DAC and DHT

Design and use of the various types.
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prazza1
Posts: 38
Joined: Tue Nov 29, 2005 12:17 pm
Location: France

DAC and DHT

Post by prazza1 »

Hello evrybody,

I'm French and I would ask you sorry for my English.

I have sent a first mail to Dave and I will continue here. Thank you to Dave to accept me in this forum.

I want DHT from source to amplifier.
So, I would like first to work on a DAC output. From a commercial device I will modify the analog part like this:
DAC + I/V resistor + Transformer 1:5 + DHT 1LE3 + OPT
For the DAC transformer, I actually have a commercial "old" Sowter mumetal 9055 specified 1+1:5. On the Sowter site (http://www.sowter.co.uk/), the new 9055 is specified differently with a ratio 1+1:18. I will see latter about this transformer if I change it or no.

I'd like from Dave a serie feed OPT for the DHT 1LE3. I remind data:
1.4V/50mA filament
90 to 100V B+
2 to 5 mA Ip
Rp = 15k
0 to -3V Vg.

According to Dave, the better material is nickel for low level signal (I asked him about amorphous or other). He tell me about 80% or 49%. I respect this choice because I know nothing about transformer, but what is difference between 80 and 49?
I'm asking myself about ratio. 25K:1K, 16K:1K, or other. What would be best?
With this DHT with high Rp what can I expect about inductance/capacitance/frequency response?

Regards.
Pierre
dave slagle
Posts: 2085
Joined: Sat Jan 22, 2005 3:54 am
Location: NYC
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Post by dave slagle »

Hi pierre,

No need to apologize or even think twice about your english!
I have sent a first mail to Dave and I will continue here. Thank you to Dave to accept me in this forum.
Thanks for bringing it here, it is so much easier to track than email.
DAC + I/V resistor + Transformer 1:5 + DHT 1LE3 + OPT
It would be interesting to compare the position of the I/V resistor. It should do the same job across the primary and the secondar (the secondary value would need to be 25X the primary) The source should still work the same, but the benefit of the secondary loading might be seen in a more behave frequency response.

I'd like from Dave a series feed OPT for the DHT 1LE3. I remind data:
1.4V/50mA filament
90 to 100V B+
2 to 5 mA Ip
Rp = 15k
0 to -3V Vg.
While the 15K would normally scare me away, the low current makes it approachable.
According to Dave, the better material is nickel for low level signal (I asked him about amorphous or other). He tell me about 80% or 49%.
This may just be my personal taste, but I find the nickel to be best at the low AC flux levels.
I respect this choice because I know nothing about transformer, but what is difference between 80 and 49?
The 80% when gapped accordingly nets you better low level behavior and linearity.
I'm asking myself about ratio. 25K:1K, 16K:1K, or other. What would be best?
The difference is pretty trivial, either or should work similarly. I would make a guess at your total overall gain and go for 5:1 unless you are a bit gain shy.
With this DHT with high Rp what can I expect about inductance/capacitance/frequency response?
Well assuming 15K and a -1db of say 15hz to start we need about 300hy's and my goal in frequency response is nothing squirrelly as close to the audio band as possible. The decision on 80% and 49% will be made by acceptable DCR.

What is the gain of the 1LE3 and the expected output voltage of the dac after I/V conversion?

Dave
prazza1
Posts: 38
Joined: Tue Nov 29, 2005 12:17 pm
Location: France

DAC and DHT

Post by prazza1 »

Dave
What is the gain of the 1LE3 and the expected output voltage of the dac after I/V conversion?
The 1LE3 is given for a gain of 14 (I provide you data sheet).
The Dac output current is 1mA (PCM1704). With a 50 ohms resistor for the I/V conversion and a transformer of 1:5 we have 250mV at the DHT input. With the 1LE3 and an OPT of 5:1, the gain is 1.7. So, the Dac output would be 425mV or 300mVRms.

Pierre
Attachments
1LE3.pdf
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prazza1
Posts: 38
Joined: Tue Nov 29, 2005 12:17 pm
Location: France

DAC and DHT

Post by prazza1 »

Sorry,

The data sheet did not appear.
Attachments
DS_1le3_Tungsol.pdf
1LE3 Data Sheet
(127.54 KiB) Downloaded 582 times
prazza1
Posts: 38
Joined: Tue Nov 29, 2005 12:17 pm
Location: France

Post by prazza1 »

Dave,

About OPT, I'd like to know what you sugest:
EI, double C
Lamination thickness
Copper, silver,
....

Thanks.

Pierre
Retsel
Posts: 47
Joined: Tue Feb 01, 2005 9:51 pm
Location: Ann Arbor, Michigan USA

Post by Retsel »

I worked with Mr. Slagle on adapting a transformer to my Sony DVP-S9000es SACD player. The long process of how I adapted a transformer to my player is here:

http://www.intactaudio.com/forum/viewtopic.php?t=12

In looking at what you want to do, I suggest trying to configure the simpliest configuration possible. I see that you want to come off of a set of current pulse DACs. It might be a better bet if your player has an earlier set of voltage out DACs, to take the output from those. It would remove another set of active devices from the signal path resulting in a more transparent sound.

What I have read about MU metal is consistent with what Dave is recommending. While amorphorous steel is a good deal when you are faced with too high a current (particularly when DC is around) that could potentially saturate the transformer core, MU metal is probably the best core material out there for "transforming" the AC. Dave can wind up a pair that can withstand the current that your transformers would see, and they would likely be a little bit larger than the amorphorous ones, but that is of little concern for these smaller currents.

I would try the transformer right off the DAC chips and then going directly to output. Adding the tube stage could be necessary if you plan on driving long cables or multiple amps. For example, I come off my SACD player, go through the transformers and go directly to output with some shunt capacitors to provide some filtering. My preamp is Dave's autoformer volume control. I then go to my SET amps and also to a Hafler solid state amp which I use to drive my subwoofers. Despite driving two amplifiers, I have sufficient current. Adding the tube stage can add another $500 or more in parts to do the power supply and output right.

I did have some occasional problems with some noise in the output of my transformer coupled player which is likely due to either a type of oscillation, or due to excess current draw from the chips. In my situation, it is not a problem if I load the chips properly.

Retsel
prazza1
Posts: 38
Joined: Tue Nov 29, 2005 12:17 pm
Location: France

Post by prazza1 »

Retsel,
I see that you want to come off of a set of current pulse DACs. It might be a better bet if your player has an earlier set of voltage out DACs, to take the output from those.
Sorry, but my DAC that I want to modify is with PCM1704, so current output.
I would try the transformer right off the DAC chips and then going directly to output.
I know, but we need gain. If we use transformer like 1:18, as we can find into some DIY projects, the output impedance will be too high, between 8k and 16k with an I/V resistor between 25 to 50 ohms (I use a transformer attenuator as amp input). We need extra stage for lowering output impedance.
If we use smaller transformer like 1:5, we will not have enough gain. We have to add an extra stage for higher gain.
Maybe I will have to use a 1:18 plus extra stage to have enough gain for a future amp project: 50 ohms + 1:18 + 1LE3 + OPT = 1VRMS.

Pierre
Retsel
Posts: 47
Joined: Tue Feb 01, 2005 9:51 pm
Location: Ann Arbor, Michigan USA

Post by Retsel »

I understand better now.

What player do you have?

Retsel
prazza1
Posts: 38
Joined: Tue Nov 29, 2005 12:17 pm
Location: France

Post by prazza1 »

I have a Wadia drive and a Bel Canto DAC 1.

Pierre
lanshan75
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Joined: Wed May 16, 2012 3:37 am

Post by lanshan75 »

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