Parallel TDA1541A non-o/s DAC Kits

[siu sin man tho]

parallel

hi leo,

I think I will not seperate to sell for them.
The total price of the PCB depends the total pieces of PCB order.
So I cannot to calculate right now.

when my test print on hand I will post to this forum. U are Hong Kong members can directly call me to take a look, But I must make sure the digital noise is low in the PCB. Then start mass production can lower & reach my standard. Otherwise I will not put into the market.

thnaks

thomas

 

[Blitz]

You are right, this is not a gain stage, but a tube-i/v-conversion. As described in the article you bring the impedance which the current output of the 1541 sees significantly down like with an opamp (which is an advantages over the resistor) - but you don't have an opamp in the signal path, but a tube which I would see as an advantage as well. Curcio audio uses the technique as well in their DACs and the feedback abut their DACs is very good in general.

 

[Bricolo]

Konnichiwa,



Depends/not quiet. What I strongly recommend however is not to use the groundplane for closing current loops effecting the signal. Yes, this has implications, like for example the requirement for seperate supplies for the receiver and the DAC (then we can use one groundplane and use it as the signal ground as it does not close a supply current loop).

Basically, my vies are:

1) keep current loops controlled and defined.
2) Keep current loops at impedances suited to the task (always low).
3) Keep traces closes to a "groundplane" to lower inductance.

It keeps such things as "ground bounce" and "noisy grounds" to a minimum, something essential (IMHO) for mixed signal circuit with wide dynamic range.

Sayonara

Hi,

I'm not sure I understood.
In fact, in my case, it's for a DAC without the reciever (it will be in the player itself, in IIS). Can I use the ground plane as a ground for the components, so?

If not, what are you calling current loops (effecting the signal)? The ground of the regs, the decoupling caps, the I/V resistor?


If we shouldn't connect anything to the groundplane, for those making theyr PCB themselves, wouldn't be the easier solution to use a double side board, leave one totally with copper (this will be the groundplane), and the other side for the signal lines, plus a groundfill for the components ground?


If I understood it correctly, you advice to do something like on the shielded cables: connect the shield to ground, but don't make any current flow in it (don't let it be a return path). Am I right?

 

[ThorstenL]

Konnichiwa,

In fact, in my case, it's for a DAC without the reciever (it will be in the player itself, in IIS). Can I use the ground plane as a ground for the components, so?

I would prefer to avoid doing that.

If not, what are you calling current loops (effecting the signal)?

The ground of the regs,

Of course.

the decoupling caps,

Certainly

the I/V resistor?

Obviously.

If we shouldn't connect anything to the groundplane, for those making theyr PCB themselves, wouldn't be the easier solution to use a double side board, leave one totally with copper (this will be the groundplane), and the other side for the signal lines, plus a groundfill for the components ground?

That is not a bad option, except it makes for difficult ground routing. I prefer dead bug hardwiring with the IC's wrapped in Copperfoil and soldered to a copper sheet adhered to additional PCB Material for a number of perfectly good reasons, all relating to this kind of thing.

Really good PCB's for the 1541 (single) would likely be 3 or 4 Layer minimum, I dread the concept of parallel 1541's....

If I understood it correctly, you advice to do something like on the shielded cables: connect the shield to ground, but don't make any current flow in it (don't let it be a return path). Am I right?

Pretty close.

The common (dumb) use of groundplanes seems similar to that of NFB, it can hide a multitude of sins and once designed with this "groundplane" you stand zero chance to ever "debug" the problems introduced in the circuit by doing so anyway, so hope the problems are going to be pretty small anyway, if not - no-one will notice anyway.

Sayonara

 

[Bricolo]

Hi,

I would prefer to avoid doing that.

Avoid what? Using the groundplane for the components, or placing the DAC in the player?

Of course.
...
Certainly
...
Obviously.

So, everything on the board

That is not a bad option, except it makes for difficult ground routing. I prefer dead bug hardwiring with the IC's wrapped in Copperfoil and soldered to a copper sheet adhered to additional PCB Material for a number of perfectly good reasons, all relating to this kind of thing.

Really good PCB's for the 1541 (single) would likely be 3 or 4 Layer minimum, I dread the concept of parallel 1541's....

