Net Audio Quad 405 Mk 3
The Hi-Fi Insight desk has just received the new Net Audio Quad 405 Mk 3 for auditioning. Interestingly the new boards use an Analog Devices AD843 op-amp instead of the Burr Brown OPA604 or OPA627.
Elna Starget electrolytic capacitors are used in the signal path, whilst Rubyicon capacitors are used elsewhere and there are also a large number of red Wima polypropolene capacitors on the board as well. Darlington MJ11016 transistors do the current dumping and all the resistors are 1% close tolerance metal film which should be vastly superior to the 5% carbon film type found on most 405 boards. All the internal wiring is done using silver plated cable from the Missing Link and Net Audio's very own dual mono power supply feeds the boards.
Our initials thoughts on how this amp sounds will be posted next week, in the meantime we have posted some gallery shots below.
This entry was posted on Thursday May 15th, 2008 at 12:26 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.
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5 Responses to Net Audio Quad 405 Mk 3
Azif ikare Says:
May 23rd, 2008 at 11:28 AM
I purchased the Mk3 from ebay the price was very good but I will be sending them back as I think they have blown a tweeter and when the amp is on it blocks the FM radio completely also the treble sounded very course but they may have been the tweeter damaged
Ketalar Says:
May 26th, 2008 at 9:48 AM
Overoscillation somewhere : more frequent with modern ICs, if not properly decoupled.
Anyway it is mandatory to install a loudspeaker protection.
Velleman K4700, for instance.
Hi-fi insight Says:
May 26th, 2008 at 6:10 PM
As readers will know we are currently in the process of putting together a first impression review of the Net Audio Mk3 boards which will be published shortly.
However we can say we have not experienced any of the above issues and the treble is certainly not harsh, there is more extended detail though at the top end and we prefer to use a simple but very high quality custom built passive pre-amp using solid silver cable, elna switch, and a military grade resistor based stepped attenuator which ensures a very neutral and transparent sound.
Does your 405 amp use the Net Audio DMSU as well as the Mk3 boards as it could be a power issue that has caused the circuits to misbehave ?
We are 99.9% sure the IC's are de-coupled as that was one of the Net Audio modifications that was done to original an 405 when upgrading the IC to Burr Brown OPA604/627
David pritchard Says:
May 30th, 2008 at 3:00 PM
Hi Ben,
Just like to thank you for the review - very pleased with your opinion of the NET Audio 405 MK3.
May I politely point out that the price you have put on the review is for the 303 MK3 boards at £160 - the 405 MK3 boards are more expensive due to the manufacture of the brackets and the cost of the power transistors and are £220 a pair.
A Monobloc version is also available which produces over 150W RMS continuous into an 8 ohm load and the conversion is £280 per 405 to full MK3 Monobloc status. I would be grateful if you could mention this at the bottom of the review for your readers.
I noticed on the comments on the boards that one of your readers Azif Ikare wrote to you stating that he had bought a 405 MK3 from eBay – I have not sold any NET Audio 405 MK3 boards on eBay as yet - and said he had problem with it – I do not have a customer of that name on my books and I have contacted the customers that have bought the MK3 and no one has experienced oscillation problems and there is no reason why they should have. The 405 MK3 boards have been designed correctly, tested for stability before they were put on the market and are stable into a pure capacitive load of 4.7uF which is a tough load for any amplifier and is my standard test for simulating electrostatic loudspeakers – they have also been used with a pair of Quad ESL 63s without any indications of instability on either test. The design is what my customers would expect from NET Audio and all boards are guaranteed against design faults.
All Opamps of audio quality can be used and are stable in the 405 MK3 board – the MK3 is shipped as standard with AD843s but others such as the OPA627 can be fitted during manufacture for an extra £10 per board at the customers request.
Thanks again for your time and the review of the NET Audio 405 MK3 amplifier, much appreciated.
Best Regards
David
Gabor Says:
November 24th, 2008 at 9:31 AM
Hi All of You,
Just visiting here a bit, but read the aboves I remember the time when I made a lot af Quad 405 replicas in late 80's. This power amp is a joy to build and very easy to "bring it alieve" once it's been ready. In fact, it's magic is the circuit automatically sets itself to the right working point so no adjust needed anyway. BUT, it is very sensitive to oscillations at the last stage so the useful trick is to place a 1 nF ceramic capacitor between negative rail side power transistors B-C (basis-collector). It cuts any oscillations and doesn't affect sonically.
The change of OP-amp is welcome but - as usual - designer choosen a less than adequate one, try the AD 825 that produces the speed and harmonics the otherwise good other parts of this amp requires. Also, bootstrap capacitor should be a tantalum type electrolytic one to avoid the known upper-bass hike of any bootstrap. Finally, take care of having a low beta transistor followed the IC. That's all, cheap but very effective mods giving a surprisingly good result.
Cheers, Gabor, Zeppelin Audio Hungary