Agreed. Besides, if you use a regular (i.e. non-plate) amp you can power multiple DIY subwoofers from that one amp.
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BASH 500S Subwoofer Amp Review
- Thread starter amirm
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The distortion figures for these amps is stunningly poor. As an excuse for poor performing sub amps many are quick to point out that human hearing is less sensitive at low frequencies (Fletcher-Munson) which is true but in a way this causes LF distortion to be more audible as the LF distortion products are perceived 20 dB to 40 dB louder than the fundamental when played at the same level. This means in many cases the amp itself is producing distortion products perceived louder than the fundamental before going to the driver. The driver then adds even more distortion. Most subs I have seen measured https://www.audiosciencereview.com/forum/index.php?threads/i-measured-10-subwoofers.49042/ have a SINAD of ~12 at 20 Hz and ones made with these amps would be worse than that. While it makes sense to have somewhat relaxed distortion standards for subs I always wonder why DAC's are considered poor at 100 dB SINAD, good mains speakers are expected to have >50 dB SINAD, but 12 dB SINAD for subs is acceptable?
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I offered my speakerpower htb-700 for testing and I believe Amir is back logged so we’ll revisit the idea in the fall.
Yes, distortion is extremely high and does not meet manual specs. I have learnt not to believe manufacturer’s specs, until I have a product on my testbench. It might be a piece fault as well.
So are most cheap subwoofers, this just being part of the equation.
PoorishDecision
Member
oh wow, curious to see how a unit like the one in my svs sb2000 would go.
Sokel
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You do have a good picture though:
I measured 10 subwoofers.
Hi, it's been a while! I would like to thank the people who made this project possible on a scale never before imagined in South Korea. I measured a total of 10 subwoofers, including my own DIY subwoofer(L26RO4Y), and measured them to the CEA-2010 standard using a Klippel TBM module. Below are...
www.audiosciencereview.com
Seems that low distortion is NOT amongst the priorities ( same for most of the subs there)
And we may now have hints about a part of the problem thanks to the latest reviews.
Mark185
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Reading this thread makes me wonder how good the Sunfire plate amps designed by Bob Carver in the 90's were. Memory tells me they had some form of dynamic power delivery that was either early Class D or something like Class H where there were multiple rail voltages that varied with music dynamics. I have several plate amps from NHT from that era that are supposedly Sunfire amps that I bought cheap after Recoton bought NHT and was liquidating everything. I think they were rated at 500 watts and were installed in VT3 tower speakers. They are still new in box. They were sold cheaply because there is a flaw in the wiring for ground but it is easily fixed. Looking at the output transistors, this is clearly not Class D. They are Bipolar devices. This plate amp does have a large toroidal transformer which I associate with quality designs. This thread has me curious enough to test this sample and see how it measures using a Quant Asylum QA403. Not as good as Amir's equipment but should still allow a good look at how this performs. I do know that NHT engineer told me not to feed it anything above 200 Hz or 'bad things happen'.
@amirm are you interested in testing one if I ship it to you?
@amirm are you interested in testing one if I ship it to you?
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Mark185
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This is straying further off the original topic of Amir's test but for those who are curious, I have studied the circuit board a bit more. On the right side of the picture, that is clearly the power supply because the wires from the toroid go there. The mylar cap and air core coil are probably a filter to reduce the amplitude of the switching transistors frequency hidden under the silver metal plate. This is pure speculation without further research but if the power supply transistors are switching rapidly with ~ plus/minus 100 volts coming from the toroidal transformer, it is possible that the power supply rails to the output transistors is varying dynamically - that is what I recall the Carver promo material saying all those years ago.
In a traditional switching power supply, the switching transistors are placed ahead of a much smaller transformer and they are turning off and on to generate an AC waveform going into the transformer. In this design, the transformer is getting 110 AC from a wall outlet and stepping that up to +/- 95.6 volts AC.
In a traditional switching power supply, the switching transistors are placed ahead of a much smaller transformer and they are turning off and on to generate an AC waveform going into the transformer. In this design, the transformer is getting 110 AC from a wall outlet and stepping that up to +/- 95.6 volts AC.
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Albrecht47
Member
Some misinformation in this thread.
@amirm It's not a "a bridged class AB amplifier fed by a switching power supply". It's a composite Class D + Class AB amplifier fed by a SMPS. In other words, the Class D amplifier is electrically in series with the Class AB amplifier, powered by an SMPS. Only the output stage of the amp is a bridged class AB amplifier.
When measuring distortion and noise, a Class D amp should be tested with an analog bandwidth limiting filter, as should this BASH amp. Did you use an AP AUX-0025 or equivalent filter when testing this amp?
I suspect the high THD+N is due to a malfunction, possibly caused by a poor modification or failed repair attempt, which IMHO should never be used as a test sample. I am surprised you did not question why your test results were so much worse than the specs. Even your forum users are asking that question. I can assure you that the specs are legitimate, or at least they were when the engineering samples were made and measured during the development of this amp platform in the mid 90s.
@kyuu Class G and Class H amps aren't just variants of Class AB amps. BASH is a Class H amp because the Class D section is effectively a modulated power supply for the Class AB output stage. Not sure why Parts Express called it a Class D amp, that's incorrect.
@babadono Those aren't potentiometers in the patent. They represent power transistors operating in the linear region.
@Mark185 The Carver is also a Class H amp but with dual single ended Class D amps per channel. Each output stage voltage rail (+ve and -ve) is generated by a separate Class D amp. The BASH design is more economical because there is only a single Class D amp feeding the Class AB output stage which is "floating" and "centered" in the middle of Class D output, which of course necessitates a bridged output configuration.
@amirm It's not a "a bridged class AB amplifier fed by a switching power supply". It's a composite Class D + Class AB amplifier fed by a SMPS. In other words, the Class D amplifier is electrically in series with the Class AB amplifier, powered by an SMPS. Only the output stage of the amp is a bridged class AB amplifier.
When measuring distortion and noise, a Class D amp should be tested with an analog bandwidth limiting filter, as should this BASH amp. Did you use an AP AUX-0025 or equivalent filter when testing this amp?
I suspect the high THD+N is due to a malfunction, possibly caused by a poor modification or failed repair attempt, which IMHO should never be used as a test sample. I am surprised you did not question why your test results were so much worse than the specs. Even your forum users are asking that question. I can assure you that the specs are legitimate, or at least they were when the engineering samples were made and measured during the development of this amp platform in the mid 90s.
@kyuu Class G and Class H amps aren't just variants of Class AB amps. BASH is a Class H amp because the Class D section is effectively a modulated power supply for the Class AB output stage. Not sure why Parts Express called it a Class D amp, that's incorrect.
@babadono Those aren't potentiometers in the patent. They represent power transistors operating in the linear region.
@Mark185 The Carver is also a Class H amp but with dual single ended Class D amps per channel. Each output stage voltage rail (+ve and -ve) is generated by a separate Class D amp. The BASH design is more economical because there is only a single Class D amp feeding the Class AB output stage which is "floating" and "centered" in the middle of Class D output, which of course necessitates a bridged output configuration.
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so can this plate amp be put into a class or category!? i'm even more confused lol
You make some interesting points. Can you provide some documentation to substantiate them?
OP
- Thread Starter
- #57
Sure but later in the fall.
OP
- Thread Starter
- #58
You are wrong. See the schematic I post from the patent application.
Yes.
OP
- Thread Starter
- #59
The test is that of the unit sent to me. Unless you have similar measurement protocol to mine that show different results, this is it. Specs don't mean anything.
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