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Old 19th June 2017, 03:01 PM   #71
minek123 is offline minek123  United States
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Quote:
Originally Posted by xrk971 View Post
You know what's a great speaker protection kit that's foolproof? Two back to back 6800uF caps bypassed with a 10uF film cap.
These caps will add more distortion. If you are building low THD amp
better avoid it if possible.
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Old 19th June 2017, 03:02 PM   #72
silverprout is offline silverprout  France
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Quote:
Originally Posted by xrk971 View Post
Not quite sure what is meant by "sniffing"? DC protection or detection?

Anyhow, for my single rail (Vcc 28v to 34v dc) SE Class A amp, the output is completely AC coupled with a 4700uF electrolytic cap (+ve polarity facing into the output device where DC is about 1/2Vcc or 14v to 17v) and also a 100uF to 220uF electrolytic in parallel plus a 2.2uF to 4.7uF MKT film cap in parallel.

There is no turn-on or turn-off transient thump. A graceful smooth decay on turn-off oer 10 seconds, and turn-on is maybe smooth rise in 1sec. I am using qnty 3 x 22,000uF caps on the PSU RCRCRC filter though.

Absolutely passive protection and passive turn-on thump protection - sort of OT for this thread - but nonetheless, shows what is possible when one lets go of the need to say "my amp is purely DC-coupled and there isn't a single cap in the signal path..." madness.
Detection for protection
I'm not the only one that uses DC decoupling on the outputs... there are turn-on or turn-off transient thump with my flickering AC sometimes, so i must use very slow recovering speakers relays any very fast recovering PSU relays.
Your amplifier can resist to a child playing very fast with the on switch in order to make it sick ?
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Old 19th June 2017, 03:26 PM   #73
silverprout is offline silverprout  France
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Quote:
Originally Posted by minek123 View Post
These caps will add more distortion. If you are building low THD amp
better avoid it if possible.
I don't know everything (tell me if i'm wrong) but the THD seems more than OK with this AC coupled design ?

Page 6 :
http://www.ti.com/lit/ds/slos611/slos611.pdf
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Old 19th June 2017, 03:48 PM   #74
xrk971 is online now xrk971  United States
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Quote:
Originally Posted by silverprout View Post
Detection for protection
I'm not the only one that uses DC decoupling on the outputs... there are turn-on or turn-off transient thump with my flickering AC sometimes, so i must use very slow recovering speakers relays any very fast recovering PSU relays.
Your amplifier can resist to a child playing very fast with the on switch in order to make it sick ?
Yes, I tried switching on/off quickly and repeatedly. Still passively works and no turn on/off thump at all. Disconnecting the RCA jacks and hot plugging in is another matter though. Volume knob needs to be turned down to do that. But that is general rule for all amps.
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Old 19th June 2017, 03:52 PM   #75
xrk971 is online now xrk971  United States
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Quote:
Originally Posted by silverprout View Post
I don't know everything (tell me if i'm wrong) but the THD seems more than OK with this AC coupled design ?

Page 6 :
http://www.ti.com/lit/ds/slos611/slos611.pdf
0.02% to 0.05% THD is typical of a good SE Class A designs and this amp is no different. Cap distortion is probably well below this level.

TPA3125D2 Class D is completely different topology but SE THD at 5w of 0.04% is very good, IMO. The profile is also important. Not just the value. Should be monotonically decreasing towards higher orders with little above 5th harmonic, preferably 3rd.
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Last edited by xrk971; 19th June 2017 at 03:56 PM.
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Old 19th June 2017, 06:15 PM   #76
silverprout is offline silverprout  France
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Quote:
Originally Posted by xrk971 View Post
Yes, I tried switching on/off quickly and repeatedly. Still passively works and no turn on/off thump at all. Disconnecting the RCA jacks and hot plugging in is another matter though. Volume knob needs to be turned down to do that. But that is general rule for all amps.
My amplifiers don't use any volume control, everything is treated at full power.

Quote:
Originally Posted by xrk971 View Post
0.02% to 0.05% THD is typical of a good SE Class A designs and this amp is no different. Cap distortion is probably well below this level.

