Hi Nando,
as AAK and Roender said / implied, and myself above - a few Volts up or down at the rails won't affect overall headroom all that much, but they will affect reliability through reduced SOA margin.
True, +3dB or even +1dB power might make the difference between clipping onset and no clipping. But even a +3dB difference in SPL sounds just a tad louder to your ears, while the difference in dissipated heat power is +100%, roughly.
Your main consideration should be: which existing transformer voltage you have at hand, if any, because this is an expensive part and may justify doing some mods to the design. If you don't have a transformer yet, I'd recommend sticking to the published and optimized design. I for instance have about 36-38V raisl from existing transformers so I'll "downgrade" from AAK's design, just because I have the trannies already. But I don't think it will hurt the performance in any signficant way.
as AAK and Roender said / implied, and myself above - a few Volts up or down at the rails won't affect overall headroom all that much, but they will affect reliability through reduced SOA margin.
True, +3dB or even +1dB power might make the difference between clipping onset and no clipping. But even a +3dB difference in SPL sounds just a tad louder to your ears, while the difference in dissipated heat power is +100%, roughly.
Your main consideration should be: which existing transformer voltage you have at hand, if any, because this is an expensive part and may justify doing some mods to the design. If you don't have a transformer yet, I'd recommend sticking to the published and optimized design. I for instance have about 36-38V raisl from existing transformers so I'll "downgrade" from AAK's design, just because I have the trannies already. But I don't think it will hurt the performance in any signficant way.
Hello !
Yes, for the ears it don't make much difference. But the speakers manufactures recomends the double of its nominal rms power to have a 100% safe performance, because when the power amp clips, it acts like DC running to the speakers, because the top of the sinewave is being cut. So, to avoid this, I need more power. I can perceive that Symasym is on its design limits, 36v is great, more than this the amp start do be less reliable. So, what you think about bridge the Symasym? DRV134 would be very nice to supply it with balanced phase without affecting quality that much. Then, I can have 180W of power @8ohms (ONLY 8ohms load will be used), using a 30v PSU. Then it would run pretty cool, and if a big attack appears at the signal, it can supply without any problems. What you think?
Best regards !
Yes, for the ears it don't make much difference. But the speakers manufactures recomends the double of its nominal rms power to have a 100% safe performance, because when the power amp clips, it acts like DC running to the speakers, because the top of the sinewave is being cut. So, to avoid this, I need more power. I can perceive that Symasym is on its design limits, 36v is great, more than this the amp start do be less reliable. So, what you think about bridge the Symasym? DRV134 would be very nice to supply it with balanced phase without affecting quality that much. Then, I can have 180W of power @8ohms (ONLY 8ohms load will be used), using a 30v PSU. Then it would run pretty cool, and if a big attack appears at the signal, it can supply without any problems. What you think?
Best regards !
RE. higher voltage amp
You are definitely right, I have to add more out put transistors (2 pairs of sc5200+Sa1943 for 56V version and 3 pairs for 68V version) and an complement darlington to put more drive current.
You are definitely right, I have to add more out put transistors (2 pairs of sc5200+Sa1943 for 56V version and 3 pairs for 68V version) and an complement darlington to put more drive current.
Hi everybody,
Now I'm wondering how to decide a good Negative feedback resistor value for my symasym amp. What's the heck of that some people use 3,3Kohm, some use 22K and the other use 10K. I'm using 3.3k but I can not figure out what's the clue is, Is that gain reduction, slew rate?
Most Symasym version use 22K value, Why 's that? I'm using 3.3 K and try to figure out the sonic difference.
Now I'm wondering how to decide a good Negative feedback resistor value for my symasym amp. What's the heck of that some people use 3,3Kohm, some use 22K and the other use 10K. I'm using 3.3k but I can not figure out what's the clue is, Is that gain reduction, slew rate?
Most Symasym version use 22K value, Why 's that? I'm using 3.3 K and try to figure out the sonic difference.
Re. Mpsa42 vs. 2n5551
Hi AAK,
I 've just purchased a hundred of mpsa42/92 from FairChild and put them in my amp in place of 2N5551-2n5401 (2N5401 is out of stock at the moment) for I can see no difference in Hfe among them when I looked at the Hfe illustration graph in the datasheet. Can you please tell me why 2N5551 is better in gain than mpsa peer.
