 4 ohm 10 inches subwoofers) and is sounds as loud in my listening room than in my car. So raw calculations gives
P=e2/r, (36v+36v, bridged mode)>2 /2ohm=2592w? rms=1832?
giving a 50% coeficient working number...916w?:scratch:
I never got the way to calculate power output capability of a power amp...but i know ohm law !! :D
Whats the thing with hearing Charlie? i dont get it at all.
For the Altec schematic, yes, show it !!!:bigeyes:
thanks
Pat Allen |
|
|
| burnedfingers |
Pat
Put a sine wave into it and adjust till it clips then back off until clean. Have your dummy load connected on the output of the amp. Connect your RMS volt meter on the output or use your scope.
If you can produce 36volts out (which I doubt). 36X36=1296 divided by the resistance of the load(example 2 ohms)
1296 divided by 2 =648 watts. 4 ohm load 324 watts 8 ohm load = 162 watts.
Thinking it sounds just as loud is not proof. Measurements need to be taken and plotted. My opinion here. |
|
|
| pat allen |
Oh well, by the way, i dont want to reinvent the wheel, i just want to know if the amp i already have can be upgraded. I am a poor man, i just bought a house...:rolleyes:
I have all the parts to build another one and maybe run 2 in bridged mode...
If i could find a better schematic to use my irfp250r, i will surely build something else. Main problem is my power supply wich can only deliver around +40 0 -40v at around 8 amps, loaded with 8x 34800uf sangamo caps.
And i know for sure that most of the amp never gives the advertised numbers, but one company that i have worked for showed very realistic numbers, Alpine power amps always felt on tap with theirs power ratings...i remember one of the last series build wich was a 1000 series if memory ok, the power supply was something like +85 0 -85 on 4 ohm loads, and it was stable until cliping. that gaves then 136db spl's with a RTA with 2 12 inches subs in a demo caravan.
I was Alpine authorized service center in the past.
thanks
Pat Allen |
|
|
| pat allen |
| quote: | Originally posted by burnedfingers
Pat
Put a sine wave into it and adjust till it clips then back off until clean. Have your dummy load connected on the output of the amp. Connect your RMS volt meter on the output or use your scope.
If you can produce 36volts out (which I doubt). 36X36=1296 divided by the resistance of the load(example 2 ohms)
1296 divided by 2 =648 watts. 4 ohm load 324 watts 8 ohm load = 162 watts.
Thinking it sounds just as loud is not proof. Measurements need to be taken and plotted. My opinion here. |
I use it in bridged mode...wich is then 36+36 volts=72. I never measure this amp on a bench, i got all the instruments to do so.
If the sounds that goes thru my ears feels as loud as i wish, then i am satisfied, and it is. :smash:
Pat Allen |
|
|
| burnedfingers |
Quote:
I use it in bridged mode...wich is then 36+36 volts=72. What is 72 volts? The ouput to the load? Please explain.
Schematic of 9444 |
|
|
| pat allen |
well, my understanding of a bridged mode power amp with rail to rail power supply is that you apply then the sum of the rail to rail voltage?
It is powered by a +36v 0 -36 volts power supply, so when bridged, the voltage capable to be sent to the sepaker is the full vcc swing and is then 72 volts, if, of course, the power supply can handle it.
The load is 2 ohm, 2x4 0hm speakers in parralel.
Pat Allen |
|
|
| burnedfingers |
| Well, I sent it. Don't know where its at now. |
|
|
| pat allen |
you might try to send it thru my e-mail?
thanks a lot
Pat Allen |
|
|
| burnedfingers |
Pat
Example:
Altec 9444 has a B+ and B- voltage of 77V. That does not mean you will see a power output of 154 volts. It is capable of running 200 watts @ 8ohms and 300 watts per channel at 4 ohms or 600
watts mono bridge mode. There are a lot of factors to consider. I could ramble on her for several pages at least making sense of it all. To sum it all up. Only clear way to tell output is to test. Roughly calculated in mono bridge mode power output is less than 4 times the normal rating in watts. The power supply and the design of the amplifier has a bearing on the output capabilities. In the case of this amp it puts out roughly 70 volts into an 8 ohm load at clipping.
