Can someone recommend a value for the bias capacitor when used in parallel for mosfets that don't need thermal compensation (2SK1058/2SJ162)?
I feel that a high value can place a capacitive load to the LME49810 and actually decrease sound quality.
I feel that a high value can place a capacitive load to the LME49810 and actually decrease sound quality.
To All,
In regards to this discussion about LME49810, how do you compare the sound quality and performance to its relatives LME49811 and LME49830 chip amps. Is LME49810 a better choice?
In regards to this discussion about LME49810, how do you compare the sound quality and performance to its relatives LME49811 and LME49830 chip amps. Is LME49810 a better choice?
I haven't done such test keeping all things equal such as output stage, power supply, bias current levels, etc and only changing out the driver part. It is possible but I also don't consider myself to be a golden ear so I don't know that I would notice any change in sound.
-SL
-SL
One pair of FJL4215 & FJL4315 are used as output stage and +/-30V supply voltage is used. My amplifier clip at about +/-20V.
I am wondering the voltage drop should not be that high?? 😕
Can anyone share the voltage drop in your design?
Thanks
I am wondering the voltage drop should not be that high?? 😕
Can anyone share the voltage drop in your design?
Thanks
ionomolo said:
Do you mean "bypass" -- I have used several and don't really detect a difference in sound quality or objective test measures -- here's a current output board (no, I still haven't sent them out for production!!!): The board uses WIMA polypropylenes from the power supply rails to ground, and one across the power supply 470nF/400VDC
Attachments
I was talking about the 30 pF cap Cce in AN-1645. Somewhere arround it says that it can also be replaced by a microfarad-range electrolityc paralleled with a polypropylene. I've also read that this cap helps reducing switchoff noise in bjt and second harmonic in the output stage, but i'm not sure if it's only aim is to give a way for the base carriers to be sucked in bjt designs. Anyways, national places these in its LM4702 mosfet design, but neither LME49810 bjt nor LME49830 mosfet typical applications have one.
Hi AndrewT
You are right. The output sinewave is +/-20V peak to peak max in my design. I am finding which parts are contributed to the voltage drop of 10V peak to peak. My design is just like the LME49810 datasheet figure 1.
Thanks for your answer.
Kim
😀 😀 😀 😀 😀
You are right. The output sinewave is +/-20V peak to peak max in my design. I am finding which parts are contributed to the voltage drop of 10V peak to peak. My design is just like the LME49810 datasheet figure 1.
Thanks for your answer.
Kim
kamwing said:
AndrewT said:
kamwing said:
AndrewT said:
😀 😀 😀 😀 😀
+-10Vpk = 20Vpp
If you have +-30Vdc on the supply rails then something is wrong if it is clipping this low.
If you have +-30Vdc on the supply rails then something is wrong if it is clipping this low.
Is clipping symmetrical? Does clipflag led turn on? Have you measured it with no load? Have you measured that the psu actually gives the expected voltage when connected to a load ?
Check mute voltage and that there is no floating ground/supply rail (sometimes when unconnected voltage develops trough decoupling capacitors and allows a thiny output (albeit severely distorted) to be present without connection.
Check mute voltage and that there is no floating ground/supply rail (sometimes when unconnected voltage develops trough decoupling capacitors and allows a thiny output (albeit severely distorted) to be present without connection.
Kam -- how much current are you seeing through the Clipping Flag indicator pin -- do you have this wired up correctly? Measure the voltage drop across the current limiting resistor.
AndrewT, ionomolo,jackinnj
Thanks for all of your kindly advice 😀
The clipping is symmetrical and led will tuun on when clipping at either at +/-20V(loaded) and +/-27.2V(no load).
When there is no load the clipping voltage is +/- 27.2V. After, a 8 ohm load is connected. The clipping voltage drops to +/-20V.
Mute pin is connected to a switch to switch 5V from 7805 and ground. It works. I can observe the mute effect in my CRO.
PSU should work well because it is the adjustable DC power supply capable of delivering max 3A current from 0-30V. I just connect two of them together to get +/-30V.
I have brought moneky29 4 output stage pcb and I got the same result by connecting the circuit just like the figure 1 in LME49810 datasheet.
