| lumanauw |
I'm aiming at making good sounding power amp. So, I decided that I have to know what kind of sound every different transistor make.
The idea is to make buffer (gain=1) with different kind of transistor. Because I'm using low rail (+/-15V), I use power transformer's primary (0-110V-220V) as load.
The configuration is differential preamp, but with different kind of transistor. With input R=4k7 and feedback R=4k7, I can get AC gain=1. I put A/B switch, so I can switch the signal feeding through the preamp or bypassed (not thru preamp), so I can hear what difference it makes compared with original signal.
A is bipolar (BD139). Compared to bypassed, it gives less detail, the sound is so-so.----having voltage gain.
B is mosfet (IRF510). Compared to bypassed, it gives more detail in sound, especially in trebles. Nice sound----having voltage gain.
C is CFP Jfet (2SK30+BD140+2k2 resistor). Nice sound. But something is strange. It don't have voltage gain. Even if I eliminate 4k7 feedback resistor, it already perform a buffer. If I put this 4k7 feedback resistor, it attenuates the sound.
Why is this CFP have no gain? How can I make it to have gain? |
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| MikeB |
hi !
i think, you shouldnt drive the jfets without any resistor to ground.
for example some 47k to ground ?
Maybe you should change this to all 3 circuits to get a more practical
testing ?
have you measured the current through the jfets ? it shouldn't
be more than ~1ma. (this might be the problem with your other amp,
maybe the current was to high, and the jfets "saturated")
according to calculations it is ~320uA (0.7v across the 2.2k)
You maybe forgot the 4th option, small bjt + cfp ?
My experience with these was very good sound (dynamics,details,mids,bass)
but something wrong with trebles. (sss and zzz with vocals)
Mike |
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| X.G. |
| quote: | Originally posted by lumanauw
Why is this CFP have no gain? How can I make it to have gain? |
hello,
the reason maybe the Idss of K30 is too small.Check the Idss,and set the idle current of K30 within the Idss( 1/2 of Idss maybe the best) |
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| wenye |
Hi lumanauw,
For circuit C, it's really a unity gain buffer with active NFB. The BD139/BD140 perform full feedback for input k30 pair.
If you want to have gain in this circuit, you should connect C pin of BD139/BD140 to negitive supply then it gain. But, in the other hand, the output distortion will increase a lot dut to None feedback was emploied.
Wenye |
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| lumanauw |
| quote: | | i think, you shouldnt drive the jfets without any resistor to ground. |
Hi, Mike,
I think the basic cct is a differential with inverting output. So the gnd in the right transistor should do it for both of the transistor's reference. | quote: | | have you measured the current through the jfets ? it shouldn't be more than ~1ma. (this might be the problem with your other amp, maybe the current was to high, and the jfets "saturated") according to calculations it is ~320uA (0.7v across the 2.2k) |
Yup, the drop in the 2k2 resistor is 0.62V. I think its OK here. | quote: | You maybe forgot the 4th option, small bjt + cfp ?My experience with these was very good sound(dynamics,details,mids,bass)
but something wrong with trebles. (sss and zzz with vocals)
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:D I got this idea of making C cct as Jfet CFP is from your design!. I wanted to compare the sound of BJT, MOSFET, JFET. For all BJT CFP, will it differs so much than cct A?
As for your experience with sss, zzz, you should try this JFET CFP. It has no sss or ZZZ at all, very nice sound. | quote: | | the reason maybe the Idss of K30 is too small.Check the Idss,and set the idle current of K30 within the Idss( 1/2 of Idss maybe the best) |
Haven't check the Idss yet. But in this CFP, it runs only less than 0.5mA. Idss of 2SK30 is less than 0.5mA?
For Jfets, we can match 2 things, Vgs and Idss. If we want to make differential pair with Jfets, which is more important to match?
| quote: | | For circuit C, it's really a unity gain buffer with active NFB. The BD139/BD140 perform full feedback for input k30 pair. |
I dont quite follow it. In CFP output stage, it is really a unity gain voltage, since we take the output from the sources of FET.
But in this design, I took the output from emitors of the BJT (---drains of the FET). How come it is still a buffer at upper output?
If you are right, then Mike's suggestion on all BJT CFP should act the same too.
How about your SIM on your design, Mike? Does all CFP is a buffer with no gain, no matter where we take the output (at top or bottom?
Usually I can trace it is a buffer or not by connecting drops of Vbe. But in this CFP differential, I still haven't found why it should perform buffer if we take the output from the top. |
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| MikeB |
hi lumanauw !
You need some correct working/bias point, which MUST be identical
on both sides. The difference between these is amplified by the
diffamp.
I think you really should add the resistor, just before the 200ohm.
I jfets are not biased correctly, they can open the gate.
Ok, drop of 0.62v is 281uA, this is not much !
I don't know the k30, can't imagine that it saturates at this current.
Do you have acess to k170 ? I know this one works !
Or bf245 ? This one is very common.
I matched the jfets only for Vgs at ~300uA (difficult enough)
Did you measure the drop on both sides ?
Did you measure both actual Vgs ?
The problems with the sss,zzz are now without jfet. With jfets
i had none of these problems. But still need to check if its the symetrical
topology. I will simply replace the bjts in this amp by sk170/sj74,
then i know ! (Maybe the bc546b/556b is too cheap ?)
I think the cfp has a great influence on all devices.
It seems that the combination jfet+cfp is very promising.
My actual amp is symetrical bjt+cfp. (the 12transistormonster)
What do you recommend as small complementary bjt ?
I like the bc546b/556b as they are fast (ft=300mhz), have a real
hfe of 300, go up to 60v and cost only 4cent...
And the CFP explodes the gain of the diffamp. Without CFP its about
1:50 (with sk170). With CFP it was > 1:1000 ! :bigeyes:
(Without emitter-degenaration-resistors)
With emitterdegeneration the gain is about Rc/Re (~98%)
This means: Re = 22ohm, Rc = 2k Gain = ~1:88
With Re = 0ohm Gain = very very high (divide by zero :D)
You can say, the CFP flattens out the Vbe-curve.
In combination with Re you get some "ideal" transistor.
Do you remember what CFP stands for ? i only remember ComplementaryFeedbackP...)
