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SpeakerPower Torpedo SP1-4000 Plate Amp
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<blockquote data-quote="Langston Holland" data-source="post: 31635" data-attributes="member: 171"><p>Re: SpeakerPower Torpedo SP1-4000 Plate Amp (2 of 3)</p><p></p><p><u>Measurements</u>:</p><p></p><p>This wasn't such an easy set of measurements to make and Brian wisely and politely tries to dissuade end users from the attempt. My dad used to tell me I couldn't do certain things and I became quite good at several of them before I figured out his trick. <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite1" alt=":)" title="Smile :)" loading="lazy" data-shortname=":)" /> This amp is bridged and requires complete isolation between input, output and power supply to measure without screwing up the results. It also emits a constant output in the post-100kHz region that isn't filtered nearly as much as an amp designed for HF reproduction. This is a very good engineering decision - it is a primary way to increase the efficiency of a class D amp. When making measurements that require high S/N such as for distortion or noise, a special (AES17 or similar) analog lowpass filter must be inserted prior to the A/D stage in one's test gear. Stuff like this isn't cheap and I'd rarely use it, thus the following measurements are made without same but are completely reliable because high S/N ratio wasn't needed.</p><p></p><p>Full range magnitude with phase. Gain with knob fully clockwise.</p><p></p><p><img src="http://soundscapesweb.com/files/PSW/AmpTests3/SP1-4000_Phase.png" alt="" class="fr-fic fr-dii fr-draggable " style="" /></p><p></p><p>Same with impulse response (IR). You'll notice a little HF "glitch" just before the main impulse. This probably would have been avoided with the AES17 filter.</p><p></p><p><img src="http://soundscapesweb.com/files/PSW/AmpTests3/SP1-4000_IR.png" alt="" class="fr-fic fr-dii fr-draggable " style="" /></p><p></p><p>Bandpass magnitude with phase, appears to be 20Hz 4th order BW highpass and 80Hz 4th order LR lowpass.</p><p></p><p><img src="http://soundscapesweb.com/files/PSW/AmpTests3/SP1-4000_BP_PH.png" alt="" class="fr-fic fr-dii fr-draggable " style="" /></p><p></p><p>Same with IR.</p><p></p><p><img src="http://soundscapesweb.com/files/PSW/AmpTests3/SP1-4000_BP_IR.png" alt="" class="fr-fic fr-dii fr-draggable " style="" /></p><p></p><p>Now for something interesting. These are nasty class D amplifiers, nasty that is unless you add expensive refinement -or- use them only in the LF, IMO. In that case they shine and are the future - at least for a while. One nasty thing they require for HF reproduction is less efficient, higher switching frequencies in addition to a large amount of output filtering. But if you're only going to power LF boxes you can use more efficient, lower switching frequencies and reduce filtering.</p><p></p><p>In the case of the SP1-4000, it has a constant 1v to 1.5v VHF output that varies in frequency somewhat due to load. To my knowledge, these frequencies are harmless to the virtual open-circuit impedance of a woofer's voicecoil. Open circuit means no sound or heat generated while lowering cost, increasing power and requiring less of the power supply - what's not to like?</p><p></p><p>Fluke 192C screenshots.</p><p></p><p><img src="http://soundscapesweb.com/files/PSW/AmpTests3/SP1-4000_Scope.png" alt="" class="fr-fic fr-dii fr-draggable " style="" /></p><p></p><p>Keele short term burst tests. Weird maybe, but comparable to the same tests performed on the following amps. See <a href="http://www.soundforums.net/live/threads/1735-Amp-Tests-(1-of-2)" target="_blank">Amp Tests post</a> for detail.</p><p></p><p><img src="http://soundscapesweb.com/files/PSW/AmpTests3/SP1-4000_BurstTable.png" alt="" class="fr-fic fr-dii fr-draggable " style="" /></p><p></p><p><em>Continued in part (3 of 3)</em></p></blockquote><p></p>
[QUOTE="Langston Holland, post: 31635, member: 171"] Re: SpeakerPower Torpedo SP1-4000 Plate Amp (2 of 3) [U]Measurements[/U]: This wasn't such an easy set of measurements to make and Brian wisely and politely tries to dissuade end users from the attempt. My dad used to tell me I couldn't do certain things and I became quite good at several of them before I figured out his trick. :) This amp is bridged and requires complete isolation between input, output and power supply to measure without screwing up the results. It also emits a constant output in the post-100kHz region that isn't filtered nearly as much as an amp designed for HF reproduction. This is a very good engineering decision - it is a primary way to increase the efficiency of a class D amp. When making measurements that require high S/N such as for distortion or noise, a special (AES17 or similar) analog lowpass filter must be inserted prior to the A/D stage in one's test gear. Stuff like this isn't cheap and I'd rarely use it, thus the following measurements are made without same but are completely reliable because high S/N ratio wasn't needed. Full range magnitude with phase. Gain with knob fully clockwise. [IMG]http://soundscapesweb.com/files/PSW/AmpTests3/SP1-4000_Phase.png[/IMG] Same with impulse response (IR). You'll notice a little HF "glitch" just before the main impulse. This probably would have been avoided with the AES17 filter. [IMG]http://soundscapesweb.com/files/PSW/AmpTests3/SP1-4000_IR.png[/IMG] Bandpass magnitude with phase, appears to be 20Hz 4th order BW highpass and 80Hz 4th order LR lowpass. [IMG]http://soundscapesweb.com/files/PSW/AmpTests3/SP1-4000_BP_PH.png[/IMG] Same with IR. [IMG]http://soundscapesweb.com/files/PSW/AmpTests3/SP1-4000_BP_IR.png[/IMG] Now for something interesting. These are nasty class D amplifiers, nasty that is unless you add expensive refinement -or- use them only in the LF, IMO. In that case they shine and are the future - at least for a while. One nasty thing they require for HF reproduction is less efficient, higher switching frequencies in addition to a large amount of output filtering. But if you're only going to power LF boxes you can use more efficient, lower switching frequencies and reduce filtering. In the case of the SP1-4000, it has a constant 1v to 1.5v VHF output that varies in frequency somewhat due to load. To my knowledge, these frequencies are harmless to the virtual open-circuit impedance of a woofer's voicecoil. Open circuit means no sound or heat generated while lowering cost, increasing power and requiring less of the power supply - what's not to like? Fluke 192C screenshots. [IMG]http://soundscapesweb.com/files/PSW/AmpTests3/SP1-4000_Scope.png[/IMG] Keele short term burst tests. Weird maybe, but comparable to the same tests performed on the following amps. See [URL="http://www.soundforums.net/live/threads/1735-Amp-Tests-(1-of-2)"]Amp Tests post[/URL] for detail. [IMG]http://soundscapesweb.com/files/PSW/AmpTests3/SP1-4000_BurstTable.png[/IMG] [I]Continued in part (3 of 3)[/I] [/QUOTE]
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