Which amplifiers for ultra-sensitive horn speakers (Klipsch La Scala)?

[andreweast]

Some ginormous La Scalas have arrived in my small to medium sized rooms. It is a shock. The Harbeths have gone upstairs, where they have more space to breathe. BBC Monitors in a big room; Huge horns in a small room. It's an upside down world.

The trouble is that all my amps are pretty powerful. My Harbeths really love the Unico Pre/DM but with the La Scalas 160W is silly. It's more the high gain on the pre that is a problem though - after all I don't need to use all that power.

To cut a long story short - after trying many different amps it seems that the pre-amp stage is critical. Any gain is a problem.

My temporary solution is to use my DAX Discrete Variable as pre-amp. This works very well with Croft 7R, Croft 7, and currently, my Albarry mono blocks, which sound very clear and compelling in this set-up. I'm attenuating around 40dB most of the time. But digital attenuation is the devil's attenuation and I can't use my turntable!

Any ideas?

I'm thinking either;

a) Passive or Unity gain pre, then experiment with power amps.

b) look for something like a 300B SET integrated. Also 12a7 has been suggested.

 

[HoopsOnToast]

Decware Zen

 

[russ abbott - royds broth]

2A3's are nice.

 

[i_should_coco]

Quiet ones! High sensitivity speakers will expose the slightest noise.

 

[bonneville]

Decware Zen

AI First Audio 2a3.

I used both with my La Scala's.

I have been trying to resist a deal bringing mine back home,in part ex for my UR mono's every time I see a thread about them I weaken a bit more.even though it would be a short term thing before I move.

 

[AmDismal]

Note that your problem is gain, not power - just moving to a lower power amp will not automatically sort you out. A two-stage SET would give lower gain than a three-stage one.

 

[john dolan]

Build a simple passive pot in a box with something like Alps blue would cost you around £20 for the parts then run the dac full output into the passive this is what I do with my M-dac.

Or you could use something like Rothwell attenuators or Golden jacks ect.

 

[James Evans]

These pots are apparently those used in the new albarry's from reading the blurb on the site, so maybe one of these in a box?

http://www.hificollective.co.uk/catalog/rv24yg20sa104k-tocos-cosmos-100k-stereo-potentiometer-p-9065.html

 

[john dolan]

These pots are apparently those used in the new albarry's from reading the blurb on the site, so maybe one of these in a box?http://www.hificollective.co.uk/catalog/rv24yg20sa104k-tocos-cosmos-100k-stereo-potentiometer-p-9065.html

Depends on how much the OP is willing to spend I built my passive using the Glasshouse Seiden 43 stepped attenuator (0.5W version) but you can get 90% or more of the signal with a Alps for £12.

Another option if the OP wants to keep his Croft is do a shunt mod on the volume pot and select resistors that will cut the gain the same as Rothwell attenuators would.i did this to the Dact attenuator in my active preamp.

 

[diceman]

Note that your problem is gain, not power - just moving to a lower power amp will not automatically sort you out. A two-stage SET would give lower gain than a three-stage one.

Quiet ones! High sensitivity speakers will expose the slightest noise.

I am not sure if you know who on the forum has a fair bit of experience with horns but these two guys certainly know their stuff.

So looks like you are after a low gain and low noise amp.

A lot of folk have a problem with pre-amps providing too much gain for their power amp and speaker sensitivity. Try running a Leak Stereo 20 with an active line stage in normal speakers and it is deafening as soon as you move the volume control from the off position. (this is probably the worst setup for your requirements BTW even though it is low power).

The croft 7r seems to have an input sensitivity of 0.5V for 45W out so assuming you have a standard 2V ish out from your CD player you will need to attenuate it by 12 dB just to avoid clipping the power amp.

If the croft is quiet enough???? it may be worth having a word with Glen croft about how the input sensitivity can be reduced on the power amp.

I would then look for either a TVC, pass labs B1 Line level buffer or a valve pre-amp with littel gain (normally seem to have output transformers on them a la Puresound L10 and L300?).

<Edit> personally I am not a fan of throwing away gain as you generate more noise than is required, shunt pot mods, line attenuator plugs etc can be used to see how you much you need to drop by as a test but a properly considered gain structure of the system is a much better engineered solution <edit>

 

[m7rso]

The django pre has a bias switch, but only two settings and its passive, so not sure if it will synergise with your system...heard it with valves though and sounds just beautiful.

