Spasticteapot said:
ThermalTrak equivalent of On Semi MJL3281/MJL1302 or Toshiba 2SC3281/2SA1302 but with higher ratings.
Vceo = 260V
Pdiss = 200 watts
Icmax = 15 Amps
http://www.onsemi.com/PowerSolutions/product.do?id=NJL3281D
Data Sheet:-
http://www.onsemi.com/pub_link/Collateral/NJL3281D-D.PDF
This is classic Silicon Chip - put a 47uF bipolar electro (what they specify) right at the start of the signal path. Yep, that won't affect the sound one bit....
Snoopy,
Leo believes that an amp with zero measureable distortion sounds the best, and that topology is everything. I believe components make a difference, too.
Hugh
Leo believes that an amp with zero measureable distortion sounds the best, and that topology is everything. I believe components make a difference, too.
Hugh
Hey Hugh,
I bet YOU could take this amp, tweak a few parts (I reckon it would be only a half dozen or so) and this amp would sound as good as any and better than most.
I think you would find the prototype will sound reasonable good because Leo knows about matching components etc, but the production kits (cheap $90 per amp) will need some close attention.
regards
I bet YOU could take this amp, tweak a few parts (I reckon it would be only a half dozen or so) and this amp would sound as good as any and better than most.
I think you would find the prototype will sound reasonable good because Leo knows about matching components etc, but the production kits (cheap $90 per amp) will need some close attention.
regards
This amp has two major problems:
1. The OPS is way overbiased (70...100mV over Re, normally should be 18...25mV) and will suffer from GM doubling when will switch from classA to classB.
2. The OPS is thermally undercompensated. The diode inside ThermalTrack devices has different TC than a silicon BE junction, -1.66mV/grdC compared with -2.1mV/grdC
1. The OPS is way overbiased (70...100mV over Re, normally should be 18...25mV) and will suffer from GM doubling when will switch from classA to classB.
2. The OPS is thermally undercompensated. The diode inside ThermalTrack devices has different TC than a silicon BE junction, -1.66mV/grdC compared with -2.1mV/grdC
AKSA said:
So do Halcro and a lot of other amp designers !! But then again I suppose if you don't have the means or the money to measure it then you won't know if an amp does measure well so you will always make an excuse as to why it is not important 😉
smithy666 said:
My loudspeakers have quite a few large value bipolar caps in the crossover that have to handle large amounts of current. Should I be worried about this one lowly capacitor that only has to handle a fraction of the current ??
roender said:
I agree. I have said it before, those thermal traks are 'me too'-s against the Sanken STD03 series, which also have internal diodes but here the diodes are carefully matched for the same tempco as the transistors.
Anyway, when you publish the distortion spec for a 200W amp at 8W, something smells...
Edit: I think they mean 8Ohm when they write 8W....
Jan Didden
As far as I know exactly these output bjts need an higher than average bias for optimum crossover distortion; I think there were distortion measurements in the Symasym-thread that showed that nicely.
Have fun, Hannes
janneman said:
Yes it is ohm. I often see W in place of the ohm symbol when the ohm symbol is not available.
h_a said:
Does that mean you could substitute the On Semi devices with the Sanken devices and get even better performance ??
Are they the same pin outs ??
h_a said:
I think Douglas Self has convinced most of us that BJT EF output stages need around 25mV across Re, no matter the value of Re, for optimum (=linear) performance.
Jan Didden
Hi Jan,
I have Selfs book, but can't find a reference to this? Could you maybe point me to a specific topic?
EDIT: my mistake, I misread 1R instead of 0.1R. I was refering to 70-100mA bias being the optimum value for that OnSemi-bjts (not 0.7A as in that schematic).
@snoopy
No you misunderstood me. I was not talking about the Sankens, just about the OnSemi parts.
Have fun, Hannes
I have Selfs book, but can't find a reference to this? Could you maybe point me to a specific topic?
EDIT: my mistake, I misread 1R instead of 0.1R. I was refering to 70-100mA bias being the optimum value for that OnSemi-bjts (not 0.7A as in that schematic).
@snoopy
No you misunderstood me. I was not talking about the Sankens, just about the OnSemi parts.
Have fun, Hannes
This looks like a crib of D.Self's designs (even down to the 6u8H and no pre-driver) with a few updates and a few mistakes incorporated.
Self discusses Vre in OutputI of his book. Vre<=25mV
The input DC blocking cap is too big. The DC blocking cap in the NFB is too small.
It needs a collector resistor in the VAS EF.
And something needs to be done with the CCSs for the LTP & VAS. This is where Self got lost trying to improve slew rate both in level and symmetry.
Self discusses Vre in OutputI of his book. Vre<=25mV
The input DC blocking cap is too big. The DC blocking cap in the NFB is too small.
It needs a collector resistor in the VAS EF.
And something needs to be done with the CCSs for the LTP & VAS. This is where Self got lost trying to improve slew rate both in level and symmetry.
omega has both upper case and lower case.
We normally associate the upper case symbol for ohms.
But the lower case symbol looks like a curly w (not W).
Could this be a keyboard problem where the posters keyboard is set up differently from the readers?
We normally associate the upper case symbol for ohms.
But the lower case symbol looks like a curly w (not W).
Could this be a keyboard problem where the posters keyboard is set up differently from the readers?
Here's my take on output stage biasing.
1. Class B only works if you have really good thermal compensation - I found that its quite difficult to get it right in a big practical amp undr all drive conditions.
2. I like to run my amp 'Class A+AB' - so first 5 watts is class A and then it goes into class B (my new iteration will run first 10W class A)
3. Yes, the distortion is higher (just like Doug told us), but this only happens >5W
4. What you get is a sweet sounding 10W class A amp with **** loads of high power class B sitting right behind it. Sounds great.
1. Class B only works if you have really good thermal compensation - I found that its quite difficult to get it right in a big practical amp undr all drive conditions.
2. I like to run my amp 'Class A+AB' - so first 5 watts is class A and then it goes into class B (my new iteration will run first 10W class A)
3. Yes, the distortion is higher (just like Doug told us), but this only happens >5W
4. What you get is a sweet sounding 10W class A amp with **** loads of high power class B sitting right behind it. Sounds great.
snoopy said:
You should try replacing these - you may be surprised by the result. The fact that it has to handle a fraction of the current is irrelevant. You should do some research on various types of capacitors. Elektor did an article some years ago where they tested each type and provided measurement results (ie objective testing). Electros were almost the worst (only beaten by tantalum caps), and bipolar caps are worse than standard electros, particularly when used in the signal path.
Most high end speakers use polypropylene caps for exactly this reason. Yours probably don't as they cut corners and didn't want to spend the extra $$$ it costs for better quality caps. But hey, if you are happy with those used in your speakers, then no problem. And if you are happy with the circuit/components proposed by Silicon Chip, then no problem either. But you did post here, so I gave you my 20 cents worth, particularly given I have been reading Leo for the past 25 years and know exactly his views of electronics and the world.
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