I've ordered a new preamp...

I wasn't going to say anything about it until I got it (which will be mid-March) but since I've already made cryptic references to it in 2 other threads I might as well let the cat out of the bag (as if it was some big secret that you're all dying to know )

Well, after all my to-ings and fro-ings about which amp I was going to upgrade to I decided in the end to go the pre/power route.

My power amp will be a DIY job based on LC Audio ZAPPulse 2.2SE modules. I'd auditioned various integrateds that met my criteria and were very good (SimAudio i-5, Krell KAV400xi amongst others) but in the end I decided that £2.5-3K is just way too much money to blow on an amplifier. I'd heard a lot of good things about the LC Audio modules and I'm convinced that PWM switching amps are the future so that's what I'm going to build . For around £700 I'll have a power amp that will (I believe and hope) to be as good as anything available.

Anyway, this thread's about a pre, not the power. So, since I was building a power amp what the hell would I do for a pre? I looked around at the options available at the £1200-1500 mark and there's precious little - and above that level things start to rapidly get very expensive and saving some money was the whole point of this excercise.

Well, the documentation for the LC Audio powers got me thinking I could just stick pot/attenuator volume control into the input path and then use the dual inputs of the amp (RCA and XLR) to meet my AV bypass requirement (AV hooked to RCAs, Chord DAC64 hooked to XLRs) but that was all starting to sound like a DIY project too far for me and I wanted to keep it simple - and I hadn't even thought about remote control yet!

However, investigation into passive volume controls led me to research the DACT attenuator. But what about a remote? Well researching that led me to the unfortunately named (for the UK ) Bent Audio. They do remote control kit for the DACT attenuator.

What they also do though is some might fine looking passive preamps based on transformer volume controls. These use a transformer with multiple output windings, to give you 20 or so distinct volume steps instead of the resistive approach to attenuation. They have many advantages, not least killing the impedance mismatch issues normally associated with passive pres at a stroke. Other benefits are complete isolation and therefore noise rejection.

Reviews of amps using the Stevens & Billington TX102 transformer have all said the same things: incredible dynamics, especially at low volumes. Because there's no resitance in the volume control the sound at low volumes is as big and dynamic as it as at higher volumes.

IMO a passive transformer based pre is about as "non-existant" as it gets. It's just wires, not a single electronic component in there.

Anyway, I ordered myself a BentAudio "NOH" pre-amp with 2 RCA inputs, 1 XLR input and RCA and XLR outputs with remote control which is going to cost me around $1400 - at today's exchange rate that's about £780. Add 22% for VAT and customs duty and that comes to about £950. Add £50 for shipping to make it a round £1K for possibly one of the best pre-amps there is. More than one person on AudioAsylum has swapped their SimAudio P-5 (£4K+) for one - one of them commenting that the P-5 was "utterly destroyed" by the NOH

They make them to order and requirements and take roughly 4 weeks from order to delivery so I'm expecting to get mine in mid March. At first I'll be using it together with my Arcam A22 (which can, at the 'flick' of an internal jumper be made into a power amp) until my LC Audio project is complete.

I'll let you know how it sounds

Michael.

 

Good luck with the DIY build. Do let us know how it goes and how it sounds. DIY can be incredibly frustrating, and yet incredibly rewarding also.

Also let us know about the preamp's performance. Always interesting to hear of new bits of kit.

PWM is an interesting technology.

In five year's time, PWM will be the norm for a great many amplifiers, particularly in mini and micro systems, as it allows large amounts of audio power for very little heat generated, and small circuitry.

However, I fear that it will lead to a very generic view of hifi. There are but a few PWM chipsets that will be widely used (Tripath (a la Bel Canto), D2Audio, Apogee, Sony S-master). As some of these are selling as modules even, rather than chipsets (Tripath sell chipsets, D2 sell modules) it lessens the input that the manufacturer of the acutal amplifier has on the sound. For example, Veritas (now gone bust) built a power amplifier that was simply a tripath reference board in a box with a large linear psu.

Of course, Class A and Class AB designs will live on, but they will become a niche thing, much as valves are viewed by many now. PWM (class D and variations of (eg Tripath's "Class T")) will become the mainstream norm.

