Net Audio Quad 405-3 Amplifier Update

Quad 405 mk3 boards

Net Audio

For the last six months or so Hi-Fi Insight has been listening to a Net Audio supplied Quad 405-3 with their own new amplifier boards which use the best components currently available (at a sensible price)
to greatly surpass the sound quality of the original Quad 405 and 405-2. The op-amp used in these new boards as standard is an Analog Devices AD843 which at around £8-10 per chip is a very high quality, low noise/distortion option.

However I recently decided to swap these op-amps for a Burr Brown OPA627 and see if there was any noticeable difference or improvement in the sound quality. For those in the know, the Burr Brown OPA627 is considered the best sounding IC op-amp currently available, but at about £20 per chip is not cheap and is available as option on the Quad 405-3 from Net Audio, but at a premium price. The general consensus about the Burr Brown OPA627 is that it sounds smooth and detailed but only offers a slight improvement in sound quality compared to cheaper op-amps and a similar performance to the AD843. In fact some readers to this site have questioned whether the original Quad 405 & 405-2 warrant the used of the Burr Brown OPA627 in a circuit plagued by poor choice of other components. This is something I half agree with as my own Net Audio Quad 405-2 only benefited slightly from swapping the standard Burr Brown OPA604 with more expensive OPA627. The sound was definitely smooth and there was slightly more detail, but you had to really listen hard to tell any difference.

Imagine my surprise then, when the Net Audio 405-3 boards were tested with the Burr Brown OPA627. There was an immediate improvement in every area of the sound reproduction and not just the '5%' type as some people say this chips offers. The bass was fuller and more defined, vocals had more air and neutrality, the top end treble was more lucid and sweet. In short, it was like listening to different amplifier.

I then spent the next four hours listening to my favourite tracks and every time, the Burr Brown OPA627 and Net Audio 405-3 combination did not disappoint. It was obvious after listening to a wide range of the music that the improved Net Audio 405-3 boards really allow the Burr Brown OPA627 to achieve its potentially in a way that older Quad 405 circuits just prohibit, and the increased detail and resolution on offer is truly amazing.

The only thing I was left slightly confused about is why the Analog Devices AD843 is used as standard in the Net Audio 405-3, because the difference in sound quality using the Burr Brown OPA627 could never be classed as '5%' improvement, it is more like about 25% and that for me like most people I would imagine is worth the extra £20 outlay. The Burr Brown OPA627 & Net Audio 405-3 combination is simply outstanding and if you choose the standard AD843 based boards, then you are not doing these new boards justice no matter what the rest of your system is.

The good news is if you have bought some of these boards with Analog Devices AD843 op amp, then it is a simple five minute job to replace them that requires no soldering thanks to Net Audio's use of IC sockets on the boards. I promise you will not be disappointed.

This entry was posted on Thursday January 22nd, 2009 at 1:00 PM and is filed under Amplifiers. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response.

11 Responses to Net Audio Quad 405-3 Amplifier Update

Rob Says:
March 7th, 2009 at 4:52 PM

I will second this analysis. I just rolled my OP amps from the AD843 to OPA627 on the Netaudio MK3 405 dual-mono and the result wasn't subtle.

I wasn't completely happy with the treble when using the 843s and sometimes thought it lacked sweetness or smoothness. Nothing major and something that my room is probably highlighting considerably. The 627s fixed this and added more punch, clarity, detail, air and bass depth.

Clearly the result you get will depend greatly on the source and speakers you're using. Mine are very detailed and boy, the 405 MK3 with 627s is good. Very.

James Says:
April 17th, 2009 at 9:06 AM

How would you say the 405 mk3 compares to a 909? I'm looking for a nice, clean, natural/neutral 'real' sounding amp with good clean controlled bass, natural midband/treble.

Juan jesãºs Says:
November 29th, 2010 at 1:24 AM

Buenos días.
Me gustaría por favor saber como puedo comprar dos módulos para la Quad 405.
Vivo en Madrid.
Spain.
Muchas gracias.

