DAC Kit - what else do I need?

[martin clark]

That looks a lot healthier.

Yes the 797 is very senstive to implementation, particularly the value/location of any cap on the output: depending on current demand , location and wiring this has certain requirements of ESR and uF value for 'domnant pole' -based stability. The compensation for the flea is setup ..for the specific use. You can do wilder things with it, but it has to be checked with a scope each time - as with any high-bandwidth circuit That's the second real utility of the small-value resistor in the opamps feed on flea- a quick sanity check on total draw by the 797.

 

[LoBo]

Nice bit of bodging there fella. I must have missed the post where Martin suggested the modification. Have you effectively fitted a VBE to the AD797?

Its a shame the flea stacking won't work. Was the HF being picked up by both the clock flea and the 5V converter flea? I imagined the XO module being more sensitive than the op-amp. It says a lot about the little transformer i think, probably contains a noisy E-I type inside.

Two boxes eh? It will give you room in the DAC to mount the extra fleas. Will you put the flea bites in the external box too? I wonder if stacking the fleas themselves will cause any problems.

 

[Bemused]

That looks a lot healthier.

Sounds better to.

Yes the 797 is very senstive to implementation, particularly the value/location of any cap on the output:

Yes I have the odd cap on the output.

 

[Bemused]

Nice bit of bodging there fella. I must have missed the post where Martin suggested the modification. Have you effectively fitted a VBE to the AD797?

The front of the flea already has VBE / capacitance multiplier / gyrator whatever, its doing sweep up duty before the 7812 regulator.

Martin is like the wind, you have to be fast to catch his posts
The pass transistor mod is on acoustica <a href="http://www.acoustica.org.uk/t/naim/35clockreg2.html" target="_blank">here</a
/\ so why does that not worky? /\

Its a shame the flea stacking won't work. Was the HF being picked up by both the clock flea and the 5V converter flea? I imagined the XO module being more sensitive than the op-amp. It says a lot about the little transformer i think, probably contains a noisy E-I type inside.

I only took measurment on the 5v0 converter flea not the 3v3 clock flea.
Just to be bizare the flea bite feeds the clock!

Two boxes eh? It will give you room in the DAC to mount the extra fleas. Will you put the flea bites in the external box too? I wonder if stacking the fleas themselves will cause any problems.

I need more thought on the matter but the anticipated five or six fleas plus flea bites will struggle fitting in. That why I have not etched any more fea bites, busy pondering over layout and board sizes.
However the mesurments solve my dilemma - the flea needs seperating from the flea bite. Just one or two flea / flea bites would fit in. It is worth noting that the R core does not seem to upset anything.
Probable doings will involve a new box with R core, hackercap, flea bites.
Multi core twisted pairs to dac box
Termination board within dac box with small tants // film. Now thats an easy etch

I have no idea what size caps to use at the dac box end of the interconnect, gut feeling is 20uf Tant 0.1uF Film, maybe a series 1R

Tony

 

[martin clark]

Nice bit of bodging there fella. I must have missed the post where Martin suggested the modification. Have you effectively fitted a VBE to the AD797?

no, - here's how to add a small pass transistor if you want to drive any small load other than an onboard XO:
http://www.acoustica.org.uk/t/naim/35clockreg2.html

Two boxes eh? It will give you room in the DAC to mount the extra fleas. Will you put the flea bites in the external box too? I wonder if stacking the fleas themselves will cause any problems.

No problem stacking fleas, the sensitivity is on the output side of the loop - easier if kept small - so keep any flea-based regs (any really wide-bandwidth regs in fact) close to the circuit served.

 

[LoBo]

Thanks Martin. The flea really is a versatile little bugger. I suppose having the flea too far from the end circuit creates impedance issues with the wiring length?

Tony, I noticed in your pic that you still have C8 fitted. On the page Martin linked to he suggests the following when fitting the pass transistor mod:

1) Remove C8 (47pF)

2) Connect Pin 8 of the AD797 to the output* with a 33 - 47pF capacitor.

(*e.g on the output side of the new transistor, at its junction with the new resistor. Keep loop area as small as possible though - use the shortest path available for the caps connections.)