The 9446 or 3200 will put out in excess of its rating into an 8 ohm load. It is rated at 1200 watts mono bridge and puts out 1250-1300 watts.
Note* Its rail is plus and minus 91 volts. It puts out about 100V RMS into an 8 ohm dummy load. I have very large fan cooled dummy loads. |
|
|
| pat allen |
well, i know physicaly how bridging an amp work for sure, you seems to under estimate my knowledge in this path, the final result and goal is to have more voltage swing at the speaker, by dephasing one of the chanel 180deg. and applying the same source to the amps, so when on channel swing at its +vcc, the other swing at its -vcc. Connecting the speaker at both channel outputs finishes the bridging mode. It should then send the (72v) to the speaker, unles that, it is useless to have a bridging operation if it dont goes thru, surely the power supply have to handle all this.
The amp i got specifically got this feature and believe it or not, it does send the full vcc swing to the speaker.
This is how bridging works and it is used specificaly in audio mobile where most of the decks have btl mode power amps, wich can deliver then more than 30w with only 12v of vcc.
Pat Allen |
|
|
| burnedfingers |
Mr. Moderator
I sent a schematic of a 9444 Altec amplifier not of current production as Altec Lansing (original company went out of business). This schematic is not proprietary information and can be disclosed without any written permission.
The schematic I fear has gone into the Twlight Zone and is not appearing. |
|
|
| burnedfingers |
Pat
I know you understand the concept of bridging however in any bridged situation you will never get the power supply voltage capability on the output. Your 36V + 36V will NEVER show up as 72V on the output of the amplifier to the speaker. Very Best case will always be less than 4X the rated output to the speaker in normal mode. I suggest that you don't take my word and do hook up a test setup and this will be the proof. |
|
|
| burnedfingers |
| You could always build this: |
|
|
| Eva |
Those +-37V rails at idle will usually sag to +-33V average when playing loud and this will produce about +-30V output swing when driving a 4 ohm load
But don't expect much more than +-22V swing when driving a 1 ohm load [2 ohm bridged]
Those +-22V from each side produce +-44V over the 2ohm load. Thats 968 W peak and no more than 534 W rms
Belive me, I routinely repair car-audio amplifiers and I have tested lots of repaired ones at full power. I use a custom built 14.4V 72A SMPS and a 1 Farad capacitor as a test power supply
What power supply do you use to provide the 100A peak current required when driving 2 ohms bridge?
The SMPS toroids of car-audio amplifiers are usually wound to show high leakage inductance and to produce controlled supply-rails sagging in order to keep output devices within SOA when driving low impedances
So supply rails sag badly and the typical bridged output power is approximately 3 times the single channel output power instead of the expected 4 times
burnedfingers :
Nice picture. Isn't there something missing? :D:D:D |
|
|
| pat allen |
Hi, i have done some measurements !!
I have connected the amp to our lab power supply (100amp, 12 volts), and a 2 ohm load wich can take 400w (resistive load), i have added a fan just in case.
I have reached 50volts peak to peak while the power supply was cliping, the protection was set at 60 amp.
The signal started to be cliped on the top of the wave only, telling me that some distortion started too.
So, that gives 50x50/2=1250w ? :bigeyes: rms beign 883w.
thats absolutely impossible, but thats it what i have measured. The signal applied was a 1khz sine wave, with a maximum of 3 volts peak to peak output.
2 volts was needed to make the amp clip.
The voltage of the power supply inside the amp, wich is a switching power supply started to drop, from 36 volts to 32v.
It is made of a big toroidal transfo, with very heavy soild coper wiring and very few wounds. There is 8 power mosfets to switch it.
So, by the end, it does realy pump a lot of watts in bridged mode on a 2 ohm load. Thats enough for me to think that it will fulfil my needs to drive two TL with the 2 350w 10 inches clarion subwoofers.
The amp is rated itslef at 250w+250w @4ohm.
