Conference hips::uk_audioo

293.0. "Amplifier kit review" by WOTVAX::MEAKINS (Clive Meakins) Tue Jul 16 1991 23:40

    I may try to have this published in the Hi-Fi press, any comments?
    
    Build yourself an "Audio Design Amplifier"
    ------------------------------------------
    
    Have you ever considered building some of your hi-fi system?  It's 
    not difficult, even if you have little or no electronics experience 
    you could build two or three simpler projects first to gain 
    experience and confidence.  A reasonably practical aptitude is 
    required,but not unduly so.
    
    I wanted to build a good quality amplifier to replace my faithful 
    Musical Fidelity A1.  Part of my reasoning for building was that to 
    better the A1 I was talking about really serious money for a 
    significant improvement, a kit should reduce the cost somewhat.  The 
    satisfaction of building an amplifier and being able to include 
    features that appeal was also a major consideration.
     
    I'm a competent electronics constructor though my theoretical 
    knowledge leaves quite a bit to be desired, so good instructions 
    were required.  A design that allowed a stereo amplifier to be built 
    to start with and could be expanded to a fully active system would 
    be very attractive.
    
    Good design principles were considered more important than exotic 
    components, these can always be added later.  You can't change the 
    basic design easily.  The finished product would need to be well 
    finished and attractive, my wife isn't too keen on home made looking 
    boxes in the house, can't think why.
    
    As shops don't stock built-up kits the real problem was, how do I 
    judge whether I would like the sound produced by the finished 
    product? 
    
    Design Philosophy and Features
    ------------------------------
    
    Having looked through various catalogues, the only contender was a 
    kit produced by Hart Electronics of a John Linsley Hood design.  The 
    designer is a well known, respected audio designer and the kit 
    producers have been around a long time.  Some years ago I built a 
    Hart kit / Linsley Hood designed budget priced cassette deck and was 
    very pleased with the results.  As the audio industry now produces 
    plenty of reasonable budget audio, Hart decided to move up market.  
    
    The Hart / Linsley Hood "Audio Design" amplifier is a power 
    amplifier kit that comes in various configurations.  It can be 
    purchased as a line level amplifier with input selector, volume and 
    balance controls or as straight power amplifiers in stereo or 
    monoblock versions.
    
    The initial design was first published in 1984 with few refinements 
    being deemed necessary since.  Considerable time was spent producing 
    a professional kit, with the designers full co-operation.  The 
    stereo amplifier is rated at 80 watts per channel, the monoblock 
    version rising to around 120 watts per channel, MOSFETS are the 
    output devices used.  The amplifier design is direct coupled and 
    comprises fully discrete circuitry, no ICs are used at all.  The 
    power supplies are stabilised featuring short circuit and DC 
    sensing, power being shutdown if DC is present on the speaker 
    outputs.  
    
    Output device failure is particularly perilous to loudspeaker drive 
    units when using direct coupled amplifiers as the output stage 
    midpoint is directly connected to the speakers.  Alternatives to 
    protection being built into the power supply would entail using 
    relays or fuses, a messy solution where currents of several amps are 
    flowing.
    
    The designer chose to use a stabilised power supply as safety 
    features could be incorporated with the additional benefit of solid 
    bass being a characterisic of using this type of power supply.
    
    Earthing systems play a very important part in sound quality, the 
    kit has had good deal of work done in this area.  The earths are 
    taken to a common point.  If you build the circuit boards into your 
    own cases it will be necessary to pay particular attention to the 
    routing of earth cables and even types of cables, more on this 
    later.
    
    The components used have been specially selected for their purpose.  
    Highly expensive and esoteric components have been avoided, the 
    strategy being one of sensibly priced, good quality and viable size 
    components being used where required.  Other components may give 
    even greater sound quality, but that the bulk of the quality gains 
    have already been achieved with the existing components.  The 
    resistors are generally 0.3 watt metal film types at 1% tolerance.  
    The capacitors tend to be a mixure of polycarbonate and polystyrene 
    with bypass capacitors being used where it's advantageous.
    