 

[john dolan]

A TVC will give top notch sound but be aware they only have 24 volume steps and why I don't use mine because even on the first notch on mine it was too loud for late night listening on radio that why I spent lots on a 43 stepped attenuator and why I recommended a Alps carbon pot as the Alps will be silent and give infinite adjustments.

If the OP ups the budget a little a change to Noble pot is worth the £40.

But to keep it simple try some Rothwells with the Croft pre or one of those cheap passives Jerry bought that I cant remember the name of sorry.

 

[rdale]

Some ginormous La Scalas have arrived in my small to medium sized rooms. It is a shock. The Harbeths have gone upstairs, where they have more space to breathe. BBC Monitors in a big room; Huge horns in a small room. It's an upside down world.The trouble is that all my amps are pretty powerful. My Harbeths really love the Unico Pre/DM but with the La Scalas 160W is silly. It's more the high gain on the pre that is a problem though - after all I don't need to use all that power.

To cut a long story short - after trying many different amps it seems that the pre-amp stage is critical. Any gain is a problem.

My temporary solution is to use my DAX Discrete Variable as pre-amp. This works very well with Croft 7R, Croft 7, and currently, my Albarry mono blocks, which sound very clear and compelling in this set-up. I'm attenuating around 40dB most of the time. But digital attenuation is the devil's attenuation and I can't use my turntable!

Any ideas?

I'm thinking either;

a) Passive or Unity gain pre, then experiment with power amps.

b) look for something like a 300B SET integrated. Also 12a7 has been suggested.

I've got a Miniwatt N3 which is dirt cheap, single ended EL84, low power 3.5 watts per channel and very quiet. I don't think its bass is the best in the world, but everything else like the treble and midrange are really quite good, especially if you change the stock valves. Only one input though, but I have read about La Scala owners trying out the Miniwatt. My other single ended EL84 amp, a Glow Amp One, sounds better in my system in the bass, but is quite noisy and wouldn't do.

 

[john dolan]

I use a AS Passion with my M-dac and seeing as the OP uses a DAX Discrete Variable maybe worth looking out for a Passion to match his dac it has 31 steps but gives enough adjustment with all the kit ive used it with and as sound goes its as transparent as preamps get and I prefer it to my TVC.

 

[roob]

Try one of these http://www.ebay.co.uk/itm/Tisbury-Audio-Mini-Passive-Pre-Amp-Stepped-Attenuator-Preamplifier-/171062829201

They sound very good and you can send it back for a no quibble refund if you don't like it.

 

[paulf-2007]

a bake off and everyone has to bring a low power amp, I have 300B 8w and two other sets of 2w and 4w to kick things off. If the thought of lots of hairy wammers wallowing about on your sofa doesn't appeal then some private visitors with suitable amps.

 

[steve 57]

a bake off and everyone has to bring a low power amp, I have 300B 8w and two other sets of 2w and 4w to kick things off. If the thought of lots of hairy wammers wallowing about on your sofa doesn't appeal then some private visitors with suitable amps.

Thats very sensible advice..

I live a little to far north but i have a few low powered amps that would make those speakers sing

 

[RobHolt]

I am not sure if you know who on the forum has a fair bit of experience with horns but these two guys certainly know their stuff.So looks like you are after a low gain and low noise amp.

Yes, plus speak with Guy at Puresound as he mentioned in another place that he would have a suitable solution.

 

[andreweast]

Lot's of interesting suggestions - thanks.

A couple of points to mention. I'm not wedded to any of the power amps I currently have, and a flea powered amp bake-off would be very interesting. In the meantime though, I've had a very generous offer from someone on AoS to bring his Corft OTL. These are legendary with La Scalas so that will be fascinating.

Regarding the Pre. Glenn Croft has one of my pre-amps at the moment and has offered to change the circuit to effectively zero-gain. He has a lot of experience with KHorns and La Scalas and knows what to do with a pre to work with them. The only thing stopping me is that I was actually going to use that pre with my Harbeths in the other system.

And passives? Well, I've tried a little Albarry passive with the La Scalas and don't like the results. Similarly with attenuators. I've always found they strangle the dynamics in the contexts that I've used them. But that's not to say I can't get one to work. The Tisbury has to be worth a try, thanks.

Also, I have mailed Guy and yes I would very much like to try one of his 2a3 amps,