Build This MoFo!

Also, has anyone had success using the ACP+ with the MoFo? I know most people say you need a high gain preamp with the MoFo, and the ACP+ is relatively low gain. So maybe that's my answer. :irked:

My speakers are 6 ohms, 88dB/W.

I use my MoFos with a B1 which has a gain of 1! I like it very much and it usually gets more than loud enough. But my speakers are around 91 dB/W and as a source I use a DAC with an output of 2 Vrms.
 
MOFO is designed for high voltage input

Also, has anyone had success using the ACP+ with the MoFo? I know most people say you need a high gain preamp with the MoFo, and the ACP+ is relatively low gain. So maybe that's my answer. :irked:

My speakers are 6 ohms, 88dB/W.

@pinkfloyd4ever, if your preamp has a high voltage output, it will make the most of the MOFO. It was designed to take ±20v swings with ease; AKSA-Lender is a natural partner, for example.

Having said that, I regularly use mine driven by a chromebook or my smart phone. Yes, I have to peg the volume at "10" to get a reasonable sound for my small mancave, but it still does the job.

I have tried driving the MOFO with the pre-out from my NAD 7250, and it does ok, but I definitely have to turn up the volume much farther than when it uses the onboard power amp. (This suggests to me that the pre-amp signal is pretty small, and the onboard power amp is performing both voltage *and* current gain.)

Kind regards,
Drew
 
Mmk cool. My most-used source is the Schiit Modius, also a DAC that outputs 2Vrms. I believe I read that's pretty much the industry standard now.

So then my next question is...100 or 150W SMPS? I know the laptop PS spec'd in MR's article is only 90w. Is there anything to gain with a 150W instead of 100w on an standard MoFo?

And anything to be gained by using a more expensive Meanwell than the LRS? I know the Neurochrome guy recommends the EPP or RPS series for his LM3886 based amps. But they are quite a bit more expensive. I'm willing to spend a little extra on upgraded parts if it makes a noticeable improvement in SQ, but otherwise I'm trying to keep this build as inexpensive as possible. Yes, another cheap-@ss DIYer :D

And is there any difference in performance of the amp or longevity of the SMPS between turning up the voltage on a 15V model and turning down a 24v model? Would turning down the 24v model cause it try to deliver more current than it's designed for?
I.e. When you adjust the voltage, does it maintain nominal rated watts or nominal rated current?

And does anyone know what the Meanwell "Active PFC function" is?
 
I use a 19V / 4.2 A computer power supply per channel (biased at 1.8A). It gets pretty hot. I do not have any experience with the Meanwell LSRs but the 100W looks ok for one channel and has also lower ripple than 150W.

The PFC function is explained here in Q19: FAQ-MEAN WELL Switching Power Supply Manufacturer

Thanks. Ahh yes, PFC= power factor correction. Duh! I should've known that one.

Anyone know if the Meanwells maintain a constant current or a constant wattage (or neither?) when you adjust the voltage? Couldn't find anything about that in the FAQs or spec sheets
 
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I use a 19V / 4.2 A computer power supply per channel (biased at 1.8A). It gets pretty hot. I do not have any experience with the Meanwell LSRs but the 100W looks ok for one channel and has also lower ripple than 150W.

The PFC function is explained here in Q19: FAQ-MEAN WELL Switching Power Supply Manufacturer


Meanwell LSR 150 24 are perfect look my project with 2 item used at 30V 4A
 
And what is the PFC function they mention in their specs?

PFC = "power factor control" or sometimes also "pulse frequency control". PFC involves variations of the switching frequency. While the switching frequency itself is in the 100 kHz range, the rate of the variations may cause intermodulation components that are well in the audible range. Some people therefore argue that PFC might affect the audio performance.
 

PRR

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...Anyone know if the Meanwells maintain a constant current or a constant wattage (or neither?) when you adjust the voltage?...

Why would they? (How could they??)

You set the voltage. The load sucks whatever current. The Watts is the V times the I.

There ARE supplies which change their voltage to hold a set current; now popular for large LEDs arrays. There are supplies to control power, with some combination of V and I. But mainstream audio design is obsessed with Constant Voltage point of view.
 
Different models of Meanwell SMPS have different behavior when overloaded. Some limit the current to maintain a more or less constant voltage, and some have a "hiccup" mode. This may be noticed upon startup into a heavy capacitance load. Check the datasheet to see which behavior is used. The less expensive LRS series use the hiccup mode.

Behavior close to overload isn't specified very closely. Usually something such as 110% to 140% of rated output power.
 
Why would they? (How could they??)

You set the voltage. The load sucks whatever current. The Watts is the V times the I.

Hmm I realize I'm not really wording my question how I meant it. This is why I'm an ME and not an EE. I think Tungsten sort of figured out what I was trying (poorly) to ask.

What I really meant to ask was: does the overcurrent protection kick in at a fixed current, regardless of where you set the voltage?

Or does it kick in at a a current that varies inversely with voltage, so as to kick in at a fixed wattage (instead of a fixed current)?
 

PRR

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Joined 2003
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....does the overcurrent protection kick in at a....?

FAQ-MEAN WELL Switching Power Supply Manufacturer

Q36
What are the protection forms of overload/overcurrent?

Ans
When current drawn exceeds the rating of the PSU, the protection circuit will be triggered to protect the unit against overload/overcurrent.
Protections of overload/overcurrent can be divided into several forms:
  • (1)FOLDBACK CURRENT LIMITING
  • Output current decreases about 20% of rated current, shown as curve (a) in the figure below.
  • (2)CONSTANT CURRENT LIMITING
  • Output current remains at a constant level and within the specified range while the output voltage drops to a lower level, shown as curve (b) in the figure below.
  • (3)OVER POWER LIMITING
  • Output power remains constant. As output load increases, output voltage decreases in proportion, shown as curve (c) in the figure below.
  • (4)HICCUP CURRENT LIMITING
  • Output voltage and current keep pulsing ON and OFF repeatedly when protection is activated. The unit automatically recovers when faulty condition is removed.
  • (5)SHUT OFF
  • Output voltage and current are cut off when output load reaches protection range.
NOTE: Protection mode of some of the products combines with different types of the forms mentioned, such as constant current limiting + shut down.

Recover method:
  • (1)Auto Recovery: PSU recovers automatically after faulty condition is removed.
  • (2)Re-power on: PSU restarts by manual AC re-power on after faulty condition is removed.
Note:Please do not operate PSU in overcurrent or short-circuit condition for a long period of time to prevent a shorten lifespan or damaging the PSU.
_______________________________________

The voltage trim is normally small. So the current change must be small. If you are that close to the edge, you probably want the next-up size.
 
Hi Folks, brand new builder here!

Project was built to spec, but every time I attempt to bias, the FET overheats despite heatsinking. Fried both channels once already. FETS replaced and same issue. Anything over .10v across L1 and things get hot.

Slowly digesting the theory but any thoughts on what I'm doing wrong? Thanks in advance.
 
Thanks guys. Pics as requested although nothing too crazy.
 

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