Buffalo II & transformers

[rolls]

Vingborg,
The very fact we provide DC to the transformer is suboptimal and not best use of transformer.

We do not provide dc to the transformer:
both inputs have exactly the same voltage, 3.05 Volts,
the resistors are connected to ground, not to a midpoint in the transformer winding. The transformer just sees the differential voltage across its input.

 

[flocchini]

AR2 says

"I decided to try just caps(very good ones) and buffer and I have to say I like it so far. I will need some time to really have some critical listening but so far nice"

Have you posted more about this and ZM's buffer in another thread?

Thanks

Bob

 

[Marek]

If you want current mode, it is mandatory, that there is always output current.
At bipolar zero, 1.65V, you have 4 * 2.112mA to ground, I can call this bias current.
If you had your bias at 1.65 V, there would be no bias current.

I believe its not true. General principle is:
Current DACs wants to see near zero load impedance to perform with minimum voltage swing.
Voltage DACs wants to see infinity load impedance to perform with minimum current swing.

ES9018 is slighty different DAC than each other. It can work LIKE voltage or current DAC but really there is no such thing like "voltage mode" or "current mode". With load impedance many times higher than ouput impedance (195ohm) there is huge voltage swing and little current swing so we call it "voltage mode" and with load impedance many times lower than 195ohm there is a huge current swing and little voltage swing and we call it "current mode". Ofcourse between there is some "mixed mode" more o less current/voltage.

If you have an opamp at the output, you connect the current output always to the neg. input, which is a virtual ground.

In case of R2R current DACs with bipolar analog power supply like PCM1704, PCM63, AD1862/5 there is no DC bias on the output so :
- in case of passive I/V you just connect R to GND
- in case of opamp stage you connect positive opamp input to GND (and on negative input you get virtual ground)

BUT

In case od D-S current DACs with single analogo power supply and with DC bias, positive opamp input should be connected to Vref so on the negative opamp input you get Vref!
look at 25 page of ES9018 datasheet: https://myl8test.files.wordpress.com/2013/05/download-es9018-datasheet-here.pdf

Some DACs like AD1853, AD1955 simply provides Vref pin wich should be connected to positive opamp input.

So IMO in D-S current DACs with passive I/V load resistors should be connected to Vref (1,65V, near zero impedance supply) not GND or connect one resistor across ES9018 outputs.

Marek

 

[CFT]

A side question.
Is ~10mv going into a LL1933/41 a bit high for an MC SUT? And 1:32 config would be pushing it.too much for 1941?

 

[rolls]

I believe its not true.
Marek

Joe Rasmussen has convinced me, I can hear it:
" Note that internal 1.65V offset, the Sabre DAC is unique in that you can still ground it to 0V (don't try this with any other current DAC - it may not survive - and don't do it to conventional voltage DACs since they all have about 2.5V). So essentially shorting the output to virtually ZERO Volt, means the offset now become a current offset of 8mA. "

 

[Vingborg]

Good evening folks

How nive to see some life in this old thread again

All right - Lot's of opinions, and some facts too..

My endless dream would be to use Lundahl LL1941 step up 1:16!!
And why is that? -- Because Lundahl claim they have "Outstanding audiophile performance" and the ratio of 1:16 will be perfect for me!
Please follow:
I have put together a tube circuit with a gain about 25. And as far as I understand is loading the dac with ca. 0,6 ohm to ground will provide me with ca. 6mV on the output.
0,006 volt times 16 is 0,096 volt. Times the gain of ca. 25 give me 2,4V output. Which is the same as my cd player! Maybe that's a bit too high but that is adjustable with the load resistors.
The tube stage is buildt around EF86 tubes and is fully ballanced. I don't know the input impedance of my finished circuit, but the EF86 tube have a very high internal impedance, way over 1M which I believe will be incredibly appropriate for the transformers to look into!

That is my goal, but what if the LL1941 dosen't have a good bass respond from this source of 195 ohm?? According to Marek a step up like LL1931 can't do the "bass" job.. And Kevin Carter says allmost the same about the source of 195 ohm vs. small primary induction of mc and mic tranni's!

Maybe I haven't been keeping up but - Rolls, you posted this:

"I have just looked into the LL 1941Ag specs:

Static resistance of each primary: 0.5 Ω
Static resistance of each secondary: 95 Ω
Frequency response (serial connection, source 10 Ω,
no load / secondaries open):
10 Hz -- 100 kHz +/- 1.0 dB

So they take 10 ohm, because 1:32 ratio is possible.
So for our task, about 1 Ohm source, it will be absolutely perfect,
and I have heard very good things from these."