With your dead bug hardwiring, the IC is shielded with the copperfoil, and this is soldered to the copper sheet.
But what are the grounds of the components soldered to? Only point to point, or also to the copper sheet? (this would contradict what you said about not connecting the components to the shield)

What do you call a good PCB? Where can I lean more about this science ?

 

[ThorstenL]

Konnichiwa,

Avoid what? Using the groundplane for the components, or placing the DAC in the player?

Groundplane for components.

So, everything on the board

Of course.

With your dead bug hardwiring, the IC is shielded with the copperfoil, and this is soldered to the copper sheet.
But what are the grounds of the components soldered to?
Only point to point, or also to the copper sheet?

Point to point, with seperate supplies for the different sections (so no shared ground returns) with the copper sheet/groundplane used STRICTLY to connect the two digital grounds on receiver and DAC and DAC digital to DAC analogue. The rest is insulated from the groundplane.

What do you call a good PCB?

One that ensures that all connecting traces are low inductance and shielded, so a 4 layer structure like this:

Top Layer Groundplane
Second layer PSU lines (and grounds) and groundplane fill
Third layer Signal lines etc.
Fourth layer Groundplane

Also, a local push-pull slew rate limited switching supply (carefully de-noised and shielded) providing seperate galvanically insulated, low leakage voltages for each and every supply pin.

Anyway, that's what I'd do IF I had no budget constraints, access to the design tools and PCB FAB's. Of course, such a PCB could hold Quad TDA1541 if we like....

Sayonara

 

[jean-paul]

Also, a local push-pull slew rate limited switching supply (carefully de-noised and shielded) providing seperate galvanically insulated, low leakage voltages for each and every supply pin.

Why switchers in this case ? Would linear regulators and separate transformers not be more easy to get quiet ( but more voluminous I agree ) ?

Not to speak of the reliability of switchers, in particular the DIY versions ....

 

[Bricolo]

Ok, so the only thing (in my case, since I use no reciever chip) connected to the groundplane, would be the DAC's digital AND andlog ground. Right?

But I didn't understand what you mean by separate supplies for the different sections.
Do you mean one dor the reciever and one for the dac (so, I would only need one). Or one for each supply pin of the DAC (3)?

But I don't see what in this prevents from shared ground returns. All supply pins have separate power supplies, OK. But they share the same groundplane, so all ground currents will flow in the same goundplane. No?

 

[Bricolo]

More on the PCB...


In fact, my question was if you had good books or websites to advice me, to learn how to design good PCBs. SImply using a 4 layer with the configuration you told don't make a good PCB, does it?

 

[ThorstenL]

Konnichiwa,

Ok, so the only thing (in my case, since I use no reciever chip) connected to the groundplane, would be the DAC's digital AND andlog ground. Right?

Ideally - yes.

But I didn't understand what you mean by separate supplies for the different sections.

Consider which sections can be made "stand alone" (Seperate ground & psu pins and related I/O Pins). Then control the current loops for those sections and confine them, lose only the I/O Current loops (ideally) through groundplanes.

Do you mean one dor the reciever and one for the dac (so, I would only need one). Or one for each supply pin of the DAC (3)?

Well, the DAC has one direct analogue supply (-15V) and two digital/helper supplies. These should seperate. The receiver needs one or two more supplies (ideally two) for a total of 4 galvanically seperate supplies (plus those for the analog stage)..

In fact, my question was if you had good books or websites to advice me, to learn how to design good PCBs. SImply using a 4 layer with the configuration you told don't make a good PCB, does it?

There is a bit of black art to this and experience plays a large part. Learn by making mistakes, not from books.

Sayonara

 

[Bricolo]

Hi,

If the DAC has 3 separate supplies. They go on the board, pass though the regs, and arrive at the DAC supply pins.
But how to control the ground return path?

Do you mean connecting the analog (digital) supply's ground close to the DAC's analog (digital) ground pin, on the copper plate?

This way, all the supplies's grounds will be connected together at the copper plate. Right?

The copper plate will be connected to the ground of the other components somewhere on the board?
Or will they have separate wires going to the player's star ground point?

 

[ThorstenL]

Konnichiwa,

If the DAC has 3 separate supplies. They go on the board, pass though the regs, and arrive at the DAC supply pins.
But how to control the ground return path?

By using seperate traces (suitably arranged with trace width and fill to give low inductance of course and closely coupled to our groundplane in our 4-layer PCB) for the return.

