advertisement


Low power Class A amps/kits advice.

Thetiminator said:
I have some high efficiency horns (105db) that I’ve been running with Class D amps with a good degree of success. On another thread the idea of low power Class A amps would be worth a try.

Jez from Arkless put the idea in my head, he’d built a couple of kits that he thought were superb (the name escapes me). A couple of prerequisites:
1. Must be monoblocks
2. Must be low(ish) power as they’re on 12-14 hours per day, and don’t want the heat or electricity bills of higher power Class A. 10-40w would be more than enough.
3. Needs to be quiet in operation as the speakers at 105db are very sensitive to noise.
4. No valves.

Has anyone built/had built any of the Pass kits, or any other experience with small Class A amps like First Watt or others etc? Budget £2-3k.
Click to expand...

Oooo where to start.... I haven't "built any kits" as such... they were all one's from DIY'ers that they were having teething troubles with and ended up basically needing rebuilding... I'm self sufficient in amplifier designs!
I did build myself a JLH class A amp (since partially pillaged for parts for other things) from scratch (no kit!) but it was the later direct coupled version.


Quite a few (not all!) of the Pass/First Watt designs will be too noisy due to the input mosfet used in them.

With low power and if willing to pay for large enough heatsinks etc (monoblocks can help somewhat here) then they can be made to run pretty cool and can be left on as much as other amps. As always it's a very bad idea to leave gear on 24/7! (like the Cyrus monoblocks I'm working on at the moment which were killed by being left on 24/7).

Monoblocks no problem other than it will be a lot more expensive.

Hiraga le monstre actually gives around 7W or so but sounds amazing when done right. Although it looks like the worlds simplest power amp i do not regard them as suitable for DIY'ers as everything about them is critical and you really need a distortion analyser, scope, low distortion oscillator etc and the knowledge to tweak each one into spec.... the one elsewhere on pfm which I rebuilt was all made according to instructions and with correct parts by the original builder but actually gave about 1.5W and about 3% THD as it arrived with me!

One of the prices you pay for the ultimate in low parts count, most direct signal path etc in many of these low power class A designs is low PSRR (power supply rejection ratio), hence they are unusually sensitive to mains hum etc on the supply rails... Now being class A they draw a lot of current continuously and this causes mains hum on the power rails... Not a happy recipe.
QED if using super efficient speakers then you are very unlikely to get low enough mains hum unless you REALLY know what you are doing... and many of the available designs/kits are likely to need better power supplies than those that are supplied with/intended to be used with.... the Hiraga and "Eastone"'s FirstWatt M2 both came in for rebuilds due to just this! and they aren't using 105dB/W speakers.
I would be temped to use fully regulated supplies (as in Naim NAP250 as most well known amp to do this) to guarantee low enough noise.
 
Arkless Electronics said:
Oooo where to start.... I haven't "built any kits" as such... they were all one's from DIY'ers that they were having teething troubles with and ended up basically needing rebuilding... I'm self sufficient in amplifier designs!
I did build myself a JLH class A amp (since partially pillaged for parts for other things) from scratch (no kit!) but it was the later direct coupled version.


Quite a few (not all!) of the Pass/First Watt designs will be too noisy due to the input mosfet used in them.

With low power and if willing to pay for large enough heatsinks etc (monoblocks can help somewhat here) then they can be made to run pretty cool and can be left on as much as other amps. As always it's a very bad idea to leave gear on 24/7! (like the Cyrus monoblocks I'm working on at the moment which were killed by being left on 24/7).

Monoblocks no problem other than it will be a lot more expensive.

Hiraga le monstre actually gives around 7W or so but sounds amazing when done right. Although it looks like the worlds simplest power amp i do not regard them as suitable for DIY'ers as everything about them is critical and you really need a distortion analyser, scope, low distortion oscillator etc and the knowledge to tweak each one into spec.... the one elsewhere on pfm which I rebuilt was all made according to instructions and with correct parts by the original builder but actually gave about 1.5W and about 3% THD as it arrived with me!