Also watch out for the combination of PWM with switchmode PSUs. Although switchmodes are normally the bane of audio enthusiasts, with a PWM amplifier it is possible to tie the PWM and the SMPS switching frequencies together, and then remove both with the output filters. Expect to see this become the normal application.

 

Hi Mike

So youre going for a passive pre?

My experience with them has shown a real need to have high input sensitivity on the power amp. Without that, the results can be lacklustre. With that caveat sorted, they can sound very transparent and real IME

Having interconnects that lose as little as possible is important with a passive also.

I know SCIDB uses a passive with high input sensitivity on his amp, so he may be someone useful to ask?

Good luck with the kit build.
Cheers
Chris

 

Good Look as well from me, I to had a go at DIY. The pre-amp i was making is still in the shed. Luckily it only cost me £20, i was checking how easy it was to make one. I see you are buying a bent audio. Let me know how it sounds, and how you get on with the LC power amp.

GAZZ

 

Hi Mike,

I share this vision too. Having just bought a second hand integrated that uses PWM technology as an experiment, I was not disappointed considering the money spent. It's no giant slayer and maybe some would find issue with its presentation, but in VFM terms I really do think at the price I paid for it it certainly does things which you'd expect to pay a lot more for money for in a non PWM design. I'd like to see more integrated PWM amps at all price points, but certainly PWM amps in general make a lot of econmical sense up to say the lower-mid high-end price point, say < £3000.

Good luck with the project, certainly will be interesting to see what you think of the finished products.

BTW, what did your findings about Audio Synthesis passive pre's turn up (I assumed you looked at this brand as it's one of the first names I think of when it comes to passive pre's / attenuators at this price point)? I was thinking about their range in the event that I change my mind about the integrated route and go instead to a passive pre/PWM power combo, but have never heard any AS amplification so wouldn't know if it would be for me or not.

 

I too agree that at the budget/mid price end of the market, switching amps are going to clean up in the future (and also in the midi system arena too). However, there is always going to be a place for good old fashoined valves and class A AB trannies in higher end products.

 

Chris (bottleneck), I think that most of the concerns you mention about a passive pre only really apply to ones that use some form of resistive attenuation for the volume control. With transformer based attenuation the common problems associated with passive pres are mostly gone. Current increases as volume decreases

Henry - tbh didn't look into Audio Synthesis :shame: I was still mostly considering adding in a passive volume control of some kind to the power amp when I more or less came across the Bent Audio site by accident and after a bit of research on that form of attenuation decided that was the way to go. There are others who do the same thing (eg: http://www.soniceuphoria.com/) (and indeed some use the same Stevens & Billington TX102 transformer) but the Bent Audio "NOH" really looked the business and the price was right.

I then checked the reviews on AudioAsylum and elsewhere and the NOH really has a huge following and there are only positive comments about it. It's a bit of a punt I know but I don't think I'll be disappointed.

Isaac - re PWM, I don't see that things will necessarily become that generic. The implementation (PSU etc) still plays a big part and there are people like LC Audio who are doing their own PWM thing rather than buying a chipset or module from one of the big boys. BelCanto have to be able to justify the £3K cost of their PWM amps that use $200 Tripath chipsets. Jeff Rowland have a new PWM integrated and some mono-blocks that use ICEPower chipsets from...yes, Bang & Olufsen....and they're charging £4-5K for those amps. Either someone is having a laugh or there is still more to it than just putting it all together.

I think the performance of relatively cheap PWM amps will force many of the high end brands to think long and hard. Just look at the threads on AudioAsylum about the $300 Panasonic SX45 PWM AV receiver which has had die hard audiophiles trading in their beloved valve monoblocks :yikes:

Michael.

 

I'll be v. interested to hear what you make of it. If I do decide to go at some point for a TT I'll need a phono stage, and dual input volume control - so this pre looks interesting.

(I'm currently running the CDP direct into the LC Audio balanced input and the radio/tv into the RCA. Works pretty well)

 

Micheal,

Looks interesting. It's always a bit of a punt what you buy things blind IMO, so I hope it works out for you. Keep us posted.

 

Hi Mike

The passive I tried from WAD had nothing apart from a stepped attenuator and hard wires inside it... no PCB, transformer or anything else at all.. didnt work very well with the not-partucularly-high input sensitivity of my pwr amp. YMMV of course

 

Re: Re: I've ordered a new preamp...