    Speaking to Hart I was advised of a customer who might be willing 
    for me to audition a pair of monoblocks.  The system I was to 
    audition fortunately comprised a Meridian 207 CD for a front end, 
    this is little different to my own Meridian 206 and I was able to 
    take along my own speakers.  So the audition was pretty meaningful, 
    we listened for a couple of hours and I very much liked what I 
    heard.  Normally before purchasing a new component for my system I 
    would want to spend more time auditioning, but I was impressed 
    enough to take the risk and purchase a pair of monoblock kits.
    
    First Impressions
    -----------------
    
    I was able to visit Hart Electronics at Oswestry to pick up the 
    kits.  On getting the kits home I found the components are logically 
    separated into easily identifiable plastic bags.  The toroidial 
    transformer is really quite hefty, a good sign.  The sheer number of 
    components was a little intimidating, but that's what you get for 
    jumping in at the deep end with two monoblocks.
    
    The instructions are very thorough, some constructional experience 
    is useful, though the instructions are full enough to allow 
    construction by those with limited experience.  I certainly wouldn't 
    recommend that this be a first project for anyone.  Building a 
    couple of kits from say, Maplin (you'll find their catalogue at your 
    local WH Smith), will help you decide if you could manage one of 
    these amplifier kits.
    
    The Build
    ---------
    Taken a piece at a time it didn't turn out to be too daunting a task 
    to build the monoblocks.  I chose to build them side by side, 
    assembling a batch of components for one channel and then doing the 
    same again for the other.  I tended to work for around two hours at 
    a time, mainly after work with rather more effort going in at the 
    weekends.  In all it took me about two weeks to complete the build.
    
    I found that a combination of electronic components getting smaller 
    over the years and my eyes being tired and the end of the day wasn't 
    a good combination.  The number of coloured bands used on resistors 
    was inconsistent so, in line with the instructions I relied more on 
    measuring the resistors with a multimeter.  The only other 
    problematic components were the diodes, these have extremely small 
    identifications on them, I even ended up using a microscope to 
    double check identification.  I suggest using daylight for the 
    identification of trickier diodes.
    
    The power supplies seem to take an age to build, the amplifier 
    boards being very quick to build up in comparison.  A nice touch are 
    the plastic mounts for most of the semiconductors, they protect the 
    delicate glass cased diodes and make for neat mounting of the 
    components.
    
    Assembling the case is an easy matter, there is absolutely no 
    drilling or other finishing to do.  The appearance of the finished 
    product is really very good, it even passes scrutiny from my wife, 
    no mean feat for commercially built equipment, let alone home built 
    hi-fi!  The cases are finished in traditional black, the monoblock 
    version simply having a power switch, green LED for power indication 
    and a "psu tripped" red LED indicator.  The white lettering is of 
    good quality and looks rather stylish.  The casework may not be up 
    to the the quality of the best, but it's certainly considerably 
    better than some very expensive pieces of equipment.
    
    As I'd built the monoblock version some form of pre-amp was 
    required.  To get me started I quickly built an ALPS pot into a 
    simple box, the intention being to assess what is needed once the 
    monoblocks were up and running.
    
    Testing
    -------
    
    The set-up procedures are fairly simple and only require a 
    multimeter.  Hart Electronics offered their services in testing the 
    monoblocks, this was an attractive offer as even though there are 
    various protections built into the design, powering up the supplies 
    gradually from a variac was rather less stressful than simply 
    switching on and praying.
    
    The components I worried the most about were the diodes, it would be 
    easy to get one the wrong way around, the reversed polarity could 
    have unfortunate results for many of the semiconductors.  Powering 
    up gradually means that polarities and voltages can be checked 
    before any serious damage could be done in the event of a reversed 
    polarity.  Electrolytic capacitors can make quite a mess if inserted 
    the wrong way around, so not having the clear up a terrible mess is 
    another benefit of testing this way.  As it happened there were no 
    component errors, so this careful testing mainly served to keep my 
    blood pressure down.
    
    To get the amplifiers ready to run the power supply low and high 
    current supplies need to be set along with the standing current and 
    DC offset for the amplifers.  These are all simple adjustments that 
    are performed with a multimeter.  The standing current can be set 
    higher in the monoblock versions as the power supply has only one 
    channel to load it and the heatsink is the same as for both channel 
    of a stereo amplifier.  Mine are set to a conservative 300mV, this 
    being double the recommended for the stereo version.
    