Mike |
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| Eva |
That test circuit is useless. Any minimal difference in bias currents between both legs will cause severe transformer saturation and severe output distortion [the transformer starts to act as a pair of resistors and push pull effect disappears]
The results obtained from that circuit in each case are much more dependent on biasing imbalance and transformer saturation than the gain devices themselves
Note also that a 220-110V dual primary is extremely inductive [both leakage and coupling] and that the voltage swing required at one leg to get +-1V at the other leg at 20Khz may be more than +-15V
The test circuit by itself is already a nice distortion generator |
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| sam9 |
My understanding, which may be faulty, is that a simple CFB arrangement has unity gain (i.e., no gain) because it is 100% feedback. I think you can create some gain by inserting resistance betwenn the source/emitter of the upstream device and the collector of the downstream device. This will reduce the feedback, of course. You see this ocassionally in output stage configurations - appearently it is thoght to subdue potential oscillation, but I'm not clear if that is the real reason.
I suggest you look around the web for audio test software that can use a soundcard. This lets you confirm frequency response, distotion, do some spectral analysis, etc. Subjective evaluations can be tricky. For instance, it's an old audio store trick to crank up the trebble a bit on units they are pushing as the impression is often heard as "more detail", "more revealing". There are even some signal processors that deliberately add distortion to high frequencies to make them sound "more alive". Since you are dealing with input stages, anything that happens here is going to be amplified approx. 30db down stream. What seems like a minor change, quirk or tweek here can end up being really big by the time it reaches the speakers. |
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| MikeB |
hmm, i've already spent some time in spice, the numbers i wrote
are from sims. In sims the cfp in this configuration creates a lot
of gain. I've already built 2 amps using cfp in the input, and they
behaved as they should.
Maybe you should look at the cfp-bjt as a helper. A slight currentchange
from the input-transistor changes the current in the cfp-transistor.
The cfp-transistor simply scales up the behaviour of the other
transistor.
I don't fully trust in spice, but spice is never that wrong...
I do fully trust realworldcircuits, and they do what spice predicted.
The CFP itself does not have gain, but it behaves like a transistor
capable of very much gain. (like a transistor with a very flat Vbe-curve)
I like CFPs, as you can use very high OL-gains, without getting an
unstable circuit. (like currentmirrors on top of diffamps tend to)
In spice the the cfp outperforms the currentmirrors. The combination
of both is getting difficult, that's too much gain. Then you get
openloopgains > 1:1.000.000
But it worked with jfets...
At 20khz full power harmonics were at -120db. (in sim)
Mike |
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| lumanauw |
| quote: | | What do you recommend as small complementary bjt ? |
For small voltages I like BC550C and BC560C. Low noise and very high gain. For bigger voltage I use MPSA06/56. | quote: | | With CFP it was > 1:1000 ! |
What gain? Current gain? Voltage gain? Strange, I got no voltage gain at all. | quote: | That test circuit is useless. Any minimal difference in bias currents between both legs will cause severe transformer saturation and severe output distortion [the transformer starts to act as a pair of resistors and push pull effect disappears
The results obtained from that circuit in each case are much more dependent on biasing imbalance and transformer saturation than the gain devices themselves
Note also that a 220-110V dual primary is extremely inductive [both leakage and coupling] and that the voltage swing required at one leg to get +-1V at the other leg at 20Khz may be more than +-15V
The test circuit by itself is already a nice distortion generator
|
What kind of distortion? 2nd harmonic?
I can use Resistor for output drop, but since the voltage is low, I choose using transformer primaries.
Thanks for the info. I will put 47k resistor in left transistor (like Mike's suggestion), but not to ground, but to wiper of 100K VR, which left and right end goes to +15V and -15V.
I also will put 10ohm resistor in 0 and 220V point to set the balanced current between each leg, adjusted by the VR.
If I can set the same current between those 2 legs, will it be that what you are saying is minimal?
EVA, you should try this preamp. Inspite of it "distortion generator"/flux imbalanced from your point of view, it sounds nicer than to put R for load. Maybe this distortions makes it sounds nicer. | quote: | | My understanding, which may be faulty, is that a simple CFB arrangement has unity gain (i.e., no gain) because it is 100% feedback. I think you can create some gain by inserting resistance betwenn the source/emitter of the upstream device and the collector of the downstream device. This will reduce the feedback, of course. |
Resistor between source/emitor of upper device and collector of down device? Isn't that is the 2k2 resistor? Or I get it wrong?Where to put the resistor to have gain in CFP? you have a drawing maybe?| quote: | | Since you are dealing with input stages, anything that happens here is going to be amplified approx. 30db down stream. What seems like a minor change, quirk or tweek here can end up being really big by the time it reaches the speakers. |
Thats exactly what I'm searching. Something good upstream will be very good downstream.| quote: | hmm, i've already spent some time in spice, the numbers i wrote are from sims. In sims the cfp in this configuration creates a lot of gain. I've already built 2 amps using cfp in the input, and they behaved as they should.
Maybe you should look at the cfp-bjt as a helper. A slight currentchange
from the input-transistor changes the current in the cfp-transistor.
The cfp-transistor simply scales up the behaviour of the other
transistor.
I don't fully trust in spice, but spice is never that wrong...
I do fully trust realworldcircuits, and they do what spice predicted.
The CFP itself does not have gain, but it behaves like a transistor
capable of very much gain. (like a transistor with a very flat Vbe-curve)
I like CFPs, as you can use very high OL-gains, without getting an
unstable circuit. (like currentmirrors on top of diffamps tend to)
In spice the the cfp outperforms the currentmirrors. The combination
of both is getting difficult, that's too much gain. Then you get
openloopgains > 1:1.000.000
But it worked with jfets...
At 20khz full power harmonics were at -120db. (in sim)
Mike |
I think you are talking about current gain between base and emitors. Is it possible that CFP have enormous current gain, but no voltage gain? |
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| Eva |
The problem with transformer saturation is that it travels continuously from push-pull mode to no push-pull at all during the audio waveform. This obviously produces even harmonics, and compression/clipping in the positive half of the output waveform
Also, in the bipolar version there is no way to set the bias since the base of the left transistor appears to be at an undefined voltage due to capacitive coupling
The transformer also attenuates high frequencies so the frequency response of the circuit should not be flat, being worse in the bipolar version due to it's lower open-loop gain compared with the other versions with dual gain devices. I wouldn't expect much push-pull action above maybe 1Khz and you should be aware that the impedance of the primary at HF [ie:10Khz] may be 100K or more so transistor saturation is likely to happen. It would be a better idea to use low voltage secondaries, maybe something rated at 5Vrms@50Hz before saturation, an audio transformer is advised
Capacitive coupling both transformer ends and providing a DC path through two resistors connected directly from collectors to supply may be an option to get the push-pull action you are expecting without distortion
In the other hand linearizing the circuit may not provide the expected results since it may end 'sounding' as if the output were connected directly to the input with nothing inbetween. At the end most musical instruments produce nothing but carefully distorted sine waves :) |
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| X.G. |
| quote: | Originally posted by lumanauw
For Jfets, we can match 2 things, Vgs and Idss. If we want to make differential pair with Jfets, which is more important to match?
