Agree with you JP. You give some great info too, stuff I wish I knew years ago instead of having to learn on my own. As an EE student the chip amps would be a fun beginner project and then the LME parts more advanced. I guess it depends on where people are at in the studies along with time, money, the usual.
-SL
-SL
martini1881 said:
Peak voltage on the load in ideal case ( no losses) =Vcc
Average power ( sinusoidal signal) in load: Vrms^2/R !!!
Vrms = Vpeak/sqroot of 2
then Vrms^2 = Vpeak/2
average power = Vpeak/2R or here Vcc/2R
So your question must be 150w requires ? Vcc for 4 ohm
Answer: 150=(Vcc^2)/2R then Vcc= sqroot ( 2*4*150) = 35 volts
Cheers
Jean-Pierre
Here my LME49810 prototype boards finding a home in a junked Crown DC-150 -- the latter being purchased for about $20 -- trying buying a transformer and cabinet for that much.
This one uses some Fairchild TIP142/147's which I had on hand.
This one uses some Fairchild TIP142/147's which I had on hand.
An externally hosted image should be here but it was not working when we last tested it.
a lot has been said about LME49810 and LM4702 except that LME49810 is almost impossible to solder on a veroboard (Yes, i've done! ... but one went to trashbin 🙁 ).
Assuming that LME49810 has higher slew rate, higher drive current and slightly higher distortion and the LM4702 has lower distortion at the expense of lower slew rate and drive current among other facts (like the mention to the word audiophile in the datasheet) has someone done a comparative test with similar output stages and can tell the differences?
I have a lot of IRFP240/IRFP9240 and TIP142/TIP147 and know that these aren't the best audio transistors ever, but i would like to do something with them. My idea is to use the LME49810 to drive the mosfets and the LM4702 for the bipolar ones (because it's easier to build). I have more LME49810 so i could also run the bipolar one using these. How does your prototype sound?
Would the IRPF pair sound good? (I know about termal issues of vertical fets) AN-1645 says that the problem is the threshold voltage, but LME49810 can have 10V from sink to source so this is not an issue anymore.
Thanks in advance
Assuming that LME49810 has higher slew rate, higher drive current and slightly higher distortion and the LM4702 has lower distortion at the expense of lower slew rate and drive current among other facts (like the mention to the word audiophile in the datasheet) has someone done a comparative test with similar output stages and can tell the differences?
I have a lot of IRFP240/IRFP9240 and TIP142/TIP147 and know that these aren't the best audio transistors ever, but i would like to do something with them. My idea is to use the LME49810 to drive the mosfets and the LM4702 for the bipolar ones (because it's easier to build). I have more LME49810 so i could also run the bipolar one using these. How does your prototype sound?
Would the IRPF pair sound good? (I know about termal issues of vertical fets) AN-1645 says that the problem is the threshold voltage, but LME49810 can have 10V from sink to source so this is not an issue anymore.
Thanks in advance
You could wait a few more weeks, the FET version of the drivers will be out soon. It doesn't have a Baker clamp or a clip indicator but it does have the rest and it can bias even higher. I have worked with the LME49810 and the FETs you list, along with others, and it works fine. As you have pointed out, the LM4702 can't get enough bias voltage for these particular FETs.
-SL
-SL
Do you know if national is planning to release the driver in another package? I think that LME49810 package is the thing that has depressed me the most as diyer.
Another question, working in a mosfet arrangement without thermal compensation, bias can be set trough a resistor between BiasP and BiasM?
Another question, working in a mosfet arrangement without thermal compensation, bias can be set trough a resistor between BiasP and BiasM?
same package, same pin out as LME49810. Some pins are NC so a single board can be made to use either device.
Bias can indeed be set with just a resistor between the bias pins for those FETs that don't need thermal compensation. Probably want a cap or two in parallel with that resistor but pretty simple bias scheme.
-SL
Bias can indeed be set with just a resistor between the bias pins for those FETs that don't need thermal compensation. Probably want a cap or two in parallel with that resistor but pretty simple bias scheme.
-SL
I think i'll go for the bipolar one, since mosfets have some stability issues and since i havn't already bought an oscilloscope it's very hard to set the gate resistor to get proper slew rate. maybe need diferent thermal compensation.
jackinnj, how does your prototype sound?
jackinnj, how does your prototype sound?
I've done it! It's one of the best defined amplifiers ever heard. I must admit that i did not like it because it sounded incredibly bright, but this was probably due to the 0.2$ 2200uF coupling capacitor between amplifier and speaker. I use always a coupling capacitor the first days i run an amplifier for speaker protection, and this time it has been a lucky decision, since after a while the output became shorted to one of the rails. One of the transistors gets warm, the other is completely cold and the emmiter degeneration resistors get extremely hot until they smoke. It looks like a bad joint.
The thing i liked the most regarding this driver is the total absence of hum, buzz and noise, but this might also be due to my new grounding scheme (keeping different star ground/supplies and connect them from dirtiest (nearest from the supply) to cleanest (signal star-ground) and using an air-core three turn choke (wire turned arround a pencil) to connect signal ground to power ground.
I guess that this will be my primary amplifier once found a tube preamp that adds a bit of warmth to the ultra-analytical sound of the LME49810.
