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Parallel TDA1541a DAC using SuperTeddyRegs
Parallel TDA1541a DAC using SuperTeddyRegs
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Old 7th December 2016, 06:44 PM   #1
sthcoaster is offline sthcoaster  United Kingdom
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Parallel TDA1541a DAC using SuperTeddyRegs
Default Parallel TDA1541a DAC using SuperTeddyRegs

Evening all

I have been collecting the BOM and eagle cad design for homemade PCBs for a multi parallel TDA1541a NOS dac using the TNT-Convertus model (2 chips but maybe 4 (have sourced 3 and may stop there). Output will be tube stage.

At the moment I have the standard 3 regs from the TNT schematic serving each chip. I am now wondering about using SuperTeddyRegs as I already have 2 of his boards to hand.

Is it possible to run both (or 4 chips) from the same STR?
Will going to multiple chips defeat the purpose of having super regulators?

I have planned an arrangement of PCBs in a vertical stack like in the Cambridge Audio CD3 or DAC3. So I could interleave the STR boards between the dac boards with the Vout wire going out the "top" to one chip and another from the "bottom" going to the other chip so the power lines are going the shortest possible distances.

e.g.. shown for 4 dacs, only 1 iteration if 2 dacs

dac str dac dac str dac
|<---|--->| |<---|--->|
----------------------------------- base pcb which will carry parallel connections

Thank you for your comments

Last edited by sthcoaster; 7th December 2016 at 06:46 PM. Reason: ascii pic was not looking v.good
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Old 9th December 2016, 05:52 PM   #2
batteryman is offline batteryman  United Kingdom
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Quote:
Originally Posted by sthcoaster View Post
Evening all

I have been collecting the BOM and eagle cad design for homemade PCBs for a multi parallel TDA1541a NOS dac using the TNT-Convertus model (2 chips but maybe 4 (have sourced 3 and may stop there). Output will be tube stage.

At the moment I have the standard 3 regs from the TNT schematic serving each chip. I am now wondering about using SuperTeddyRegs as I already have 2 of his boards to hand.

Is it possible to run both (or 4 chips) from the same STR?
Will going to multiple chips defeat the purpose of having super regulators?

I have planned an arrangement of PCBs in a vertical stack like in the Cambridge Audio CD3 or DAC3. So I could interleave the STR boards between the dac boards with the Vout wire going out the "top" to one chip and another from the "bottom" going to the other chip so the power lines are going the shortest possible distances.

e.g.. shown for 4 dacs, only 1 iteration if 2 dacs

dac str dac dac str dac
|<---|--->| |<---|--->|
----------------------------------- base pcb which will carry parallel connections

Thank you for your comments
Have you not considered dual differential configuration.
You need one of Iancanada's I2Stopcm boards which provides the necessary dual simultaneous outputs for the dacs from the I2S signals, as well as reclocking them.

For my I/V converters I am using 4, AD844 current feedback opamps driving a pair of Sowter transformers as the 'output stage as they have a 'gain' of 5x.
This is ample to drive my Quad 405 via an Alps pot.
I am using low noise discrete regulators from Dexa (pin compatible with 78xx type)
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Old 9th December 2016, 09:59 PM   #3
sthcoaster is offline sthcoaster  United Kingdom
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Parallel TDA1541a DAC using SuperTeddyRegs
Quote:
Originally Posted by batteryman View Post
Have you not considered dual differential configuration.
Thanks batteryman.

I'll need to read more about this approach.

So far I have made design decisions based on my skill/understanding level - I want to make the pcbs myself as far as possible. Also I don't have gear that accepts balanced inputs (except for a Chord power amp I was recently gifted) - I understand this dual differential treatment provides a balanced output? And because the rest of my kit is not particularly high-end I worry about that law of diminishing returns.

I've recently been adding a DEM clock sync to this project as well.
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Old 10th December 2016, 06:57 AM   #4
batteryman is offline batteryman  United Kingdom
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Quote:
Originally Posted by sthcoaster View Post
Thanks batteryman.

I'll need to read more about this approach.

So far I have made design decisions based on my skill/understanding level - I want to make the pcbs myself as far as possible. Also I don't have gear that accepts balanced inputs (except for a Chord power amp I was recently gifted) - I understand this dual differential treatment provides a balanced output? And because the rest of my kit is not particularly high-end I worry about that law of diminishing returns.

I've recently been adding a DEM clock sync to this project as well.
Dem reclocking is on my list as well, but there are several ways to do it.

The differential to single ended conversion is done by the transformers, which also have some lp filtering and of course common mode noise & rubbish cancels out. The 5:1 step up means no additional preamp is needed so avoids the psu & hardware of a valve output stage, but they are not a cheap option.

DAC OUTPUT TRANSFORMERS

You can connect them direct to the dacs across an I/V resistor and I was using this method, but a brief try using a single dac and an AD844 supplying the transformer produced more solid, more gutsy bass & lower midrange.

