Buckeye Hypex NC252MP Amplifier Teardown

[mdsimon2]

It is all spelled out in the data sheet in terms of how to calculate input sensitivity and how power/distortion change when bridging. For the NC252MP specifically as it nominally has power ratings that double when impedance is halved (125W x 2 @ 8 ohm, 250W x 2 @ 4 ohm, 500W x 1 @ 8 ohm) the input sensitivity stays the same.

Calculations from the data sheet shown below.

Input Sensitivity = sqrt(P*R) / 10^(G/20)

125W x 2 @ 8 ohm
Input Sensitivity = sqrt(125*8) / 10^(25.5/20) = 1.7V

500W x 1 @ 8 ohm
Input Sensitivity = sqrt(500*8) / 10^(31.5/20) = 1.7V

Michael

 

[Buckeye Amps]

It is all spelled out in the data sheet in terms of how to calculate input sensitivity and how power/distortion change when bridging. For the NC252MP specifically as it nominally has power ratings that double when impedance is halved (125W x 2 @ 8 ohm, 250W x 2 @ 4 ohm, 500W x 1 @ 8 ohm) the input sensitivity stays the same.

Calculations from the data sheet shown below.

Input Sensitivity = sqrt(P*R) / 10^(G/20)

125W x 2 @ 8 ohm
Input Sensitivity = sqrt(125*8) / 10^(25.5/20) = 1.7V

500W x 1 @ 8 ohm
Input Sensitivity = sqrt(500*8) / 10^(31.5/20) = 1.7V

Michael

I was trying to use the equation but I see where I made a small mistake in my math....was using the wrong value for G

Much appreciated!

 

[Buckeye Amps]

Follow-up dumb question: how did you calculate/know the Gain value to use for bridged? That's where I was having trouble. I know 25.5 is listed. But how did you get 31.5?

 

[DonH56]

Bridging doubles the voltage swing and thus theoretically quadruples the power.

dB = 20*log10(V2/V1) = 10*log10(P2/P1)

So for a doubling of voltage dB = 20*log10(2) = 10*log10(4) = 6.021 dB

If the base gain is 25.5 dB then the gain bridged should be 6 dB higher so 31.5 dB.

HTH - Don

Basic equations for voltage (Volts) = V, current (Amps) = I, power (Watts) = P, resistance (Ohms) = R:

V = I*R, I = V/R

P = V*I = (V^2)/R = (I^2)*R -- note if you double the voltage (or current), power goes up by the square, thus a factor of four.

 

[mdsimon2]

+1 on everything Don posted. I personally think that sec. 10 of the NC252MP data sheet lays out a simple but good explanation of how bridging works. It also specifically calls out the +6 dB voltage gain increase when bridging.

To be honest prior to owning a NC252MP I never really thought conceptually about what was happening when bridging, I just knew that I could I could get the same power in to one channel at double the impedance of stereo operation. Because the Hypex requires the user to invert one input signal and modify the amp output wiring it becomes pretty clear that the voltage across the speaker terminal is doubled (+6 dB voltage gain) when bridging.

Michael

 

[Buckeye Amps]

Thank you! Didn't mean to have someone else "do the work for me" but I really appreciate the step by step.

Now a usage question past the math: is there any benefit/detriment in regards to sound quality or measurable differences (such as THD) of using a bridged module vs a single channel, outside of power?

 

[DonH56]

Bridging puts two amplifier channels out of phase (invert one side). The biggest benefit is greater power. However, each amplifier now effectively "sees" half the load, so an 8-ohm speaker looks like a 4-ohm speaker to a bridged amplifier. The amplifier must be able to tolerate the reduced load impedance and most manufacturers rate min load when bridged at 2x that of the unbridged connection. E.g. an amp rated for 2-ohm loads is only rated for 4-ohm loads when bridged.

It may run a little hotter due to the lower effective load, but you have more power on tap, so hard to say how much difference in the real world.

Output impedance doubles due to the two amplifier outputs, so damping factor is halved. A difficult speaker load in terms of impedance becomes more difficult.

Distortion is typically a little higher but with more power may not be noticeable. Uncorrelated noise goes up by sqrt(2) (3 dB) so you might actually gain 3 dB in SNR but there are many other factors that contribute to noise, and there are other types of noise that may not change, go up, or go down, so it's usually pretty much a wash.

Stability may be degraded but that is rarely an issue these days and with a well-designed amplifier.

For class D amps, output-of-band noise from the output stage modulation ("switching") across the speaker will typically be higher. Again, a don't care in the real world.

All I can think of off-hand.

HTH - Don

 

[Buckeye Amps]

I really appreciate it!

If you were building an amp and you had access to 502's and 252's and your LCR were 4ohm speakers (JBL HDI's), would you just use two 502's or three bridged 252's, knowing that the cost difference is actually cheaper using the 252's?