Thanks
Hi AAK,
I 've just purchased a hundred of mpsa42/92 from FairChild and put them in my amp in place of 2N5551-2n5401 (2N5401 is out of stock at the moment) for I can see no difference in Hfe among them when I looked at the Hfe illustration graph in the datasheet. Can you please tell me why 2N5551 is better in gain than mpsa peer.
Thanks
Hi Nando,
bridging has crossed my mind as well, and the DRV134 did well when I have used it as a balanced line driver. I suppose with a true 8 Ohm load you'll be safe if using 30V rails bridged. The debate on clipping has two sides though - true, clipping is the worst that can happen to your speakers. So one philosophy is to use a higher power amp to make sure clipping never happens. But a clean, powerful amp with clean speaker drivers won't warn you of how loud you are actually playing. So, you might play things louder than expected... until even the higher power amp will start clipping at some point - but now at 2x the delivered power. So that's now a personal choice, which risk is more acceptable...
Also, consider that the fused rails of Symasym will actually (should) prevent severe clipping (by melting, before any voice coils do
).
bridging has crossed my mind as well, and the DRV134 did well when I have used it as a balanced line driver. I suppose with a true 8 Ohm load you'll be safe if using 30V rails bridged. The debate on clipping has two sides though - true, clipping is the worst that can happen to your speakers. So one philosophy is to use a higher power amp to make sure clipping never happens. But a clean, powerful amp with clean speaker drivers won't warn you of how loud you are actually playing. So, you might play things louder than expected... until even the higher power amp will start clipping at some point - but now at 2x the delivered power. So that's now a personal choice, which risk is more acceptable...
Also, consider that the fused rails of Symasym will actually (should) prevent severe clipping (by melting, before any voice coils do
).
-_nando-_ said:
I think that is nonsense, with double the power you simply clip at double the power and hurt the speakers even more... You don't really recognize double the power (+3db is at the threshold of perception), so you run into the same clipping, just at higher power levels.
Typically, the speaker manufacturer recommends high power to have adequate damping factor. Too low damping can damage the woofer, as it moves uncontrolled.
Clipping will damage the tweeter because of excess of high frequencies.
Bridging might be a really good idea, (keeping 8ohm speakers), BUT, it is very likely that bridging will alter the sound as the dominant 2nd harmonic will be canceled.
If you want enough headroom, you have to heavily increase power to values like ~500w... It's "easier" to have more efficient speakers.
PhongVuTuan said:
Please, don't mess around with the feedback network... Did you also change the input resistor from 22k to 3.3k? And did you change the other resistor in feedback divider to maintain feedback ratio? If not:
R14 and R29 must be identical (ideally even matched), otherwise you get large DC-offset and unbalanced operation.
Lowering R30 means that you should also increase C19. (is already too big, so no real problem)
Lowering r29 means you have to readjust c14. Lowering closed loop gain for symasym without adding r16/19 will make symasym unstable.
I choose 22k input impedance to have a good match to a simple volume pot instead of preamp. Lower is "better", but requires better signal source.
Do not try to add triple darlington to symasym for higher current capability, it will oscillate!
Mike
Hi Mike !! Good to have your posts here again. 😉
The bridged Symasym would be so good... What sonic changes can I expect with the 2nd hamonic cancelation? A more "cold" sound?
Best Regards !
The bridged Symasym would be so good... What sonic changes can I expect with the 2nd hamonic cancelation? A more "cold" sound?
Best Regards !
re. Feedback modification
Thanks MikeB for the reply. You are deinitely right again. In fact, I have to change all the resistor values you quoted. R30=500-> 150; R14=10K; r29=3.3K;C14=12pf; and a (serial R=33ohm;C=1000pf) at colectors of Q1,Q2.
I have a DC servo to eliminate unfavourableDC output.
As a matter of fact I 've got a good bufer preamp and I'd like to make use of that. My problem is I have to compensate the gain of the Power Amp to the Pre.
I have alot of mpsa 42/92, will these OK in place of Q4,5,9,12. A lot of people prefer 2n5551 which are not available in my place. A I've look at the Hfe graph, they are almost Identical in gain.
Coud you give me more advice
Thanks MikeB for the reply. You are deinitely right again. In fact, I have to change all the resistor values you quoted. R30=500-> 150; R14=10K; r29=3.3K;C14=12pf; and a (serial R=33ohm;C=1000pf) at colectors of Q1,Q2.