Once I've fitted Iancanada's board I'll probably try them connected directly again - I am trying to avoid active devices in the audio signal path.
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Old 10th December 2016, 07:08 AM   #5
quantran is offline quantran  Viet Nam
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The suggestions by batteryman are good. If you don't use a differential configuration, multiple DAC chips don't have any technical advantage than a single chip.

The ad844 is able to produce sparkling sound from top to bottom but it work best with a buffer at the output.
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Old 10th December 2016, 07:24 AM   #6
batteryman is offline batteryman  United Kingdom
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Originally Posted by quantran View Post
The suggestions by batteryman are good. If you don't use a differential configuration, multiple DAC chips don't have any technical advantage than a single chip.

The ad844 is able to produce sparkling sound from top to bottom but it work best with a buffer at the output.
I am considering an OPA1632 differential opamp connected to pin 5 of the pair of 844s on each channel. Then the transformer across the outputs.

I think the reason the transformers weren't ideal connected directly to an i/v resistor is because they really need driving from a much lower impedance source.
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Old 10th December 2016, 09:30 AM   #7
batteryman is offline batteryman  United Kingdom
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Quote:
Originally Posted by sthcoaster View Post
Evening all

I have been collecting the BOM and eagle cad design for homemade PCBs for a multi parallel TDA1541a NOS dac using the TNT-Convertus model (2 chips but maybe 4 (have sourced 3 and may stop there). Output will be tube stage.
Might a collaboration be possible to share the pcb manufacturing costs? Should be possible to design a semi-universal 1541 nos dac pcb and I was thinking of designing my own (I have Labcentre's Isis/Aries schematic capture / pcb software which produces the Gerber files.)

My requirements are for differential working in simultaneous mode, I2S inputs with attenuators, 78xx pin compatible low noise regulators, dem clock derived from bck.

Preferably no smd parts. (the OPA1632 is soic and I can solder these)

The analogue section need not be on the same pcb (might be better if it wasn't) but if so, this would use 4x AD844, 2x OPA1632, +- 15v supplies with own regulators.
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Old 11th January 2017, 04:42 PM   #8
sthcoaster is offline sthcoaster  United Kingdom
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Parallel TDA1541a DAC using SuperTeddyRegs
Quote:
Originally Posted by batteryman View Post
Might a collaboration be possible to share the pcb manufacturing costs?
Hi batteryman

Sorry just saw this invitation in your post last month.

Thanks for the offer. I don't think I am quite in the same league as your plans - yet! I am happy being low-tech at the moment with making my own boards and following the basic implementation that I have been settling on - need to start somewhere and though i know that I am making some design choices that are based on outmoded thinking and I will not end up with the ultimate on the first attempt, there will always be a next project to aspire to.

Best

Clayton
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Old 12th January 2017, 12:55 PM   #9
batteryman is offline batteryman  United Kingdom
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Quote:
Originally Posted by sthcoaster View Post
Hi batteryman

Sorry just saw this invitation in your post last month.

Thanks for the offer. I don't think I am quite in the same league as your plans - yet! I am happy being low-tech at the moment with making my own boards and following the basic implementation that I have been settling on - need to start somewhere and though i know that I am making some design choices that are based on outmoded thinking and I will not end up with the ultimate on the first attempt, there will always be a next project to aspire to.
Best Clayton
Yes everyone needs to start somewhere and I will eventually get round to designing my dual differential pcb later this year. I bought a pair of bare 1541 pcbs from Ebay but haven't had time to wire them up. At 13 a pair with on board psu, they were cheap enough for experimenting with but I could see where there was scope for improvements in the design and layout.

Ian
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Old 1st June 2017, 12:12 PM   #10
sthcoaster is offline sthcoaster  United Kingdom
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Parallel TDA1541a DAC using SuperTeddyRegs
Default PCB critique please

Still working on this project. And haven't reviewed this thread for a while and now that I just have I see plenty of good comments that would benefit more attention.

However, must put my toe in the water and ask for feedback on the attached PCB design. Using attenuation and DEM reclock from ECDesigns post #2748.

Chip will be fed from separate pcb of same size containing multiple iterations of superegs in a vertical sandwich as per my first post.

The space for decoupling caps is tight/overlapping as I am using orange drop type capacitors and will alternate their placement top and bottom - even with the soldering just on one side I should be able to solder them all if I do them in the right order.

GND_A is the bottom layer
GND_D is the top layer

Using Eagle I was trying to make additional pad/holes to allow a small format capacitor - I used an extra pad on the schematic and so it appears on the screen print - is there a different way to do this to allow multiple component choices in the same spot?

All and any help much appreciated.

I know that there will be suggestions for different DEM clock or DAC implementations and they are always interesting to read. However, I am wanting to also better my PCB design skills so please bear that in mind.

Best to all and advance thanks
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File Type: png schematic.png (334.6 KB, 183 views)
File Type: png screen.png (282.8 KB, 178 views)
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