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The DIY method which expert recommend is mathing Idss. and checking the Idss,you can know the max output/saturate current of J-fet.of cource,you match Idss and Vgs will be better;) .
The 2SK30 is product of Toshiba.the label of 'O','Y','GR','BL' on Toshiba J-fet show its Idss range.if your sk30's label is GR or BL,the Idss should be above 2ma. |
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| lumanauw |
Hi, EVA,
I wanted to ask you 2 questions.
1. What do you think about tube amp which uses output transformer? Will it have defected frequency response, especially the KHZ's?
2. What do you think of ZEN V7-T (you can see it in passdiy.com). There is alot-lot-lot-lot of current flowing in this amp towards the 0-110V-220V transformer. | quote: | | Also, in the bipolar version there is no way to set the bias since the base of the left transistor appears to be at an undefined voltage due to capacitive coupling |
I see differential quite differently. I still think the ground at the right transistor is enough for both transistors, eventhough the base of the left transistor is cap coupled. | quote: | | Capacitive coupling both transformer ends and providing a DC path through two resistors connected directly from collectors to supply may be an option to get the push-pull action you are expecting without distortion |
Good idea! Will it sounds different with R load only (in this there is R and inductor+C in parrarel). Or.... wait a minute. Where should I take the output? Between C and L? Or in the R?| quote: | | In the other hand linearizing the circuit may not provide the expected results since it may end 'sounding' as if the output were connected directly to the input with nothing inbetween. At the end most musical instruments produce nothing but carefully distorted sine waves |
But I do hear different transistor sound. Bipolar gives less details compared to bypass. Mosfet gives more detail. I use the same ccs and the same transformer. Can this indicate the sound of each kind of transistor? (all other factors being the same?) |
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| MikeB |
hi lumanauw !
"I think you are talking about current gain between base and emitors. Is it possible that CFP have enormous current gain, but no voltage gain?"
The CFP has enormous current gain. Of course you can get only
voltage gain with a resistor on the "upper" side. (or currentmirror)
My testcircuit had 5k, this resulted in a gain of ~1:1405. In the real
amp i use 1k, thus reducing the gain to 1:281. (input was 1mv, output
"measured" 281mv.
I did some more research why cfp performs so good. It increases
the gain of the diffamp without destroying bandwidth. With emitter-
resistors it still increases the gain a little, but does a great job
in linearizing. The ratio output:harmonics drops to -70db.
Bandwidth is then ~20khz (-1db)
With normal diffamp the ratio is ~-40db
I found another way to achieve similar results. I "castrated" a currentmirror.
Without this castration bandwidth dropped above 100hz.
(Not a realistic value as there was no load at all)
With 33ohm emitterresistors and a 22k between the 2 collectors
i dropped the gain to that of a cfp with 10ohm Re's. Then
bandwidth is above 10khz, and harmonics drop to -80db.
(2nd harmonic mostly,other at noiselevel)
The gain in this circuit was ~1:100. (sk170 as transistors,bc556b
as currentmirrors)
I now believe that proper bandwidth through the whole amp is
very important. Important enough to give up some numbers on THD.
(means low OL-gain)
Will do some more research...
Mike |
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| lumanauw |
Thinking about what Wenye and Sam9 said, maybe CFP is really a buffer with 100% feedback. This have advantage and disadvantages in audio power amp.
So, CFP is a good candidate for differential and final stage, but not in VAS.
I was inspired by Mr John Curl amp. He uses mosfet as driver and bipolar as output stage. The advantage is this mosfets blocks the final stage from previous stage. I wanted to build class AB amp, so bipolar output stage is the choice here.
A. Is the one Mr John Curl uses. The driver also drives output by resistors.
B. Is the one Doug Self suggested (he use all bipolars). The driver doesn't drive output directly.
C. CFP. I was impressed by the behaviour of CFP. So I think this is also a good candidate.
Which one is the best for output stage?
Which is the most similiar to discrete IGBT? |
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| lumanauw |
Hi, Mike,| quote: | | The CFP has enormous current gain. Of course you can get only voltage gain with a resistor on the "upper" side. (or currentmirror) |
You are right. We can get voltage gain if we put R in a device which has current gain.
But the question is, why in my experiment preamp (that doesnt use R but transformer's primary) as load, the CFP acts differently than A or B cct? Both A and B doesnt use R, but they have gain. CFP doesnt have it in this experiment preamp. | quote: | I found another way to achieve similar results. I "castrated" a currentmirror.Without this castration bandwidth dropped above 100hz.
(Not a realistic value as there was no load at all)
With 33ohm emitterresistors and a 22k between the 2 collectors
i dropped the gain to that of a cfp with 10ohm Re's. Then
bandwidth is above 10khz, and harmonics drop to -80db.
(2nd harmonic mostly,other at noiselevel)
The gain in this circuit was ~1:100. (sk170 as transistors,bc556b
as currentmirrors)
|
Dont follow it. My english is bad. Drawings please?Thats the important thing. |
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| MikeB |
Hi lumanauw !
For your outputstage, i think 'A' is closest to IGBT. For ClassAB
output i would prefer 'B', it has the advantage that the drivers
operate pure ClassA. With 'A' you have the risk that one of the
drivers closes, but on the other hand it has the advantage of
a local feedback.
A typical CFP-output has the 0.22ohm at the collectorside of the
outputdevices, with the source/emitter connected to the collector
of the output. But you need a large current through the drivers,so
the 100ohm might be too large. I would prefer some 10-20ohm.
that makes ~50mA. Otherwise you might not have enough current
to charge/discharge the inputcapacitance of the base. (would give
bad on/off times, in theory). But Elliott uses 220ohm... Take a look:
http://sound.westhost.com/project3a.htm
I think he loves CFP-output... :D
At this moment i'm not at home, i can upload a schematic later.
(the currentmirrorthing, but was only a quick check, have to check
if this really works in a complete amp, or changes anything)
I had the experience that cfp-vamp might not work if it's output is
connected to a "fix" voltage. I had problems getting a cfp into
your folded cascode amp. It only worked with an additional resistor.
