[drtechno]

What is wrong with the Fikus design of tis solution?
 

I don't know who Fikus is.
 
But looking at the schematic above it doesn't really show where he is getting the plate supply from. If this person is tapping off the primary of the transformer, then this would be an very unsafe unit indeed.

 

[drtechno]

but this thread is old old.
 
an probably the people who made that dac probably have a different version. Of course it smells of cheap chinese ebay.

 

[mateusfig]

  What is wrong with the Fikus design of tis solution?
 

I don't know who Fikus is.
 
But looking at the schematic above it doesn't really show where he is getting the plate supply from. If this person is tapping off the primary of the transformer, then this would be an very unsafe unit indeed.

Why would this unsafe because the fact you said? 

 

[Sodacose]

The schematic seems to show a simple bridge rectifier with some CRC filtering afterwards to derive 150VDC.  It appears that the input to the bridge is 120VAC.  If that is directly connected to mains input, it is definitely not the recommended or safest way to do it.  However, the circuit also assumes a 6.3V heater supply, so some kind of addition of a power transformer is likely intended (maybe two 6.3V transformers back to back).
 
I'd echo other comments here that the grounded cathode gain stage is probably not the best way to add some glass to a DAC (unless it is woefully low output).  With a tube gain stage, output will end up very high and you'd just end up throwing the extra gain away in a volume knob downstream.  If you really want a tube in your DAC, take a look at cathode follower types instead.  That would offer unity gain (or close to it) and a low output impedance.  The coloration will be lower, but still tubey in nature (monotonically decaying harmonic structure is the money word).

 

[mateusfig]

Nice reply

  The schematic seems to show a simple bridge rectifier with some CRC filtering afterwards to derive 150VDC.  It appears that the input to the bridge is 120VAC.  If that is directly connected to mains input, it is definitely not the recommended or safest way to do it.  However, the circuit also assumes a 6.3V heater supply, so some kind of addition of a power transformer is likely intended (maybe two 6.3V transformers back to back).
 
I'd echo other comments here that the grounded cathode gain stage is probably not the best way to add some glass to a DAC (unless it is woefully low output).  With a tube gain stage, output will end up very high and you'd just end up throwing the extra gain away in a volume knob downstream.  If you really want a tube in your DAC, take a look at cathode follower types instead.  That would offer unity gain (or close to it) and a low output impedance.  The coloration will be lower, but still tubey in nature (monotonically decaying harmonic structure is the money word).

Nice reply! Thanks.
 
Is this another aproach or same stuff? 
 

Source: http://singlevalve.web.fc2.com/lampizator/schematics/Lampizator_sch.jpg

 

[mateusfig]

Nice reply

  The schematic seems to show a simple bridge rectifier with some CRC filtering afterwards to derive 150VDC.  It appears that the input to the bridge is 120VAC.  If that is directly connected to mains input, it is definitely not the recommended or safest way to do it.  However, the circuit also assumes a 6.3V heater supply, so some kind of addition of a power transformer is likely intended (maybe two 6.3V transformers back to back).
 
I'd echo other comments here that the grounded cathode gain stage is probably not the best way to add some glass to a DAC (unless it is woefully low output).  With a tube gain stage, output will end up very high and you'd just end up throwing the extra gain away in a volume knob downstream.  If you really want a tube in your DAC, take a look at cathode follower types instead.  That would offer unity gain (or close to it) and a low output impedance.  The coloration will be lower, but still tubey in nature (monotonically decaying harmonic structure is the money word).

Nice reply! Thanks.
 
Is this another aproach or same stuff? 
 

Source: http://singlevalve.web.fc2.com/lampizator/schematics/Lampizator_sch.jpg

 

[Sodacose]

That's an SRPP arrangement and so it will still be increasing the gain of the circuit.  That provides a little better details of the power supply though, showing something much safer than connecting to mains.  
 
I'm not saying adding some gain will sound awful though.  A stage that adds gain will usually also add much more of the characteristic tube distortion profile and you might like that.  The gain itself is kind of wasteful because you'll end up running your volume control lower for the same listening level.  If you have too much gain you may find that the volume knob becomes too sensitive, too (eg way too loud at a setting of "3" and not loud enough at a setting of "1").  The advantage of SRPP over the previous example is that it will have a lower output impedance.
 
Here's a very simple 12AU7 buffer (one can simply drop the vol pot and 1M at the input if it's following the DAC):
 

 
There are a thousand and one variations on this kind of circuit but this is about as simple as it gets.  It will provide a very high input impedance for the DAC and a reasonably low output impedance to drive longer cables or a low value vol pot at the input to a preamp.  Distortion is very low, but it has the tube shape to the harmonics.  Solid state rectification would also work fine.  


Edit: after reading back through comments, I must have missed that this is connected directly to a current out DAC chip and so the comments about unnecessary gain aren't really accurate. I'll leave the above though because someone may find it useful for a situation where no gain is needed.

 

[mateusfig]

   

Edit: after reading back through comments, I must have missed that this is connected directly to a current out DAC chip and so the comments about unnecessary gain aren't really accurate. I'll leave the above though because someone may find it useful for a situation where no gain is needed.

 
Of course. Well, in my case (same approach of this thread) I need get gain (to replace the original solid state gain of the DAC using opamps), because I will be amplifing the DAC output directly. I don't want a simple buffer but a gain stage. 
 
Your informations were very usefull, mainly for newbie in this subject, like me.