Modifying time delay when starting a track

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This page originates from two Reciva Forum threads, copied here to help with completeness of information.

Description of problem

In an IR100, when a stream or track starts, the radio is initially muted. The amplifier takes 2-3 seconds to kick in before the track plays plays, so the first few seconds of a track is always missing. In addition, the headphone output will "thump" when a track starts or ends - this doesn't do much for comfort on headphones or one's faith in not damaging expensive HiFi speakers !

Both are very annoying, particularly if listening to streamed media tracks where the first few seconds are invariably missed.

Software fix may exist !!! (Jan 19 2008) See the Config.txt File page, and the option "dynamic-mute" which suggests problem can be (partially?) fixed with a configuration change.

Hardware wiring modification

(Edited text from two Reciva Forum postings by Reciva Forum user "GSUM")

I cured this, if anyone's interested, though requires soldering.... (and the story's a bit long....)

The radio can be thought of as three sections: 1) the computer 2) the power supply (transformer, rectification, filtering, regulation) 3) the analogue audio circuitry

The computer section has only one 'status' signal that it sends back to the rest of the radio, a 'mute' signal. When the computer says 'mute', this logic signal switches off the power supply to the audio section (12V unregulated). The 5V and 3.3V regulated supplies to the computer part remain on at all times.

The power/audio section has no way of knowing if the computer is muting because you've put it into standby, or because there is no audio at the moment because you've switched stations/tracks and it's connecting or buffering. As a consequence of this, if you change stations or reach the end of the track and it has to buffer something new, it mutes and turns off the power to the audio section. When it starts playing again, it un-mutes but the power supply takes a few seconds to come up and stabilise again, and you miss some sounds.

I don't really use my radio for streaming MP3s, but I do listen to it through headphones and the loud thump every time it powered up the audio section when I changed stations was annoying to say the least.

So I tweaked the radio to leave the audio part powered up all the time, just like the rest of the radio. The audio part actually uses much less power than the rest of the radio. Bill888 measured 7 watts in standby and 9 watts playing music at moderate volumes. The audio section comprises a dual op-amp (buffer), a quad op-amp (filter/eq), another dual op-amp (headphone) and a small IC power amp (speaker). The op-amps consume tiny amounts of power and the speaker driver will be probably be operating mostly in class B which means it only consumes much power when it is actually moving the speaker cone (i.e. there is music playing).

I would say that this change probably only adds an extra watt to the consumption. I've certainly not noticed the unit get any warmer in the few months since. The extra that Bill888 measured was probably because he was actulay playing at moderate volume.

The cable from the power board to the front computer board (not the one that goes under it to the volume control) is the one you want.

See 2nd and 3rd photos here: You can see the top wire (the red one) says 'MUTE' on it. If you unplug this, you can see that individual pins on the cable are held in by plastic lugs. These can be gently prised and the pins can be slid out. You need to slide out the red MUTE one. Fold it back along the cable and tape it there so it is insulated from everything else. That's only half the game, as now the radio will be permanently muted! The input end of this signal on the power board needs to be pulled down to 0V to unmute and power up the audio circuits. You do this by soldering a small wire from the mute pin or track that the red wire connects to, to a nearby ground (0V) point. You can use a component pad on the track that comes from the centre pin of the nearby regulator. If you can't figure out a ground point you probably shouldn't be soldering in here anyway (friendly advice!).

The red wire in the ribbon is detached and insulated (the mute control line from the control board).

Mute board ir100-1.jpg

Mute board ir100-2.jpg

The other end of the (now free) red wire currently goes to the solder pad on the bottom right of the board. I attached a new wire to this board trace (a little further up) and connected the other end of it to this circuit's ground (0V) point. I hope this is clear. You should thus have continuity from the loose wire on the ribbon to the fat ground trace on the board.

When you reassemble the radio, it's always worth making sure the cable that goes from the audio board to underneath the computer board (to/from the volume control) bends in such a way that it is in front of the speaker, or it will pick up some clicking sounds from the computer/wi-fi parts (it is a high-impedance point).

As well as curing the annoying thumps that spoiled my headphone listening, it now streams from my PC without missing a beat. If the slightly higher power consumption bothers you, you can always turn it off at the mains when you're not using it. I don't bother.

I also previously moved the mains transformer - I don't need to tell you that if you haven't cured the hum, then it will be permanent if you leave the audio circuits powered up!

Remember, this is only for people who know what to do with a soldering iron and have at least a basic knowledge of electronics.