Hi Guys,
I just purchased a DAC board with dual AD1865 pre-assembled from ali. I couldn't find any info on it not could I get anything out of the vendor. I figured I'll get it and see how it goes.
The DAC arrived today and my first impression is that it uses decent components and it's well built.
I'm planning to use it as I out coupled with transformer + I/V resistor + tube output. This combo is currently running on a parallel TDA1541A with great success so I figured I'll also try the AD1865. The trafo's are sowter 1465 which sound great.
As I don't know anything about this board, I was wondering if anybody had any experience with it since it's been out for many years with different versions of it. Is it setup for I out or is it V out? I will start tracing to find out more about it as well and will post the results.
Thanks
I just purchased a DAC board with dual AD1865 pre-assembled from ali. I couldn't find any info on it not could I get anything out of the vendor. I figured I'll get it and see how it goes.
The DAC arrived today and my first impression is that it uses decent components and it's well built.
I'm planning to use it as I out coupled with transformer + I/V resistor + tube output. This combo is currently running on a parallel TDA1541A with great success so I figured I'll also try the AD1865. The trafo's are sowter 1465 which sound great.
As I don't know anything about this board, I was wondering if anybody had any experience with it since it's been out for many years with different versions of it. Is it setup for I out or is it V out? I will start tracing to find out more about it as well and will post the results.
Thanks
Yes - the SOIC28 package has Iouts on pins 26 and 17 which have tracks going to the NE5532s. They're doing I/V - presumably on anti-phase outputs - then the following NE5534 is doing bal-SE conversion.
Thanks for your feed back. Attached is the output stage of the the Left channel. The 2x I out come from the same AD1865 IC.
I'd like to take the I outs and use my own output stage comprised of transformer + R I/V + tube amp. This already exist and I only need to find the right R I/V value.
My question, can I just sever the link for the 2x I outs going to the opamps, combine them together and send it to my step-up trafo and the rest? Again, each IC represents one channel.
I'd like to take the I outs and use my own output stage comprised of transformer + R I/V + tube amp. This already exist and I only need to find the right R I/V value.
My question, can I just sever the link for the 2x I outs going to the opamps, combine them together and send it to my step-up trafo and the rest? Again, each IC represents one channel.
The Iouts are in-phase and anti-phase so ideally would be sent into the two phases of a centre-tapped trafo winding, the CT going to 0V. Don't sum the Iouts or you'll get nothing at all.
Unfortunately the trafo primaries are connected in parallel for the other tda1541 dac. My goal is to create a switchable system between ad1865 and tda1541.
To make it simpler, lets forget about the trafo. Given the schematic of the output stage attached previously, how can I replace the current opamp output stage with a simple R i/v that can be voltage amplified?
Thanks
To make it simpler, lets forget about the trafo. Given the schematic of the output stage attached previously, how can I replace the current opamp output stage with a simple R i/v that can be voltage amplified?
Thanks
A resistor I/V would indeed be very simple. What's more difficult is optimizing the value of the resistor, given the DS for AD1865 doesn't give any indication about the DAC's output compliance range. So perhaps experiment is in order - I'd start off with a lowish value like 47R (between Iout and GND) and see how you go. You'll need a gain stage of X30 after the 47R to reach 1VRMS output.
The downside of passive I/V is higher noise and the lower the resistor value, the higher the noise so you'll want to choose the highest resistor value which doesn't distort too much at full signal.
The downside of passive I/V is higher noise and the lower the resistor value, the higher the noise so you'll want to choose the highest resistor value which doesn't distort too much at full signal.
Since each IC represents one channel and each IC has 2 I outs, which I out do I use? Can I use both or only one per IC per channel? You mention that if I combine the 2 I outs I will get nothing which indicates that I can only use one I out per IC. Is that correct? With TDA1541in parallel I can combine the 2 I outs which provide 8 mA pp instead of 4 mA.
My plan is to measure THD with a bunch of resistor values. My tube output stage has a very high gain.
My plan is to measure THD with a bunch of resistor values. My tube output stage has a very high gain.
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I take it that there's a digital inversion being done on half of the data feeds to the DAC. If you want to parallel the Iouts to get more current then you'll need to locate and bypass the inverters. My best guess is those inverters are U19 and U20. It would be a shame to only take one Iout and ignore the second one as that wastes half the DAC chip.
Looks as though R26,27 are series terminations of the inverter outputs (double check this with a continuity tester to the AD1865 data pins, pin5 for R and pin10 for L), if I were modding this I'd rotate those resistors though 90degrees so one side of the resistor is still connected to the DACs (bottom pad in the pic) and the other terminal of the resistor is floating in space. Then run a wire (use 30AWG solid core) from the floating end of the resistor to the input pin of their respective inverters.
Looks as though R26,27 are series terminations of the inverter outputs (double check this with a continuity tester to the AD1865 data pins, pin5 for R and pin10 for L), if I were modding this I'd rotate those resistors though 90degrees so one side of the resistor is still connected to the DACs (bottom pad in the pic) and the other terminal of the resistor is floating in space. Then run a wire (use 30AWG solid core) from the floating end of the resistor to the input pin of their respective inverters.
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R27 goes to pin 6 and 9 of Left IC and R26 goes to the same pins on Right IC.
Also pin 5 on both IC's are connected together and so is pin 10.
Would it work if on Left IC I lift pin10 and connect it to pin 5 and on Right IC I lift pin 5 and connect it to pin 10? Basically putting the same non-inverted input to both pins?
It's a bit cumbersome to work on this as everything is to tiny. My eyes are cross already.
Also pin 5 on both IC's are connected together and so is pin 10.
