Dear David
I have browsed the book and would agree that it could contain useful information for an audio enthusiast.
I am not doctrinaire about any particular "topology, ideology or methodology" either and I commend you for highlighting some advantages and disadvantages to the thread starter.
With my sarcastic remark I lost total sight of the focus of this forum - that of helping our fellow enthusiasts in making informative decisions regarding the amplifier he will eventually invest in.
Krell Look Alike
This should be a much closer schematic of the amp you propose in the first post and yes it is almost identical to a Krell KSA50 from the 80's. I just chose transistors that came to mind. Resistor values are not optimised but this amp will work. And it is dual complimentary symmetry throughout and this is possibly biased as Class A.
This should be a much closer schematic of the amp you propose in the first post and yes it is almost identical to a Krell KSA50 from the 80's. I just chose transistors that came to mind. Resistor values are not optimised but this amp will work. And it is dual complimentary symmetry throughout and this is possibly biased as Class A.
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OT remarks and bickering removed. Stay on topic.
Hi Nico .
I did not propose any amplifier.. I was simply asking questions about its topology. The faulty scematic i posted is supplied by the manufaturer. The amplifier its self works fine . I am in the process of modding it into a dual mono . and i m also intrested in upping the bias . I am aware of the extra heat it will produce and have a choice of much larger heatsinks i can use.. Lower bias = less heat = less heatsink = less cost.. I am trying to remove some of the costing departments compromises.. Also the efficency issues do not matter as im only after 10 to 15 Watts class A.. Ps thankyou for the krell schematic
I did not propose any amplifier.. I was simply asking questions about its topology. The faulty scematic i posted is supplied by the manufaturer. The amplifier its self works fine . I am in the process of modding it into a dual mono . and i m also intrested in upping the bias . I am aware of the extra heat it will produce and have a choice of much larger heatsinks i can use.. Lower bias = less heat = less heatsink = less cost.. I am trying to remove some of the costing departments compromises.. Also the efficency issues do not matter as im only after 10 to 15 Watts class A.. Ps thankyou for the krell schematic
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Madtecchy, if you are not going to use the amplifier for listening at high levels of pure class A, then upping the bias has very little positive effect.
In my humble opinion, bias it into class A for the average power you expect and do not be surprised that normal listening is less than 5 watts although peaks of +20dB and higher is quite feasible, but for these small duration peaks it can switch to class B operation. I can vouch that you would never hear the difference. Let's hear from other Class A enthusiasts what they think is the optimum class A power or bias.
In my humble opinion, bias it into class A for the average power you expect and do not be surprised that normal listening is less than 5 watts although peaks of +20dB and higher is quite feasible, but for these small duration peaks it can switch to class B operation. I can vouch that you would never hear the difference. Let's hear from other Class A enthusiasts what they think is the optimum class A power or bias.
If you start with the premise that -20dB is your average listening level and that -10dB is reached frequently then ClassA at the -10dB level might be a sensible target and any peaks that call for currents exceeding the -10dB level will be in ClassAB.
That would result in 5W of ClassA in a 50W ClassAB amplifier.
Since 50W of ClassAB is 28.28Vpk that would require ~+-35Vdc from the PSU.
5W of ClassA would require ~1.2Apk of output and the bias required would be ~600mA (total for all output device pairs).
Dissipation would be ~40W,
Certainly doable.
That would result in 5W of ClassA in a 50W ClassAB amplifier.
Since 50W of ClassAB is 28.28Vpk that would require ~+-35Vdc from the PSU.
5W of ClassA would require ~1.2Apk of output and the bias required would be ~600mA (total for all output device pairs).
Dissipation would be ~40W,
Certainly doable.
Take for example a 30W class-A amp. Upping the bias will usually improve the sound, even if we listen below 5W, or even if we simulate THD for 0.3 volt input (which usually is below 5W).
With high capacitance HEXFETs, it is easy to listen to the difference (5W signal) even if current has reached 5A. With BJT, my experience was that up to 1A it becomes less significan. With LATFET, often upping the bias has no noticeable sound improvement.
BTW I'm still searching an example of high end amp where LATFET is used and highly biased. I want to know how far they might go.
Hi Andrew.
Doable at 8 ohms . I guess not so doable into 4 Ohms. Well doable but with dramatically increasing cost. I was looking for a low cost introduction to class A . Do i want class A i dont know . the closest i have come to listening to class A amplification is a big old Pa amplifier at approx approx 1 Watt . Not a good introduction To class A i Know btu there it is . I have bee listening to A 80 watt onkyo from the 90,s . Wide bandwidth , Low distortion . Highish slew rate 150 V ms. It gives a cold impression . Loads of feed back maybe to get good mesurement .. The Tangent sounds more neutral and all about the music . In fact very nice
Doable at 8 ohms . I guess not so doable into 4 Ohms. Well doable but with dramatically increasing cost. I was looking for a low cost introduction to class A . Do i want class A i dont know . the closest i have come to listening to class A amplification is a big old Pa amplifier at approx approx 1 Watt . Not a good introduction To class A i Know btu there it is . I have bee listening to A 80 watt onkyo from the 90,s . Wide bandwidth , Low distortion . Highish slew rate 150 V ms. It gives a cold impression . Loads of feed back maybe to get good mesurement .. The Tangent sounds more neutral and all about the music . In fact very nice
Hi Madtecchy,
I am stating my own subjective experience only and not general to DIY, but in my opinion there is a bigger difference in sound character between single ended class A and push-pull class A than between push-pull class A and class AB.
