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Got Fleas?

Mus said:
Strange that Martin's picture is missing two SMDs as well though.

Ah, that would be because when Martin got his kits the 33R and 100R SMDs hadn't arrived ;)

Has anyone built their flea yet? I'm really anxious to make sure the kits and everything are ok!

Cheers,
Carl
 
Dont be anxious Carl!

Mines built except C1 because as mentioned earlier in the thread i didnt prepare and have a suitable xfr, I could run off the Arcams existing power but would rather do the job right first time, this means either a bigger cap and the nice little encapsulated xfr i have here or a trip to Maplin and some luck if they have the right xfr tomorrow (fat chance!)
 
I found a 22uf 100V Panasonic NHG, will that be ok for C1 to cope with my higher input power (30ish V)

I have soldered it in anyway, can someone cast their (less tired) eyes over my board to see if i havent done something stupid (which wouldn't suprise me in the slightest)

flea1.jpg


Thanks
 
Ok the flea is alive!
(well the LED comes on ;))

I measure just under 14V on pin 7 of opamp and about 1.95 on pins two and three. Six and eight about 5V

Thats seems about correct to me (?!) going by Andy W's old schematic.

I see a wave on the scope but my scope isnt quite fast enough, just looks like a very sharp sine wave / triangle.

Im powering from a 30V wall wart, enough for tonight but am i ok to try this in the player in the morn?

Goodnight :)
 
Cheers Martin (and all who participated), very nice work. I just had a quick look at the manual, wow, more than just professional, it's really impressing!!!

BTW, a quick question. Have you tried using a darlington instead of the BC547C?

Looking forward to try it, Teddy
 
A question on power supply:

The best solution is to provide an independent PSU just for the Flea. Although this
may sound extravagant, a suitable transformer (0-15 or 0-18v, 3VA) will be both very
compact and cheap. Follow it with a simple rectifier and reservoir cap (1000uF is
plenty), and fed the raw DC into the Flea . The clock circuit is then galvanically
isolated from the player, and the output wiring is only carrying the clock signal.
When
the Flea is powered by an existing onboard supply via a single +ve lead, then all the
noise currents from the raw supply bypassed by caps C1, C2, C4 are returned to the
raw supply circuit via the shared 0v wire – which is also carrying the clock signal
return. Providing an independent supply prevents this intermodulation happening, and
the audible benefits are not subtle.



If I use an external supply, I connect the "power in" +18V and 0V leads direct to the Flea.....but do I connect the Flea Output 0V to the CD player, or just the clock output? The manual is confusing me slightly as it mentions the galvanic isolation benefit of the external supply and implies no 0V connection to the CD player by saying that the output wiring is only carrying the clock signal.

Sorry to be slow on the uptake....!
 
Jo,

when using a stand alone/external PSU for the flea you will need to connect the 0v to the CDP ground at some point.

Graham
 
Jo Sharp said:
do I connect the Flea Output 0V to the CD player, or just the clock output? The manual is confusing me slightly as it mentions the galvanic isolation benefit of the external supply and implies no 0V connection to the CD player by saying that the output wiring is only carrying the clock signal.

You need to connect +/- from your dedicated psu and clock 0v at one point on the cdp ground plane, near to the DAC. Even if you're using two feeds from the clock (one for DAC, one for decoder) you still only need one connection to the ground plane. See acoustica for more details.

Cheers,
Carl
 
Ok i checked the voltage from the output of the 7812 to pin 7. I get just over 5mV , I guess its the effect of my cheapo meter?

My bigger query is i seem to have a perfect sine wave on pin 8 of the op amp, at very high frequency, pin 6 is perfect, is this correct and is it the capacitor doing its job ?
 
Graham, Carl,

Thanks for the clarification...I thought this would be the answer as I was pretty sure that the Flea would have to have a 0V connection somewhere, but wanted to be certain before starting construction.

Jo
 
Sorry Jo - I should have made that clear. I've added the following diagrams to the manual to clarify matters:

Common supply connections:
com.jpg


Independant supply connections:
sep.jpg
 
Trancera;

Ok i checked the voltage from the output of the 7812 to pin 7. I get just over 5mV , I guess it's the effect of my cheapo meter?
No, that's perfect - 10mA drawn by the AD797 driving the Tent XO is quite normal, these devices seem to have a spread of runing current, I've seen 8-20mA as 'normal' here. You have one well-behaved Flea!

My bigger query is i seem to have a perfect sine wave on pin 8 of the op amp, at very high frequency, pin 6 is perfect, is this correct and is it the capacitor doing its job ?
Yes and yes.

Pin 8 is a moderate-impedance input, and the 47pF cap is providing feedback into it from the output. What you are seeing is the spurious clock output on the 5v line being fed through by the 47pF cap. I suspect you're seeing a sine because you're o'scope has a limited bandwidth- a 20Mhz scope will only see the fundamental and maybe first harmonic (eg 22.5Mhz in your case).

All oscilators are *noisy*, and because of the sheer speed of the switching no regulator can keep up with the 11Mhz (and higher odd harmonics!) that consitute this noise - it's ameliorated only by the SMD cap inside the Tent module and our 0.1 and 10uF output caps. The result is quite a lot of switching noise appearing on the 5v rail. It's why L1 is fitted next to the clock, to help contain it, and there's nothing to worry about - the low power consumption you're seeing says all is well.
 
Martin, sorry to bug you again (ouch!) but im unsure where to feed the clock into, its the extra circuitry in the Arcam 5 Plus thats confusing me, I think the plus version does some sort of re clocking?

Arcam5Clock.jpg


Will the extra circuitry actually mean I wont benefit so much from the flea, if so I have standard board I can put in.

Arcams are popular here so hopefully someone else might benefit from this clarification.

Thanks.
 
No, that could be very good, because it doesn't rely on the SAA7220 to supply the clock to the TDA1541 (of which more some other time).

Can you confirm that the 'XIN' input disappearing off the bottom of the schematic is to the SAA7220?

If so, what I'd do is lift R221 and R209 and feed in the two clock outputs from the Flea here (or direct to the pins those traces lead to). That way, the Flea clocks the digital filter and also directly reclocks the I2S signals through the flipflops (top left). The result could be *very* interesting - it's the ideal way to do it.
 
I have updated the above image for a little more clarity but it is as you asked Martin.

The only trouble is I have it Non OS'd but I can as you say still connect at those points. My standard board isnt Non OS.

I have OFTEN wondered if a well produced SAA7220 would sound very good an that the only reason non os appear to be better is because they are less complex.

Anyway I'll try and get it installed now ...
 
OS / Non-os makes no diffference to the clocking - only the data on the I2S lines.

The problem with the SAA7220 is simply that it only has one connection each for +5v and 0v, a long way apart - so there's lots of crosstalk between the digital filter, and clock sections internally. In otherwords it's noisy, and prone to data-correlated jitter, and taking responsibility for the bitclock clock away from it is the Right Thing To Do.

Let us know what you hear when it's running...
 
Martin, where best to put 0V output to, closest Dac, filter or anywhere where short wire can be used?

martin clark said:
Let us know what you hear when it's running...

Might be tricky, a girlfriend texted to say she just bought some new hold ups in Ann Summers, which is just round the corner, do I go for fleas or flies :rolleyes:
 
My inclination would be connect Flea 0v close to the flipflop 0v.

As to the rest - if your still holding a soldering iron and reading this, yer a fool ;)
 


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