Just try and add 1k/2k to your testcircuit.
Mike |
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| sajti |
| quote: | Originally posted by lumanauw
Thinking about what Wenye and Sam9 said, maybe CFP is really a buffer with 100% feedback. This have advantage and disadvantages in audio power amp.
So, CFP is a good candidate for differential and final stage, but not in VAS.
I was inspired by Mr John Curl amp. He uses mosfet as driver and bipolar as output stage. The advantage is this mosfets blocks the final stage from previous stage. I wanted to build class AB amp, so bipolar output stage is the choice here.
A. Is the one Mr John Curl uses. The driver also drives output by resistors.
B. Is the one Doug Self suggested (he use all bipolars). The driver doesn't drive output directly.
C. CFP. I was impressed by the behaviour of CFP. So I think this is also a good candidate.
Which one is the best for output stage?
Which is the most similiar to discrete IGBT? |
I think the B is the best. The C is not really stable for bias. Maybe real CFP with MOS+BJT sholud be better. So move the 0R22 resistors to the collector of the output BJTs, and connect the sources to the collectors as well.
Generally I have no too good results with IRFs in push pull application.
I think the best is to use BJTs at the output stage. I use triple darlingtons, because they provide really lo output impedace without large feedback.
sajti |
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| sajti |
| quote: | Originally posted by MikeB
Hi lumanauw !
For your outputstage, i think 'A' is closest to IGBT. For ClassAB
output i would prefer 'B', it has the advantage that the drivers
operate pure ClassA. With 'A' you have the risk that one of the
drivers closes, but on the other hand it has the advantage of
a local feedback.
A typical CFP-output has the 0.22ohm at the collectorside of the
outputdevices, with the source/emitter connected to the collector
of the output. But you need a large current through the drivers,so
the 100ohm might be too large. I would prefer some 10-20ohm.
that makes ~50mA. Otherwise you might not have enough current
to charge/discharge the inputcapacitance of the base. (would give
bad on/off times, in theory). But Elliott uses 220ohm... Take a look:
http://sound.westhost.com/project3a.htm
I think he loves CFP-output... :D
Mike |
You have right regarding the low value resistor for CFP output stages. But there is another solution: Add small capacitor -say 10-22nF- between the bases of the output BJTs. This speed up the turn off, without increase the bias on the driver. I tested it, it works
sajti |
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| lumanauw |
Hi, Sajti,| quote: | | . But there is another solution: Add small capacitor -say 10-22nF- between the bases of the output BJTs. This speed up the turn off, without increase the bias on the driver. I tested it, it works |
Do you mean cross C 10-22nF put between base of PNP and base of NPN? I hope my interpretation is right.
Back to CFP. It's properties is unique, I think it is perfectfor making current mirrors. But I dont know how to connect 2 CFP's to make current mirror.
In ordinary current mirror, there are 2 transistors, with small emitor degeneration. Both bases are tied together, and also tied to the collector of one transistor.
1. In ordinary current mirror, what is the purpose of these base junction is tied to one collector? To give current to bases? If it only tied bases only (without one to one collector), the current mirror wont work?
2. I tried to sketch this method with 2 cfp's and it doesnt work. The whole configuration is a mess.
Anyone knows how to tied 2 cfp's to make a working current mirror? |
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| sajti |
| quote: | Originally posted by lumanauw
Hi, Sajti,
Do you mean cross C 10-22nF put between base of PNP and base of NPN? I hope my interpretation is right.
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Yes, Your interpretation i right! As I found 22nF capacitor reduces the current with 80%, when I drive the amp with 20kHz square wave without load. So it's succesfully reduce the cross conduction.
sajti |
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| lumanauw |
| quote: | | Yes, Your interpretation i right! As I found 22nF capacitor reduces the current with 80%, when I drive the amp with 20kHz square wave without load. So it's succesfully reduce the cross conduction. |
You have made great experiment. Why other people uses up to 2u2 for this cap? Isn't that too big?
One more thing. Cross Conduction. Is this the same thing as bias value? We give bias in class AB amp hoping that no transistor will off at all operating point. Is this cap will make one transistor fully off / eliminating the bias effect? |
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| sajti |
| quote: | Originally posted by lumanauw
You have made great experiment. Why other people uses up to 2u2 for this cap? Isn't that too big?
One more thing. Cross Conduction. Is this the same thing as bias value? We give bias in class AB amp hoping that no transistor will off at all operating point. Is this cap will make one transistor fully off / eliminating the bias effect? |
In normal darlington connected situation 2.2uF no problem. But with CFP connected output transistors this cap makes turn on transient on the bias. As I found 22nF no problem, but 2.2uF may kill Your output devices...
Cross conduction means, that one of the output transistor opening faster, as the other close. I CFP connection this is real problem, because the driver can open the output BJT with -say- 1A current, but the 220ohm resistor close it with 3mA current.
You can measure it with no load. Apply current meter to measure the curretn from the PSU. Without input signal, You can measure the bias only. If You apply input signal and increase the frequency You will measure higher and higher current. This is the cross conduction.
sajti |
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| lumanauw |
Hi, Sajti,
Sorry, I dont realize you are talking about CFP! You are right, 2U2 I saw is in ordinary darlington.
Hmm.... 22n between bases of CFP.... Thats new to me.
Sajti, could you help me a little? I'm planning to make class B (AB) output stage, with CFP configuration, but with parrareled bipolar.
The driver will be K1058+its complementary, and the final will be 2 pairs of C2922+its complementary.
What will be the CFP resistor, and what will be this "22nf" cap?
In cfp (single output) the RE is in collector of final transistor. I saw parrareled CFP in Slone's book, the driver has 10 ohm in its source and 100ohm in its drain, while the 0.22 are all placed in the emitors of final transistors, not in collectors. This is confusing, the single CFP and parrareled CFP have different place of 0.22ohm resistor.
How do you suggest to make best CFP with K1058 driver and 2 pair of C2922? |
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| MikeB |
hi lumanauw !
The one transistor where base and collector are tied together simply
becomes a diode, but with exactly the voltagedrop (Vbe) of the
other transistor. You could replace this transistor with a diode, but
matching is difficult.
I have built an amp with cfp-diffamp + currentmirror, it worked without
big problems. Or did you use the cfp inside the currentmirror ?
I don't think that this makes sense.
I'm not sure if the combination is good, you get hell of gain, but bad
bandwidth inside the diffamp. (too many transistors ?)
