Re: Thanks...
CRO = Cathode Ray Oscilloscope. Use this to observe the waveform across the source resistors and see if the waveforms are of similar size. Do this with a sine wave test into a resistive load of no less than 8 ohms.
Cheers
Q
BlacK_Chicken said:
CRO = Cathode Ray Oscilloscope. Use this to observe the waveform across the source resistors and see if the waveforms are of similar size. Do this with a sine wave test into a resistive load of no less than 8 ohms.
Cheers
Q
Hi
I have finished my two channels quasi amp sucessfully. 2 pairs irfp240 every channel. dc voltage is +-50v. I use my own layout. The sound really not bad. I trust the sound will become more better after a period of time running. thanks quasi and everyone who give good hint here. 🙂 🙂 🙂 🙂
the first stage i use 2sc1845 hfe at 550 ~ 600, the output valtage very easy keep in 0 mv.
I plan to use 649/669 in VAS and driver at the begining , but i have some to-126 2sa1507/2sc3902, so i try them in VAS. The current of VAS is 12ma if the R15 use 47R, I change R15 to 68R, the current drop back to 10ma , I feel the transistor rather hot even I use a big To220 heatsink for the transistor in VAS , so 647/667 may be not the best choice in this schematic.
649/669 use for driver working OK. I mount them on main heatsink. Bias curent set to 160mA total one channel
Maybe I could upload the picture of amp later ......
cheers
I have finished my two channels quasi amp sucessfully. 2 pairs irfp240 every channel. dc voltage is +-50v. I use my own layout. The sound really not bad. I trust the sound will become more better after a period of time running. thanks quasi and everyone who give good hint here. 🙂 🙂 🙂 🙂
the first stage i use 2sc1845 hfe at 550 ~ 600, the output valtage very easy keep in 0 mv.
I plan to use 649/669 in VAS and driver at the begining , but i have some to-126 2sa1507/2sc3902, so i try them in VAS. The current of VAS is 12ma if the R15 use 47R, I change R15 to 68R, the current drop back to 10ma , I feel the transistor rather hot even I use a big To220 heatsink for the transistor in VAS , so 647/667 may be not the best choice in this schematic.
649/669 use for driver working OK. I mount them on main heatsink. Bias curent set to 160mA total one channel
Maybe I could upload the picture of amp later ......
cheers
M.Y. said:
The 2sa1507/2sc3902 look like a nice choice for the second stage and should be fine there. I've never used these before so it would be good to see how they go.
The 2SD669 / 2SB649 should be ok too for 50v rails running into 2 FETs (per rail). The MJE350 / 340 is stronger though at higher voltages.
Dropping the second stage to 10mA is cool and I toyed with this as well. The second stage does run very warm but with MJE350 / 340 that's quite ok.
In my view running 80mA bias per FET pair is a bit much, but everyone to his own I guess. Try dropping it to 50mA and see if there is any difference in performance.
I would be interested to see your PCB layout showing components and tracks and any thing else you care to post.
Finally congratulations on a successful build, it's good to see some component flexibility being used.
Cheers
Quasi
DIGORA said:
Hi Digora,
The 2SD667 / 2SB647 is not suitable for the second stage, as they will not be able to dissipate enough heat.
See my answer above for 2SD669 / 2SB649 for the driver stage.
Cheers
Q
DIGORA said:
Looks like a nice design, but I only had a brief look. In this case the 2SD669 / 2SB649 is driving into a much smaller gate capacitance than the FETs I specified in my amp. Indeed the characteritics of the 2SK1058 is quite different to an IRFPxxx.
In any case this schematic is completely different to the versions posted here so it's difficult to make any other comment
Cheers
Q
The sound of them?
You are all doing a great job gentleman! I'm really impressed!
I know, that others already asked this, but please, tell me something about the sound of these amps. How do they sound?
You are all doing a great job gentleman! I'm really impressed!
I know, that others already asked this, but please, tell me something about the sound of these amps. How do they sound?
testing N MOS amplifier
Hi,
I am back again, with somme new information about my amplifier 🙂 Output offset voltage , very low 0.3 mV , easy to adjust . Bias curent is set at 50 mA . The amplifier sound is warm 🙂 I forget to mention , voltage rail +/- 30 V to first step , and after +/- 63 V . I readjust offset , and bias curent to new rail voltage and everything go perfect , now I'm 😀 http://i13.tinypic.com/2yjzo6b.jpg
Hi,
I am back again, with somme new information about my amplifier 🙂 Output offset voltage , very low 0.3 mV , easy to adjust . Bias curent is set at 50 mA . The amplifier sound is warm 🙂 I forget to mention , voltage rail +/- 30 V to first step , and after +/- 63 V . I readjust offset , and bias curent to new rail voltage and everything go perfect , now I'm 😀 http://i13.tinypic.com/2yjzo6b.jpg
hi quasi
what 's the effect of r9 and c3. I found the sound effect will change go with the changing value of r9 and c3. When I remove them , the sound become hard . and use the your value print in diagram the sound become more soft . so I guess r9 c3 will change the evenness of frequency response besides adding a pole -- zero. Is it right?
thanks
what 's the effect of r9 and c3. I found the sound effect will change go with the changing value of r9 and c3. When I remove them , the sound become hard . and use the your value print in diagram the sound become more soft . so I guess r9 c3 will change the evenness of frequency response besides adding a pole -- zero. Is it right?
thanks
Quasi,
any chance you could add links to each of your schematics to your sign off?