TPA3125D2 Class D is completely different topology but SE THD at 5w of 0.04% is very good, IMO. The profile is also important. Not just the value. Should be monotonically decreasing towards higher orders with little above 5th harmonic, preferably 3rd.
I use it in a BTL configuration (fully balanced 20W at 8ohm) and the first board is ready for measurements but i don't have any spectrum analyzer.
There is 3.7mV of DC before output caps and no background noise at all (perhaps thanks to the high PSRR of the chip and high quality EI transformers) and no oscillation.
I must admit, that chip is great (through hole single sided PCB is not dead )
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Last edited by silverprout; 19th June 2017 at 06:16 PM. Reason: everything word mistake
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Old 19th June 2017, 06:26 PM   #77
xrk971 is online now xrk971  United States
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TI makes great Class D chips and I used TPA3116D2 and 3118D2 extensively for years. I was one of the first few people on DIYA to make my own TPA3118 amp from scratch before the cheap eBay variants flooded the market. However, once I built my first good discrete output stage Class AB amp and heard the difference, there was no going back to Class D. One thing I noticed is that Class D sounds fine until you hear the bass authority on a Class AB or Class A with a huge MOSFET output transistor that is 8x the size of the entire Class D chip! The flow of current is effortless. Plus, try connecting some 112dB/mW headphones to a Class D output. Is it silent to the point of you can't know if it's turned on even? I tried this and even with 96dB cans, there was a very audible hiss (remains of the switching noise leaking through). Sounds fine on a speaker and is tolerable - but not on headphones.
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Old 19th June 2017, 06:47 PM   #78
silverprout is offline silverprout  France
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Quote:
Originally Posted by xrk971 View Post
TI makes great Class D chips and I used TPA3116D2 and 3118D2 extensively for years. I was one of the first few people on DIYA to make my own TPA3118 amp from scratch before the cheap eBay variants flooded the market. However, once I built my first good discrete output stage Class AB amp and heard the difference, there was no going back to Class D. One thing I noticed is that Class D sounds fine until you hear the bass authority on a Class AB or Class A with a huge MOSFET output transistor that is 8x the size of the entire Class D chip! The flow of current is effortless. Plus, try connecting some 112dB/mW headphones to a Class D output. Is it silent to the point of you can't know if it's turned on even? I tried this and even with 96dB cans, there was a very audible hiss (remains of the switching noise leaking through). Sounds fine on a speaker and is tolerable - but not on headphones.
I still have vintage stock components and i will build one class AB amplifier for a direct comparison.
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Old 19th June 2017, 07:00 PM   #79
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From Doug Self:

The distortion generated by an AC-coupled amplifier's output capacitor is more serious, as it is not confined to low frequencies. A 6800uF output capacitor driving 40 W into an 8-Ohm load gives mid-band third-harmonic distortion at .0025%, as shown in Fig 32. This is five times more than a Blameless amplifier generates mid-band. Also, the LF THD rise is much steeper than in the small-signal case.
=============

I guess in this case, for 5W output, maybe it doesn't matter much...


Quote:
Originally Posted by silverprout View Post
I don't know everything (tell me if i'm wrong) but the THD seems more than OK with this AC coupled design ?

Page 6 :
http://www.ti.com/lit/ds/slos611/slos611.pdf
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Old 19th June 2017, 08:42 PM   #80
silverprout is offline silverprout  France
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Originally Posted by minek123 View Post
From Doug Self:

The distortion generated by an AC-coupled amplifier's output capacitor is more serious, as it is not confined to low frequencies. A 6800uF output capacitor driving 40 W into an 8-Ohm load gives mid-band third-harmonic distortion at .0025%, as shown in Fig 32. This is five times more than a Blameless amplifier generates mid-band. Also, the LF THD rise is much steeper than in the small-signal case.
=============

I guess in this case, for 5W output, maybe it doesn't matter much...
SE=10W
BTL=20W

.0025% of THD is low (very, very low)
No?
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