corrieb said:
Hi,
This is explained in Self's books is it not ?
This may help : http://www.angelfire.com/ab3/mjramp/ampdes1.html
/sreten.
!
corrieb,
there is no fixed rule. Generally, keep it in th e range 10mA -50mA.
Why?
Below 10mA, the VAS standing current will be modulated by the output stage current when driving low speaker load resistances leading to distortion. Above 50mA you encounter dissipation problems in the VAS.
I like fully complimentary designs, so that's a little different to Doug Self's approach, but the rationale applies to his topology as well. I run my VAS at 30mA with good results (250W amp)
corrieb,
there is no fixed rule. Generally, keep it in th e range 10mA -50mA.
Why?
Below 10mA, the VAS standing current will be modulated by the output stage current when driving low speaker load resistances leading to distortion. Above 50mA you encounter dissipation problems in the VAS.
I like fully complimentary designs, so that's a little different to Doug Self's approach, but the rationale applies to his topology as well. I run my VAS at 30mA with good results (250W amp)
BTW, I run my LTP at 5mA per side with Cdom = 47pF in order to ensure good slew rate performance. Don't be shy on LTP standing current - a lot of people run their LTP's at 1-2 mA - wimpy in my view. WRT the LTP bias current demands when running the LTP 'hot' - just use low value f/back and input bias resistor values.
corrieb said:
Hi,
HF gain is set by the input stage gm and Cdom of the VAS.
For a typical output stage and Cdom stabilisation you can get away
with up to ~ 30dB excess gain, or feedback factor at ~ 20Khz. The
exact numbers are always imprecise, the question being usually
how much phase margin is enough ? never an exact answer ....
/sreten.Hi,
Thank you for all the replies.
I have designed a spreadsheet that calculates my values/components required for a input & vas stage that will be stable based on the recommendations throughout this threat and another one which should produce a very linear design but I am concerned with the stability.
Attached you will find the circuit, graph 1 (OLG=Red, CLG=Blue and Output=Green); (Phase=Green), graph 2 (3rd Distortion measured in volts); graph 3 (3rd Harmonic measured in dB) and a printout of the spreadsheet.
Can someone please look at the ouput of the input&vas and advise whether I can pursue this design based on my current configuration.
Thank you,
CorrieB
Thank you for all the replies.
I have designed a spreadsheet that calculates my values/components required for a input & vas stage that will be stable based on the recommendations throughout this threat and another one which should produce a very linear design but I am concerned with the stability.
Attached you will find the circuit, graph 1 (OLG=Red, CLG=Blue and Output=Green); (Phase=Green), graph 2 (3rd Distortion measured in volts); graph 3 (3rd Harmonic measured in dB) and a printout of the spreadsheet.
Can someone please look at the ouput of the input&vas and advise whether I can pursue this design based on my current configuration.
Thank you,
CorrieB
examples loopgain.asc and loopgain2.asc in ltspice are used to plot the open loop gain.
example audioamp.asc is refered as to look the gain and phase margins.
which one is better to be used?
if we have a 30db gain amplifier ,can we plot the open loop gain based on the formula on loopgain example,then go at 30db at the open loop gain graph and look at the phase margin corresponding there??
example audioamp.asc is refered as to look the gain and phase margins.
which one is better to be used?
if we have a 30db gain amplifier ,can we plot the open loop gain based on the formula on loopgain example,then go at 30db at the open loop gain graph and look at the phase margin corresponding there??
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