The loop:

PSU +V
Reg +in
Reg +Out
IC +V pin
IC -V pin (often mislabeled gnd as it doubels as signal ground)
Reg -V pin (often mislabeled gnd as it doubels as signal ground)
PSU -V

Can be closed without even ONCE refering or connecting to the circuit "ground". That way our imaginary electrons in the current flow go exactly where we want them to.

Do you mean connecting the analog (digital) supply's ground close to the DAC's analog (digital) ground pin, on the copper plate?

This way, all the supplies's grounds will be connected together at the copper plate. Right?

Yes. basically, "signal ground" and "Power Supply Return" are separated out into the respective loops and thus controlled.

The copper plate will be connected to the ground of the other components somewhere on the board?

Why would it? All components relevant to a given current loop blong conneted to the relevant returns for that current loop and nowhere else.

Or will they have separate wires going to the player's star ground point?

What is "star ground"? A methode to maximise loop area and length and thus problems.

Sayonara

 

[siu sin man tho]

parallel

Hi Blitz,

You are right, this is not a gain stage, but a tube-i/v-conversion.

The circuit was used BD140 & run in CCS than pass to tube buffer. I agree this is a good method. Thisd is a common grid method. But U need to match the BD140. This circuit also use the resister to i/V. The 100Ohm is the i/V resister. But I don't like CCS. Why I not choose AD844 + 6DJ8 SRPP or AD844 + parallel 6dj8 two triode buffer. Looks will more simple.

This is my opinion.


Bricolo & Kuei Yang Wang.

I had no opinions for How many layers of the PCBs.
But I must considerate the price. The best PCB that my friend's opinions that how to lower the digital noise is use ground plate in the middle layers. Include the top & bottom plate ground area.
The ground area is quite large. But my friend ( He was the boss of one computor monther board, display card & power transformer company, he produce above item by himself in taiwan) This is his website.

http://www1.2themax.com/index.asp
And he said the signal path would electroplated a very thin layer of silver or gold. The signal will run more smooth, shorter path to prevent the error message.

I think Bricolo opinions is every signal path was cover by two ground plate to lower the noise. Is it right??

If the DAC has 3 separate supplies. They go on the board, pass though the regs, and arrive at the DAC supply pins.

Bricolo,

Not three seperate supply, sorry for my english is not good.

Monther Board---- Monther Board Power supply~~~ CS8412/8414, resisters, Two TDA1541a, cap TL431a etc.

Three seperate board.
a) 6X4 receifier tube with two 6dj8 SRPP board or change to 6dj8 buffer with AD844 OP=amp.
b) 6X4 receifier tube with two 6dj8 SRPP board.
c/ AD844 was pre-lay on the monther board & up to the user choice to solder or not. He can use AD844 with tube buffer.

I had not enough time to test more power transformer.
But I will choose single c-core power trans. (one is for digital & analog, another is for tubes ( filament & HV). Seperate power trans can lower the noise. But this is option for the diyers.


thanks

thoams

 

[siu sin man tho]

parallel

hi mr wang,

What is "star ground"? A methode to maximise loop area and length and thus problems.

Do U think that star ground in DAC circuit is better?

I open one audionote DAC (AD1865) non-oversampling one.
I saw the grounding method in every parts was ground in the short path. the closed area it can do. Then at last connect together. It looks not like the standard star ground method. Any method to advise. When I collect the monther board, I will post the ground that I reference Different DAC & use in my kit to reference. Hope U can give me more advise. Because now is the test print. I can correct!!


P.S. I was testing use the amorphous paper on the top of the chips to lower the noise.


any comment??

I can get them in low price because I order amorphous c-core to wind the OPT from this Lab.
~National Amorphous and Nanocrystalline Alloy Engineering Research Center~

Their Engineer told me that for D/A CHIPS. Amorphous paper will be better.


If it really a good one. I will considerate options to the kits.

very thanks

thomas

 

[siu sin man tho]

parallel

hi all,

this is the amophorous paper that the

National Amorphous and Nanocrystalline Alloy Engineering Research Center~
will supply, is it same as the Mu-metal??

anyone can help me.

thanks

thomas

 

[ThorstenL]

Re: parallel

Konnichiwa,

Bricolo & Kuei Yang Wang.