One of the prices you pay for the ultimate in low parts count, most direct signal path etc in many of these low power class A designs is low PSRR (power supply rejection ratio), hence they are unusually sensitive to mains hum etc on the supply rails... Now being class A they draw a lot of current continuously and this causes mains hum on the power rails... Not a happy recipe.
QED if using super efficient speakers then you are very unlikely to get low enough mains hum unless you REALLY know what you are doing... and many of the available designs/kits are likely to need better power supplies than those that are supplied with/intended to be used with.... the Hiraga and "Eastone"'s FirstWatt M2 both came in for rebuilds due to just this! and they aren't using 105dB/W speakers.
I would be temped to use fully regulated supplies (as in Naim NAP250 as most well known amp to do this) to guarantee low enough noise.
Click to expand...

Thanks Jez. You see that’s what scares the carp out of me...getting something built and there’s too much hum or other associated noise. Then you’re stuck a bit. A single amp not too bad, but when you’re doing monoblocks it’s going to end up a decent wad of cash in the end.
That’s why I’m loving the Class D amps at the minute, they are perfect in every way except you don’t get that Class A naturalness associated with the simple signal path. Everything is a trade off in our hobby I suppose.
Ballpark - a pair of suitable Class A monos, done really well with top of the line parts, inc build costs...what are you talking roughly?
Would £2k do it?
 
Thetiminator said:
Thanks Jez. You see that’s what scares the carp out of me...getting something built and there’s too much hum or other associated noise. Then you’re stuck a bit. A single amp not too bad, but when you’re doing monoblocks it’s going to end up a decent wad of cash in the end.
That’s why I’m loving the Class D amps at the minute, they are perfect in every way except you don’t get that Class A naturalness associated with the simple signal path. Everything is a trade off in our hobby I suppose.
Ballpark - a pair of suitable Class A monos, done really well with top of the line parts, inc build costs...what are you talking roughly?
Would £2k do it?
Click to expand...

Hmm.... your figure earlier in the thread was £2-3K and that would do it... £2k should do, depending on exactly what was required... "top of the line parts" well there are different peoples opinions on what that means, to put it mildly! You could spend say £1000 on 1 capacitor for some of the most "out there" "boutique" parts! Not that I recommend such things...

It must be made clear that there are so many aspects to the design of an amp beyond what class it works in as well. One see's on forums loads of talk about class D or sometimes indeed class A as if there is a specific sound you are guaranteed to get by using a particular amplifier class.... strange that the other 90% of amps that are class A/B do not get lumped in one basket together... god knows where the class S amps (Sandman not Rf Switching type) I've been doodling with in sims come into it all!
 
Just positioning and speaker cables not being long enough....don’t even ask :p

See that’s the risk you take isn’t it...you can drop £2500 on something bespoke, but if you don’t like it, what’s it worth....you could lose £1500 in a couple of weeks...and I have a wife to take care of the chucking away wads situation :rolleyes:
 
My Avantgarde horns are about 103db sensitivity and I run them with some rather unusual vintage 80s Pioneer monoblocks (M-Z1a) plus the matching preamp and MC head amp. They’re 60w class A and even loud I don’t see the power LEDs go further than 0.7w each.

Just about the only alternative I’d fancy is a custom SIT amp with <8 watts max available - plenty of headroom!
 
Thetiminator said:
Just positioning and speaker cables not being long enough....don’t even ask :p

See that’s the risk you take isn’t it...you can drop £2500 on something bespoke, but if you don’t like it, what’s it worth....you could lose £1500 in a couple of weeks...and I have a wife to take care of the chucking away wads situation :rolleyes:
Click to expand...

It's just that monoblocks makes it so much more expensive and for little or no advantage... By the nature of the beast large sturdy cases are needed and ain't cheap... then there's two lots of labour in the metalwork side of things etc etc. I can't really think of any situation where suitably long interconnects and speaker cable wouldn't allow a stereo chassis rather than monoblocks....

FWIW bespoke kit I've built has kept its value pretty well. An item I built for someone for £500 was, after several years use, re-sold for £400 just a few weeks back.... but yep ultimately it's a risk you take.
 
If you’re worried about resale then something Hiraga or Pass derived makes a lot of sense, far easier to sell on with a name attached.
 
eastone said:
If you’re worried about resale then something Hiraga or Pass derived makes a lot of sense, far easier to sell on with a name attached.
Click to expand...

And then there's lead time to consider. If you're hot to trot now and have money burning a whole then DIY commissions could take longer than your interest holds and you could always change your mind in the mean time...
 
stevec67 said:
Jez, what did you think of the JLH 1969?
Click to expand...

