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Tizman
10
Mar 1, 2018
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I’m wondering if it would be possible to drive an 8 Ohm speaker with this amp? I have a pair of Klipsch La Scala speakers that are very loud with a two watt tube amp, and this amp puts out 6 watts into a 16 Ohm load, with no specification given for 8 Ohms. Does anyone know if it will work? I’m very interested in a THX amp at this price point.
Mar 1, 2018
@Tizman while it's designed for low impedance headphones, it isn't designed for 8 Ohm loudspeakers. The peak currents could be problematic. But you've touched on a good idea for a future product - a Massdrop speaker amp using AAA.
Mar 1, 2018
roissy
44
Mar 1, 2018
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True, I might be interested in Massdrop speaker amp using AAA.
Mar 1, 2018
Jimster480
375
Mar 1, 2018
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I think I would be interested in one too. Especially if it has passthrough just like this one. I can just add it into the chain and have nonpowered speakers on my desk!
Mar 1, 2018
Tizman
10
Mar 2, 2018
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HI AndrewMason. Thanks for your reply. Although I*m mostly interested in running the La Scalas with this amp, another option is running a two way through an electronic crossover using the bass bins of the La Scalas with one amp, and the highs, from 500 Hertz and up, through an Altec 500B horn hooked up to a Renkus-Heinz compression driver. The Renkus-Heinz driver is 16 Ohm, and I usually use a 2 watt DIY EL84 tube amp with it in this configuration. Given that I am probably using under half a Watt into the highs, and that the compression driver is 16 Ohm, do you think this might work?
Mar 2, 2018
pospos
68
Mar 3, 2018
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Hi Andrew, same question as Tizman regarding the use of that amp specifically on a compression driver, in an active setup. The compression driver I plan to use is a 16 ohms nominal load, with a minimum of 12 ohms around 5 kHz: https://materion.com/-/media/files/electrofusion/a_truextent_info/tds2003_bex4008_16.pdf?la=en&hash=70EDC11630FA264D86207716FF340EC4C4A24255 (impedance plot on the second page, pretty typical of a 16 ohm compression driver from JBL or TAD)
Is that too low of a load? Would the SE output be more appropriate?
Mar 3, 2018
Tizman
10
Mar 4, 2018
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Is there any way to contact AndrewMason directly? I’m joining the drop for sure if it will drive the horns I have.
Mar 4, 2018
pospos
68
Mar 4, 2018
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I don't know if he is still around, his last message was 3 days ago: https://www.massdrop.com/profile/AndrewMason/comments
Too bad we cannot send PM in here...
Mar 4, 2018
Hi @Tizman , that would probably be fine so long as you don't trip the 789 peak current limit at around 0.8-0.9 Amps peak. Sounds like a nice setup!
Mar 6, 2018
Tizman
10
Mar 6, 2018
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Thanks for the info Andrew. I’m not sure how many amps the horn and driver combo will require. I’ll do some research. The setup is pretty good, but it’s difficult to get the two parts properly integrated using the electronic crossover. So far, I prefer the La Scalas as they are to the two way. That’s why I was curious about driving the La Scalas with the Massdrop amp. Also, are there any review samples around? Based upon what I’ve been reading, it would seem your amp is going to sound fantastic. That said, I think a lot of people would love to hear what a reviewer has to say about the amp. I’m pretty sure that it would drive sales if it’s as good as it I think it will be.
Mar 6, 2018
pospos
68
Nov 1, 2018
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Hi Andrew, the manual states "The 789 balanced and unbalanced outputs are designed for headphones loads with a minimum 12 ohm impedance, and the 789 can tolerate loads between 12 ohms and 16 ohms if the amplifier is driven to no higher than 4 V peak across the load. Usage outside of these parameters may void the warranty. Do not use the 789 to drive loudspeakers." This seems in contradiction with some discussion here. So a few questions if I may:
  1. Is that really 4V P-P, or 4Vrms?
  2. Why is the SE output limited to the same value as the balanced/bridged one?
  3. With the 0.9A limit stated above, I would have thought the maximum voltage on a 12 ohm load would have been 9V
  4. What happens when the current limit is reached? Isn't the unit protected? Can it really be damaged?
Amir tested this in his ASR review, and managed to trigger the protection circuit on a 24 ohm load at 5.5W (more than 11V!) with unstable behavior after that: https://bit.ly/2SGTMWv So, is it safe to drive 12 ohms compression driver to full power with this device?...
