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Choosing Your Amp

"Which of your amplifiers would you recommend for use with my speakers" is one of the most frequently asked questions. With this page I hope to shed some light on the choices available from Neurochrome. A quick overview is shown in the image below.

Neurochrome amplifier product line overview


Full-DIY or Preassembled Modules?

If you want to solder every component yourself, I have two choices for you: Modulus-86 and LM3886 Done Right. The Modulus-86 offers the best performance, but it is also the more expensive of the two. Modulus-86 uses an error correction circuit with a composite amplifier to dramatically reduce the distortion of the amplifier. The lower distortion results in a clarity and precision in sound reproduction that is unrivalled and well worth the additional cost. Also note that the build cost of a DIY amp tends to be dominated by the cost of the chassis, heat sinks, and power supply. As these components would be identical for the two amps, the difference in cost between the Modulus-86 and the LM3886DR in a stereo build only amounts to about 10% of the total build budget (or roughly $40-45). For this reason I tend to nudge DIY builders in the direction of the Modulus-86. That said, if you would like to shave a bit of cost and don't need the ultimate performance, for example in the surround channels in a home theatre, the LM3886DR is an excellent choice for the DIYer.

If you would rather build your amp using preassembled modules and want the highest performance, the Modulus-286 and Modulus-686 are your best options. They differ mainly in cost and output power.

The Modulus-186 offered lower power than the Modulus-286 but not much lower cost. It has been discontinued.

"I'm on a budget! What would you recommend for a good all-round amplifier?"

All of my amplifiers can easily drive both 4 Ω and 8 Ω speakers. They handle the various dips in impedance that many speakers exhibit easily as well. I recommend using the Modulus-86 or the LM3886DR with a ±28-30 V power supply for a good allround amplifier. This will result in 40-45 W into 8 Ω and 65-70 W into 4 Ω.

I recommend using a Power-86 with a 2x22 VAC (160-200 VA) power transformer to power a stereo amp. Those who prefer to use a switching power supply will find the ±30 V version of the Connex SMPS300REh to fit the bill nicely.

I generally recommend a 2U tall chassis, such as the ModuShop 2U x 300 x 440 mm Dissipante for a stereo build, though 'bryanschremp' on DIY Audio managed to squeeze his stereo Modulus-86 amp into a 2U x 330 x 250 mm ModuShop Mini Dissipante chassis. Nicely done, Bryan!

A reasonable build budget for a stereo Modulus-86 amp is about $400-450.

"My speakers are 8 Ω nominal impedance and I want more than 40 W. Which amp would you recommend?"

With the Modulus-86 and LM3886DR you have the option of optimizing the amplifier for 8 Ω operation. You can do this by using a power supply voltage of ±35-36 V. This will result in an amplifier that can deliver 60 W into 8 Ω. The drawback of using ±35-36 V supply voltage is that the LM3886 will engage its internal SPiKe protection circuit earlier when driving a 4 Ω load. As result, operation of the Modulus-86 and LM3886DR with ±35-36 V supply and 4 Ω load is not recommended. 

A Power-86 with a 100-160 VA, 2x25 VAC power transformer and the ±36 V version of the Connex SMPS300REh would be excellent choices for the power supply for a stereo amp optimized for 8 Ω use. The 2U ModuShop chassis mentioned above are well-suited for this amp as well.

For even higher power, use the Modulus-686, which delivers 240 W into 8 Ω.

"I want more power and am willing to spend a bit more to get it. Which amp would you recommend?"

The Modulus-286 uses two LM3886 ICs in parallel and, therefore, offers twice output current capability of the Modulus-86 and LM3886DR. This makes it possible to use the Modulus-286 with a ±35-36 V power supply and get 125 W into 4 Ω and 65 W into 8 Ω. 

I recommend using a Power-86 or Power-686 with a 2x25 VAC, 200-300 VA power transformer to power a stereo Modulus-286 amp. The ±36 V version of the Connex SMPS300REh would be suitable as well. I recommend using a 2U tall chassis with a minimum depth of 300 mm for the Modulus-286

If you're able to cut the necessary holes in the chassis yourself, expect a stereo Modulus-286 build in a ModuShop chassis to set you back around $1000-1100. A build in a fully customized ModuShop chassis will run closer to $1300-1400.