    All set up and ready to go, I first of all used an old pair of car 
    speakers, just to check everything was alright, not wanting to 
    destroy my main speakers.  Everything turned out to be working, so I 
    switched over to my main speakers.  The protection built into the 
    power supplies was soon tested.  It became apparent that deep bass 
    played loudly trips the DC sensing facility within the power supply.  
    Indeed, Chris Rea's Road to Hell is a very effective track to do 
    this with.  When tripped, the amplifer needs to switched off for 
    around two minutes, presumably to allow a capacitor to discharge.  
    The standard component values that control the shutdown in this 
    situation are very conservative for the monoblock version.  
    Alternative values can be advised on request from Hart.  I have 
    stuck to the standard values as I've only tripped the power supplies 
    when trying to demonstrate how loud the amplifiers will go, in 
    normal listening there is no drawback.  Those using inefficient 
    speakers or high power handling ones for parties might need to go 
    for less protection for added power.  I'm happy with the standard 
    values saving me from my own stupidity.  I can't comment on the 
    short circuit protection as I've not tested it, hopefully I never 
    will.
    
    Sound
    -----
    
    Assessing the sound using my Meridian 206 CD and Musical Fidelity 
    Reference 2 speakers, my initial impression was that it lacked a 
    little bass and was a touch hard.  This was no great surprise, it is 
    normal to have to "burn in" electronic components.  Some commercial 
    equipment is left switched on for a considerable period after 
    testing to help in this area.  It took me some time to get the sound 
    as I wanted, but that had more to do with the room acoustics.  
    Replacing the wire from the power amplifier circuit boards to the 
    output sockets surprisingly produced a very significant and 
    rewarding change to the quality of bass, it became deeper and 
    tighter.
    
    Changing the main earth wire from the amplifier board to the the 
    central earthing point to be a length of speaker cable also had a 
    surprising effect.  The sound became totally undynamic, I had to 
    restore the original wire.  More tests should be carried out as I'm 
    uncertain whether the problem was due to the cable type, or 
    soldering rigid speaker cable onto the push on connectors that form 
    the terminations for most of the internal wiring.  It could be that 
    my soldering of the rigid speaker cable wasn't up to scratch for 
    carrying high current loads.
    
    Moving back to the sound characteristics of the monoblocks when 
    run-in, the best way I can describe the sound is that they are 
    transparent, open and capable of good soudstaging.  They produce 
    solid and tuneful bass.  If I change any other component in the 
    system it is very easy to hear the effect of that change.  When 
    changing cables used with my old A1, I frequently couldn't detect 
    much of a difference between cables.  The qualities of differing 
    cables is now easily discernible in the system.  Upgrading my 
    speakers to EPOS ES11s has let the music shine through even more.  
    It seems obvious, but the monoblocks simply to amplify the signal.  
    They just don't add any character of their own, if the recording is 
    bright the reproduction is bright, if it's dull it comes across as 
    recorded.  I've heard amplifiers that impart a character, this may 
    be useful when trying to cover deficiencies elsewhere, but is hardly 
    ideal.
    
    The speaker binding posts on the amplifiers proved rather useful 
    when bi-wiring the ES11s.  I use Naim NAC5 cable which is pretty 
    inflexible stuff and nigh on impossible to double up into the 4mm 
    Arcam plugs I was using.  It turns out that the binding posts will 
    take a second pair of plugs verically through the post as well as 
    the usual way, horizontally into the post.  These posts are 
    available gold plated as an option, an option I chose.
    
    The amplifiers are generally quiet but with some mains frequency 
    hum.  This hum is at a very low level for a single channel, though 
    switching on the second monoblock does rather more than double the 
    hum level.  Stacking one monoblock on top of the other may not be a 
    good idea and this is probably the cause of the increased hum.  Even 
    so, the level is not intrusive, though I may try a sheet of aluminum 
    between the monoblocks sometime.
     
    Turning my attention to the passive preamp I found changing the ALPS 
    pot I was using to be very rewarding.  I used a metal film Sfernice 
    pot available from Russ Andrews Turntable Accessories, this gives 
    greater clarity and yet more tuneful bass.  The ALPS does have 
    excellent channel balance on it's side though.  It would be very 
    interesting to try a switched attenuator , such as the kit produced 
    by Audio Synthesis.
     