Would it work if on Left IC I lift pin10 and connect it to pin 5 and on Right IC I lift pin 5 and connect it to pin 10? Basically putting the same non-inverted input to both pins?
It's a bit cumbersome to work on this as everything is to tiny. My eyes are cross already.
Yes I think your suggestion will work, assuming you're comfortable with bending pins on relatively expensive DAC chips.
My understanding of the schematic seems in error - R27 is feeding the 'latch' pins of L and R26 feeds latch on R channel. So its still to determine where pin5 and pin10 are fed from, the fact that they are getting the same signal is rather confusing to me. Given I've not understood how its working, take my advice above with a large pinch of salt.
My understanding of the schematic seems in error - R27 is feeding the 'latch' pins of L and R26 feeds latch on R channel. So its still to determine where pin5 and pin10 are fed from, the fact that they are getting the same signal is rather confusing to me. Given I've not understood how its working, take my advice above with a large pinch of salt.
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I traced some more, maybe it will make more sense.
U19 (C04F) is an inverter from what I gather. I couldn't find that specific IC datasheet.
U18 (74HC1640) pin 10 (Q4 output) goes to Pin 5 of both IC's via R28 (39 ohm). It also goes to U19 (C04F) inverter. The output of the inverter U19 goes directly to pin 10 of both IC's.
U15 (75HC157A) pin 4 (Y0 output) goes to Right IC via R26 (39 ohm) to pin 6 & 9 (Left/Right Ch Latch pin). It also goes to U20 (C04F) inverter. The output of the inverter goes to Left IC via R27 (39 ohm) to the same pins 6 & 9.
I've attached a diagram to be easier to understand.
Let me know if I should trace other pins.
U19 (C04F) is an inverter from what I gather. I couldn't find that specific IC datasheet.
U18 (74HC1640) pin 10 (Q4 output) goes to Pin 5 of both IC's via R28 (39 ohm). It also goes to U19 (C04F) inverter. The output of the inverter U19 goes directly to pin 10 of both IC's.
U15 (75HC157A) pin 4 (Y0 output) goes to Right IC via R26 (39 ohm) to pin 6 & 9 (Left/Right Ch Latch pin). It also goes to U20 (C04F) inverter. The output of the inverter goes to Left IC via R27 (39 ohm) to the same pins 6 & 9.
I've attached a diagram to be easier to understand.
Let me know if I should trace other pins.
Attachments
I bought this board mainly as a hobby and to see how it stacks up against a dual TDA1541. I intend to keep all the other amp stages identical as I'm happy with the sound. Can't say I have a lot of experience with expensive sound but I invested and build the rest of the system so I have to integrate this DAC into it.
I am planning to hook it up as is before I start to mess with it, mainly to make sure it works. But the idea is to run a dual DAC so I can switch between TDA1541 and AD1865. Each DAC will also have 3 switchable output options: R i/v + tube pre + amp, Sowter 1465 (secondary in series) + R i/v + amp, Sowter (secondary in parallel) + R i/v + tube pre + amp. All 3 have different sound and I like to switch between all 3. Adding a second DAC will give me 6 options. I can tell you that the best sounding is the second option. For a bit more tuby sound 3rd option is the best (my fav).
It does not look that bad. Imagine it sounding neutral and fine without any peculiarities. You would then first need to listen to it and give it a few days as normal with new electronics. You’ll have to cope but you’ll survive 😉
Maybe you will discover that it does not need tubes and high ohmic outputs to color the sound. Switches and wiring will certainly not make things better. As in never really.
Maybe coloring the signal both in DAC already and further in the chain is just a tad too much.
Anyway, just make sure to build it in a metal case connected to PE. I can recommend the 10VA Talema molded PCB mount toroids as these are silent and affordable. It would help to know the actual power consumption especially of the 9V part. A mains input filter would not hurt.
Maybe you will discover that it does not need tubes and high ohmic outputs to color the sound. Switches and wiring will certainly not make things better. As in never really.
Maybe coloring the signal both in DAC already and further in the chain is just a tad too much.
Anyway, just make sure to build it in a metal case connected to PE. I can recommend the 10VA Talema molded PCB mount toroids as these are silent and affordable. It would help to know the actual power consumption especially of the 9V part. A mains input filter would not hurt.
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Thanks, that helps a lot. What threw me was assuming the DACs were latched at the same time, they're not so there'll be a phase difference between L and R channels. I doubt that's of much consequence.
I suggest a slight variation on what you originally proposed - raise both pin10s (L and R) and wire both to their nearest pin5s.
That makes sense.
Should I also lift pin 6 and 9 from the inverted IC and connect them to the non-inverted IC pin 6 or 9? Not sure if it’s important as I don’t know the purpose of the ch latch pin.
Should I also lift pin 6 and 9 from the inverted IC and connect them to the non-inverted IC pin 6 or 9? Not sure if it’s important as I don’t know the purpose of the ch latch pin.
jean-paul, thanks for your advice. You can't reason with a tube freak...lol.
I already ha a case and everything is ready to go. I just need to integrate this DAC into that setup. That's why I can't change the config for the step-up trafo.
I already ha a case and everything is ready to go. I just need to integrate this DAC into that setup. That's why I can't change the config for the step-up trafo.
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Going from the schematic you've drawn, there's not 'an inverted IC' (assuming by 'IC' you refer to the AD1865) and a non-inverted IC, rather there's a L chan (inverted and non-inverted) IC and a R chan (ditto) IC. If you wire pin6 and pin9 in common between the two DACs you'll get either all L or all R outputs, not stereo. Grabbing both L and R data requires latch pulses at different times.