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Output transformers for DACs
Output transformers for DACs
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Old 7th June 2021, 06:30 PM   #591
Supersurfer is offline Supersurfer  Netherlands
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Quote:
Originally Posted by bisesik View Post
Hi Stefan.
Yes, there was some comparisons from TioFrancotirador, read his posts in this thread please.



Regarding the the i/v stage for TDA1541A (or other rare DACs from the past), I reminding again, you will never hear "Hi-End" sound form them until you goes down the 20 ohms. The showned tracks are done at 1.4 Ohm of i/v. I believe it is very far from adequate i/v stages comparison, when you trying to get the sound at such a huge values of the i/v resistor like 50 or even more Ohms impedance seen by DAC itself.



To all who uses tube stages in their systems.
Do you know "tube guys" why is your tube stages sounds best at so high input levels like 2, 3 or even 4 volts of input signal? Because the input impedance of your preamps/amps is TOO high to transfer what is really matters, the signal power! Not the current or voltage, but the wattage, the both together: I*A.

Thus instead of beating/hiting the DAC itself by irrationaly high load impedance (i/v) trying to get the high signal voltage (noise level is horribly high), much better approach is to:
1) decrease the output impedance after i/v stage;
2) decrease the input impedance of the preamp/amp.

I have 14 Ohm of the DAC output impedance and 300 Ohm of the input impedance of amplifier. Of course it is not possible to do for the DAC, without active components like jfet buffer for example (voltage amplification is less than 1). Another really well sounding DACs are these which uses trafos+tubes with high mu of voltage amplification. BUT I prefer to use a better (as for me) approach - to use another one transformer for voltage amplification+jfet buffer to get suitable voltage swing at lower output impedance. Transistors for voltage amplification are just faulty for my ears, no matter the technology (fets, bipolar, silicon, germanium...), but the current amplification on jfets is just a briliant for sound.
Hi,

I have read the comparison you referenced and he prefers your transformer over a Finemet transformer. I cannot judge this verdict because I do not know the other variants of both transformers (winding technique and winding ratio), I do not know how he tested, with what kind of system (what is his reference) and how his overall listening experience is.

I just wondered if you could get your hands on finemet core material and design a transformer with it.

I also do not understand what you mean with the IV stage problems of the old TDA1541A. I use an IV resistor of 27ohms with a tube stage after the resisitor. The dac sees a low impedance so it wil transfer I into V with low distortion.

A tube stage for amplifying this low level signal is nothing special IMHO. There are numerous phono stage designs with tubes for MC and MM cartridges.
The best way for MC is even a step up transformer with following tube stage.

So I would guess the same can be done with this dac. But maybe I am missing something
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Old 7th June 2021, 09:16 PM   #592
bisesik is offline bisesik  Kazakhstan
Output transformers for DACs
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Output transformers for DACs
Quote:
Originally Posted by Supersurfer View Post
Hi,

I have read the comparison you referenced and he prefers your transformer over a Finemet transformer. I cannot judge this verdict because I do not know the other variants of both transformers (winding technique and winding ratio), I do not know how he tested, with what kind of system (what is his reference) and how his overall listening experience is.
Hi, OK.

Quote:
I just wondered if you could get your hands on finemet core material and design a transformer with it.
Well... I hope, you understand that Finemet is just a brand name of Hitachi Metals Ltd material. I do not see any reason to use exact this brand name as there are japanese masters available I suppose like Teramoto for example. Take a look for prices on their transformers BTW too.

Quote:
I also do not understand what you mean with the IV stage problems of the old TDA1541A. I use an IV resistor of 27ohms with a tube stage after the resisitor. The dac sees a low impedance so it wil transfer I into V with low distortion.
It depends on what you call low distortion and from your own preferences. But 27 Ohms is OK I think. Step-up transformer will allow to decrease i/v even more anyway. I remind best i/v for DAC is ZERO.

Quote:
A tube stage for amplifying this low level signal is nothing special IMHO. There are numerous phono stage designs with tubes for MC and MM cartridges.
The best way for MC is even a step up transformer with following tube stage.
Sure, I just shared my experience of using trafos/bufs cascades instead. It is up to user.

Quote:
So I would guess the same can be done with this dac. But maybe I am missing something
No, you didn't!
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Last edited by bisesik; 7th June 2021 at 09:19 PM.
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Old 9th June 2021, 08:47 PM   #593
Supersurfer is offline Supersurfer  Netherlands
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Hi,

I know Fimenet is a trade mark of Hitachi. They claim it is a very high quality amorphous core material with some specific quality that can be advantageous for our audio signal transfer.
I use f.i. nickel, permalloy and amorphous core transformers in my amplifiers and recognize the differences, that is why I have the feeling that this Finamet material can be a very nice choice for the low level signals your products are used for.

I have no clue if there are other suppliers of this material. Is Teramoto just a brand that is using the Hitachi core materials under their own brand name for instance?
I think however that production of such material is expensive and only big companies with big offset market can produce such stuff. So it would not surprise me if all Finamet material in the world is produced at one factory and used under other brand names.

Regarding the prices of Teramoto and such: I have been in the audio business and know that the asking price of a product, in a lot of cases, is not related to the costs of the product or the final quality! In the High-end audio market there is a lot of crap put a nice case that is sold with some marketing and a nice brand name for big bucks to dumb people with money

So are you willing to use this material?