Nov 1, 2018
Hi Pospos. The manual should say "... can tolerate loads between 12 and 8 Ohms if the amplifier is driven to no higher than 4Vpk across the load. Usage outside of these parameters may void the warranty. Do not use the 789 to drive loudspeakers." The manual guidelines are conservative. That said, I believe you are asking for questions related to driving loudspeakers. I cannot provide help here since warranty is at risk. Experiments are at your own risk. For any load you intend to use, first look at its Z vs freq curve.
Nov 1, 2018
pospos
68
Nov 1, 2018
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Thanks 16 ohms compression drivers, should be an easy load :) What happens when the current limit is reached? Is there a risk for the device, and potentially also a risk for the driver?
Nov 1, 2018
When current limit is reached, the output devices hard clip (limit) the output current and send a flag to turn off the output relay for a few seconds. We'd need to a bunch of stress testing and statistics to figure out the reliability implications of this, for all relevant devices (not just the output devices). It's kinda like putting a Ferrari V12 engine into a 5-ton truck chassis :) . It might work fine, or might cause harmful stress on the engine/transmission/etc.
Nov 1, 2018
pospos
68
Nov 1, 2018
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Current limit is already potentially reached for any load lower than 32 ohm on the balanced output, so I hope this is tested and working... If the Ferrari engine does not have the torque to drive my truck then I can install a gearbox in the form of an autoformer ;)
Nov 1, 2018
pospos
68
Nov 2, 2018
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Does using only one channel (leaving the other one open loaded) help in any way in improving the max achievable current?
Nov 2, 2018
pospos
68
Nov 2, 2018
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Andrew, I will try to be a little bit more specific, ignoring the possible implication of driving this or that type of driver and simply concentrate on the actual limits. You talked about a 0.8 to 0.9A limit above, but it looks like 0.48A was enough to trigger the current protection in Amir measurement (5.6W into 24 ohms). It might be a little above that, as I don't know the steps he used in his measurement. (here is the link again, it did not work in my previous posting: https://bit.ly/2SGTMWv) Now the specifications mention 6W into 16 ohms (1% THD) on the balanced output, which is 0.61A. Is this actually reachable, or will the protection circuit kick in at around 0.5A (ie 4W) ? So what is the actual current limit? Is the 0.9A figure given above a limit for the whole unit, ie 0.45A per channel? What about 2 channel vs 1 channel operation, can we go use 0.9A on a single channel? Can I assume that any load and power combination is safe as long as it does not exceed the given current limit (let's say 0.5A) ?
Nov 2, 2018
Current limit is instantaneous peak. Remember 0.9Apk = 0.63Arms. I think it's better we work on an actual speaker amp, instead of pushing the limits using a headphone amp to drive speakers :P
Nov 2, 2018
pospos
68
Nov 2, 2018
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That would be great :D That said I already bought two of these units to drive my compression drivers ans tweeters. Should I sell them right now, after a 9 month wait? ;) Any ETA for that loudspeaker amp?
Nov 2, 2018
I was just joking. No plans for any speaker amp right now.
Nov 2, 2018
pospos
68
Nov 2, 2018
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Too bad ;) So for now can you confirm that if I stick to a 0.5Arms limit I can be safe, regardless of the load? I can use a single channel per unit only, does this helps?
Nov 2, 2018
Again, I cannot confirm using with "12 Ohm" loudspeakers will be ok, since we haven't tested it and there's explicit warnings against it. It might be fine. But you are right near the edge of thermal, SOA, and current stresses, especially if your Z drops below 12 Ohms at some frequencies. Using just 1 channel instead of 2 would barely reduce the localized stress in each output device.
Nov 3, 2018
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