Of course you can increase bandwidth again by reducing gain with
some resistors.
My ckt had 2x sk170 + 4x bc556b + 100ohm emitterresistors at
the currentmirror. I had some problems stopping oscillation.
Sorry, still had no time for schematics...
Mike |
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| lumanauw |
Hi, Mike, | quote: | | Or did you use the cfp inside the currentmirror ? |
Yes. I think about building current mirror with CFP transistor (not for use in differential, but for other purpose). I cannot figure out how to use 2 CFPs to become current mirror. Do you have suggestion how to make current mirror with 2 CFPs? |
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| MikeB |
| Dou you want some VAS with CFPs ? |
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| Eva |
| quote: | Originally posted by lumanauw
[B]Hi, EVA,
I wanted to ask you 2 questions.
1. What do you think about tube amp which uses output transformer? Will it have defected frequency response, especially the KHZ's?
2. What do you think of ZEN V7-T (you can see it in passdiy.com). There is alot-lot-lot-lot of current flowing in this amp towards the 0-110V-220V transformer.
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I have no personal experience with tubes but I do have experience with transformers in solid state applications. In any transformer coupling frequency response at LF and HF is strongly dependent on transformer design. Production of odd order 'ugly' harmonics is also highly dependent on transformer saturation on non-class-A applications
Audio transformers tend to use sandwitching [primary-secondary layer interleaving] in order to improve leakage inductance and allow for higher turn counts to prevent saturation at LF. Some degree of core gapping is almost mandatory to allow for small DC errors without causing deep saturation. Nothing of that is found on mains transformers
I've tried mains transformers for some other applications. Last one was mains current sensing through en EI core 25VA unit and results were even worse than expected, leakage inductance and inter-turn capacitances ruined the current waveform
ZEN V7-T is a tricky thing since no particular load is specified when distortion and frequency response are measured in the mains transformer version and mains transformers suffer big design-parameter changes from model to model and from manufacturer to manufacturer. The article says that the resistive loaded version has its -5dB point at 10Khz but the inductive loaded version is only 3dB down at 70Khz, this is obviously inconsistent since I think most mains transformers would start to roll-off at 1..5Khz when loaded with 4..8 ohms. The article also mentions the crucial importance of careful bias balance trimming to minimize saturation and the circuit includes potentiometers for that purpose
Have you tried to measure some parameters of the transformer, like leakage inductance, primary to primary capacitance, resonant frequency, DC resistance of each primary, etc.. in order to determine its suitability to your design?
Have you looked at current and voltage waveforms of your circuit with an oscilloscope?. This allways reveals what's happening
Finally, I think that 'Transformer sounds' would be a more appropiate name for that thread since you are almost ignoring transformer behavior and blaming innocent gain devices |
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| lumanauw |
Hi, EVA,
Thanks for the explenation.
In ZEN V-7T the author do not exactly balanced the current or voltages, the best is obtained by setting the whole cct to get minimum distortion (that means this operating point is no voltage balanced or current balanced). How come this happens? The best point can be the non-balanced flux?
Some SS amps have transformer output like MCIntosh. Whats the purpose of OT for transistor output? I would like to see this MCIntosh cct, do you have it?
Hi, Mike,
:D You got me. Since the CFP differential has already got alot of current gain, I would like to make a VAS ("level shifter" is more appropriate) that has no gain, only to provide full swing. This can be done by folded cascode, VAS differential or current mirror. All of it have no current gain, but behave differently, as current adder or current substractor. I wanted to use CFP(due to its unique characteristic) for current mirror, placed as VAS. But still cannot figure how. |
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| Eva |
I think that the obvious reason for the optimum working point not being the zero idle current nor the zero idle voltage is that the transfer characteristics of both MOSFETs are neve the same, so the working point with signal applied is not actually the same as the idle working point
Also, it's important to understand that any harmonics produced by the MOSFETs cause DC to be applied to the transformer since even order means 'asymetric waveform distortion that produces DC' and odd harmonization applied to sound waveforms [asymetric by nature] also produces DC. This is a common problem with transformers and low feedback amplifiers. There was a thread some time ago discussing a similar problem with a transformer coupled solid-state open-loop design suffering unexpected transformer saturation
THD>0.1% appears to be enough to unexpectedly saturate some transformers at high levels [I think this complex non-linearity is part of the 'tubes+transformers myth']
Capacitive coupling and/or medium to high feedback are two alternatives to prevent transformer saturation |
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| lumanauw |
Hi, EVA,
In my experiment cct (post #1), the transformers drivers is pushpull, 2 legs from differential.
You suggest to put R directly to supply and put cap before transformer. I did this and it works well.
The difficult thing is to balance the current (voltage drop in the 2 R's). How do you suggest to balance this current? I tried current mirror, but it doesnt produce sound (have to check this later).
What do you think if the transistor is only 1 (not 2 like differential), the emitor is to CCS, collector is to 0V via R, the 220V is to +15V, and parrareled C to this 0V. ----->transformer only becoming a choke. Will this saturate the transformer, since I use single ended, not pushpull? |
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| MikeB |
hi lumanauw !
As i said, i now replaced in my amp the diffpair-bjt's with jFet's.
(bc546b -> sk170,bc556b -> sj74)
The only additional change was replacing the cap in the inputfilter
from 33pF to 100pF.
The jfets definitely show better trebles, the "sss" and "ffff" are gone...
Now the amp sounds crsytalclear, without beeing bright. Now it's nearly
what i am looking for, an amp with good trebles/details but without
glare or hard sound.
But i am not sure if the overall sound with jfets is better, i have the
feeling that with bjt's the mids were better. I need some more listening...
I should use a socket for these devices ! :D
It's annoying, it looks like that depending on the recording the one
amp is better than the other... (bjt <-> jfet)
At least you can't say that jfets outperform bjts in the inputstage,
but they definitely sound different.
Maybe i now try some cascoding ? Or different outputstages...
It's a never ending Odysee ! There's always a single detail not
beeing perfect...
Mike |
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| lumanauw |
Hi, Mike, | quote: | | Now the amp sounds crsytalclear, without beeing bright. Now it's nearly what i am looking for, an amp with good trebles/details but without glare or hard sound. |
:D Thats what I got too, with CFP Jfet. | quote: | | feeling that with bjt's the mids were better |
My BJT version is kind of harsh, especially in trebles. Maybe I bias them too high. For good trebles, you should try plain mosfet differential (IRF510).