The version I built was not the original 1969 one but an updated and "improved" (quotation marks because I haven't been able to compare to the original... but I would expect this version to be better) one which IIRC I found on TCAAS web site that has all the info on JLH amps. Again IIRC, it has further improvements over even the 1996 update by JLH himself and it was basically in tune technically with pretty much everything I would have done myself to improve and modernise the design so I thought "I'll go for that version". It was direct coupled and had a long tailed pair at the front end (is/was... it's partially dismantled as I needed things for other experiments but easily put back together if I got the urge).

It was very good. It's been probably 6 years since I used it... I recall it as doing nothing wrong, sounding just a touch valve like, no "solid state glare", "chromeplatedness" or anything like that, quite organic sounding. For sheer "hear through" transparency the Hiraga was better still though. Not that the JLH was lacking in transparency! It would beat anything I can think of from the usual suspect amp companies from Cambridge and Salisbury for example.

The Hiraga seemed to (if we can pardon a hi fi aphorism...) remove another veil... one I thought had already been removed by the best examples of other amps in my system. It brought "cut glass transparency" and "etched detail" to a new level, but do not for one millisecond be thinking it was in any way "hard" "clinical" "solid state like" in doing this! Soundstaging etc were equally stunning. In spite of a damping factor of only something like 8 iy had bass that could turn on a sixpence as well... within it's 7-8 ish Watts truly amazing but in spite of the design looking like "the simplest amp you could make" it's a complete twat to get right! All the semiconductors have to be matched, some are quite rare and not cheap and you need to get way more than you will use to find enough matched ones... and there is no way I could have got this one performing correctly without a heap of test gear. There must be loads of DIY ones around that sound nowhere near what they are capable of I would guess:eek::rolleyes:
 
Woodface said:
Sounds like a lot of bother. Why not just buy a Sugden integrated?
Click to expand...

The Sugdens are good, but there are better circuits out there that make the a21a sound pretty euphonic. (The A21SE is a lot cleaner sounding apparently, but it’s not cheap).

The First Watts I’ve had here (F6 and M2) really are a step up in transparent and refinement, not to mention dynamics.

I also reckon 25W it’s going to be serious overkill for those speakers - unless the OP lives in a barn?

Come to think of it though - what preamp are you planning to use? Or have I missed that?
 
Thetiminator said:
I have some high efficiency horns (105db) that I’ve been running with Class D amps with a good degree of success. On another thread the idea of low power Class A amps would be worth a try. Budget £2-3k.
Click to expand...

I have posted this many times before, but these two Tron Convergence amplifiers were specifically designed to drive both conventional speakers, as well as high-efficiency speaker designs (i.e. horns), at the flick of a switch on the rear panel. They are also in budget as the stereo amp is £2000 and the monoblock amps are £3000 a pair new. They produce up to 70 watts per channel so will drive anything made for the domestic environment and are super quiet even on the most efficient of horns.

Convergence-1.jpeg


Properly made in nice casework with very high-quality internal components.
 
G T Audio said:
I have posted this many times before, but these two Tron Convergence amplifiers were specifically designed to drive both conventional speakers, as well as high-efficiency speaker designs (i.e. horns), at the flick of a switch on the rear panel. They are also in budget as the stereo amp is £2000 and the monoblock amps are £3000 a pair new. They produce up to 70 watts per channel so will drive anything made for the domestic environment and are super quiet even on the most efficient of horns.

Convergence-1.jpeg


Properly made in nice casework with very high-quality internal components.
Click to expand...

Thanks Graham. Paul Coupe has been on at me to get in touch. Are these Class A or (I’m assuming) Class A/B? Would they have that rich sound I’m looking from a good Class A amp?
 
The Hiraga that Jez worked on is mine and I am using it to drive Celestion Axi 2050 compression drivers that are quoted at 108dB for 1W. With no music playing and the volume on full there is a slight, and I mean slight, hiss with ear in the horn but absolutely zero humming or buzzing to be heard. The hiss cannot be heard from a metre away and certainly not from the listening seat. At normal listening levels with ear in horn no hiss can be heard.
 
You must log in or register to reply here.


advertisement


Back
Top