Seen with my eyes, you say we can put down the output Z of the dac from 195 ohm to about 1 ohm by adding resistor's to ground? Is that possible?
If in fact yes - Then there will be no issues at all for select betveen transformer's

If someone in here have 2 Lundahl LL1941 that I can borrow to try this out and actually hear for myself the sound of the bass respond and the hole sound stage of these damn can's.. My great god that person will be more than normal welcome!!!

If the transformer actually has to have an input impedance of 200 ohm to match ES9018 output impedance, how can I found out about that? I mean, Lundahl dosen't tell us the impedance - Only the primary dcR and the ratio in ther program.. Or is it me there just can't compute that for myself?

LL1941 - My sweet dream

Best from Henrik Vingborg

 

[AndriyOL]

LL1941 - My sweet dream And why is that? -- Because Lundahl claim they have "Outstanding audiophile performance"

Why Lundahl LL1941 is so precious? You so desperately trust Lundahl? Is this the best transformer to be used with ES9018 dac, based on specs or other facts? Otherwise sounds like advertisement.
You say small primary induction and not good bass responce. Can't you just remake it for your needs to have higher induction or made transformer by yourself? Or is there something special in these step up transformers?

I may trust also if Marek, Joe Rasmussen confirm )

 

[CFT]

It became clear to me how the current mode and volt mode configs work when I started reading this thread from pg 38, ie, the time when rolls walked in..

I noticed LL1933 was used by mars2 and sounding very good reportedly (LL1941 has higher ratio with amorphous core)...however both Thomas Mayer and Kevinkr I communicated with said its too a high a voltage for these step up transformers here...I am trying to.find out more about it...but apparently mars been enjoying with his......

 

[Marek]

Good evening folks

I have put together a tube circuit with a gain about 25. And as far as I understand is loading the dac with ca. 0,6 ohm to ground will provide me with ca. 6mV on the output.
0,006 volt times 16 is 0,096 volt. Times the gain of ca. 25 give me 2,4V output. Which is the same as my cd player!

Correct.

Seen with my eyes, you say we can put down the output Z of the dac from 195 ohm to about 1 ohm by adding resistor's to ground? Is that possible?

If you load DAC with 1ohm resistor (so ES9018 works more o less like current source) you get 1ohm voltage source which has more than low enough impedance. So in this configuration LL1931/33/41 should work fine, unlike in "voltage mode" whose 195ohm output impedance if far far too high for those trannies.
So, it is important to decide which "mode" you choose because diffrent type of trannies will be needed.

If the transformer actually has to have an input impedance of 200 ohm to match ES9018 output impedance, how can I found out about that? I mean, Lundahl dosen't tell us the impedance - Only the primary dcR and the ratio in ther program.. Or is it me there just can't compute that for myself?

Yes, this is problem with lundahl and theirs datasheets - no primary inductance, desired source impedance. The only usefull information is source impedane used for frequency response test which IMO more o less determines source impedance trafo is desired for.


I'll check "current mode" with my LL1931 (1:16) and active tube gain stage as soon as I find some free time.

 

[Marek]

Why Lundahl LL1941 is so precious? You so desperately trust Lundahl? Is this the best transformer to be used with ES9018 dac, based on specs or other facts? Otherwise sounds like advertisement.
You say small primary induction and not good bass responce. Can't you just remake it for your needs to have higher induction or made transformer by yourself? Or is there something special in these step up transformers?

I may trust also if Marek, Joe Rasmussen confirm )

I think many pepole trust Lundahl because this in main supplier for professtional audio gear. Furthemore LL1931/41 and maybe other ones use uncommon cobalt amorphous core, Cardas copper and winding technique which is probably not achievable to most of us.

 

[CFT]

Mr. Lundahl just confirmed to me that "10mV signal level is not a problem" for LL1933/43 in this application.

 

[Marek]

CFT,

I used LL1931 in "voltage mode" with great success (besides low freq rolloff) so even 3Vpp seems not to be a problem.

 

[AndriyOL]

How Lundahl transformers LL1933/41/43 compare with Teramoto FINEMET, which are better?

 

[Marek]

I doubt anyone got both of theme - price of Finemet trannies is inadequate.
Personnally I got L1931 and Finemet CC cores which I bought from Teramoto (for 6n30p tube output transformer) but unfortunetally they never left project stage...
Maybe its good idea to make Finemet step-up trafo...

 

[CFT]

Marek, great! Looking forward to your report on trying out the current mode with your 1931

 

[Magz]

I use a Lundahl LL1676 with my Buff III, wired 2+2:1+1 for a 2:1 stepdown, no ground connection for the output of the Buffalo, just straight into the two sides of the primary. In this configuration it has more than 200H primary inductance, which is more than enough to provide thunderous bass performance with the ES9018.

The Lundahl provides HF filtering and I've arranged the secondary snubber plus primary resistance to give me the "Rasmussen rolloff" of 1.3dB at 20kHz. Sounds EXCELLENT feeding the output stage, a 26 DHT tube in parafeed to a Bent Audio silver autoformer!