I have a DC servo to eliminate unfavourableDC output.
As a matter of fact I 've got a good bufer preamp and I'd like to make use of that. My problem is I have to compensate the gain of the Power Amp to the Pre.
I have alot of mpsa 42/92, will these OK in place of Q4,5,9,12. A lot of people prefer 2n5551 which are not available in my place. A I've look at the Hfe graph, they are almost Identical in gain.
Coud you give me more advice
Re: re. Feedback modification
R14 and R29 really should be identical, if you want r14 with 10k, also use 10k for r29. This also eliminates the need for a DC-servo, or did you skip c19?
Yes, you can use mpsa42/92 in place of 2n5551/5401, but they sound slightly brighter.
Mike
PhongVuTuan said:
R14 and R29 really should be identical, if you want r14 with 10k, also use 10k for r29. This also eliminates the need for a DC-servo, or did you skip c19?
Yes, you can use mpsa42/92 in place of 2n5551/5401, but they sound slightly brighter.
Mike
Re. Feed back
Thank MikeB,
How do you know that, I have bypassed c19, furthermore, I increase quiecent current for Q1,Q2 to 3mA, Q4, Q12 to 4.2ma each peace, and Q3,4,9,12 got quite warm and so I add a current source in place of r10 with rated current of 8,4ma for fear of thermal instability. My C2 is 1500 pf Mylar, is this OK
After all these changes, the mid range is better.
Now I will change r14 and r29 to nice 1% tolerance ones.
Thank MikeB,
How do you know that, I have bypassed c19, furthermore, I increase quiecent current for Q1,Q2 to 3mA, Q4, Q12 to 4.2ma each peace, and Q3,4,9,12 got quite warm and so I add a current source in place of r10 with rated current of 8,4ma for fear of thermal instability. My C2 is 1500 pf Mylar, is this OK
After all these changes, the mid range is better.
Now I will change r14 and r29 to nice 1% tolerance ones.
Re. more damping
Hi Mike,
I'm running my symasym amp with +/-48 power supply. With 10,000 mf capacitor per rail. Power output: 2sc2922,2sa1216.
I would like to improve damping factor by either
- additional 10,000 mf capacitor per rail.
- An additional pair output transistors.
will this work? Can only additional capacitor improve the situation.
Regards,
Hi Mike,
I'm running my symasym amp with +/-48 power supply. With 10,000 mf capacitor per rail. Power output: 2sc2922,2sa1216.
I would like to improve damping factor by either
- additional 10,000 mf capacitor per rail.
- An additional pair output transistors.
will this work? Can only additional capacitor improve the situation.
Regards,
Why improving damping factor? Symasym already has DF of ~10.000 (1khz) and PSRR > 80db.
What do you really want to improve?
BTW, 1.5nf for the inputfilter is way too big, this will degrade frequency response. I designed the inputfilter to give constant input impedance 10hz-20khz.
By skipping c19, you gave up the nice balanced operation, this is a change i absolutely can't recommend unless you use jfets as input devices. But then you need cascodes.
A ccs instead of r10 is critical unless you used jfet (or current mirrored ccs), the voltage situation here is too low for proper bjt-operation and a resistor is completely adequate. Or did you have thermal instability?
Have you readjusted r15/17 for proper symetrical clipping?
Mike
What do you really want to improve?
BTW, 1.5nf for the inputfilter is way too big, this will degrade frequency response. I designed the inputfilter to give constant input impedance 10hz-20khz.
By skipping c19, you gave up the nice balanced operation, this is a change i absolutely can't recommend unless you use jfets as input devices. But then you need cascodes.
A ccs instead of r10 is critical unless you used jfet (or current mirrored ccs), the voltage situation here is too low for proper bjt-operation and a resistor is completely adequate. Or did you have thermal instability?
Have you readjusted r15/17 for proper symetrical clipping?
Mike
Probably semantic problem.
In case he wants more "tough" output, he can:
- use transformer at higher power rating,
- increase capacitance of rectifier capacitors and use low ESR types for switching PSU purposes,
- last but not least parallel output devices 😉
In case he wants more "tough" output, he can:
- use transformer at higher power rating,
- increase capacitance of rectifier capacitors and use low ESR types for switching PSU purposes,
- last but not least parallel output devices 😉
PMA said:
Ah, yes, you're right! In this case your 3 points are the way to go, maybe also choose drivers with high hfe?
Mike
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