"I would like to build the Modulus-686, but am unsure of how to proceed. Any advice?"

If you want the maximum output power from your Modulus-686 build, you need to use a ±35-36 V power supply. With this supply voltage the Modulus-686 dissipates quite a bit of heat and will need a chassis with a sizeable heat sink. The ModuShop 4U x 400 x 440 mm Dissipante chassis is a good choice. I recommend using a 2x25 VAC toroidal power transformer (600-800 VA) and a Power-686 for a stereo build. Those who wish for more supply capacitance should use two Power-686, one per channel. The options for switching power supplies are very limited for this voltage. The Connex SMPS800RE (get a custom ±36 V version) appears to be the best option. You'll need one SMPS800RE per Modulus-686. The finished Modulus-686 will provide 240 W into 8 Ω and 360 W into 4 Ω.

For those who don't need the full 240 W but would like to get at least 100 W into 8 Ω, there is another excellent option: The Modulus-686 Safe-n-Sane Build. By lowering the supply voltage for the Modulus-686, its maximum output power is lower, but it also dissipates much less heat. This offers two advantages:

  1. A stereo amp will fit in a 3U x 300 x 330 mm ModuShop Mini Dissipante chassis.
  2. The amp can be powered by two Mean Well RPS-400-27-C switching power supplies, which are available from Mouser (P/N: 709-RPS400-27-C). 

These things combined make for a really nice and compact build. The amp will provide 130 W into 8 Ω and 200 W into 4 Ω. 

Should you wish for a traditional transformer-based power supply instead, a Power-686 with a 2x22 VAC, 400 VA power transformer would be an excellent supply for this amp as well. You may want the 3U x 300 x 440 mm Dissipante chassis for that, though, as the transformer-based supply is considerably larger than the SMPS.

A stereo Modulus-686 amp can be built for about $1500 if you're reasonably frugal with the chassis. Should you opt for a fancier chassis, such as the one I provide CAD drawings for on the Modulus-686 product page, the total build cost will be closer to $1800.

Which amp would you recommend for a pair of Linkwitz LXmini? 

The LXmini uses two speaker drivers: An 8 Ω for the woofer and a 4 Ω for the tweeter. My recommendation for those who wish to build the amp from scratch is to use four channels of Modulus-86 powered by a Power-86 and a 2x22 VAC, 300 VA power transformer. In fact, I run my LXminis with such an amp.

If you enjoy listening to loud music with the LXmini, you will likely want a little more power than the 4 x Modulus-86 amp can provide. In that case, an amp with two channels of Modulus-86 for the woofers and two channels of Modulus-286 for the tweeters would work well for you. I recommend powering it by a Power-86 (or Power-686) and a 2x25 VAC, 300-400 VA power transformer.

In my own unscientific listening tests I did find that the LXmini cleans up a bit at high volume levels when powered by the Modulus-286, compared to the Modulus-86. I did not perceive any difference between powering the LXmini with the Modulus-286 versus the Modulus-686.

Do note that the woofer equalization (EQ) filter in the LXmini has a 6 dB peak at 50 Hz. This could explain some of the harshness I experience at high volume levels with my 4 x Modulus-86 amp running on ±30 V supply rails. It may simply be that 40 W is not quite enough to provide a clean output at 50 Hz due to the peaking EQ.

How about the LXmini+2?

The LXmini+2 adds a 4 Ω subwoofer to the LXmini. It also eliminates the 6 dB 'hump' in the EQ in the woofer channel. Therefore, six channels of Modulus-86 running on a ±28-30 V power supply (Power-86 or Power-686 with 2x22 VAC, 300-400 VA) would be a good choice for a stereo pair of LXmini+2.

Those who prefer to have a bit more power reserve available should consider using the Modulus-286 on the subwoofer and tweeter channels and drive the woofers with a Modulus-86. Such an amp should be powered by a ±35-36 V power supply (Power-86 or Power-686 with 2x25 VAC, 500 VA).

Which amp would you recommend for the Linkwitz LX521.4?