    For those who require RIAA input, Hart do produce a kit that resides 
    in a separate box, there are also quite a few other circuits 
    available.  The quality of your turntable should determine the 
    quality of your RIAA requirements, an LP12/Ekos/Troika would justify 
    something rather special.
    
    The design doesn't need tweaking, but if you have any ideas or 
    preferences it is a simple matter to incorporate them.  The obvious 
    one, though hardly a tweak, is for completeness using the same 
    interconnects and speaker cable internally as used externally.  If 
    you feel the need to experiment with different capacitors and Holco 
    resistors, the opportunity is there.  Having built the amplifiers 
    yourself, it's really up to you.  
    
    I've been aware that it's natural to think that the sound is great 
    as you've built the amplifier yourself, this is an easy trap for 
    home constructors to fall into.  These are well designed kits and 
    they do sound good too.  Also I find it rewarding to be listening to 
    something that really is so good that I've built myself. 
    
    

.0�    I may try to have this published in the Hi-Fi press, any comments?
    
    Clive, were you seeking comments on the content of this, or the writing
    itself? I personally think the content is fine, but would suggest that
    the grammar/syntax be reworked before submitting this for publication.
    
    Keith

    Keith,
    
    Thanks for your suggestion.  I'm looking for comments on content, style
    of writing etc and any difficult parts that are difficult to
    understand.
    
    I'd also be happy to enter into general exchanges on the amplifiers
    themselves, if anyone's interested.

    
    I thought it was interesting, but I agree with Keith about the style. I
    know there's at least one tech. author who reads this conference
    (Jack), so perhaps he could comment on it !

    Are the comments about style down to presenting the information in a
    more "chatty" style that might be more suitable for the Hi-Fi press?

>    I thought it was interesting, but I agree with Keith about the style. I
>    know there's at least one tech. author who reads this conference
>    (Jack), so perhaps he could comment on it !

	thanks trevor....ok, but it'll probably be the weekend before
	i get to it

	jack 

     Hi Clive,
     
     Sounds like you're more than a little happy with your decision.  

     I found your note detailed without being baffling.  I too play with 
     electrical equipment, but do not know the difference between resistance 
     and impedence.  I guess that's about average for a money conscious 
     audiophile.

     Stick with the concise style, chatty can sometimes appear patronising.
     
     Perhaps inclusion of a few sales and fault statistics from the supplier 
     might liven it up a bit.  I did enjoy reading the bit about potential 
     faults!
     
     
     BTW  I'm still really happy with the A1 Amp, I finally decided on 
     Linn Index 2's to complete my system.  I'm glad you managed to avoid 
     putting my money towards something too immoral!
     
     Cheers,
     Robert.


     p.s. did things suddenly get very literary in here?

    Re .0, I am DIY'er and I belive I can do reasable good solder jobs and
           have sufficent knowledge in audio. Does the Hart kit which you
           mention in the base note offer oversea mail order ? What is the
           spec, cost and which dealer should I write to as I may be
           interested to build the amp kit.
    
           How does it compare to Cyrus II as I own one ?
           Pleas post the full address here as I am a remote noter from
           Singapore, a small country from the Far East.
    
    Thanks
    Parry ( Singapore)
          

    Parry,
    
    I don't have the address with me, I'll enter it on Monday.  Hart will
    do overseas mail order, though I'm not sure what impact the heavy
    transformer would have on cost.  Maybe it's possible to get one
    locally.
    
>How does it compare to Cyrus II as I own one ?
    
    Not having heard the Cyrus II it's hard to say.  I'm hoping to do some
    comparisons by putting the amp into friends systems.  I'll be doing
    this when I get back from holiday (mid August) and after I've changed
    the negative feedback capacitor for a better type.  There maybe one area
    where the amp isn't up to the standard set by some very good amps.  My
    system doesn't reproduce quiet notes clearly when louder ones are being
    played.  Don't let me mislead you, it's quite good in this area, though
    I have heard some better.  
    