Babylondrifter Says:
March 27th, 2012 at 10:34 AM

HELLO!
Got 2xQUAD405mk3`s with monobloc conversion,
They should deliver sufficient power to my good old B&W 804 Matrix series (N`s) from the mid 90`s.
Has anyone any experience how the quads will sound, I`m looking for advice on a pre-amp. Considered everything from HEGEL HD11 dac/pre (totally digital), Xindak3200mk2 (tube) pre, The Quad Elite pre from the new series, Cambridge dacmagic+, the Custom Passive preamp, Does anyone got any good tips to what I`m missing in my setup? what kind of pre and cables, and a DAC as well that suits the B&W804matrix N/QUAD405mk3 setup. All help Massively appreciated

Loathecliff Says:
May 13th, 2012 at 4:34 PM

Why all the fuss about the 405? If ever an amplifier sucked the life out of music, this is the one. I will grant that it does not offend the ears & brain in the usual transistor way by de-constructing the music; but if ever there was an award for the most boring amplifier on the planet, the 405 would win it.
Luckily it has a famous badge, so just like certain not-so-good items wearing a L*nn (sorry for swearing) label, it can be off-loaded without too much pain onto to another innocent.

Pete Says:
June 4th, 2012 at 11:33 AM

I obtained a 405 mk3 with dual psu a few days ago to attach to my Musical Fidelity M3i integrated amp . I am using a Marantz cd5400 as a transport, Musical Fidelity Trivista 21 Tube DAC, Epos M22i floorstanders, Chord Rumour cable and Chord Cobra 3 I/Cs. The M3i has a class A pre-amp inside and has a pre-out phono connection.
I am very pleased with the result. The definition and soundstage on complex tracks has increased by one if not two levels of performance. Timing, detail and dynamics are all improved.The bass may not be quite as deep but my initial impressions are that it is more focussed and tight. The quality of vocals and acoustic instruments in uncomplicated songs is more neutral.
I would recommend exploring upgraded classic gear as an alternative to more expensive new uprgrades.

Harry fenton Says:
September 1st, 2012 at 7:17 PM

Am I the only person on the planet to have a mono pair of Quad 405s? And a Quad 44 modified to match? I can't be. But someone else will have the delight of such ownership in the near future as mine are going up for sale. :¬)

Babylondrifter Says:
September 14th, 2012 at 8:58 AM

I have a pair of 405`s on their way to become mkIII monoblocks. I have gotten a good deal on an oldschool Aragon 24K pre-amp. The speakers are the B&W Matrix 804`s from late 90`s. Any thoughts on the setup, condsidering the preamp, or should I NOT send the 405`s for upgrade and go for another poweramp with the Aragon and B&W`s?

Stanford Says:
September 21st, 2012 at 1:41 PM

To Cliff Loathe-some. Don’t spoil people’s fun. If you have anything worthwhile to say please speak from experience on the equipment involved not just your hatred. The Quad 405 was a milestone in design and won the design council award. This amplifier was mass produced and sold in thousands. No biasing was required. The amplifier was not tweaked and sold at ridicules prices but revisions at no extra cost. Because of its modular design and not surface mount technology it could be modified by the end used easily, hence its popularity for modifications. The Quad 405 amplifier I use is a modification No.4 by Keith Snook using Darlington output transistors. Just Type is name in Google and look at his website. From experience I do not believe that an OP AMP makes much difference or expensive interconnect cables. It is all in the design of the circuit and your driving load (speakers). The quad 405 is a great sounding amplifier and even better with a competent modification. Don’t forget one thing the source (recording and musician) this is what it is all about music. Rubbish in rubbish out.

Clifford wright Says:
March 4th, 2014 at 9:58 AM

Well I've been using improved local 405 copies for over 20 years. In fact I found much more effect on distortion levels (always VERY low) by careful choice and design of the low value emitter resistors.
In fact the THD was reduced from 0.001% @ 10 watts 1kHz into 8 Ohms to 0.0003%. Right down near the limit of measurement on my equipment.
Frankly I do NOT believe the subjective results of the op amp changes. The only thing that would actually be improved would be the noise floor.
After all the Quad is designed as an AUDIO amplifier and rolls off at 30 kHz or so.
FYI I am a professional electronics engineer with 60 years of experience and have spent many years working with "real music" auditorium design, so I have a very good idea what live music actually sounds like!!
In fact I have built and used more than 30 of these amplifiers ranging from 40 watts to 300 watts output by scaling the design. Peter Walker who founded Quad was an aquaintance of mine and I happen to have been born in the town where they were manufactured.

Charles borg Says:
September 15th, 2016 at 4:23 PM

what has happened to net audio since the passing away of david Prichard cannot buy any thing from the company are they still in business?

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