 The LX521.4 uses four driver types:

  • Two 4 Ω tweeters in series (combined total: 8 Ω)
  • One 4 Ω upper midrange
  • One 8 Ω lower midrange
  • Two 4 Ω woofers

I recommend the following amplifiers:

  • Tweeter: Modulus-86 (or Modulus-286)
  • Upper Mid: Modulus-286
  • Lower Mid: Modulus-86 (or Modulus-286)
  • Woofers: Modulus-286 (or Modulus-686 - see below)

I recommend powering the amplifier from a Power-686 and a 2x25 VAC, 400 VA transformer per speaker (i.e. 800 VA for a stereo pair of LX521.4) for a supply voltage of ±35-36 V.

Those who wish to have more power available for the woofers should use the Modulus-686 for the woofer amps. In that case, I recommend building a stereo Modulus-686 amp for each speaker. The remaining three channels will fit nicely in a 2U tall, 400 mm deep ModuShop chassis.

What about speaker protection?

Speaker protection circuits, such as my Guardian-86, protect your speakers in case of catastrophic amplifier failure. The LM3886 is a very rugged chipamp and it is unlikely to fail. But 'unlikely' is not 'impossible', and many sleep better knowing that their speakers will be protected if the amplifier fails. If you fall in this category, you will likely want to use a speaker protection circuit.

A speaker protection circuit should be completely transparent, yet quickly disconnect the speaker if the amplifier fails. It turns out this is a rather tall order, but the Guardian-86 accomplishes exactly that. It is sonically transparent and interrupts the output in the event of an amplifier failure. It also provides a turn-on delay which helps eliminating clicks and pops on amplifier startup. 

The Guardian-86 is a mono circuit. It supports amplifiers with single-ended outputs as well as those with fully differential (bridged/BTL) outputs. It is suited for one channel of Modulus-86, Modulus-286, Modulus-686, or LM3886DR.

Would you recommend using a soft start circuit?

The toroidal power transformers used in audio amplifiers draw significant inrush current – 100s of ampere in some cases – when the power is turned on. This results in blown fuses even if the steady-state current draw is relatively small. 

The 'easy' solution is to oversize the fuse, but simply increasing the ampacity of the fuse also makes the fuse less protective in the event of a short circuit. A much better solution is to use a soft start circuit, such as my Intelligent Soft Start.

I generally recommend using a soft start circuit with transformers larger than about 200-300 VA. If you're curious about what led to this recommendation, please see my Ultimate Guide to Soft Start Design.

OK. I now know which amp to build. Which boards should I buy?

Mono Modulus-86 (or LM3886DR):

  • 1 x Modulus-86 (or LM3886DR) circuit board.
  • 1 x Power-86.
  • 1 x Output Inductor (optional – I do provide instructions for how to make these in the design documentation, but the pre-made inductors are much nicer).
  • 1 x Guardian-86 (optional, see "Speaker Protection" above).

Stereo Modulus-86 (or LM3886DR):

  • 2 x Modulus-86 (or LM3886DR) circuit board.
  • 1 x Power-86.
  • 2 x Output Inductor (optional – I do provide instructions for how to make these in the design documentation, but the pre-made inductors are much nicer).
  • 2 x Guardian-86 (optional, see above).
  • 1 x Intelligent Soft Start (optional, see above).

Mono Modulus-286:

  • 1 x Modulus-286 module.
  • 1 x Power-86.
  • 1 x Guardian-86 (optional, see above).

Stereo Modulus-286:

  • 2 x Modulus-286 module.
  • 1 x Power-86.
  • 2 x Guardian-86 (optional, see above).
  • 1 x Intelligent Soft Start (optional, see above).

Mono Modulus-686:

  • 1 x Modulus-686 module.
  • 1 x Modulus-686 wiring harness.
  • 1 x Power-686.
  • 1 x Guardian-86 (optional, see above).
  • 1 x Intelligent Soft Start.

Stereo Modulus-686:

  • 2 x Modulus-686 module.
  • 2 x Modulus-686 wiring harness.
  • 1 x Power-686 (or 2 x Power-686 if you prefer more power supply capacitance).
  • 2 x Guardian-86 (optional, see above).
  • 1 x Intelligent Soft Start.