Project x part XII - simplification

This series of articles dates back to 2015 with the last entry from May of 2018 where we change the amplifier to better quality one.
Unfortunately when I went to put it one a couple of weeks ago the red power indicator came on for a second followed by a deep thud. Subsequent tests show it blew a few fuse and a number of transistors in the power amp.
This was a good time as any to try and simplify matters by adding one of the popular mini hifi components that have been around for the last fifteen or so years that typically comprise of a amplifier with built in cd player and tuner unit.
Denon are a very well respected maker of hifi components whose systems like that are frequent hifi award winners in that category.

The UD-M31 is a typical example of the breed being small , remote control driven with a RDS radio built in that does looks really smart.
There is a small 3.5mm headphone socket on the front that automatically switches out the loud speakers which were optional with model and not supplied .

 Looking at the rear panel you have antenna sockets for AM and FM radio and unlike the latest units two sets of line sockets that comprise of inputs AND outputs which means you can plug in recorders such as a cassette deck or MiniDisc easily and for MiniDisc there is an optical output for recording from cd which was the main digital input connector for them used for recording.
There are the pair of spring clip loud speaker connects right, then left for this units 22 watts per channel RMS which is the same as the previous one and notably higher than the original which will work well with the Wharfdale Delta 30's

 The cassette deck wired in with all its fancy tape tuning and display adjustment has a mechanically operated draw and the ability to insert four second pauses between recordings that helps when using tape searching systems like APSS.
It has a dedicated headphone output with its own volume control for monitoring.

Project X, Part V, playing tapes

Project X is alive and well playing music in Lossy and Lossless forms from my Fiio music players line output from one of Eight micro sd cards as well as from a elderly Toshiba cd player.
I like quite a few people have a good number of cassettes not least pre-recorded ones I bought from the mid 1970's to mid 1990's I moved from cassette based portable listening to MiniDisc and had been thinking of how to play them back on this mini system.

Enter a unused Sony TX 313 mini sized fully functional cassette deck from a MiniDisc system I got from someone who never ever used it so it was still boxed and shrinkwrapped from the late 1990's.
Oddly enough it uses a car type side slot way of loading the tapes into it but unlike car units this does record and has auto tape type sensing to read the extra tabs for type II ('Chrome') and IV (Metal) tapes although the latter are no longer available new plus I seriously doubt it's tape heads really are up to making full advantage of such tapes electrically

The rear has RCA line in and outs, with the out going via a expensive Cambridge Pacific interconnect to the input selector with a maximum of 0.5 volts out depending on the program loudness and the AV bus for Sony mini systems it was sold with for synchronized cd to tape copying.
The unit is blessed with switchable Dolby B noise reduction for proper replay and recording of such tapes plus auto reverse so it can play one  side of the tape and switch by itself to the other. 
According to the specifications it reproduces up to 14khz for type I tapes and 15khz for types II and IV which is decent if not as wide as most full sized hifi cassette decks so the high frequencies will be clear but not quite as extended as the best units can achieve.
It is making an excellent job of replaying my 1980's EMI UK dolbyized Beatles pre-recorded cassettes which were amongst the best sounded tapes manufactured and part of reason I held out so long against the cd as portable listening was and remains a big part of my life and why my Fiio is my 'to go' digital playing device on headphones or connected to this system.
I like high quality portable formats more

Project X Part IV, Rationing the sound

Just been enjoying some Nielsen here on what has been a dry sunny but cool  day.
The amplifier is working rather well but one issue is the output from things like a cd player or my digital audio players line out is a lot higher than its input stage can handle so I have to turn the volume way way back and it sounds a bit strained on very loud passages.

It's a common problem cause by the strange decision in the early 1980's to standardize the output from digital to analogue converters typical found in cd players to around 2 volts where in the past it was rare for any device to have an output over 0.75 volts r.m.s. and often around  .250 to 0.5 volt which devices were and still are designed to 'see' into.
In simple terms, it means it's likely the very first stages of an amplifier are likely receive so much signal from such a source that they distort before the volume control can ration it, sounding harsh.
I've ordered up a pair of high quality 10db inline attenuators by Rothwell to put between the signal lead and the switching box which should cure that and allow it to use more of the volume controls rotation. 
They use 'audiophile' grade metal oxide resistors in a padded network in a plug enclosure to achieve that without compromising the transparency of the sound while being neat. 
Postscript: They arrived the next day from Bacup, Lancashire, England and it cured it leaving to sound very impressive playing a 96/24bit HD version of Rush's a Farewell To Kings on Closer To The Heart and the Christian Ferras recording of Sibelius's Violin Concerto (with BPO/H v Karajan on DG) via a Fiio X1 digital audio player's line  output.

Project X

I've been interested in how things work for quite sometime which in the old days was fairly straight forward in that often you could see just by looking at all the key bits and that often was connected with audio equipment as getting good sound has always mattered to me.
Sometimes I'd buy either a full kit to assemble or boards with all the main components mounted on to just wire up and a few bits to make say a radio unit or an amplifier for not much money.
Sometimes it was worth it just for the learning experience alone.
As a good number of you know in recent years because of my acquired difficulties with my hands, that whole avenue has been denied me simply cos I can't solder and screw things together anymore. That really hacks me off big time.
I've bought something more or less ready done to experiment a bit with though and it is this.
It's a SA 36A Pro 'amplifier' ready assembled from board similar to what can be bought part done with a power unit.
The first and in many ways intriguing aspect to it is it uses a special low power integrated circuit to produce approximately 25 watts per channel made by TI Instruments, the TPA3118D2DAP, which is a Class D high efficiency one that a number of people are raving about for its sound..
I won't bore the pants off of you by explain all about Class D as there's a good entry on Wikipedia explaining all but it's why such a small cheap board can equal the output of a more conventional amplifier of a similar power using less electricity and getting less hot.

The front panel shows just how small it is and  also why  I put parenthesise around the word amplifier as while it has a volume control, it does lack an input selector which at a later stage of this project I intend to tackle.

This is the actual board as fitted with the integrated circuit the small black object in the centre and you'll also see how careful design has removed the need for trailing wiring from back to front.

This is the back panel of the SA 36, original version which only accepted 12 volts dc input, the 36A Pro accepts up to 24 volts for higher output via black switched mode (transformerless) power unit that is supplied.

There are binding posts to connect 4 to 8 ohm loud speakers to, left and right line input and that 2.5mm inner, 5.5 outer socket for the power unit.

The supplied power unit is 12 volts but only 2 amp maximum which I feel is a bit restricting so I've ordered a 60 watt max, 5 amp one to use with it as if the amplifier draw more than the supplied power unit can give it's protection circuits are more likely to need to kick in and some have found the quality of these units is compromised  by the rather basic supplied units, that are not the manufacturers own. 

That unit also has a fused UK mains lead where as the supplied unit is a unfused continental 2 pin one with a basic unfused adapter which I wasn't happy about on safety grounds as serious conditions could develop before your mains circuit tripped, knocking off the power.

I'm interested in two things, the first being just how good is this chip? and secondly as advocate of getting good sound into peoples lives, can budget hifi equipment by non mainstream manufactures provide a way in for people who end up with so-so all in one music systems to enjoy more of their music.