The numbers are, i think, realistic. The ratio of the transfo is (36v/12)=3, so the current have to be 3xtime too, 50 volts /2 ohms=25 amps, x3=75 amp, so the amp should draw 75 amp on the 12 line at full power. With all the losses and drop, it should raw maybe less, the power supply was actving its protection set at 60 amp telling me that it is logical.
BTW, the resistor pack was realy hot:devilr:
Pat Allen |
|
|
| pat allen |
| quote: | Originally posted by burnedfingers
Pat
I know you understand the concept of bridging however in any bridged situation you will never get the power supply voltage capability on the output. Your 36V + 36V will NEVER show up as 72V on the output of the amplifier to the speaker. Very Best case will always be less than 4X the rated output to the speaker in normal mode. I suggest that you don't take my word and do hook up a test setup and this will be the proof. |
Sorry, never meant to be harsh or hard headed. I understand the fact that the power will never go all thru to the speaker because of the disign itslef, i wanted to mean that its the starting numbers.
I REALY want to see this schematic !!!
thanks a lot,
Pat Allen |
|
|
| pat allen |
| quote: | Originally posted by burnedfingers
You could always build this: |
I already have build this...
I plan to use this enclosure for my project, along with the power supply and some more caps that i have.
Pat Allen |
|
|
| burnedfingers |
| That is nice too. |
|
|
| burnedfingers |
Quote:
burnedfingers :
Nice picture. Isn't there something missing?
Ok, what is missing other than several additional pairs of outputs, sinks, and emitter resistors. Its a single channel subwoofer amp with crossover on board.
Yes, still trying to send the schematic. |
|
|
| darkfenriz |
hey pat allen
one of the pros of this schematic is symetry...
I like the idea of symetric amps with current feedback..
if you don't like the op amp, throw it away then with r120 & r133 and give 150k r131 & r132 for high input impedance
and instead of these bloody diodes d105/d105/d107 five a Vbe multiplier with pot to set nice biasing (say 60mA per pair)
Maybe also some power darligtons at output.
results may be nice I think
cheers |
|
|
| Eva |
| quote: | Originally posted by burnedfingers
Quote:
Ok, what is missing other than several additional pairs of outputs, sinks, and emitter resistors. Its a single channel subwoofer amp with crossover on board.
|
The main heatsink for the output devices is missing :bigeyes::bigeyes::bigeyes::bigeyes: This picture is probably a bad joke since these small stamped-aluminum-sheet heatsinks are rated at more than 15ºK/W and would reach funny temperatures when playing loud in any circuit with rails above +-30V and/or driving loads below 8 ohm, particularly in a closed case with no air flow
Also, there is no thermal tracking between output devices so big current mismatching is guaranteed to occur
NOTE: A transistor mounted on a 15ºK/W heatsink and dissipating 10W will heat up to 15*10=150ºK above the ambient temperature :hot: :hot: :hot:
And I'm not going to ask how did you burnt your fingers... [just kidding but be careful with hot surfaces :)] |
|
|
| burnedfingers |
Eva
Thank you so much for trying to point out the flaws in my design.
Unfortunately you didn't bother to find out the particulars before finding faults.
This picture is probably a bad joke since these small stamped-aluminum-sheet heatsinks are rated at more than 15ºK/W and would reach funny temperatures when playing loud in any circuit with rails above +-30V and/or driving loads below 8 ohm, particularly in a closed case with no air flow.
Well, looking at it from a view not shared by this picture there will be a 105 cfm fan cooling those small heat sinks. The B+ and B- voltage is 65 volts. The later version I built had a sensor on the heatsink to switch the fan from medium speed to high speed.
Funny thing is that it never switched to high speed unless it was being tested.
Also, there is no thermal tracking between output devices so big current mismatching is guaranteed to occur
Well, the amp is debiased on purpose as to not have a problem with thermal runaway of any type. Distortion was still way below .1%
NOTE: A transistor mounted on a 15ºK/W heatsink and dissipating 10W will heat up to 15*10=150ºK above the ambient temperature
Well, one has to account for the type of usage of the amplifier. In its application (subwoofer usage) it normally does not see anything close to what a full range channel would see. In normal operation it doesn't heat up and run hot. I don't consider it a problem then. Only when run into a load at full power does it heat up. With a full set of outputs it is 2 ohm stable.
