Amp upgrade needed

[LouisB]

Hi,

So, I've been thinking I probably would benefit an amp upgrade at some point. My current amp is the Arcam A85 which has been a trusty and versatile amp, no big complaints there.

I've been thinking along two fronts.

1. One of the new(er) amps out there, such as the CA 851W (rave reviews) or the Rega Elicit-R or maybe Naim supernait 2 (not a complete Naim fan, but maybe). Possibly others, Sugden, Roksan and so on.

2. Get an older classic, possibly even revamp it a bit too. Along these lines probably a Quad 405.2 or 606 or 909 even. But I don't know so much about these, other than they get good reviews. One thing that puts me off is old amps possibly with old transformers, I don't want to end up with something with a noisy transformer.

And I've an external pre-amp for my TT so I may make a volume box to run it straight into the power amp for the time being. That + a selector so that all my normal AV runs through the A85 as a pre and the TT runs straight into the power from its own pre. If that makes sense.

Later I might get a pre and then get rid of the A85. But first step is to upgrade the power amp.

Requirements - I'd rather not get something that sounds thin, bright or weedy. Accuracy and transparency, detail and dynamics are important to me. I'm not afraid of bass, although it doesn't need to be overly bass heavy.

Speakers are Audes Blues. 4 Ohm, 130 RMS. I'd like something that can drive them with plenty of spare reserve. They have quite big meaty woofers so something that can deliver current and keep control of the speakers would be good.

I listen to all sorts, electronic to jazz. I'd like something that can deal with the detail and finesse of fine jazz recordings as well as belt out some rock or electronic music.

Any thoughts on this?

[struth]

There are nice Restek mono's in the classifieds... 70w pc i think so should do you nicely, and Chris is a nice guy to deal with. think he has a croft for sale too

http://theartofsound.net/forum/showt...Amp-monoblocks

[LouisB]

There are nice Restek mono's in the classifieds... 70w pc i think so should do you nicely, and Chris is a nice guy to deal with. think he has a croft for sale too

http://theartofsound.net/forum/showt...Amp-monoblocks

Hey, thanks. I'm not familiar with this make but I'll take a look.

thanks, Louis

[cloth-ears]

The 405 is a fantastic piece of kit. When introduced back in the 70’s its specifications were so high that no available analogue source could match it. New methods of distortion measuring had to be employed just to test it.

Unlike conventional solid state amplifiers the 405 runs in Class “C”. It’s actually two amplifiers in one, a small highly linier Class “A” amplifier provides the full voltage swing and a pair of unbiased Class “B” dumpers provide all the current.

The closest analogy I can think of is power steering. As the driver you still have full control over the vehicle but when cornering of at reduced speed and road wheel friction is at its highest the power steering kicks in to ease the strain on the driver.

There are several kits available from outlets such as eBay (at very little cost), typically around the £20 mark that further improve the 405. Once these simple mods are applied the 405 is one of a handful of amps that will match or in most cases exceed any availably input source.

[Reffc]

The 405 is a fantastic piece of kit. When introduced back in the 70’s its specifications were so high that no available analogue source could match it. New methods of distortion measuring had to be employed just to test it.

Unlike conventional solid state amplifiers the 405 runs in Class “C”. It’s actually two amplifiers in one, a small highly linier Class “A” amplifier provides the full voltage swing and a pair of unbiased Class “B” dumpers provide all the current.

The closest analogy I can think of is power steering. As the driver you still have full control over the vehicle but when cornering of at reduced speed and road wheel friction is at its highest the power steering kicks in to ease the strain on the driver.

There are several kits available from outlets such as eBay (at very little cost), typically around the £20 mark that further improve the 405. Once these simple mods are applied the 405 is one of a handful of amps that will match or in most cases exceed any availably input source.

It was (and remains) a great amp. The Net Audio mods improved it no end though. I had one, fully modded out for a while and thoroughly enjoyed it albeit it was limited in power delivery despite the rating. The 405 was the fore-runner of ever improved and more powerful versions and in itself may not be suitable for some low impedance high current speakers as it cannot deliver it's rated output into highly reactive loads. The design used some very conservative protection circuitry with the Quad electrostatic speakers in mind. It also uses a very basic power supply stage (simple Zener shunt regulator of pretty poor performance in the mains noise stakes) which can be the cause of a lot of hum, and many examples will, by now, have been up-rated.

Personally, I dont see the point in the 405/2 when you can buy something like a Mk1 909 which (imho) was better in every respect and could drive difficult loads with ease. It keeps the same current dumping design. Mk2 onwards I think lost their way and were later manufactured in China where QC suffered to the extent that there were numerous reports of variable component quality leading to some problems with the initial run of Mk2 909s.

You can pick a decent Mk1 up used for well under £500 these days and that's something of an audio bargain.

[cloth-ears]

The power supply is more than good enough for the 405. Remember that a good amplifier can’t see the power supply. With a chip change and a recap the SNR is 100db

The DC offset is 0 and overall distortion is down to .001

The protection can be removed, simple job. Because of its clever design and unconditional stability it is not fussy about load or odd capacitance so special leads are unnecessary

They still use 405’s in recording studios because of their totally transparent sound. If a refurbished 405 sounds bad then the problem lies before or after the amp.

[spendorman]

The 405 is a fantastic piece of kit. When introduced back in the 70’s its specifications were so high that no available analogue source could match it. New methods of distortion measuring had to be employed just to test it.

Unlike conventional solid state amplifiers the 405 runs in Class “C”. It’s actually two amplifiers in one, a small highly linier Class “A” amplifier provides the full voltage swing and a pair of unbiased Class “B” dumpers provide all the current.

The closest analogy I can think of is power steering. As the driver you still have full control over the vehicle but when cornering of at reduced speed and road wheel friction is at its highest the power steering kicks in to ease the strain on the driver.

There are several kits available from outlets such as eBay (at very little cost), typically around the £20 mark that further improve the 405. Once these simple mods are applied the 405 is one of a handful of amps that will match or in most cases exceed any availably input source.

I have never fully understood the way the 405 / 405-2 works. When idling my 405 (from memory) got slightly warm, and the 405-2 seems to get quite warm. So why is this heat being generated if the output stage is Class B? If the output stage is biased, therefore Class AB, is there a difference in the biasing between 405 and 405-2?

[cloth-ears]

The warmth is from the Class “A” stage which is mounted on the same heat sink. The output “Dumpers” ate totally unbiased Class “C”. As with all Class “A” stages, when idling they produce the most amount of heat as they are always fully biased for full output.

Class “A” amplifiers actually get cooler as they near their full output as that energy is now driving the speaker

[spendorman]

The warmth is from the Class “A” stage which is mounted on the same heat sink. The output “Dumpers” ate totally unbiased Class “C”. As with all Class “A” stages, when idling they produce the most amount of heat as they are always fully biased for full output.

Class “A” amplifiers actually get cooler as they near their full output as that energy is now driving the speaker

Surely the plastic enclosed transistors that are on the heatsinks are drivers for the dumpers?

[cloth-ears]

Its all built on one board, just put your fingers on R30 and R31