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Old 16th February 2012, 01:24 AM   #301
hkminn is offline hkminn  South Korea
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Quote:
Originally Posted by pietjers View Post
Hi hkminn,

Interesting approach!
The Sowter datasheet suggests that the IV resistor may also be used across the secondary winding of the transformer (taking into account that the value of the resistor is reflected on the primaries by the ratio of the transformer (18.7) squared: 18.7 x 18.7= 350). Did you try that also?

What are the drawbacks of the high transform ratio? Or is there something like a free lunch?
Datasheet for Sowter 8347 and 9055:
Sowter Type 8347 DAC INTERFACE TRANSFORMER

Peter
Hi Peter,

I have not tried I/V resistor on the secondary yet. I was trying Joe's suggestion, and carried away a little bit ending up using 1R resistors.

The reason why I picked 8347 was just because I happen to have one. But the high ratio(1:17) turns out to be an advantage to me. Since 8347s have a quite amount of gain, I could use a lower value resistor and lower-gain tube stage. It is a sure advantage for DIYers.

Soundwise, I have not done much comparison yet, but I definitely prefer this approach to the opamp virtual ground I/V.
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Old 16th February 2012, 07:51 AM   #302
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Hi hkminn,

The opamp IV stage that you used before, was that an IVY or another opamp based design?

I wonder what the drawbacks are of such high transformation rations. Increased distortion? Capacitive losses? Can someone with knowledge about this matter give some additional information, or is there a link or website with information regarding this subject?

Peter
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Old 16th February 2012, 03:11 PM   #303
hkminn is offline hkminn  South Korea
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Quote:
Originally Posted by pietjers View Post
Hi hkminn,

The opamp IV stage that you used before, was that an IVY or another opamp based design?

I wonder what the drawbacks are of such high transformation rations. Increased distortion? Capacitive losses? Can someone with knowledge about this matter give some additional information, or is there a link or website with information regarding this subject?

Peter
My other DAC is Buffalo32 with built in I/V. Maybe it is the matter of taste, but I prefer Buffalo24+transformer+tube to Buffalo32.

About the high transformation ratio, I do not have enough knowledge to answer. However, people use step-up transformers for phono cartridges, and the transformation ratio is higher in some cases.
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Old 17th February 2012, 05:35 PM   #304
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Question....
Using Buff2's in dual mono with tranformers ... should the ouputs on each board be simply parelled (+ to + and - to -)before feeding the transformer, OR should the ouputs be connected + to - and - to + (out of phase). This is with the dip switch on each board set appropriately to dual mono and each board set for lef and right channel. Note: I am not using a Volumite in my application.

Thanks

JD

Last edited by Jeffrey Davison; 17th February 2012 at 05:37 PM.
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Old 18th February 2012, 01:18 AM   #305
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You should parallel the outputs but it is not a matter of joining the + and + outputs because one side of each DAC's output (in dual mono) is in anti-phase. The following is the best explanation of how to do it (which I copied off the Twisted Pear support forum):-

For the left channel configured Buf 2 you will wire DAC outputs to output stage inputs like this:
Left + and Right - (both joined in parallel)to OSL in+
Left - and Right + (both joined in parallel)to OSL in-

For the right channel configured Buf 2 you will wire like this
Right + and Left - (both joined in parallel)to OSR in+
Right - and Left + (both joined in parallel)to OSR in-

OSL = output stage left
OSR = output stage right

Last edited by ihear21khz; 18th February 2012 at 01:22 AM.
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Old 18th February 2012, 08:06 AM   #306
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Wouldn't that put the left and right outputs at opposite polarities?

Shouldn't both output stage be the same and let the switch 1 & 2 of dipswitch select which channel is left and right?

Outputstage is single ended in my application.

I understand on "each" board configured as a "mono" board that the outputs are to be joined counter phase to each other.

Then should not both the left mono board and the right mono board be the same as each other.... as they are going into there respective channel and should have the + and - in the same orientation? They are after all "independant" channels, hence "dual mono".

Your description as each mono dac channel, that is, each separate board, with the polarities reversed relative to each other as their output enters their respective output stage.