Last edited by Supersurfer; 9th June 2021 at 08:49 PM.
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Old 9th June 2021, 09:06 PM   #594
Zoran is offline Zoran  Serbia
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Location: Belgrade
Yes. Hithachi cores are new and obtainable. For some steady and constant quality production it is a choice.
Personaly I prefer M types Siemens style (probably made by VAC?) high permaloy laminations. But they are close to unobtainable and in case of find some that is not so big quanitities for few transformers only.
And they are hard to form the core. Thick, sensitive and M types. Also is harder to find with smaller gap. Byt for my opp they are the best sounding (with propper implementation of windings and all additional construction elements.)
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Old 10th June 2021, 01:59 AM   #595
bisesik is offline bisesik  Kazakhstan
Output transformers for DACs
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Output transformers for DACs
Quote:
Originally Posted by Supersurfer View Post
Hi,

I know Fimenet is a trade mark of Hitachi. They claim it is a very high quality amorphous core material with some specific quality that can be advantageous for our audio signal transfer.
Finemet is not amorphous material.

Quote:
I have no clue if there are other suppliers of this material. Is Teramoto just a brand that is using the Hitachi core materials under their own brand name for instance?
I cannot know for sure and of course only they themselves know the answer, but I have not seen any mention of the other material usage within their products.

Quote:
I think however that production of such material is expensive and only big companies with big offset market can produce such stuff. So it would not surprise me if all Finamet material in the world is produced at one factory and used under other brand names.
No, it is not so. There are manufacturers in Europe, Russia and China as well.

Quote:
So are you willing to use this material?
I see absolutely no point for this, since the initial data I need to know about cores is in their datasheet. Nothing extraordinary I see in their specs compared to what I use. All the futher sucess depends on the practical implementation and usage. In this terms most likely it will be Teramoto who is the measure of quality when using it's material in the field of audio. I mean there is hardly a more authoritative opinion in the framework of audio than Teramoto, which Hitachi will refer to. If they will refer at all, of course. I hope you understand that no one has ever made cores specifically for audio. Audio is just a fortunate by-product of these cores and materials. These materials were created for energetics, however, a similar story with radio lamps, and indeed with almost all other radio components. Well, you know I suppose the circumstances...

But what I am disagree... In this context, I do not like at all how ineptly uses all the advantages of such a unique core material for low-signal transformers in Teramoto products for example. Cutting such a core is just a mistake. When I take the naked core in my hand, it is very flexible, like it is made from a jelly. I mean it is impossible to tight the two pieces together with precise accuracy without stressly squizzing it... Gapped, strong big trafos/chokes for big currents/swings, working at a constant current offsets (tubes interstage, output trafos) - is just another story.

That is why I am able to see competitors for my technique/trafos within the toroidal transformers only. It is not Teramoto at least. In this terms winding in automatic mode (like Teramoto, for example) using my hand winding technique simply won't work. Well, unless you start using something very similar to two human hands. The cost and complexity of such a machine will clearly be beyond the scope of the DIY I believe.
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Last edited by bisesik; 10th June 2021 at 02:23 AM.
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Old 10th June 2021, 07:50 PM   #596
Supersurfer is offline Supersurfer  Netherlands
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Hi Ivan,

I now understand that you do not feel the need to use the Finemet material.

A note however that it IS an amorphous material as stated here: FINEMET Transformer

“ FINEMET® is Nanocrystalline soft magnetic metal which is special amorphous metal. It's phase characteristics is far better than conventional core material such as Ni and Co-based amorphous metal.”
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Old 10th June 2021, 08:04 PM   #597
bisesik is offline bisesik  Kazakhstan
Output transformers for DACs
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Output transformers for DACs
Hi Stefan. Well, I haven't seen such interpretation within the metal manufacturers (amorphous usually mentioned as a predecessor). Teramoto as a user is free to call it how they want/feel to be understanded by customers I suppose.
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Old Yesterday, 08:01 AM   #598
bisesik is offline bisesik  Kazakhstan
Output transformers for DACs
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Output transformers for DACs
Here is the version of PCB using jfet buffers. SE output ONLY.
PCB.jpg
jfet.JPG

Some tips:
1) To have quick access to both PCB sides (for jumpers re-settings, components resolderings, etc.) it is better to have possibility of transformers dismounting using the receptacles:
5391-0-15-15-07-27-10-0 Mill-Max | Mouser Europe
2) M3 spacers 4mm in height for proper gap between PCB components and transformer plate will be needed to place as well.
3) Better to use a matched pair of 2SK170V/2SJ74V (output impedance better, no offset) instead of using the trimmer between transistors Sources (for set zero output offset).
4) For better thermal/current simmetry stability it is better to tight this pair of transistors together using a copper foil and/or small radiator.
5) The PSU quality is VERY important. Based on my experience I highly recommend to use UCs or/and battery PSU for powering jfets.


All the corresponding files (CAD, gerbers) can be found here:
jfet.zip
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Last edited by Sangram; Yesterday at 08:45 AM. Reason: Edited post per poster's request.
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Old Yesterday, 05:03 PM   #599
stew1234 is offline stew1234  United States
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Output transformers for DACs
Is there a minimum watt rating for the resistors to use on the boards?
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Old Yesterday, 05:35 PM   #600
bisesik is offline bisesik  Kazakhstan
Output transformers for DACs
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Output transformers for DACs
any from 0.1W
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