Or is the hair splitting of possible differences you outlined above negligible?

The other small consideration is the rest of my speakers are all run off 252's so if I did a bridged setup for the front I would be able to correctly set input sensitivity on my HTP-1 (whereas right now it's splitting the difference between Vrms of the 252s and 502s I'm using).

Just, now that I have access to the modules and have refined my building, taking a second look at the amps I built for myself before I started the business.

 

[AdamG]

I really appreciate it!

If you were building an amp and you had access to 502's and 252's and your LCR were 4ohm speakers (JBL HDI's), would you just use two 502's or three bridged 252's, knowing that the cost difference is actually cheaper using the 252's?

Or is the hair splitting of possible differences you outlined above negligible?

The other small consideration is the rest of my speakers are all run off 252's so if I did a bridged setup for the front I would be able to correctly set input sensitivity on my HTP-1 (whereas right now it's splitting the difference between Vrms of the 252s and 502s I'm using).

Just, now that I have access to the modules and have refined my building, taking a second look at the amps I built for myself before I started the business.

The JBL HDI’s either model are both 4ohm loads, 90/92 efficiency and recommended 300 watts. IMHO I would go with the 502’s all day long. Unabridged, work them much less harder, less heat always good for electronics life span and room to grow should you some day upgrade to even higher speaker loads. But what do I know.

 

[Matias]

Correct me if I am wrong, but by bridging a module, it gets more voltage (2x) but the effective load on each module halves, so it is more demanded on current anyway. And 2x current not only is the limit of the power supply, but also thermally it gets stressed.

I prefer to use a higher powered module instead, NC50xMP provides 500W at 4 ohms cheap and cool. Perfect imo.

Edit: fixed per Don's explanation below.

 

[Buckeye Amps]

Thanks. I'll stick with my 502's and just dress up my existing amp with the recent changes.

 

[DonH56]

Correct me if I am wrong, but by bridging a module, it gets more voltage (4x) but the load halves, so the module is more demanded on current anyway. And 2x current not only is the limit of the power supply, but also thermally it gets stressed.

I prefer to use a higher powered module instead, NC50xMP provides 500W at 4 ohms cheap and cool. Perfect imo.

Bridging provides twice (2x) the voltage, not 4x; power increase by 4x if everything else can support it.

The load itself does not change, but the effective load seen by the amplifier is halved. Think of each side of the amplifier driving half the load, with a virtual common point in the middle.

I really appreciate it!

If you were building an amp and you had access to 502's and 252's and your LCR were 4ohm speakers (JBL HDI's), would you just use two 502's or three bridged 252's, knowing that the cost difference is actually cheaper using the 252's?

Or is the hair splitting of possible differences you outlined above negligible?

The other small consideration is the rest of my speakers are all run off 252's so if I did a bridged setup for the front I would be able to correctly set input sensitivity on my HTP-1 (whereas right now it's splitting the difference between Vrms of the 252s and 502s I'm using).

Just, now that I have access to the modules and have refined my building, taking a second look at the amps I built for myself before I started the business.

All else equal (it never is), I would always choose a single amplifier of suitable power over bridging an amplifier. (Note some high-power amps are bridged by design.) A single amp typically provides lower noise floor (SNR may be higher bridged but the actual noise floor is higher since two amps -- noise sources -- are driving the speaker), lower distortion, lower output impedance (higher damping factor), lower risk of running into thermal or current limiting since the effective load impedance is higher, typically greater stability, etc.

You do have look at each case and do a detailed analysis and comparison of each amplifier in the appropriate use case, but as a rule of thumb I would choose a single higher-powered amp over bridging two channels of a lower-power amp.

To explicitly answer your question, if it were me, I would use the 502's.

 

[Matias]

Long story short TL/DR: we should not bridge, high power = NC502MP.

 

[jjmcubed]

I really appreciate it!

If you were building an amp and you had access to 502's and 252's and your LCR were 4ohm speakers (JBL HDI's), would you just use two 502's or three bridged 252's, knowing that the cost difference is actually cheaper using the 252's?

Or is the hair splitting of possible differences you outlined above negligible?

The other small consideration is the rest of my speakers are all run off 252's so if I did a bridged setup for the front I would be able to correctly set input sensitivity on my HTP-1 (whereas right now it's splitting the difference between Vrms of the 252s and 502s I'm using).

Just, now that I have access to the modules and have refined my building, taking a second look at the amps I built for myself before I started the business.

You using three of the four channels of your 502 amp to power your LCR?

 

[Buckeye Amps]

You using three of the four channels of your 502 amp to power your LCR?

Yea. I still, even to this day, don't really want to carry or order single channel NCxxxMP modules. The price difference I would charge for a 3 channel vs. a four channel would honestly, after I did the math recently, be negligible.