Please note Thomas that we hi-jacked a little your thread. The comments there do not as such apply to your design, but are my "green table" considerations on the subject.

Rather than answering individual points I think I'll make a sweeping Statement.

Regulary people ask "Is this kind of grounding good?".

Now if "good" is in the sense within which Winnie the Poo says "Hunny is good", fine. Then it is good.

Now if "good" is understood as "is it the best available solution for my specific problem" then the answer is INVARIABLY, ABSOLUTELY and UNASSAILABLE NO.

There is no "formula", no "dogma" that allows itself to be used indiscriminatly and gives consistently the desired result. So in reality, in a normal, always compromised design (if not by you than by the semiconductor designer) you are likely to find a pragmatic and ecclectic mix combining star grounding, bus grounding and scatter grounding via groundplane. Often this is done artless and without cosideration, the results are often sub ideal.

However, to be simple and straightforward with this. There are three fundamental axioms in this:

1) Ground isn't
2) Consider where the current(s) flows
3) Make sure current(s) flows where you want it and via the shortest possible, lowest impedance loop

You can USUALLY completely disregard the static PSU Currents, we are only interested in Audio in the AC current loops and behaviours, but there are disciplines where static currents play their role....

I hope this explains why asking me:

"Okay, groundplane "scatter" grounding is 'bad', is star grounding good?" makes no sense whatsoever. There is no answer to this question, except "NO".

Sayonara

 

[Bricolo]

Konnichiwa,



By using seperate traces (suitably arranged with trace width and fill to give low inductance of course and closely coupled to our groundplane in our 4-layer PCB) for the return.

The loop:

PSU +V
Reg +in
Reg +Out
IC +V pin
IC -V pin (often mislabeled gnd as it doubels as signal ground)
Reg -V pin (often mislabeled gnd as it doubels as signal ground)
PSU -V

Can be closed without even ONCE refering or connecting to the circuit "ground". That way our imaginary electrons in the current flow go exactly where we want them to.



Yes. basically, "signal ground" and "Power Supply Return" are separated out into the respective loops and thus controlled.



Why would it? All components relevant to a given current loop blong conneted to the relevant returns for that current loop and nowhere else.



What is "star ground"? A methode to maximise loop area and length and thus problems.

Sayonara

I'm lost

What is the DAC's V-? Is it the pin labelled GND, or the -5V?
If it's the -5V, I don't see how I can use your method, since the DAC has 2 positive supplies and one negative supply.

And if it's the GND pin, there is also a problem, since there are 3 supply pins, and only 2 grounds.

BTW, what are the analog and digital supplies? I haven't founs this in the datasheet. One is called Vdd, the other Vdd2, and the last one Vdd3


So, the pins called GND, are connected to theyr correspondinf return paths (that I still can't represent) AND to the groundplane?
Is this groundplane connected to the player's ground? Or does the connection to the DAC's GND pins makes this connection?


"Why would it?" It was obvious to me that all grounds have to be at the same potential. So, they must be connected together.

 

[ThorstenL]

Konnichiwa,

I'm lost

Okay. Simple. Remember, THERE IS NO GROUND.

What is the DAC's V-? Is it the pin labelled GND, or the -5V?
If it's the -5V, I don't see how I can use your method, since the DAC has 2 positive supplies and one negative supply.

The DAC has a digital +5V Supply and +/- supply for the "analogue" section. Hence it has two "PSU common" (aka -V in case of positive supplies) pins, which should be used to form independent supply current loops. I really cannot explain it any better, sorry.

And if it's the GND pin, there is also a problem, since there are 3 supply pins, and only 2 grounds.

BTW, what are the analog and digital supplies? I haven't founs this in the datasheet. One is called Vdd, the other Vdd2, and the last one Vdd3

I have/had somewhere an expanded set of details, but the -15V and the +6V (in most Philips applications this is 6V not 5V) are the analogue section and there is a corresponding PSU pin, the other PSU Pin and Ground are logic.

So, the pins called GND, are connected to theyr correspondinf return paths (that I still can't represent) AND to the groundplane?

Yes.

Is this groundplane connected to the player's ground? Or does the connection to the DAC's GND pins makes this connection?

