F5 with THAT corp. balanced input. - diyAudio
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Old 31st July 2016, 12:16 PM   #1
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Default F5 with THAT corp. balanced input.

Hi all,
I have built an F5 and drive it with an Es9018 Dac. (Built as a nested pair with internal dac chip volume controll)

Nested F5.jpg
Sounds fantastic but dac introduces some very slight humm at the speakers and the combination is also short on voltage gain for these. The Dac has the ESS data sheet op amp implementation single ended output. This differential amp circuit has a gain of 0.84X.

I plan to implement a THAT 1200 balanced line reciever (circuit from data sheet) with 17v rails in my F5. This would solve the humm problem as the amp itself is dead quite and also give me an extra 9db of gain. Perfect in theory. I was going to tap into the F5 power supply as in diagram.

proposed banced F5 power supply.jpg

I thought the 4.7ohm will buffer F5 from any regulator noise. Is This ok or would it be better to install a small auxiliary transformer. (Amp case space is quite tight)

I hope to continue with diff amp Dc coupled to f5 as with the origonal dac circuit but as they would now share ps rails can I expect on/off noise. Thanks for any comments,
Regards, Nick
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Old 31st July 2016, 03:03 PM   #2
Zen Mod is offline Zen Mod  Serbia
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just go for it

one thing - what's output of LM regs ?

be sure to have enough headroom in/out
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Old 31st July 2016, 03:12 PM   #3
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Excellent idea.

But...

Consider this: THAT Receiver: Differential line receiver / preamp

The "Stereo" version of the above has it's own +/- 15VDC supply. The "Mono" version does not due to space constrictions.

Cheers,
Anand.

Last edited by nycavsr2000; 31st July 2016 at 03:15 PM.
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Old 31st July 2016, 06:44 PM   #4
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Thanks guys,
I hope the +-17v supply will give enough headroom to drive the F5, This has 200ohm feedback resistors to give 9x gain(taking into account input resistors).


THAT Receiver: Differential line receiver / preamp,
This looks great but the import tax to UK from the states is punitive. A set of matched lsk jfets from the DIYaudio store cost an extra 15 sterling in tax at the post office.
Besides who doesn't love bread boarding? I was going to solder surface mount decoupling caps directly on the IC socket legs and get as compact as possible.
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Old 31st July 2016, 07:23 PM   #5
Zen Mod is offline Zen Mod  Serbia
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enough headroom for proper operation of reg chips
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Old 31st July 2016, 11:02 PM   #6
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Sorry Zen mod,
yes I measured an lm317 circuit I have driving four op amps at 17v and from unregulated 24v it only draws 62 mA per rail so 24v should be more than plenty, even with the drop over the 4.7 ohm, to give the regs the 18.3v needed to reg. 17v
Thanks again.
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Old 1st August 2016, 03:51 AM   #7
plasnu is offline plasnu  United States
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Quote:
Originally Posted by nycavsr2000 View Post
Excellent idea.

But...

Consider this: THAT Receiver: Differential line receiver / preamp

The "Stereo" version of the above has it's own +/- 15VDC supply. The "Mono" version does not due to space constrictions.

Cheers,
Anand.
Very nice. I only have heard good things about THAT 1200, but for $190, does it have big advantage over transformer solution?
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Old 1st August 2016, 09:16 AM   #8
AndrewT is offline AndrewT  Scotland
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Build you own balanced pre-amp from parts sourced in the UK.
There is the B.Putzeys' version that works well. This has a passive cold balanced output. The extra voltage is not available on the cold output.
The dif opamp datasheets give lots of implementation data.
There are lots of diff output circuits on this Forum.

A balanced and diff circuit gives effectively twice the output voltage compared to Single ended. The F5 needs ~2.6Vac to take it to clipping.
If you double the output of a Source you then need only 1.3Vac to drive the combination of balanced diff preamp plus F5 to clipping.
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Last edited by AndrewT; 1st August 2016 at 09:19 AM.
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Old 1st August 2016, 09:31 AM   #9
AndrewT is offline AndrewT  Scotland
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Supply rail voltage required for an unclipped out is easy to determine.

Take the 2.6Vac voltage required to drive the F5 to clipping.
That is equivalent to 3.68Vpk of maximum signal.

A single ended pre-amp would require ~5Vdc for the supply rails to get 3.68Vpk as maximum output. But this takes the output close to the supply rails and NFB has to work hard to keep the distortion low. Better to use >10Vdc for a single ended pre-amp.

You could run a balanced diff pre-amp from supply rails of ~3Vdc for that same 3.68Vpk of maximum signal. Again increasing the rail voltage to around >6Vdc would make for an easier job for the NFB.

BTW, the Putzeys mentioned earlier uses 12Vdc for supplies so can easily manage a 3.68Vpk signal with lots of voltage headroom to spare, even though it is passive cold.
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Old 2nd August 2016, 12:23 AM   #10
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Quote:
Originally Posted by plasnu View Post
Very nice. I only have heard good things about THAT 1200, but for $190, does it have big advantage over transformer solution?
The THAT Receiver mono board is $35 while the stereo board is $50. Doesn't cost more than $10-15 to populate including shipping. If you want him to build it for you then of course you pay for his time.

So even at $50 + $15 for parts = $65 is definitively nice. Can also implement gains of 0 dB, -3dB and -6dB. Designed by Whitlock. CMRR of about 90 dB and a phenomenally wide frequency response. And of course Tom Christiansen is a talented layout designer in addition to being a bonafide engineer with a sound background and EXCELLENT customer service.

The THAT Receiver board is basically the front end of his Modulus-86.

Best,

Anand.
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