Hi All.
I am building a 3 way active crossover with double op-amp (NE5532).
A silly question.
Because I use 1/2 op amp af filter and the other 1/2 as output buffer (voltage follower), if I want bias in class A the op-amp with a resistor or a CCS, witch one must I bias: the first one, the buffer or both? (or nothing).
Thanks a lot to averybody.
Ciao.
I am building a 3 way active crossover with double op-amp (NE5532).
A silly question.
Because I use 1/2 op amp af filter and the other 1/2 as output buffer (voltage follower), if I want bias in class A the op-amp with a resistor or a CCS, witch one must I bias: the first one, the buffer or both? (or nothing).
Thanks a lot to averybody.
Ciao.
I suppose the reason for wishing to force the opamp in Class A is for improving the sound of the signal.
To me it would make no difference whether one of both amps in the 5532 acts as a buffer stage, as the signal passes both forcing both in class A would be the logical choice.
Personally i would go for a 634 combined with an opamp with a much higher slewrate than the 5532.
I admit it adds considerable to the cost with a 3-way filter but compared to overall cost the relative increase in cost is justifiable.
To me it would make no difference whether one of both amps in the 5532 acts as a buffer stage, as the signal passes both forcing both in class A would be the logical choice.
Personally i would go for a 634 combined with an opamp with a much higher slewrate than the 5532.
I admit it adds considerable to the cost with a 3-way filter but compared to overall cost the relative increase in cost is justifiable.
Re: Op amp csall A biasing.
Just try and listen.
A good starting point whould be about 2k2 - 4k7 to - supply both outputs. The exact value depends on signal current drawn from output. You choose that resistor that the current thru it is at least equal to signal current calculated from load and Vout max.
Uli
PS: Your only criteria should be your ears!!!
pro said:
Just try and listen.
A good starting point whould be about 2k2 - 4k7 to - supply both outputs. The exact value depends on signal current drawn from output. You choose that resistor that the current thru it is at least equal to signal current calculated from load and Vout max.
Uli
PS: Your only criteria should be your ears!!!
not necessarily
Biasing class A changes the kind of distortion.
Look at peranders site -> the GC with class A biasing.
Go to www.passdiy.com and read NPs articles about biasing single ended class A which is the same as biasing an opamp with a resistor (CCS) at the output.
Uli
pro said:
Biasing class A changes the kind of distortion.
Look at peranders site -> the GC with class A biasing.
Go to www.passdiy.com and read NPs articles about biasing single ended class A which is the same as biasing an opamp with a resistor (CCS) at the output.
Uli
Well, I am gonna using a 2134 for the high section, two M5238P for the mid section and a 5532 (the slowest) for bass section.
Now, if the filter drives the buffer, it means that looks at an input inpedence of the buffer very high. Isn't it 2k2 to 4k7 to high current for that (at 12V rail it's 5.4 and 2.7 mA), and the buffer with those values, must drive a 2k2 hom in parallel with 34K of the amp, that is about 2K. Isn't it a value a bit low for an Op-amp?
Ciao.
Now, if the filter drives the buffer, it means that looks at an input inpedence of the buffer very high. Isn't it 2k2 to 4k7 to high current for that (at 12V rail it's 5.4 and 2.7 mA), and the buffer with those values, must drive a 2k2 hom in parallel with 34K of the amp, that is about 2K. Isn't it a value a bit low for an Op-amp?
Ciao.
Upupa Epops said:Or build discrete opamp - example you can find on Bryston's pages ( they are using only eight cheap transistors ).
Pavel, I strongly advise you to try to be more helping (if you really want to help that is) not telling "pro" to do something totally different.
We have seen pretty many posts of yours lately where you are to no help at all. So please Pavel.....
pro said:
Pro, it's normal to have a class A circuit between an opamp output and a buffer input but how much good this circuit does is hard to know if you don't know how the output stage is designed in the opamp. It's not certain at all that you really will get an improvement, just by adding a circuit not knowing if you should tie it to V+ or V- or how much current you should have.
