Hello there,
I am looking to build a Neurochrome mono amp just for measuring speakers.
Currently I am using an Adcom GFP-565 preamp and Adcom GFA-5002 power amp connected to a Focusrite Scarlett Solo, but I am looking for something more "portable/compact". Ideally it would be half an Adcom GFA-5002/535 with a volume knob and a single input.
There are several possible amp options from Neurochrome, mainly the LM3886 DONE RIGHT and the MODULUS-86 that would fit the bill.
I am not sure which of the two to build, one is easier and cheaper, but I only want to do this once.
What else do I need?
Obviously a power supply, I could either build the Neurochrome POWER-86, or possibly buy the Connex Electronic SMPS300RE. Is there a big difference between the two? What other high quality off the shelf power supplies are commonly used for either amp? Unfortunately Neurochrome has discontinued the SMPS-86 power supply or I would simply buy that.
I see many builds with a toroidal transformer, so I assume I will need one as well?
What type of potentiometer is used for "volume" control, and where would it fit into the signal chain?
Is an INTELLIGENT SOFT START circuit or GUARDIAN-86 MONO SPEAKER PROTECTOR required/highly desirable?
Anything I have missed?
Obviously these are all noob questions and no, I have not built an amplifier before, but I do know which end of a soldering iron to hold and have build electronics in the past.
Thank you,
David.
I am looking to build a Neurochrome mono amp just for measuring speakers.
Currently I am using an Adcom GFP-565 preamp and Adcom GFA-5002 power amp connected to a Focusrite Scarlett Solo, but I am looking for something more "portable/compact". Ideally it would be half an Adcom GFA-5002/535 with a volume knob and a single input.
There are several possible amp options from Neurochrome, mainly the LM3886 DONE RIGHT and the MODULUS-86 that would fit the bill.
I am not sure which of the two to build, one is easier and cheaper, but I only want to do this once.
What else do I need?
Obviously a power supply, I could either build the Neurochrome POWER-86, or possibly buy the Connex Electronic SMPS300RE. Is there a big difference between the two? What other high quality off the shelf power supplies are commonly used for either amp? Unfortunately Neurochrome has discontinued the SMPS-86 power supply or I would simply buy that.
I see many builds with a toroidal transformer, so I assume I will need one as well?
What type of potentiometer is used for "volume" control, and where would it fit into the signal chain?
Is an INTELLIGENT SOFT START circuit or GUARDIAN-86 MONO SPEAKER PROTECTOR required/highly desirable?
Anything I have missed?
Obviously these are all noob questions and no, I have not built an amplifier before, but I do know which end of a soldering iron to hold and have build electronics in the past.
Thank you,
David.
David,
If you want low distortion in your test amp, the Modulus-86 is where it's at. If you don't care as much about distortion, the LM3886DR would be a good option.
Some may (rightfully) argue that the speaker is likely to distort more than the amp, at least mid-band. Towards the ends of the audible frequency range, the distortion of the LM3886DR starts to approach that of a good speaker at lower excursion. The cost difference between the LM3886DR and the Modulus-86 adds up to maybe 10% of your build budget, so I tend to nudge people in the direction of the Modulus-86. The expensive bits are the chassis, heatsinks, and power supply.
Both the Power-86 + transformer and the SMPS300 from Connex are good options. If you go the Connex route, I'd get the newer SMPS300REh, though. Get the ±30 V version. The REh has a heat sink on the bottom, which is nice. The output diodes in the SMPS300RE tend to overheat if you push the power supply (as you potentially will in a test amp).
I recommend using my custom wound output inductors. They really make life easier. That said, if you'd rather wind your own, you can. I do provide the instructions in the design doc. All you need is a ~3ft length of AWG 18 enamelled magnet wire.
Whether you want to add speaker protection is up to you. The Guardian-86 protects against DC on the output of the amp, which can happed during catastrophic amplifier failure.
I recommend using a soft start such as my ISS with larger toroidal power transformers. You can read my thoughts on soft starts, including how to design one here: Soft Start for Power Transformers in Audio Amps.
Hope this helps.
Tom
If you want low distortion in your test amp, the Modulus-86 is where it's at. If you don't care as much about distortion, the LM3886DR would be a good option.
Some may (rightfully) argue that the speaker is likely to distort more than the amp, at least mid-band. Towards the ends of the audible frequency range, the distortion of the LM3886DR starts to approach that of a good speaker at lower excursion. The cost difference between the LM3886DR and the Modulus-86 adds up to maybe 10% of your build budget, so I tend to nudge people in the direction of the Modulus-86. The expensive bits are the chassis, heatsinks, and power supply.
Both the Power-86 + transformer and the SMPS300 from Connex are good options. If you go the Connex route, I'd get the newer SMPS300REh, though. Get the ±30 V version. The REh has a heat sink on the bottom, which is nice. The output diodes in the SMPS300RE tend to overheat if you push the power supply (as you potentially will in a test amp).
I recommend using my custom wound output inductors. They really make life easier. That said, if you'd rather wind your own, you can. I do provide the instructions in the design doc. All you need is a ~3ft length of AWG 18 enamelled magnet wire.
Whether you want to add speaker protection is up to you. The Guardian-86 protects against DC on the output of the amp, which can happed during catastrophic amplifier failure.
I recommend using a soft start such as my ISS with larger toroidal power transformers. You can read my thoughts on soft starts, including how to design one here: Soft Start for Power Transformers in Audio Amps.
Hope this helps.
Tom
Would the SMPS300REh (Output Voltage:+-30V, Aux. Output Voltage:+-18V) be preferable to the POWER-86?
"I also find that the Modulus amps provide the same or better performance on an SMPS as they do on a transformer-based supply. The only exception would be short-term overload, where the transformer-based supply acts more gracefully. The SMPS will shut down when the over-current limit is reached whereas the transformer-based supply will just sag. " - tomchr Jan 29, 2019
Thank you,
David.
"I also find that the Modulus amps provide the same or better performance on an SMPS as they do on a transformer-based supply. The only exception would be short-term overload, where the transformer-based supply acts more gracefully. The SMPS will shut down when the over-current limit is reached whereas the transformer-based supply will just sag. " - tomchr Jan 29, 2019
Thank you,
David.