    I'm wondering whether a change of the all important NFB capacitor
    mentioned earlier might make a difference in this area.  
    
    As for comparisons, I can only say for sure that it's a significant
    improvement over the Musical Fidelity A1.  Let me assure you (and Rob
    who bought it!), that this is high resommendation indeed.  The A1
    suited me well and it takes a seriously good amp to improve on it
    (unless shear power is required). 

Mmmmm... I used to own a Cyrus II/PSX, and have listened to an A1. To 
characterise the sound against an A1 does depend on the type of front-end 
you've got but I found the A1 more musical than the Cyrus, but less detailed 
(especially when I'd added the PSX). The A1 had a lovely warm sound, while 
the II was perhaps smoother. Neither provided the explicit detiling of notes
which you can get with good pre/powers, nor a really good phono stage - I felt
that the Cyrus had a better one than the A1 (again the PSX helped).

     >       What is the spec, cost and which dealer should I write to 
     >       as I may be interested to build the amp kit.
    
    The address is:    Hart Electronic Kits Ltd
                       Penylan Mill
                       Oswestry
                       Shropshire
                       SY10 9AF
                       England
    
    The price for the two monoblocks was around 500 pounds (included 15%
    tax).  I also managed a 10% discount, but that's another story.  Can't
    remember what a stereo amp would cost, probably around 320.
    
    All I can say on specs are, 80W per channel for the stereo amp, 117W
    for the monoblock.  Input impedance 150K and 175 mV sensitivity, it's
    designed to be used without active preamp circuitry.
    
    The performance of the monoblocks (that's all I've heard) is very good
    in relation to their cost.

    The good news is that Hi-Fi News and Record Review are to publish my
    review posted at the begining of this note.  There are some changes,
    mainly additions covering comparisons with other amps.  Should be in
    the Feb edition.

>    The good news is that Hi-Fi News and Record Review are to publish my
>    review posted at the begining of this note.  There are some changes,
>    mainly additions covering comparisons with other amps.  Should be in
>    the Feb edition.
    
    Don't suppose anyone's rushing out to buy the article, but it now
    scheduled for the March edition, on the streets around 10th Feb.

    Congratulations !
    
    read your article in the April edition of HiFi News, and thought it
    excellent. I really feel that all the magazines could benefit from more
    articles aimed at DIY. Whilst in Foreign countries I often pick up HiFi
    magazines and normally find far more emphasis on kit building or even
    building from scratch.
    
    I thought your article very objective , which is extremely hard when
    it's something you just made yourself. 
    
    Do you plan any more ?

>    I thought your article very objective , which is extremely hard when
>    it's something you just made yourself. 
    
    Thank you for the congrats.  I was very aware that it's very easy to
    think the amp you've just built is a world beater, so I tried to remain
    objective and make plenty of comparrisons.  It would have been too easy 
    to listen in isolation and pretend it's the best ever.
    
    BTW The editor cut the article down from 3800 words to around 2000 and
    I should have charged for the photos.  I know for next time. 
    
>    Do you plan any more ?
    
    I'm waiting to find out how this article goes down.  I could write a
    follow up on tweaking the amps as I have now done quite a lot to them
    as well as my CD player.  A major lesson here was that it seems the
    cheaper the tweak, the more effective it tends to be.  By this I mean
    the spending big bucks on expensive components isn't necessarily cost
    effective.

    Hi,
    
    It anyone out there has compare the kit to QUAD power amp 606 or your
    opinions about the QUAD 606 ? Does QUAD 606 match well with passive
    preamp ?
    
    Thanks
    Parry

>    It anyone out there has compare the kit to QUAD power amp 606 or your
>    opinions about the QUAD 606 ? 
    
    Can't compare the kit, but think of the kit a have a Naim-like sound,
    but not quite so analytical.  Naim fans - don't take that as a
    criticism, it's not.  The Naim designs are actually based on some
    original Lindley Hood work.
    
>   Does QUAD 606 match well with passive preamp ?
    
    As long as the Quad 606 has a reasonably sensitive input you should be
    ok.  Passives need very careful cable selection, cables that make a
    small differnce on active preamps can make a massive difference on
    passive.
    
    Could you take your preamp and speakers to the Quad shop?