The answer is in the mantra "Where does the current flow in this loop? If you send the three I2S Data Lines from the Player they need to cary also a ground line. This ground line MUST connect to the digital signal reference (sadly shared with the digital PSU -V pin) so of course it does NOT connect to the groudnplane. It is a signal line that will be routed if possible diretly to the signal reference pin without connecting ANYWHERE else.

"Why would it?" It was obvious to me that all grounds have to be at the same potential. So, they must be connected together.

Yes. But if you do connect them all together WITHOUT separating the current loops you have sucessded in ensuring that they are NOT at the same potential. How much of an issue that is depends upon a lot of factors.

If you must share one dual polarity, common ground supply between DAC analogue, DAC digital and receiver using a groundplane with "scatter grounding" may be the lesser evil in context, leading to the best possible perfomance from a compromised design.

In that case carful mechanical arrangements (physical layout, orientation etc.) becomes of tantamount importance to avoid circulating PSU ground noise through the section of the groundplane where signal current flow. This often implies carefully introduced partial breaks in the groundplane, producing in impedance terms "raised" and "lowered" areas in the plane.

I can see reasoning for doing that in commercial gead. In DIY Gear no-body stops you from using a dozend small, electrstatic screen equipped transformers to give you a distinct and seperate supply per pin. As DIY'er you should not worry much about a dozend wires, so you can carry the supply voltages via a Coax Cable to exactly where they are needed, closing the loop throughthe coax cable without any reference to the main groundplane.... Basically, stop thinking in concepts introduced in the first place to handle severely compromised situations.

Sayonara

 

[Bricolo]

but the -15V and the +6V (in most Philips applications this is 6V not 5V) are the analogue section and there is a corresponding PSU pin

I assume you meant "and there is a corresponding ground"?

The answer is in the mantra "Where does the current flow in this loop? If you send the three I2S Data Lines from the Player they need to cary also a ground line.

Why have they to carry the ground too? Can't I simply connect 3 short wires to the DAC. And connect the DAC's ground and the player's ground together? (I fear that this will look to you as a big sin)

This ground line MUST connect to the digital signal reference (sadly shared with the digital PSU -V pin) so of course it does NOT connect to the groudnplane. It is a signal line that will be routed if possible diretly to the signal reference pin without connecting ANYWHERE else

So, if I use the player's I2S+GND (so, 4 lines coming to the DAC) I connect the GND wire to the DAC's digital ground pin. But this pin won't be connected to anything else on the DAC board? Not even the groundplane? It will loose the beneficts from the groundplane, won't it?

Yes. But if you do connect them all together WITHOUT separating the current loops you have sucessded in ensuring that they are NOT at the same potential. How much of an issue that is depends upon a lot of factors.

Tell me if I'm wrong, but if all return paths are done correctly, connecting all grounds together will only hold them at the same potential, without any current flowing in the connection between them. Thiss will be good, no?



Can you explain what is "scatter grounding" please?


Thank you
Alex

 

[ThorstenL]

Konnichiwa,

I assume you meant "and there is a corresponding ground"?

No, I wrote "corresponding PSU pin" and meant "PSU return Pin".

Why have they to carry the ground too?

Because you need the signal current (pulsed and quite high as the inputs are not CMOS on the TDA1541)

Can't I simply connect 3 short wires to the DAC. And connect the DAC's ground and the player's ground together?

That is what I suggest, except I suggest to use the Players -V/Signal Reference pin as "takeoff" point for the that ground and connect it with further "ground" connections directly to the DAC digital ground pin. And if you use a ribbon cable with one "ground" wires per signal wire you have near 100 ohm transmission lines with additionally a low impedance ground connection for the signal current loop.

So, if I use the player's I2S+GND (so, 4 lines coming to the DAC) I connect the GND wire to the DAC's digital ground pin.

Yup.

But this pin won't be connected to anything else on the DAC board?

No, it MUST be connected to other parts on the PCB. For starters, you need the supply return connected to this pin and you need to connected it to the groundplane.

Tell me if I'm wrong, but if all return paths are done correctly, connecting all grounds together will only hold them at the same potential, without any current flowing in the connection between them.

Yes, but currents will flow where they "feel" like, rarely where you want them to.

Can you explain what is "scatter grounding" please?

It means you scatter your components across the board as you feel like and connect all the grounds to the groundplane, hoping it remains low impedance to high enough frequencies as to not cause problems. So, you "scatter" your grounds all over the place. I use it as deragotory term....

Sayonara