I see some designs, usually they use BJT for VAS and BJT as output stage (class AB). Front stage, Jfet. | quote: | | Or different outputstages... |
Why dont you try CFP output stage, K1058 pairs as driver and C2922 pairs as final stage |
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| MikeB |
Yes, i think it will be some CFP-outputstage...
But before i have to try cascoded VAS, or buffered VAS.
In the BJT-version, i had the feeling that trebles were somehow
distorted. But there is a possibility that the amp was exact enough
to show me how bad some recordings are. I had these problems
only with older CDs. But this would mean, that a "perfect" amp is
not recommendable ?
Mike |
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| lumanauw |
Hi, Mike,
I want to share my experience with cascoded VAS. I made one with LED drop reference. (LED gives the most stable drop compared to diode drops or zener). It gives a "more detailed" sound, you can hear it instantly in trebles.
I have difficulties of drawing final stage CFP, with K1058 as driver and 2 of C2922 for final stage. Single transistor CFP differ from parrareled CFP. One has degeneration on bottom, the other has degeneration on top (thats what I read in Slone's book). How do you suggest the CFP with those parts?
About a perfect amp sound. It will be a never ending story. I try not to think about it. Right now, I just want to built a really nice sounding class AB SS audio amp. |
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| MikeB |
Hi lumanauw !
You're right, thinking of the "perfect" amp seems philosophical...
Ok, i will try cascoded VAS. You use a single green LED ? Can i work
with 2 red leds ? (i only have red LEDs in my box)
I am not that familiar with CFP-outputstage, the problem is of course
to ensure proper currentsharing. The Slone's version seems good to
me, or you would need 1 extra driver per outputdevice.
The other possibility would be giving all devices their own emitterresistor,
and let them all share the cfp-resistor ?
Mike |
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| sam9 |
| quote: | Ok, i will try cascoded VAS. You use a single green LED ? Can i work
with 2 red leds ? (i only have red LEDs in my box)
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Just as a matter of interest, someone in another thread reported on measuring the noise from various LEDs. I seem to recall IR LEDs came out quietest. If the voltage drop will wirk for you . . . |
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| MikeB |
Yes, i can remember this post. I think i have the textfile lying around
somewhere here. Must have been hell of work measuring all these
devices.
I was just asking, because i have only normal red LEDs at this moment...
Mike |
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| lumanauw |
I havent read the thread (where is it?) and dont know how far better is IR LED. But colour LED has cosmetic advantage. I've measure the drop of colour leds, the red and green and yellow doesnt differ much (about 1V6 drop). The blue one has higher drop, more than 2V. The biggest drop is from the white LED.
If people stack zeners, so why not with LEDs?| quote: | | or you would need 1 extra driver per outputdevice. |
This brings back my memory. I remember I've seen a power amp that uses parrareled CFP, but each has driver of its own. So its like parrareling several single CFP. |
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| sam9 |
| Self wrote that he measured the noise of somel different biasing methods and concluded the difference become moot if they are bypassed by a 47uF cap. |
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| MikeB |
hi lumanauw !
For me it seems best to use one "driver", and multiple outputdevices
sharing the one cfp-resistor, and all having an own emitterresistor.
Of course the biascurrent in the driver must be very large.
I made more listeningtests to my amp with the symetrical jfet-cfp-inputstage.
After optimizing (adjusting) the feedback-cap, i only have one word: WOW !
It now sounds so "sweet", reveiling any detail and having clear but
somehow smooth trebles. It does not show any kind of hardness.
The most fascinating thing is, the recordings that sounded best with
the BJT-version now show that these were the bad ones, missing
trebles. I couldn't stop listening to this amp...
I think this will be my amp, but i could not live without having tried
the cascoded vas before. Whenever you believe that it can't sound
even better, you might be surprised that it can get better...
Mike |
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| lumanauw |
Hi, Mike,
:D Nice to hear you got yourself a good sounding amp. No wonder designer like Mr.JohCurl is so stubborn about FET input, also about the topology.
For CFP output stage, I certainly will try Sajti's 10-22nF crossing the bases. | quote: | | After optimizing (adjusting) the feedback-cap |
What are you adjusting?
The "more detailed" sound sometimes have a limit. Mr.Pass, who has patent on cascodes, doesn't use it much. I wonder why.
Also, the most "detailed" audio power amp comes from current feedback topology. But some people says it sounds "Fatiquing". |
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| MikeB |
Hi !
With feebackcap i mean the one in paralell to the resistor in feedback
setting the gain. In my case a 22k+500ohm. I reduced the cap from
20pf to 10pf. This had an immediate impact on the sound.
Yes FET-input is fine, and helps getting rid of DC-offset as jfets create
nearly no inputoffset. Due to not perfectly matched jfets i have
a DC-offset of 30mv-40mv. But without any compensation other than
the feedback. No DC-servo or blockingcap.
My amp is detailed, but does not punch these details into your ears.
It does not exaggerate anything.
I will try the cascoding, just need to know/hear for myself.
I am still trying with CFP-output. It definitely reduce distortions, but
tends to create high order harmonics. Haven't tried Sajti's 10-22nF yet...
With the complementary diffamp, i have the feeling that it produces
better/tighter/deeper bass. And i can confirm that this topology has
a cleaner sound, but somehow "less emotions".
And with this topology i have absolutely no turnon/off-thump.
Mike |
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| lumanauw |
I have strange experience with this small (pf) cap in the feedback resistor. Never can get the right value (with ear standard). Some even cause oscilation. I end up never use this pf cap//with feedback resistor.
Is this pf cap really necessary? |
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| MikeB |
yes, these little caps are nasty...
If too big, your amp WILL oscillate, if too small, your amp might oscillate.
The size of this cap depends on the speed of the other stages,
means like how big your cdoms are. (for example)
It's all about phaseshifting. 1st you must avoid phaseshift >= 180°,
this turns you negative feedback into a positive.
2nd, these phasehifts seem to be the key of the sounding of an amp.
If your amp is stable without, this cap is not really necessary.
But my experience is, that working without this cap is not the best idea
if you want a "proper" ralloff in bandwidth.
It's also necessary to avoid ringing or heavy overshoots.
I work out the basic values in spice and check in the amp for signs
of oscillation and then try different values.
In my amp the cdoms are 33pF, the feedbackcap is now 10pF.
AKSA suggested 100pF for cdoms, and 22pF for feedbackcap.
As he said, the adjusting of these caps can make an amp musical or not.