Now, it is easy to find fault with others work. By the way what have you built that has survived over 14 years? I have over 50 of these in different theatre systems along with custom designed subs and drivers and they are still running without any problems. |
|
|
| pat allen |
I knew someone should say something good about it, because it does sounds respectably good and gives incredible power for what it is.
Defenitively try the biasing with a plain transistor and a pot like the amp of the 80's. I guess it will reduce overall distortion specificaly at low volumes, as one would expect from an amp with poor/low bias.
thanks a lot !
Pat Allen |
|
|
| gearheaddruid |
Hi, all. I would like to address the question of power output. I think you are forgetting to derive the r.m.s. value from the rails before doing the math for power.
The rails would be the peak of a sine wave. The formula to derive r.m.s. value is peak voltage X .707. An example:
50 volt rails using this as a.c. value:
50 X 50 = 2500 / 8ohm = 312 watts.
50 volt rails using the formula:
50 X .707 = 35. 35 X 35 = 1225 / 8ohm = 153 watts. Quite a difference! This is why some of the power outputs may seem way exagerated. This also is assuming a perfect world where there are no losses in the amp and the power supply would be regulated rock solid.
In the real world, an amp with 50 volt rails would likely produce about 100 watts into 8ohms.:att'n:
As for the stamped heat sinks, I have seen an awful lot of commercial amps with this same setup. It must work okay as long as the fan runs.;) I do not find it "sexy" but it is cheap and functional. Regards, Steve |
|
|
| burnedfingers |
Quote:
Defenitively try the biasing with a plain transistor and a pot like the amp of the 80's. I guess it will reduce overall distortion specificaly at low volumes, as one would expect from an amp with poor/low bias.
I started that way with a T0-220 all plastic case transistor
mounted on top of a T0-3 metal case output and as one would expect it was very easy to achieve a .003 distortion figure. This however would not deliver the long term life and durability I was after. I figured that sense it was a subwoofer amplifier I could live with a distortion reading of less than .1 but not the .003 I had before. The difference is not audable in a subwoofer amplifier. I was after long term life from a piece of equipment that may likely run 15 hours in a day and I got it.
It might be interesting to note that the amp started as a full range fully complimentary quad diff input amplifier and ended up as a sub amp. Overkill to say the least and still running.
Did you get the schematic I posted? |
|
|
| burnedfingers |
Pat
After looking at your schematic and your heatsinks...is there a problem of C rise for you also? As mentioned before the 4558 is a dirty Op amp only slightly better than the 1458. I would try a 5532 in its place. A 5532 is a common commercial Op amp that is pretty clean and doesn't suffer from the problem of latching up to the rail like some Op amps do. It might also be a good place to try an OPN. Unless I missed it I didn't see decoupling caps close to the Op amp. You might want to add some small ones. |
|
|
| pat allen |
No, i have no problems with overheating at all, this amp runs good during summer.
One thig i may say, they dont suggest to run it in bridged mode with a 2 ohm load, but a 4 ohm one. I do run it at 2 ohm at full volume, i ran very hot and never run out. :D
There is no caps around the op amp, so i may add few if i redo the pcb.
The amp pictured above is not the amp on the schematic, but it will.
This pictured amp is a Zen amp. :angel:
Pat Allen |
|
|
| pat allen |
| quote: | Originally posted by gearheaddruid
50 volt rails using the formula:
50 X .707 = 35. 35 X 35 = 1225 / 8ohm = 153 watts. Quite a difference! This is why some of the power outputs may seem way exagerated. This also is assuming a perfect world where there are no losses in the amp and the power supply would be regulated rock solid.
In the real world, an amp with 50 volt rails would likely produce about 100 watts into 8ohms. |
I run it a 2 ohm. Did i say that i run it a 2 ohm?
I run it a 2 ohm.
1225/2=612.5w then.
Pat Allen |
|
|
|
|
