Buffalo II & transformers

[hazard500]

I just received my Buffalo 3 DAC from the good guys at TP, and have been pondering what to do about an IV stage - so this thread has been an interesting read., mainly because TX seems like a very simple solution, and secondly, becasesI already use a TX output on my Cirrus Logic DAC (I have a CS4398 DAC eval board, which conveniently has take-off points on the board directly from the DAC output, before it goes to the op-amp output stage). So 2 questions:
1. Will my Lundahl 1527XL be suitable to with the Buffalo? It's 1+1:1+1, primary DC impedance = 54 ohm, freq response with 800 ohm source = 10Hz to 150kHz +/- 0.2dB - yes, 0.2dB!
2. I hate preamps, and tend not to use one - I have a source selector, and my phono stage has variable gain so nothing else required, however I do have a passive preamp for my existing DAC. Buit can i build variable gain into the TX output by using a switched attenuator across the primary of the TX - this should act as a voltage divider with the output impedance of the bufffalo (I'll work out the resistor values later). I would prefer to switch just one resistor between the +ve and -ve terminals, rather than bother with switching 2 resistors with an ground at the mid point, seems reasonable to me and if it works then the passive pre-amp is gone!! Good, I like minamalist solutions, not complex engineering.

BTW I should have said - buiold quality of the Buffalo DAC is superb. Thanks to fellows at TP!! I'm looking forward to getting the DAC built up.

[zoka959]

Originally Posted by Joe Rasmussen

I know where you are coming from. But the Sabre DAC is different from any other DAC, not just that it can be used in both modes - but arguably sounds best in Current mode IMO.

If you go back through the posts, see the ones that discusses the lighter tonal balance of the Sabre DAC is Voltage mode.

If you want to use Voltage, then transformer is the way to go. Many have heard me say that many times over, that with a differential voltage output where any DC offset will not be seen by the Primary of the transformer. But the Sabre DAC is not a conventional Voltage DAC.

The Sabre DAC has a much higher output Z than is usual for a Voltage DAC and hence there is reason to point to it as the cause of the light tonal balance when used as such. We need to reduce that Z and also force the DAC into current.

So, Voltage mode, use:



The two resistors force the Sabre DAC into 3.14mA current offset while reducing offset voltage from 1.65V to about 1V. The output will be 1.3V RMS.

But how could this be applied to using Tubes and Current mode.

Pretty much all the post-DAC Tube designs I have seen avoid full-on Current mode. But with the Sabre DAC there is and opportunity if employing above suggestion repeated here:



We can force the Sabre DAC into Current mode by pulling it virtually down to 0V DC and then get an offset current of 8mA. Using the same 1:1 transformer, it now opens up the way to use Current mode with Tubes.

So the above example shows how it can be done.

The point is that the Sabre DAC has flexibilities in the way that no other DAC has and using it in Plain Vanilla Voltage mode can be avoided as IMO it gives worst performance.

Cheers, Joe R.

Joe ,
is it possible to use Broskie's Unbalancer as tube line stage in your advice as
beau2317 does it in this thread
Buffalo III DAC Tube Output Stage
Zoran

[hazard500]

Originally Posted by hazard500

I just received my Buffalo 3 DAC from the good guys at TP, and have been pondering what to do about an IV stage - so this thread has been an interesting read., mainly because TX seems like a very simple solution, and secondly, becasesI already use a TX output on my Cirrus Logic DAC (I have a CS4398 DAC eval board, which conveniently has take-off points on the board directly from the DAC output, before it goes to the op-amp output stage). So 2 questions:
1. Will my Lundahl 1527XL be suitable to with the Buffalo? It's 1+1:1+1, primary DC impedance = 54 ohm, freq response with 800 ohm source = 10Hz to 150kHz +/- 0.2dB - yes, 0.2dB!
2. I hate preamps, and tend not to use one - I have a source selector, and my phono stage has variable gain so nothing else required, however I do have a passive preamp for my existing DAC. Buit can i build variable gain into the TX output by using a switched attenuator across the primary of the TX - this should act as a voltage divider with the output impedance of the bufffalo (I'll work out the resistor values later). I would prefer to switch just one resistor between the +ve and -ve terminals, rather than bother with switching 2 resistors with an ground at the mid point, seems reasonable to me and if it works then the passive pre-amp is gone!! Good, I like minamalist solutions, not complex engineering.

BTW I should have said - buiold quality of the Buffalo DAC is superb. Thanks to fellows at TP!! I'm looking forward to getting the DAC built up.

Can anybody provide advice? Thanks, Paul

[reactivepower]

A2: Try the volumite. It doesn't get any more minimalist then that. I use one with the buffalo and transformers and it works fine.

[milen007]

sorry repost, i think this is the right place for ideas

hi guys

i setup my buffalo to run stereo mode using the Leon's guide. Thanks Leon.

i use qls qa 550 as a source for the I2S inputs. when connected to the sabre. the lock LED is on.

then i use transformer for the output. i connect the out + and out - to the primary of the 600:600 transformer. then connect the ground to the secondary side of the transformer to have the Single Ended out from the transformer.

I does sing nicely. but there is a distorted sound that follow the music. its very obvious when playing vocals and music seems noisy.

All the switches are set to OFF. input voltage is 5.25v and using all tridents.

any idea is really welcomed and appreciated.

regards,
erwin

[staccatiss]

Try to disconnect the GND-to-Secondary connection.


/S

Originally Posted by milen007

sorry repost, i think this is the right place for ideas

hi guys

i setup my buffalo to run stereo mode using the Leon's guide. Thanks Leon.

i use qls qa 550 as a source for the I2S inputs. when connected to the sabre. the lock LED is on.

then i use transformer for the output. i connect the out + and out - to the primary of the 600:600 transformer. then connect the ground to the secondary side of the transformer to have the Single Ended out from the transformer.

I does sing nicely. but there is a distorted sound that follow the music. its very obvious when playing vocals and music seems noisy.

All the switches are set to OFF. input voltage is 5.25v and using all tridents.

any idea is really welcomed and appreciated.

regards,
erwin

[milen007]

Hi Staccatiss

I have tried disconnect the ground. Still distort

Any other idea?

How to try just the buffalo without any analog stage? Can I put capacitor on the out (+) and ground for the output? Does it tell anything?

Thanks
Erwin

[Ciu]

Hello !

Do you connect ESS output to transformer's primary, without any resistor ?
What is transformer's DCR value ?

R.C.

[milen007]

Hi RC

yes without any resistor. straight from output of BIII to transformer. the dcr of the transformer is around 500R

i have few transformers. the other i tried has less than 100ohm

regards,
erwin

[Ciu]

So , I've done the same without any problem :
ESS V2 +- connected directly to Jensen JT11-HFMPC, secondary to RCA out, but no grounding ! Works perfectly !
R.C.