 

[Buckeye Amps]

Update: now offering Neutrik speakON connectors as an optional add-on

 

[cheardone]

I just reviewed the 6-channel Buckeye Hypex class D amplifier. This is a follow up teardown to that review.

The amplifier is an assembly affair as all active electronics are contained in the Hypex NC252MP stereo class D amplifiers with integrated switching power supplies:

View attachment 100587

So the main job is routing the wiring to each module and input/output terminals. I was pleasantly surprised by the quality of the construction. While I will comment on some areas of improvement, they are really minor.

AC power input is from top right through the fuse and routed using the twisted read and white wires. While this coloring scheme is consistent with DC wiring, it should not be used for AC wires. Otherwise someone working on them may confuse them with DC low voltage wires with catastrophic consequences. The convention when AC and DC circuits are present in the same device as is the case here, is to use black or brown for "hot" and white or blue for neutral. The grounding terminal likewise uses a black wire and should instead use solid green or green and yellow wire:

View attachment 100588

I was pleased to see that the anodization was sanded off where the screw terminal is for safety ground. An ordinary washer is used. For belts and suspenders purpose, it is better to use a barbed washer that has "teeth" that really dig into the metal.

Plastic double sided taped clamps hold the wires (e.g. mains). These come loose over time and should be avoided. There are screws near all the wires so I suggest using a screwed in clamp. That said, I can't see anything bad happening if they come loose as they are not going to touch any sharp/hot metal.

Throughout the unit I found fine aluminum shavings/bits. Many were tiny but some were large enough to dislodge and cause a short in the fine pitch surface mount PC boards. You can see the specs in my larger shot above on the right near the speaker/XLR terminals.

Speaking of those terminals, they are all screw mounted which rules out me critiquing the soldering job. All were tight and tidy:

View attachment 100589

Using adhesive lined shrink tube is a very nice touch and above norm for such builds or even commercial ones. The adhesive keeps air out and should keep the tubing in place past my lifetime probably.

Zooming in a bit into Hypex modules we see the same practice of using second or third tier electrolytic capacitors:

View attachment 100590

There are large vents on top that should keep the ambient temps low inside the unit and help with longevity of the unit. Note however that the main source of heat are hidden power transistors that couple to the bottom of the chassis. Don't put the amplifier on top of any other heat generating component. I can't tell if there are heatsink compounds between the amps and the bottom plate. If not, some should be there.

Conclusions
I usually expect the worst when an audiophile decides to build such amplifiers before the teardown. I was super happy to see that some of the best safety and signal integrity rules have been followed here leaving me with some minor nits. While the overall unit has no safety or regulatory certification (although the modules are likely such rated), I personally would not be concerned about using this amplifier in my own system.

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As always, questions, comments, recommendations, etc. are welcome.

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Hi Amir, I see the XLR connectors are grounded. Is it done correctly? Thanks.

 

[gentlejax]

your amps are looking fantastic!

 

[Buckeye Amps]

Looking for some input/feedback. Attached is a rendering of the case bottom for my smallest case, the 12"x12" one, that can fit two NC252's or a single 502. As you can see, I have added cutout slots in this rendering as I am finally ready to order more cases from my manufacturer and can now incorporate some amount of bottom air intake.

The idea is to maximize positioning of the cutouts in areas of need while working around all the existing pre-drilled holes in the case (used for mounting modules, parts, and zip ties). Hence why the cutouts are not perfectly in line (OCD warning, I know).

The large group of cutouts in the middle are meant to allow air draw around the side edges of a single 252 or 502 and if using two 252's would allow air intake between the modules. The single group of cutouts in the back would allow general airflow around the back of any amount of modules. And similar concept with the two small cutout groups towards the front.

Thoughts?
This would also be the same approach when I update the larger cases.

 

[AdamG]

Looking for some input/feedback. Attached is a rendering of the case bottom for my smallest case, the 12"x12" one, that can fit two NC252's or a single 502. As you can see, I have added cutout slots in this rendering as I am finally ready to order more cases from my manufacturer and can not incorporate some amount of bottom air intake.

The idea behind these cutouts is to maximize positioning of the cutouts in areas of need while working around all the existing pre-drilled holes in the case (used for mounting modules, parts, and zip ties). Hence why the cutouts are not perfectly in line (OCD warning, I know).

The large group of cutouts in the middle are meant to allow air draw around the side edges of a single 252 or 502 and if using two 252's would allow air intake between the modules. The single group of cutouts in the back would allow general airflow around the back of any amount of modules. And similar concept with the two small cutout groups towards the front.

Thoughts?
This would also be the same approach when I update the larger cases.

Looks great. Any increase in conventional air flow will help prolong life. I would apply the same approach to the other size cases. This will make the units possibly self cooling. A big plus in my book. Symmetry is not a major concern since it’s really out of sight on the bottom. Improved air flow in any electrical/electronic component is always a plus and sigh of good engineering design.