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?
lumanauw said:
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
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?
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?
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
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
lumanauw said:
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
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,
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.
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,
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.
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
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
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?
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?
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 !
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
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 !
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
Hi, Mike,
Thats what I got too, with CFP Jfet.
I see some designs, usually they use BJT for VAS and BJT as output stage (class AB). Front stage, Jfet.
Thats what I got too, with CFP Jfet. 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.
Why dont you try CFP output stage, K1058 pairs as driver and C2922 pairs as final stage
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
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
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.
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.
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
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
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?
If people stack zeners, so why not with LEDs?
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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