Worth a go?

 

[Bemused]

I think Martin means move C8, its probably to do with the original board traces.
On Rays board things are a little different trace wise.
C8 is the cap that closes the special internal sensing loop in the 797, I think its what makes it special.

I have effectivly moved C8 as per his schematic so as to take feeb back from the true load (14mA)
I must admit the path for C8 is not the shortest, I could reduce by maybe 2mm

I will gve this some more thought
Thanks

 

[martin clark]

Definitely. In fact - try running a wire with 10-50R right at the feedpoint of the target load even if off-board, back via 47pF into pin 8 (ie 10 to 50R in series with the 47pF, for a unique feed into pin 8)

...must I give all the good stuff away

 

[LoBo]

Ah, yes I keep forgetting Ray's boards are different sorry. I wonder why he made these changes?

Keep the free tips coming Martin... if you really want we could give you 20p a tip. You would have made a pound so far

Cheers

 

[LoBo]

Another development in the reference supply. This time combining an adjustable reg booster and reference buffer circuit.

It works very well indeed. I'll be honest it's only a slight improvement on the original reference using the LED's. However physically and electronically speaking it should be doing the business in terms of low noise etc. It's just on the Buffalo at the moment with 3.4V output. The whole thing sounds cracking.

This circuit is what I'm aiming to do in Eagle and eventually etch.

Tony, I might make one up for you to play with and stick the scope on. I'd be very interested in what you find with the output.

 

[Bemused]

Ah, yes I keep forgetting Ray's boards are different sorry. I wonder why he made these changes?

Keep the free tips coming Martin... if you really want we could give you 20p a tip. You would have made a pound so far

Cheers

Only 20p
That pass transistor bodge has could have easly been a thousand pound boost if the kit was in a shop window.

 

[Bemused]

Grrr. pear shaped again

Implemented the remote load feed back to the double led flea doing clock duty.
I used 40R as the series resistance, this bit worked out quite nifty as 40 is already fitted in the CS4821 clock input and fitted some of Rich's dill socket pins to some spare pads vacated by the original XO. Nifty little pins Rich, I used them as plug and socket.
You got a link for them? I can use lts of these.
Anyway the sad part is I sat on my converter , all the bug mount decoupling caps are bent / snapped, one of the CS4398 pins has torn up and one has torn off.
Sad bunny is I.

Are they available from Giga?

Edit
Duh...
I have also just realised that I have wired the XO output into the AD797 pin 8 feedback circuit
So the flea would be switching at 24MHz had I not knackered the converter.

 

[martin clark]

That's not good

 

[Sparts155]

Grrr. pear shaped again

Ahh, sorry about that. You know what, we should have a thread called "Dumb Ways I've Sh@gged My Hifi", with a prize going to the most shameful. I think it would be a long and interesting thread - I've certainly got some material I could contribute.

Dan

 

[Greg Erskine]

I was hoping to show you a nice 3D pic of your board but it's not rendering. Maybe you can figure it out.

hi Lobo,

I've been using Eagle 3D for years, flick me the .brd file and I generate it for you.

Here's an example:

http://users.tpg.com.au/gerskine/greg/jlh add-on shunt regulator.htm

Can you get me email via PM?

regards

 

[LoBo]

Grrr. pear shaped again

Implemented the remote load feed back to the double led flea doing clock duty.
I used 40R as the series resistance, this bit worked out quite nifty as 40 is already fitted in the CS4821 clock input and fitted some of Rich's dill socket pins to some spare pads vacated by the original XO. Nifty little pins Rich, I used them as plug and socket.
You got a link for them? I can use lts of these.
Anyway the sad part is I sat on my converter , all the bug mount decoupling caps are bent / snapped, one of the CS4398 pins has torn up and one has torn off.
Sad bunny is I.

Are they available from Giga?

Edit
Duh...
I have also just realised that I have wired the XO output into the AD797 pin 8 feedback circuit
So the flea would be switching at 24MHz had I not knackered the converter.

Sorry I didn't reply sooner Tony. You've had some troubles there mate.

