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Buffalo II & transformers

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#64
OK

io
 

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#69
Hello chaps,

I've recently put an order in for a BII and am going to go down the transformer route with a pair of Sowter 9762's and had a couple of questions.

1. Can someone recommend what type of resistors to use? My understanding is that they can have quite an effect on the sound. What should I try out?

2. The datasheet for the 9762 states that using the secondaries in parallel will improve the bandwidth but most schematics here use the secondaries in series - why?

3. I'm going to be using an OPA1632 to buffer the outputs and allow me to switch between the DAC outputs and my HT surround amp. Given I have a buffer with which I could add some gain, does this have any influence on my resistor choice? How much effect does using a lower resistance have?

4. Does anyone plan on using the 9545 and its bifilar windings with the dual mono mode of the BII/ES9018?

Thanks.
 
#70
Just my opinions as I am using Onetic OPTs with my Buff2:

1. I recommend at least trying no resistors on the primary.

Simply connect each DAC channel's + output to one side and the - output to the other side of the primary. Let the DAC's ground reference float....it's there to provide a signal ground voltage reference if opamps are used for I/V conversion -not needed with voltage output and transformers.

2. Secondaries in parallel have half the voltage but twice the current output compared to series connection. Take your pick.... Need more current to drive the next stage? Wire them in parallel. Need more gain? Wire them in series.

3. ¡Ay, caramba! Why use transformers when you intend to add a later opamp?!? You are on your own here as I've given up on opamps with their massive NFB for this application.

4. I'm not using a Sowter, so have no opinion here.
 
#71
steve jones said:
Just my opinions as I am using Onetic OPTs with my Buff2:

1. I recommend at least trying no resistors on the primary.

Simply connect each DAC channel's + output to one side and the - output to the other side of the primary. Let the DAC's ground reference float....it's there to provide a signal ground voltage reference if opamps are used for I/V conversion -not needed with voltage output and transformers.
On the secondary side you might need a resistor IF the transformer has high frequency ringing when connected to a load. That would need further investigation, or contact Sowter.

2. Secondaries in parallel have half the voltage but twice the current output compared to series connection. Take your pick.... Need more current to drive the next stage? Wire them in parallel. Need more gain? Wire them in series.

3. ¡Ay, caramba! Why use transformers when you intend to add a later opamp?!? You are on your own here as I've given up on opamps with their massive NFB for this application.

4. I'm not using a Sowter, so have no opinion here.
Click to expand...
 
#72
steve jones said:
Just my opinions as I am using Onetic OPTs with my Buff2:

3. ¡Ay, caramba! Why use transformers when you intend to add a later opamp?!? You are on your own here as I've given up on opamps with their massive NFB for this application.
Click to expand...

Well, my original thinking was that I'm using the transformer as a simple I/V stage rather than not using opamps altogether. However, I'm really just experimenting so I will add transformer only to my list of listening tests. 🙂

Thanks for the feedback.
 
#73
hello

Sowter 9762,9545 the Sabre is too large referral.
Recommended maximum of 1+1:2,2+2,2 bifilar, DAC Complete secunder primer per page 200 ohms. Secondary R load 1800 ohms.
My transformer core Permaloy blue silk-insulated wire
Set the correct primary resistance, secondary to the DAC + / - terminals between the measured signal 1Veff-1kHz, 0 dB . Then the DAC 200 ohm resistors to see. Output voltage of the secondary 6Vpp

io
 

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#74
sjalloq said:
Well, my original thinking was that I'm using the transformer as a simple I/V stage rather than not using opamps altogether. However, I'm really just experimenting so I will add transformer only to my list of listening tests. 🙂

Thanks for the feedback.
Click to expand...

Absolutely keep experimenting. What sounds best to you is what is correct.

Keep in mind that the Sabre chip is operating in its voltage output region with these transformers. You need a more specialized, usually a higher gain design, for transformer I/V conversion. 🙂
 
#75
Hey there io,

can I just try to confirm my understanding of your post...

Are you saying that the Sowters have too much gain? That I should use a maximum winding ration of 1:2.2?

I'm afraid I didn't understand what you were saying about the primary and secondary resistances.

Thanks.
 
#77
Can someone help me out here -I'm trying to work out how you calculate the Vout after the transformer and all the talk previously in this thread about RMS single ended and differenetial and specs being incorrectly quoted has muddled my mind.

Going back to basics, given we have a 3Vpk-pk output from the DAC with an output impedance of 195R, how do I calculate the voltage output after my transformer?

Assuming that I'm using the Sowter 9762 which has a primary DCR of 6R5, a secondary DCR of 1K25, I have the secondaries in series with the recommended secondary I/V resistor of 8K2.

I thought what I should be doing is calculating the secondary impedance as seen by the DAC and then using that value in a potential divider calc with the Rout of the DAC? Or have I got that completely wrong?

Thanks.
 
#79
Sowter 3575 anyone?

alboran said:
Hello
I can tell my personal experience with buffalo dac (es9018) + transformer.
I have tried many Transformer, Current and Voltage ..
Stevens & Billington TX-103 - Audio Tekne LT-8310 - UTC HA-108 (UTC A20) - UTC HA-101 - Jensen JT11-P-1 and others ...
the best sound I got with the two Jensen, I recommend trying these very Jensen.
wishes for the tests, good plays
Click to expand...

Hi all,

It seems that some folks have tried several transformers with the Buffalo and those that have seem to be telling us that the Jensen JT11-P-1 sounds best.

I like the idea of using Sowters for my coming BII as they offer an OCC wire option (yay!) and are in the UK where I am. Their 3575 seems to do basically what the JT11 P-1 does - 10K:10K balanced to SE conversion & isolation, so I reckon I'm gonna plump for one of these. Brian Sowter has also been very helpful in discussing this which is a big plus.

The 3575 is cheaper than Sowter's 9762 or 9545, it just doesn't say "DAC transformer" on its datasheet. Anyone got any thoughts here before I flash my non-existent cash? I'm not hugely experienced in DiY audio, but I've studied the forum posts on this topic very carefully and reckon this should be a good bet, with high impedance for working very decisively in voltage mode...

Datasheet:

3575

In this other post "Ciu" also recommends the Jensen for a Buffalo Dac (albeit Buff24) after trying several others:

http://www.diyaudio.com/forums/digi...c-ouput-using-transformer-14.html#post1994388
 
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