JD

Quote:
Originally Posted by ihear21khz View Post
You should parallel the outputs but it is not a matter of joining the + and + outputs because one side of each DAC's output (in dual mono) is in anti-phase. The following is the best explanation of how to do it (which I copied off the Twisted Pear support forum):-

For the left channel configured Buf 2 you will wire DAC outputs to output stage inputs like this:
Left + and Right - (both joined in parallel)to OSL in+
Left - and Right + (both joined in parallel)to OSL in-

For the right channel configured Buf 2 you will wire like this
Right + and Left - (both joined in parallel)to OSR in+
Right - and Left + (both joined in parallel)to OSR in-

OSL = output stage left
OSR = output stage right
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Old 18th February 2012, 08:24 AM   #307
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When a board is in mono, the so called "L" and "R" outputs are the same, but one side is in anti-phase. The + and - markings were silk screened on the Buffalo board for normal stereo operation. It does not "apply" when you go dual mono.

What you want to do is to sum the outputs of the positive phase on both sides and the same for the negative phase. If you just tied + and + as silk screened on the board, you would effectively cancel out the signal as you would be adding the "in-phase" signal with the "anti-phase". The output of the DAC has been configured like this when in dual mono mode. You need to follow the instructions, though it may seem counter intuitive.

If you think about it for as moment, the - of a negative phase is +. So you add this with the + of the positive phase, you get 2+ (or in this case twice the output).

I followed the instructions and it worked fine.

Last edited by ihear21khz; 18th February 2012 at 08:47 AM.
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Old 18th February 2012, 03:13 PM   #308
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I got that...

It's just that description has one Buffalo 2 board in mono + and - (summed) and the other Buffalo 2 board + and - (summed) going into opposite polarites of the Output stage relative to the other output stage.... THAT"S what is the confuser. I just drew out on paper how you initially described the hookups.

JD


Quote:
Originally Posted by ihear21khz View Post
When a board is in mono, the so called "L" and "R" outputs are the same, but one side is in anti-phase. The + and - markings were silk screened on the Buffalo board for normal stereo operation. It does not "apply" when you go dual mono.

What you want to do is to sum the outputs of the positive phase on both sides and the same for the negative phase. If you just tied + and + as silk screened on the board, you would effectively cancel out the signal as you would be adding the "in-phase" signal with the "anti-phase". The output of the DAC has been configured like this when in dual mono mode. You need to follow the instructions, though it may seem counter intuitive.

If you think about it for as moment, the - of a negative phase is +. So you add this with the + of the positive phase, you get 2+ (or in this case twice the output).

I followed the instructions and it worked fine.
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Old 19th February 2012, 08:16 PM   #309
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all is well. just have to physically complete the build this weekend , wire and test.

JD
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Old 20th February 2012, 04:37 AM   #310
GaryB is offline GaryB  United States
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Default another transformer output build

Hello all,
I've got an older / original Buffalo DAC - the original ESS9008 design from circa 2008. I built it using the LCDPS supply for the DAC and the LCBPS +-15v supply for the IVY output stage. I'd tweaked the DAC with the Va mod where one generates 3.3v from an LED reference but otherwise things were pretty stock. In some circumstances I found that the DAC sounded outstanding but it was very system/equipment dependent.
I had some good input transformers, so I thought I'd give the transformer option a try. The transformers I used are Tamura GA80071 as used in the Yamaha PM1000 mixing console. They are 600:1350 ohms which translates to a 1:1.5 step up ratio. These are often found on ebay and I picked up a few of these a couple of years back. Since these are input transformers, I decided to follow them with a diamond buffer to make sure there was sufficient drive. I loaded the secondary of the transformers with 15k ohms. I suspect that tweaking the loading of the primary and/or the secondary will have benefits but even fresh off the soldering iron, it sounds great. Definitely a nice step up from the original IVY stage.

I've also got some other transformers lying around and will eventually try a few different ones. I've got some surplus 150/600ohm:15k ohm input transformers that would let me load down the buffalo more into current mode. And I've also got a pair of the Sowter 8347 DAC (1:17) transformers which would let me use even lower resistive loading. But for now, I'm going to let these burn in and get used to the sound.

---Gary
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