Connecting Unbalanced DAC output to Balanced Power Amp

[jls001]

Ha!! Success.

Nice!

What SMPS or LPSU are you planning to use?

Any idea what would be a realistic power output into 8 Ohms with let's say 0.1% THD?

The board seems to be PBTL so power shouldn't be wanting.

 

[SanjeevM]

I am planning to use a LPSU for this amp.

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[SanjeevM]

Power should be 100+ watts per ch on a 24v supply for 8 ohm spkrs. More than enough for me.

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[SanjeevM]

Hi Sanjeev,

here's the link : TPA3251D2 2CH Class D Audio Amplifier

now, what i can see on the pcb, it is written: IN A, B, C , D and there's also a jumper to select SE(Single ended) and DIFF(Differential) inputs. so, probably this kit is 4 channel amp in SE mode and 2 channel amp in DIFF mode,

It uses one chip in BTL mode to make a 2 channel amp, and there are op-amps(NJM4580, these are good) on the pcb as buffers for the TPA chips. One op-amp per channel. So, if you wish to use this kit in 2 channel Bridge tied load configuration, then you have to provide differential inputs. It needs an inverted signal to properly work in push-pull configuration.

I couldn't find any documentation for the kit, so my opinion is based on pics of the module.

Regards,
Aniket

The input impedance in this board will come from the i/I of the op-amp circuit. How does one find out how much is that? And how do I find out the output impedance of the Boss DAC ? Without these two values,, a proper interface will not be possible.

Can a ferrite core transformer with a dual secondary and matching impedances serve this purpose?

 

[Aniket]

The input impedance in this board will come from the i/I of the op-amp circuit.

yes right.

How does one find out how much is that? And how do I find out the output impedance of the Boss DAC ? Without these two values,, a proper interface will not be possible.

If you can read out on pcb, check resistor from input to ground. or check with a multi meter resistance between input pin and ground. will there be any, it should be in the range of 10k - 100k(could be higher also), which is fine.
for the DAC, it should be mentioned in the manual. If not, then still its no problem, as I believe the DAC could easily handle high impedance loads. if it can drive headphones, then great, it can handle low impedance loads easily.

In either case, designing an interface wont be any issue.

Can a ferrite core transformer with a dual secondary and matching impedances serve this purpose?

yes it was done earlier. even for converting balanced to unbalanced, in pro equipments. you can do that also but it will be better if you go active.

Regards,
Aniket

 

[saikatbiswas82]

If you want to go the purist way of using transformer as suggested in the same page, there's a firm in Mumbai that builds such RCA-XLR impedance matched transformers (but very costly).

How much cost are we talking about here? Any pointers towards the source will be helpful.

 

[Hari Iyer]

If budget is not an issue look out for Jensen transformers or edcor ones. The conrction is very simple and straightforward.

I initially thought of using Balanced to unbalanced for my setup and later gave up as transformer ne3d to be of very high quality to get this right which was costing as much as 8000/- bucks.

 

[jls001]

How much cost are we talking about here? Any pointers towards the source will be helpful.

About Rs 3500 per piece so Rs 7000 for a pair. Promedia, Mumbai custom made as per our requirement of connector types.

 

[saikatbiswas82]

About Rs 3500 per piece so Rs 7000 for a pair. Promedia, Mumbai custom made as per our requirement of connector types.

Thanks a lot.
One more query. Do you know what core material is being used in these transformers? What impedance values do they supply?

 

[jls001]

Don't know core material. They only mentioned that they use Neutrik transformers. Impedance must be 600R on balanced side and 75R on unbalanced.

 

[Hari Iyer]

I suggest check Jensen transformer catalogue/ brochure and get them made as per that specs.

 

[saikatbiswas82]

I suggest check Jensen transformer catalogue/ brochure and get them made as per that specs.

I've already checked. They are $70 a piece. I need half a dozen so it will be a bit out of my budget.