I am so satisfied that I have no intentions of tweaking this any further. It destroys the PCM1704 DAC in my CD player. Not even close.

 

[CFT]

Excellent preamp! I have a 26 too which I plan to use after the tranny. Mr. Lundahl said it should be fine to connect it in a 1:32 config here...still, its the overall gain I may get issue with...using current mode and a low mu tube..

Suggest those that would like to see more about volt vs current mode to start reading from page 38
http://www.diyaudio.com/forums/twisted-pear/164294-buffalo-ii-transformers-38.html

 

[Vingborg]

Why Lundahl LL1941 is so precious? You so desperately trust Lundahl? Is this the best transformer to be used with ES9018 dac, based on specs or other facts? Otherwise sounds like advertisement.
You say small primary induction and not good bass responce. Can't you just remake it for your needs to have higher induction or made transformer by yourself? Or is there something special in these step up transformers?

I may trust also if Marek, Joe Rasmussen confirm )

Advertisement? I never thought of it that way, but now you mention it - It really could sound like that but that is certainly not my intension!
I don't have any fact's about these step up's from Lundahl because I don't have a pair. I can't construct a transformer or remake one or another.. But as Marek says:

I think many pepole trust Lundahl because this in main supplier for professtional audio gear. Furthemore LL1931/41 and maybe other ones use uncommon cobalt amorphous core, Cardas copper and winding technique which is probably not achievable to most of us.

This is completely my version
There are many reasons why I have a "feeling" for these Lundahl LL1931/41 especially 1941.
As Marek allready have written: Uncommon Amorphous core, Cardas copper, special winding technique, solder pinds instead of wires.. And from my point of view, maybe a bit silly but something I still have in mind - The physical design! I am very good at design so it dosen't hurt me that these transformers from Lundahl is far more pretty than fx. Sowter.. Furthermore I'm from denmark and I like merchandise from Sweden (Location is not a main reason)
BTW I have at the moment borrowed a pair of LL1684 1:1 with amorphous core and these tranni's sounds really nice. But to force the dac down with 0.5 ohm needs a heck of gain to reach my goal.
That's also why I think of the LL1941 made of these nice materials and with 1:16!

If you load DAC with 1ohm resistor (so ES9018 works more o less like current source) you get 1ohm voltage source which has more than low enough impedance. So in this configuration LL1931/33/41 should work fine, unlike in "voltage mode" whose 195ohm output impedance if far far too high for those trannies.
So, it is important to decide which "mode" you choose because diffrent type of trannies will be needed.

Sorry me for being slow.. I just have to hear this again for making sure before I throw myself into more money waste
I'm going to use my Buffalo III fully balanced all the way to my preamp (my system is fully balanced all the way to the speakers)
I will connect dac output + and - to the primary of LL1941 with load resistors of 0.5 ohm from each phase to ground.
This approach will bring me 0.005 volt to the primary and times 16 on the secondary which will go straight to the grid of the tube stage with gain about 25. This bring me 2 volt on the input of my preamp.. That's perfect!
But will there be a weak bass respond on this?
I mean - does the LL1941 transformer really see a source of 0,5 ohm?
Because in that case it does, this LL1941 will be absolutely perfect for my application!! I hope
And with that low output impedance of 0.5 ohm it could be like a "free choice" between transformers.. Have I understood this correctly?

I tested the 28 db (25 times) gain stage with EF86 tubes and it had a really good sound with very low noise.

Best from
Henrik Vingborg

 

[Marek]

I mean - does the LL1941 transformer really see a source of 0,5 ohm?
Because in that case it does, this LL1941 will be absolutely perfect for my application!! I hope
And with that low output impedance of 0.5 ohm it could be like a "free choice" between transformers.. Have I understood this correctly?

From Thevenin law:

you can replace DAC (1,65V +195ohm) + Rload circuit with equivalent e voltage source with r resistance (in this case R2=0).

You can quickly calculate your new source equivalent with online calculator on boottom of this page (enter R2=0,000001ohm because it doesn't accept 0 value):
Thevenin's Theorem

So do the math and come back with results

 

[Vingborg]

Hello

All right, I tried to enter the data that I have - dac, load and so on.. The picture look like this:

An externally hosted image should be here but it was not working when we last tested it.

I must admit that I don't understand much of these numbers or the calculater..
I never heard of Thevenin law, but hey, I'm a carpenter

For me it looks like transformer is served an output impedance of 0.49872222 ohm from dac on primary winding when I load the dac with 0.5 ohm!
Is that true??

Can you Marek.. Or somebody else bring a light on this for me

I would be so enormously happy if it is possible for me to present the LL1941 for a source impedance as low as 0.5 ohm!

Very best regards
Henrik