Also your question regarding 4 and 8 ohms. No there need not be an increase in power dissipation if you set the power into 4 ohms the same as 8 ohms.
In other words, although you would increase the bias current to accommodate 4 ohm load, you would decrease the supply voltage accordingly and the heat caused by dissipation would remain basically unchanged. In other words a 10 watt into 8 ohms class A amp would get just as hot as a 10 watt into 4 ohm class A amp.
I am stating my own subjective experience only and not general to DIY, but in my opinion there is a bigger difference in sound character between single ended class A and push-pull class A than between push-pull class A and class AB.
Also your question regarding 4 and 8 ohms. No there need not be an increase in power dissipation if you set the power into 4 ohms the same as 8 ohms.
In other words, although you would increase the bias current to accommodate 4 ohm load, you would decrease the supply voltage accordingly and the heat caused by dissipation would remain basically unchanged. In other words a 10 watt into 8 ohms class A amp would get just as hot as a 10 watt into 4 ohm class A amp.
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Hi Nico .
I Understood it was your subjective expirience. yours and jays and andrews advice became a good aid while i was thinking about what to do next. for now i have decided to Mono block the amp so i can place an amp directly behind each loud speaker. I have read a few krell ksa50 reviews and cant help wonder how much the topology of the amplifier has in the krells sound character . From what i am hearing at the moment on the tangent i would say quite a bit .
Kindest regards
I Understood it was your subjective expirience. yours and jays and andrews advice became a good aid while i was thinking about what to do next. for now i have decided to Mono block the amp so i can place an amp directly behind each loud speaker. I have read a few krell ksa50 reviews and cant help wonder how much the topology of the amplifier has in the krells sound character . From what i am hearing at the moment on the tangent i would say quite a bit .
Kindest regards
Madtecchy, your amp has different topology than the Krell, or what Nico has posted.
(1) Your amp has a CFP driver, or the output takes the input from collector of the driver.
(2) Your amp has its driver's NOT connected to the output.
The Krell has emitter follower driver with emitter tied to the output.
Both of the 2 points above make a big different in character. And I favor your amp!
(1) Your amp has a CFP driver, or the output takes the input from collector of the driver.
(2) Your amp has its driver's NOT connected to the output.
The Krell has emitter follower driver with emitter tied to the output.
Both of the 2 points above make a big different in character. And I favor your amp!
I learned to use the word "better" very selectively here on DIY as it can get you into a ton of trouble. It appears that Jay has learned this lesson too.
Hehehe I understand what you mean. But I think I have never learnt that one
I used "favor" because I'm 100% sure that the Krell will be favored by at least 75% listeners, may be even including Madtecchy (no surprises for me, and I'm firmed with my opinions). So it was not because I didn't want to get into trouble, but I tried not to mislead people.
I'm aware that the more experience people have, their preference may change. For me, speaker is the most important. From amps (and from audio system), what I need is musical enjoyment, and that means no fatigue. Fatigue may come from IMD or whatever, I don't care. I just know it when it is there, and I don't want it. It is for me the most important criteria of an audio system, period.
I mean 30W class-A (full power), but listened at 5W output.
Take for example, a case where we listen to music at 300mW, and assume we get 300mW at class-A with 400mA bias. Now, isn't it obvious that THD and listening tests show differences with changing bias from 600mA to 1.5mA? So listening in class-A region (no crossover distortion) is not really the point.
Theoretically we don't listen to watts or power but SPL
You seem to be missing my point.
If your average listening level is really of the order of 5W and you are using a 30W amplifier then you have an overhead of ~ 8dB to allow for peaks in the audio signal of just 8dB above the average level.
That means that even for highly compressed music the audio signal will be frequenctly and repeatedly clipped.
If the overhead is increased to say 16dB then the clipping events will be less frequent.
If you choose to listen to less compressed audio signals then your are more likely to need an overhead (from average level to peak level) of 20dB and some music can require upto 30dB of overhead to avoid clipping of the Audio Signal.
You can't listen at average levels of 5W from a 30W amplifier without risking very frequent clipping of the audio signal.
I don't fully understand your point. May be I don't understand at all
I like to shoot for the lowest THD at 5W, instead of 0.3 volt input (the 5W number came from my experience listening to small chip amplifiers). It is supposed to be a class-A amp with clipping above 30W. Of course some music have dynamic short term power. But what is the context that I cannot listen at average level of 5W from a 30W amp? That I will experience clipping? What happen then if I experience clipping? Why did you hope I do most of my listening with average level below 300mW, not 5W?
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