The pins and sockets are from here:

http://cgi.ebay.co.uk/Turned-pin-SI...etTopBoxes&hash=item1c0b47a295#ht_1081wt_1138

So you have NO DAC converter? They are available from gigaworks and Snow46_8. Get quotes from both as Snow is usually cheaper.

Ian Ma: giga1668 (@) yahoo.com

Wei Zhou: snow468 (@) gmail.com

It will take two weeks to arrive which is far too long to go without a DAC so I will send you my spare CS4398 adapter to get you going until a new one arrives. Do what you want to it. It has a track cut linking pins 15 to 28. But if you are planning a dedicated feed to VREF on pin 15 thats not a problem.

I'll send it later today or tomorrow

I can just imagine the moment you realized you sat on the converter. I bet the air was blue for a bit...

 

[LoBo]

hi Lobo,

I've been using Eagle 3D for years, flick me the .brd file and I generate it for you.

Here's an example:

http://users.tpg.com.au/gerskine/greg/jlh add-on shunt regulator.htm

Can you get me email via PM?

regards

Nice one Greg, I'll certainly take you up on that mate. That JLH shunt reg you rendered is ace.

The board mentioned above is just Tony's flea bite board and has no components really. Hopefully soon I will get the hang of eagle and have a couple of boards myself to try. If you could PM me your email address I'll send some files.

A couple of questions -

What OS are you using? Eagle 3D and POV-ray are for the XP platform and I'm using windows 7 64bit. I have tried both 32 and 64 installations and even running them in compatibility mode they won't work. Pov-ray runs the script but no render window appears.

I was having trouble with Eagle's library files so created a couple of components from scratch. I assume these new components wont render unless I include component dimensions? Basically how do Eagle 3d / pov-ray know how to render components?

cheers

Rich

 

[Bemused]

Sorry I didn't reply sooner Tony. You've had some troubles there mate.

The pins and sockets are from here:

http://cgi.ebay.co.uk/Turned-pin-SI...etTopBoxes&hash=item1c0b47a295#ht_1081wt_1138

So you have NO DAC converter? They are available from gigaworks and Snow46_8. Get quotes from both as Snow is usually cheaper.

Ian Ma: giga1668 (@) yahoo.com

Wei Zhou: snow468 (@) gmail.com

It will take two weeks to arrive which is far too long to go without a DAC so I will send you my spare CS4398 adapter to get you going until a new one arrives. Do what you want to it. It has a track cut linking pins 15 to 28. But if you are planning a dedicated feed to VREF on pin 15 thats not a problem.

I'll send it later today or tomorrow

I can just imagine the moment you realized you sat on the converter. I bet the air was blue for a bit...

Thanks Rich, but hold fire on the postage the converter adapter is now stripped and cleaned up and I may be able to get the leg back on the chip as there is a teeny bit of leg sticking off of the CS chip. Its all ready to put back together tonight. I just need a steady hand and some luck
I will need to buy a new converter as its only going to be problamatic.

Just ordered the Turned pin SIL socket & Header strip 20 Way 0.1" pitch Thanks

 

[Bemused]

 

[Bemused]

So now the Dac is back in the land of the living I tried a flea with a BC547C pass transistor in the position that feeds 5v0 to both up-sampling module and S/PDIF receiver chip.
No worky, current on this circuit turns out to be 95mA !
That’s an awful lot.
The fleas led dimmed a little and the output volts dropped from 5v0 to 4v4, I guess the BC547 feeding the 7812 is not up to the job.
Took the flea out and put the booster back in, I fixed the MKS in the booster to 3.3uF, I had fitted a 100nan ages ago by mistake.

Might think about splitting the loads down a little.
The CS8416 receivers VL Burdon is less than 10mA (7.8mA @3v3 with a 192KHz frame rate dropping to 2.8mA at 48KHz) This seems like a nice little load for a standard flea. Could even reconfigure for VL 3v3 and use the improved 3v3 double diode flea.

So were is the rest of the load?
Surly not just down to the up-sampling module.
So I checked the data sheet and yep CS8421 is a greedy little bugger.

Tony

btw Rich, did I thanks you for your kind offer.