My advise here is that you start with no class A circuit to begin with.
From what I have seen not very many have bothered to used this class A ciircuit on this rather (or very!) old opamp. I have mostly seen it together with an OPA627, AD8610 or LT1115.
Notice also that it's not suitable to have this circuit if you have a normal load. It's best suited if you have a high-ohmish buffer as load.
Currents for the current generators are normally 1-2 mA, not more.
Inspiration can be found here:
http://tangentsoft.net/audio/meta42/misc/schematic6.pdf
http://www.sjostromaudio.com/hifi_files/qrv/qrv04r0schema_p1.pdf
http://www.linear.com/prod/datasheet.html?datasheet=202
http://www.sjostromaudio.com/hifi_files/qsx/qsxm3r0schema_p1.pdf
OK. Thank you to all for the advices.
I think i'll start without class A, and then I'll arrange a small module where insert a j-fet or bjt CCS with the op-amp, inset it in the op-amp socket , maybe only for high and midrange section, and then listen to the difference.
I didn't find the Class A GC in the Peranders site. Because I am interested to it, could somebady give me the right link?
Thanks again.
I think i'll start without class A, and then I'll arrange a small module where insert a j-fet or bjt CCS with the op-amp, inset it in the op-amp socket , maybe only for high and midrange section, and then listen to the difference.
I didn't find the Class A GC in the Peranders site. Because I am interested to it, could somebady give me the right link?
Thanks again.
I'm afraid there aren't any such Gainclonespro said:
I can say so much that I haven't been able to pick any difference with and without this class A circuit but others can I'm sure.
You have the lnks above in those two project I have used this class A circuit. You may notice that Tangent has used a cascoded JFET, slightly better than a single transistor but you will loose some voltage.
Hi,
Yeap, I'm going to get burned for this one!! lol..
I've heard of certain respected engineers rave about doing this to a 741 for audio purposes, I guess if you have nothing else around. So now I'm thinking for anyone who's really curious about this, it might be neat to experiment first with a totally abhorrent op amp like a 741, should be able to tell real fast what kind of difference it makes.
Though I of course agree for your actual circuit, do try it without first, it's not a hard addition to make later.
Also, I have it on good authority you should tie your CCS, or resistor, to the power rail which displays the least PSRR according to the data sheet, and that all it really does to improve things is bypass this 20dB worse PSRR, but then again I'd think since it is working class A the improvement should be two fold.
Keep an eye on the temperatures too.
Regards
Yeap, I'm going to get burned for this one!! lol..
I've heard of certain respected engineers rave about doing this to a 741 for audio purposes, I guess if you have nothing else around. So now I'm thinking for anyone who's really curious about this, it might be neat to experiment first with a totally abhorrent op amp like a 741, should be able to tell real fast what kind of difference it makes.
Though I of course agree for your actual circuit, do try it without first, it's not a hard addition to make later.
Also, I have it on good authority you should tie your CCS, or resistor, to the power rail which displays the least PSRR according to the data sheet, and that all it really does to improve things is bypass this 20dB worse PSRR, but then again I'd think since it is working class A the improvement should be two fold.
Keep an eye on the temperatures too.
Regards
I was under the impression that you need to connect it to move current from the output stage device that is in the emitter follower mode, in cases of quasi-complementary design. Is this right? e.g. in a classical NPN output stage the top transistor will be EF and the bottom CFP. You connect from output to -ve rail.
uli said:
Depends on the design of the outputstage of the op.
As normally OPs arent complementary in design for best result you should take a look into the datasheet. Normally there is a circuit shown.
Uli
Hi,
To what end?
I'm just guessing you would do that with the intention of using the NPN in class A and biasing off the PNP, however it doesn't seem to make sense if the NPN has -20dB less PSRR.
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