Mike |
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| lumanauw |
In Doug Self and Randy Slone book, this Cdom have the "exact" value, if Im not mistaken there is a formula that connected bias in differential, bias in VAS, Cdom and bandwith.
Is this Cdom can be value-changed without these calculations?
This comes back to old questions. If we "try-error" these caps value, and our ear agrees on one value. Then we put this Cdom value to that equation, it turns out bad design (like bandwith only 8khz), what should we do? Still put the same cap (gives nice sound) or change it (so fits the equation with good bandwith)? |
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| sajti |
| quote: | Originally posted by MikeB
Hi !
With feebackcap i mean the one in paralell to the resistor in feedback
setting the gain. In my case a 22k+500ohm. I reduced the cap from
20pf to 10pf. This had an immediate impact on the sound.
Yes FET-input is fine, and helps getting rid of DC-offset as jfets create
nearly no inputoffset. Due to not perfectly matched jfets i have
a DC-offset of 30mv-40mv. But without any compensation other than
the feedback. No DC-servo or blockingcap.
My amp is detailed, but does not punch these details into your ears.
It does not exaggerate anything.
I will try the cascoding, just need to know/hear for myself.
I am still trying with CFP-output. It definitely reduce distortions, but
tends to create high order harmonics. Haven't tried Sajti's 10-22nF yet...
With the complementary diffamp, i have the feeling that it produces
better/tighter/deeper bass. And i can confirm that this topology has
a cleaner sound, but somehow "less emotions".
And with this topology i have absolutely no turnon/off-thump.
Mike |
For CFP output the 10-22nF works properly. It increase the speed, without increase the dissipation on the driver, which can be problem in bias regulating.
sajti |
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| sajti |
| quote: | Originally posted by lumanauw
In Doug Self and Randy Slone book, this Cdom have the "exact" value, if Im not mistaken there is a formula that connected bias in differential, bias in VAS, Cdom and bandwith.
Is this Cdom can be value-changed without these calculations?
This comes back to old questions. If we "try-error" these caps value, and our ear agrees on one value. Then we put this Cdom value to that equation, it turns out bad design (like bandwith only 8khz), what should we do? Still put the same cap (gives nice sound) or change it (so fits the equation with good bandwith)? |
Cdom is not easy to predict. I think, that the best solution to start with high value. First time the stability is the most important. If You have scope You can check the square wave response set the Cdom to avoid the overshot, and ringing, even with 8ohm+1uF paralell load.
Without scope it's not easy to set the Cdom. The only possibility to find the biggest value which still results oscillation, and apply twice value of this capacity.
sajti |
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| MikeB |
hi lumanauw !
Here's the schematic from my amp... Haven't tried the cascoded vas yet,
but sims say that it's a must have !
Maybe it inspires you...
Mike |
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| lumanauw |
Hi, Mike,
:D Nice design, and you said sounds nice too....
The CFP is about the same as I use, but I use K30, 2k2, and no R5-6-8-9 (33R)
Is this degeneration R5-6-8-9 is really necessary? I experimented with it, and found that the best details comes from not using them. It makes the OL gain higher, but sounds better (to me)
What is bad about not using them?
You got no blocking DC cap in R21-22 and got no DC offset problem? |
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| MikeB |
Hi lumanauw !
The 4 emitteresistors were absolutely necessary. I've first built this
amp without them, it was useless. Thermal drift moved the bias
in the vas between 300ua and 2ma (~every 30secs). This can't work.
So i added these resistors and everything was steady.
The problem with cfp is, that it also amplifies thermal drift...
I had no big change in sound, except it got a little smoother, but i
found this positive.
I believe that jfets tend to sound bright if used without degeneration,
but i only tried the sk170/sj74.
I try avoiding this blocking DC cap. This amp has a DC-offset of ~30mV.
With better matched transistors it should drop below 10mV.
With jfets in the inputstage you can even work in asymetrical design
without this DC-cap, as long as you use the emitterresistor. These also
hide some mismatch of the devices.
The circuit i posted to thanh has 1mV dc-offset in sims. In real world
it should still be possible to keep below 10mV. (With perfect matching)
Mike |
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| lumanauw |
Hi, Mike,
There are CCT that uses CFP differential, but don't use RE degeneration. I forgot where it is but Cyrus power amp and preamp by Graham Maynard are 2 of them. |
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| MikeB |
hi !
I believe that these amps are asymetrical. In this case the thermal
drift creates only a DC-offset that can be nearly eliminated by the
feedback.
This does not apply to symetrical design. Here the thermal drift can
be "symetrical". Let's say thermal drift moves the current to the "left"
side, DC does not change, but the bias in the vas explodes. -> Smoke !
Mike |
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| Cortez |
MikeB !
Please try out the increased feedback resistors
before the cascoded VAS, this is an easier mod,
and i'am curious about the results is your amp !
For example with 10x bigger values.
The DC would be probably higher, but if its not
so high, it should be tested and listened with real
speakers too ! Thanks !
Cortez |
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| MikeB |
Hi cortez !
Do you mean replacing the 22k+500ohm by 220k+5k ?
This might be difficult, as the 10pF need to be adjusted.
I will check this problem in sims...
Mike |
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| Cortez |
Yess ! Possibly U have to adjust the feedback
cap, but maybe it will be an easy thing.
BTW: bd139/140 isnt better sounding instead of mje15030/1 ?
And also the sajti-style little film cap between the
power trs bases would be an intresting test, or already tried ? |
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| MikeB |
Hmm, i thought the mje15030/1 is superior to bd139/140 ?
Maybe i try the mje243/253, i have some left, these are quite fast...
(but sadly completely different format than TO220AB)
Yes, my amp is still missing the cap between the bases, still a lot of
potential for trying !
Sajti recommended these small caps for CFP-outputstage.
Mike |
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| Cortez |
> Hmm, i thought the mje15030/1 is superior to bd139/140 ?
The BDs are faster than these MJEs, isnt ?
> Sajti recommended these small caps for CFP-outputstage.
No, he use this at his triple-darlington amp too !
He just said, that in CFP only little values are good. |
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| sajti |
| quote: | Originally posted by Cortez
> Hmm, i thought the mje15030/1 is superior to bd139/140 ?
The BDs are faster than these MJEs, isnt ?
> Sajti recommended these small caps for CFP-outputstage.
No, he use this at his triple-darlington amp too !
He just said, that in CFP only little values are good. |
I don't think that the speed is so important in this case. 30MHz, or 50Mhz doesn't make any difference. But MJE has better SOA.