Where can I find the schematic that shows c3 & r9? Ive just gone back 180 posts.
any chance you could add links to each of your schematics to your sign off?
Where can I find the schematic that shows c3 & r9? Ive just gone back 180 posts.
hi Andrew T
the symbols "r9 c3" come from " nchan mos 350 1v4 schmatic". That's a rc network connect two defferinece input transistors' collector . sorry I have not indicated it clearly in my previous post .
the symbols "r9 c3" come from " nchan mos 350 1v4 schmatic". That's a rc network connect two defferinece input transistors' collector . sorry I have not indicated it clearly in my previous post .
Hi,
I have v1.1 & v1.2 saved and it appears they are similar to v1.4
The cap rolls off the treble response and limits it's effect at about 15MHz where 33r (r9) becomes dominant.
Is that roll off the same as an integrator? Where the feedback cap (c3) rolls of the treble (but without the series r) in a voltage feedback amp. Here we have a voltage to current amp with feedback. Is the operation of feedback similar?
I have v1.1 & v1.2 saved and it appears they are similar to v1.4
The cap rolls off the treble response and limits it's effect at about 15MHz where 33r (r9) becomes dominant.
Is that roll off the same as an integrator? Where the feedback cap (c3) rolls of the treble (but without the series r) in a voltage feedback amp. Here we have a voltage to current amp with feedback. Is the operation of feedback similar?
As AndrewT has suggested the network reduces the gain of the input stage at high frequencies. It is included to guarantee the stability of the amp providing some immunity from anything lurking around.
The components can be left out if desired. I am surprised that the sound is affected as much as you have described. Can you check the value of the components you have installed. It is easy to mistake the value of a ceramic capacitor or a badly printed resistor.
Cheers
Quasi
The components can be left out if desired. I am surprised that the sound is affected as much as you have described. Can you check the value of the components you have installed. It is easy to mistake the value of a ceramic capacitor or a badly printed resistor.
Cheers
Quasi
Hi Quasi,
can you confirm if the way it would operate in a VFB amp is the same as here in the V to C amplifier?
can you confirm if the way it would operate in a VFB amp is the same as here in the V to C amplifier?
hi
I have tested the componets with my digital multimeter, the C and R value 's error are all in allowable range.
I sure the RC network affect the gain of the input stage at high frequencies. but when C =330p r=470R, I feel no only high frequencies gain drop£¬low frequency also drop obviously¡£I have no other meter instrument£¬so that's only my subjective feel¡£
I didn't use a preamplifier?maybe it's a reason.
I have tested the componets with my digital multimeter, the C and R value 's error are all in allowable range.
I sure the RC network affect the gain of the input stage at high frequencies. but when C =330p r=470R, I feel no only high frequencies gain drop£¬low frequency also drop obviously¡£I have no other meter instrument£¬so that's only my subjective feel¡£
I didn't use a preamplifier?maybe it's a reason.
AndrewT said:
I'm not sure what you mean Andrew. Do you mean to compare the network at the input stage to the feedback network?
Cheers
Q
M.Y. said:
In the Nmos200 the network involved is C3 and R6. These should be 330pF and 33 ohms.
In the Nmos350 & 500 these are labelled C3 and R9.
Andrew is right it can be confusing. Maybe I should have started another thread for the Nmos200.
Cheers
Q
Hi Quasi,
in a normal voltage feedback amplifier (output to inverting input), adding a feedback cap converts the amp to an integrator. Giving constant -6db slope in the response curve.
Adding a series resistor to the FB cap levels off the response at the turnover frequency of the RC pair.
The LTP is a voltage to current amplifier and not a voltage feedback amplifier.
I wonder if the same rules and results apply when the RC is added across the two collector loads?
I get the impression that the results are the same but I am looking for confirmation and/or conditions when this might not work.
in a normal voltage feedback amplifier (output to inverting input), adding a feedback cap converts the amp to an integrator. Giving constant -6db slope in the response curve.
Adding a series resistor to the FB cap levels off the response at the turnover frequency of the RC pair.
The LTP is a voltage to current amplifier and not a voltage feedback amplifier.
I wonder if the same rules and results apply when the RC is added across the two collector loads?
I get the impression that the results are the same but I am looking for confirmation and/or conditions when this might not work.
Yes the effect would be similar. I.e adding an RC to the collectors of T6 and T7 will have a similar effect. Current will be shunted away from the network around T8 reducing the voltage at the bases of the next stage. I imagine this could be applied in other designs where the available current is controlled or limited.