Note: Used 10 pF to get 50V/us slew rate and it does not show any stability issues.
The thing i liked the most regarding this driver is the total absence of hum, buzz and noise, but this might also be due to my new grounding scheme (keeping different star ground/supplies and connect them from dirtiest (nearest from the supply) to cleanest (signal star-ground) and using an air-core three turn choke (wire turned arround a pencil) to connect signal ground to power ground.
I guess that this will be my primary amplifier once found a tube preamp that adds a bit of warmth to the ultra-analytical sound of the LME49810.
Note: Used 10 pF to get 50V/us slew rate and it does not show any stability issues.
ionomolo said:
Hello Ionomolo
I do not remember having seen such grounding scheme.
If possible, please post your schematics.
Thanks!
this is my grounding layout (shematic is identical to the one in typical application):
I know that this is probably the strangest thing ever said in an audio forum, but somebody has used some kind of night vision glasses to debug audio circuits? I'm using an amperimeter and cutting wires to see where is all current going and my amplifier has started to look as if it has been used at war.
An externally hosted image should be here but it was not working when we last tested it.
I know that this is probably the strangest thing ever said in an audio forum, but somebody has used some kind of night vision glasses to debug audio circuits? I'm using an amperimeter and cutting wires to see where is all current going and my amplifier has started to look as if it has been used at war.
In literature I got from local National guys on new products in Q4 shows the LME49811 also but it is not found on the National site. It is a mono version of the LM4702 but in the same package and pin out as the LME49810 and the new FET driver. Hmm, one board for 3 options. Would be fun to compare sound differences between the parts. The new LME49811 has more drive current than the LM4702 but still only like 10mA. Since it is in the literature it must be close to release.
-SL
-SL
I forgot to tell another important difference between my design and the typical application. My amplifier supresses both input and feedback coupling capacitors and uses a buffer (LM4562) to minimize offset due to bias current. Is this a bad idea?
Yesterday i did another prototype and also the same problem... emmiter degeneration resistors smoking, transistors warm but not hot and LME49810 completely hot.
It seems it is a much harder design than the usual gainclone, assuming you are trying to keep the feedback loop short and use good grounding techiques.
Since i found the feedback cap really ear-hurting in gainclones i'll probably design a board using a dc-servo.
I will start doing a spice model (Hey, only an ideal opamp with two outputs raised BiasP-BiasM and its footprint) and post the results. Maybe a board with optional "base" degeneration resistor and cap would be a great idea since it could be used equally with mosfets (remember IRFP240/9240 have the same pinout than TIP142/147 B C E - G D S). The last week my neighbour told me he earned a living etching pcb's, and asked if i did know what a pcb was : ).
You guys who have done a prototype, how did you do? Veroboard/P2P seems a no-go.
It seems it is a much harder design than the usual gainclone, assuming you are trying to keep the feedback loop short and use good grounding techiques.
Since i found the feedback cap really ear-hurting in gainclones i'll probably design a board using a dc-servo.
I will start doing a spice model (Hey, only an ideal opamp with two outputs raised BiasP-BiasM and its footprint) and post the results. Maybe a board with optional "base" degeneration resistor and cap would be a great idea since it could be used equally with mosfets (remember IRFP240/9240 have the same pinout than TIP142/147 B C E - G D S). The last week my neighbour told me he earned a living etching pcb's, and asked if i did know what a pcb was : ).
You guys who have done a prototype, how did you do? Veroboard/P2P seems a no-go.
ionomolo said:
I usually test out my amplifier designs with a Tektronix PS5010 power supply -- it is current limited to 400mA when you go to +/- 30VDC, If it hits this right out of the box I know I have done something incorrect.
The final testing supply is built into an old Hewlett Packard regulated supply and it will do 5 amps +/- 80VDC. I bought a Crown theatre amplifier which is just going to be used as a power supply for testing.
What values of resistors did you use in the bias circuit?
Emmiter resistors are 0.1 Ohm. Bias transistor BC139C (NPN Beta [measured] = 500) Resistors are (348+200) and 1.21K as in typical application. Output transistors are TIP142 & TIP 147. Feedback is as in typical application but witout the cap (I expect this to increase offset, not bias current). Using the tester's diode fuction i've measured Vce with the circuit turned off and found 0V! where is that damn current going?
I use a promax power supply and a diy one with a voltimeter attached [2N3055 based] (not current limited but has enough output impedance to show a huge voltage fall when it's sourcing too much current. Voltage falls from 20 V to 5 at 1.5A).
I use a promax power supply and a diy one with a voltimeter attached [2N3055 based] (not current limited but has enough output impedance to show a huge voltage fall when it's sourcing too much current. Voltage falls from 20 V to 5 at 1.5A).
ionomolo said:
Try using a lower value for the 1.21K -- and instead of 200R I use a 500 ohm potentiometer. I can easily set the bias current this way.
As National notes -- you must have the clip flag attached to something -- even to a current source.
I hadn't noticed i must connect the clipflag to something, but the last board does have a LED+470R+7805.
How have you done your prototype? PCB or P2P?
How have you done your prototype? PCB or P2P?
ionomolo said:
I just send out for some boards -- it's frustrating at my advanced age to do P2P.
I can get the Sanken diode incorporated boards to work with the LM4702, but not the LME49810.