I expect to get at least 25Vp-p at the output due to some drop in LME49810 or output stage. However, I just adopt one pair of output stage which are the pair of FJL4215&FJL4315 or MJL21195&MJL21196. I got the same peak to peak voltage either in loaded or no load condition.
Therefore, I am wondering the voltage drop should be originated at output stage transistors.
What is your expected voltage drop in a standard audio power amplifier😕
Thanks for all of your kindly advice 😀
The clipping is symmetrical and led will tuun on when clipping at either at +/-20V(loaded) and +/-27.2V(no load).
When there is no load the clipping voltage is +/- 27.2V. After, a 8 ohm load is connected. The clipping voltage drops to +/-20V.
Mute pin is connected to a switch to switch 5V from 7805 and ground. It works. I can observe the mute effect in my CRO.
PSU should work well because it is the adjustable DC power supply capable of delivering max 3A current from 0-30V. I just connect two of them together to get +/-30V.
I have brought moneky29 4 output stage pcb and I got the same result by connecting the circuit just like the figure 1 in LME49810 datasheet.
I expect to get at least 25Vp-p at the output due to some drop in LME49810 or output stage. However, I just adopt one pair of output stage which are the pair of FJL4215&FJL4315 or MJL21195&MJL21196. I got the same peak to peak voltage either in loaded or no load condition.
Therefore, I am wondering the voltage drop should be originated at output stage transistors.
What is your expected voltage drop in a standard audio power amplifier😕
kam -- try hooking it up as in the test circuit diagram -- with 10R resistors between sink and source, the bias pins connected together and the output board disconnected -- then see if it clips.
Note as well -- if you are using the circuit per schematic 1 your input impedance is dominated by R(s) -- 6.81K -- could it be that your source is running out of gas?
Note as well -- if you are using the circuit per schematic 1 your input impedance is dominated by R(s) -- 6.81K -- could it be that your source is running out of gas?
Hi Kam,
you are still confusing me with your measurements of voltage units.
3A DC supply will just work for a resistive 8r0 load on a +-30Vdc supply.
For a reactive 8ohm speaker load you can have peak currents of (30-4)/8/0.35~=9.3Apk
Note: I have used a 4V loss for a short term voltage/current peak.
Is the extra 6.3A coming from decoupling capacitance downstream of the PSU?
you are still confusing me with your measurements of voltage units.
3A DC supply will just work for a resistive 8r0 load on a +-30Vdc supply.
For a reactive 8ohm speaker load you can have peak currents of (30-4)/8/0.35~=9.3Apk
Note: I have used a 4V loss for a short term voltage/current peak.
Is the extra 6.3A coming from decoupling capacitance downstream of the PSU?
gmikol said:
I'll go along with earlier suggestions to increase the feedback resistors by an order of magnitude. Anything below about 25 Hz in any source you'd be likely to use (CD, tuner, [especially] phono]) is likely to be a mistake, and it's doubtful that your speakers could handle it gracefully anyway. With electrolytic capacitors, you need to go to around 5x the theoretical value to avoid distortion, but if you can get the amp's parameters to the point where you could reasonably use an 8--12 uF cap in the feedback ground leg, a film or even tantalum (they're more reliable nowadays) could be used.
Resistor noise is grossly overestimated as a problem. An RN60D has a maximum inherent noise of around 0.10 uV/V, so if we have a dozen resistors in the audio path putting out 20V peak (50W), we have around 24 uV or less of resistor noise -- about the noise level of the famously quiet OPA124 at 10kHz. Inaudible even in the hypersensitive fantasy world of The Absolute Sound.
Wow craig4cc...I had to go back a little bit (Post #35!!!) to figure out what you were quoting me on. I had every intention of prototyping that board...but then I fell off the grid for a few months & then started a new job, so it fell by the wayside.
By the time I got back to this thread, it was all about monkey29's board and FET stuff.
The schematic I drew was a literal reading of the datasheet. If I ever build it, I probably will increase the resistor values a bit, and get rid of the cap in the feedback.
--Greg
By the time I got back to this thread, it was all about monkey29's board and FET stuff.
The schematic I drew was a literal reading of the datasheet. If I ever build it, I probably will increase the resistor values a bit, and get rid of the cap in the feedback.
--Greg