Dean (SCIDB) has one, IIRC. Seem expensive new, but I've seen older versions around secondhand a fair bit. Never heard one.

I've actually tried a Creek passive pre into my ATCs (over a 6 metre cable run) and it worked OK, I think passives are definitely a suck it and see thing. Hard to generalise at all, I've heard them sounding either lifeless or very good indeed.

I posted something about this on the myth busting day thread, and no one took the bait, but anyone who wants to hear how good a budget digital amp can sound should listen to cookiemonster's new Sony micro. I'm really not kidding, it's entirely plausible hi-fi, and £150 including speakers, cd player, tuner, and amp... Don't listen to it if you have an expensive setup you're dissatisfied with.

-- Ian

 

......you forgot the auto reverse tape deck.





(what does PWM stand for BTW? something, something, module?)

 

PWM = Pulse Width Modulation.

CD's and DVD-As use PCM, Pulse Code Modulation.

 

Cheers Isaac.

Mike - welcome to the future

 

That was sort of my point It uses a stepped attenuator which uses resistors to do the attenuation and that's where the input sensitivity (ie impedance mismatches) problems arise. Using a transformer to do the volume control gets around those problems.

Michael.

 

Re: Re: Re: I've ordered a new preamp...

Doesn't prevent Sony from publishing ridiculous numbers for it:

http://products.sony.co.uk/productdetail.asp?id=6_64_2667#

140W RMS...fair enough but at what cost? 10% THD

Just goes to show that Watts are king on the spec sheet for Joe Public

Michael.

 

Also the 70w p/ch rating is into 4 ohms which i have also noted.

(I have to say though - i haven't really noticed any distortion of grim proportions - though i also have not had the requirement to use all 140w rms, as it is more than loud enough at much lower levels - maybe the packaged speakers are quite sensitive? It certainly plays loud enough anyway in my 15"*9" den. (There is a 200w model for the more demanding listener)


It would be wrong to buy on spec though Michael surely?

As with Bubs ATC's it is paramount to demo in the home, correctly set up, and over an extended listening period, DBT optional, before a balanced judgement can be made of fine audio equipment.

Joe Public

 

Could that figure allure to when the dynamic boosty thingy is employed? I don't use that, as it sounds a bit duff.

Maybe the blu-tac i've carefully positioned under the speakers has sapped away the THD badness?

Is THD that important? I don't really know - i thought it was a legacy of the 70s/80s, where the manufacturers went to great lengths to illustrate THD's <0.000000000001% at full throttle, and yet they weren't always that much cop anyway? I don't know really. Have to say 10% does look a bit grim on paper, but it sounds alright in the flesh

I'm happy to demo

 

It'll only reach 10% THD when you're thrashing the knurdles out of it.

The size of the transformer is one way to tell about any hopes for maximum power output, except that it will almost certianly be an SMPS unit in it so that's no indicator either.

Just don't worry about it.

Cheers

 

Hi,

All interesting stuff.

Yes I do own a Audio Synthesis passive pre. Mine has a nice romote control. I have been messing around with passives. I had been using a NVA passive to good effect. I tweaked this with Dact attenuator to very good effect. A good passive will improve detail & resolution. It's like a veil is taken off the sound. Subtle changes in the music come out more to the fore. The downside is that they don't offer any drive capabilities. You are at the mercy of the load of the power amp & cable. Also the drive qualities of the source can be important.

I have a Border Patrol which has a high input impedance & is quite senitive. (doesn't need much signal to get full power.) If your cables are of low capacitance & quite short (less than a meter) then it could be a winner.

There are a few different types of passive. The cheaper ones will use a normal potentionmeter. These can & do vary in quality & price. Pots like Noble, Alps & Panasonic can be used. The better ones can go for a stepped attenuator system. These are made up of discret resistors mounted on a many way switch. The ultimate quality depends on the resistor quality. These resistors can be costly & of high tolerance. makes like Holco, Vishay & Roherstein can be used. The switches need to be of a high order, also the wiring & soldering will make an effect.

Stepped attuenators come in 3 types. A ladder type, a Shunt type & a L pad type. Each ahs their own strengths & weaknesses. Look here for more details.

The pre I use is here.

I must admit, I have been hearing good things about passives with transformers. The Bent audio looks like it is a winner. I may look into this a bit more.

SCIDB