I use capacitors in every ouput stage. The capacitors helps to speed up the output devices, and avoid cross conduction with high frequency driving. With CFP I used 10-22nF. Higher value works too, but it results inrush current in the output stage when I switch on the amp. In the triple darlington construction the inrush current not as big, because of the capacitor across the bias network, which slowing down the switch on transient.
I measured some different capacitors in triple darlington configuration. With 4pairs of MJL21193/94 330nF was enough, and there was no any cross conduction up to 100kHz. Increasing the capacitor makes no more changes in the performance. I use speed up capacitor at the drivers base too. 22-33nF works properly here.
sajti |
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| MikeB |
Hi sajti !
How does speedup-caps at the drivers help if they operate ClassA ?
I thought these caps help reducing on/off-times ?
Mike |
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| lumanauw |
| quote: | I believe that these amps are asymetrical. In this case the thermaldrift creates only a DC-offset that can be nearly eliminated by the feedback.
This does not apply to symetrical design. Here the thermal drift can be "symetrical". Let's say thermal drift moves the current to the "left" side, DC does not change, but the bias in the vas explodes. -> Smoke !
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Yes, you are right. Both examples are single differential design. So, you are saying, if the design is single differential, it is OK not to use RE degeneration in differential? |
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| sajti |
| quote: | Originally posted by MikeB
Hi sajti !
How does speedup-caps at the drivers help if they operate ClassA ?
I thought these caps help reducing on/off-times ?
Mike |
This speed up not only the on/of times. But gives more current to increase the speed of charge/discharge the internal capacitors. I didn't test the drivers current, because it much lower than the current on the output stage..
sajti |
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| MikeB |
| quote: | Originally posted by lumanauw
Yes, you are right. Both examples are single differential design. So, you are saying, if the design is single differential, it is OK not to use RE degeneration in differential? |
Principally, Yes. But i think at least small values are good for
stabilizing biasing/DC.
| quote: | Originally posted by sajti
This speed up not only the on/of times. But gives more current to increase the speed of charge/discharge the internal capacitors. I didn't test the drivers current, because it much lower than the current on the output stage..
sajti |
I will make some experiments...
Mike |
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| Cortez |
> I don't think that the speed is so important in this case. 30MHz,
> or 50Mhz doesn't make any difference. But MJE has better SOA.
They are much faster ! and at 24V i guess the SOA is not
so an important aspect, isnt ? So please try out the BD-s
too, but only with mark phillips ! Thx !
Check this for the speed, and other datas: http://home.planet.nl/~midde639/specs/BD135_137_139.PDF |
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| MikeB |
| hmm, but i only have original onsemi... :D |
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| MikeB |
according to the philips-datasheet, the bd139 is better then some
wannabe smallsignaltransistor !
What do you think, are the ON-devices of same speed and beta ?
The ON-Sheet is ****...
Mike |
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| Cortez |
Then try to find a place, where you can buy phillips bd-s ! ;)
And after all did you tried with onsemis BD ? |
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| sajti |
| quote: | Originally posted by MikeB
according to the philips-datasheet, the bd139 is better then some
wannabe smallsignaltransistor !
What do you think, are the ON-devices of same speed and beta ?
The ON-Sheet is ****...
Mike |
The chip inside the BD139 is same as in the BC639. So practically this is a small signal transistor in power package...
sajti |
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| MikeB |
Ah, then i will try this this evening with the ON-devices !
Mike |
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| Cortez |
| And where are the results ? :) |
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| MikeB |
| quote: | Originally posted by Cortez
And where are the results ? :) |
Hmm, had no time yet to heat up the iron...
It's not a simple replacement, the to220 are screwed to the heatsink,
for the smaller bd140 this hole is too far up, and the pinout is different.
So i need a separate heatsink for those. As i use bias of 40ma, i can't
drive them without heatsink.
Mike |
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| Cortez |
| Ok ! :D I'am just curious about the result... ;) |
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| lumanauw |
Hi, Mike,
Got a question. Is there any difference if we built a CCS with MOSFET or Bipolar? What the SIM tells? Which is better audibly? |
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| Cortez |
Try it ! I'am affraid that's the only way to know it ! :rolleyes: ;)
The simus maybe can help in simple electronic situations,
but the sound is a much more complex thing... :xeye:
The listening tests are good to get real (!) information ! |
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| MikeB |
| quote: | Originally posted by lumanauw
Hi, Mike,
Got a question. Is there any difference if we built a CCS with MOSFET or Bipolar? What the SIM tells? Which is better audibly? |
hi lumanauw !
I made some sims, ccs for diffamp and vas.
Output was 30v,20khz into 4ohm
The results: (2nd,3rd harmonic)
normal bjt
531uV
298uV
normal mosfet
640uV
271uV
cascoded mosfet
523uV
303uV
cascoded bjt
534uV
306uV
cascoded jfet
528uV
301uV
There's no big difference in harmonics, i would say use the normal
ccs with 2 bjts. The mosfet-ccs in the vas might not be the best
choice because of big Vgs. You will get asymetrical clipping.
I did not test the 2diodes version, in recent simulations it was
outperformed by the 2bjt version. I will never use it again...
I did the mosfet-ccs with 1bjt+1mosfet.
The jfetversion is one jfet+1resistor+cascode.
"normal jfet" is missing because jfets don't withstand that high voltages.
Of course this does not say much about the sounding.
Mike |
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| lumanauw |
Hi, Mike,
Thanks for exploring. If there's no big difference, I will go with bipolars, since it has small VBE and small drop, and the VBE is much-much predictable than mosfets.
I usually made this bipolar CCS with LED drop for reference. How is this compared with 2 bipolars like you used? |
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| Cortez |
That interest me too ! And what about the cascoded CCS ?
A lot of people have a good opinion about this solution ! |
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| MikeB |
| quote: | Originally posted by lumanauw
Hi, Mike,
Thanks for exploring. If there's no big difference, I will go with bipolars, since it has small VBE and small drop, and the VBE is much-much predictable than mosfets.
I usually made this bipolar CCS with LED drop for reference. How is this compared with 2 bipolars like you used? |
Hmm, can't say, have no sim-model of LEDs...
| quote: | Originally posted by Cortez
That interest me too ! And what about the cascoded CCS ?
A lot of people have a good opinion about this solution ! |
I don't know, in sims it didn't make a big difference, it might be much
bigger if you work with diodes or leds. But like always, sims don't tell
you about the sound...
Mike |
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