oh man...
datasheet say that OUTPUT IMPEDANCE of DAC chip is 1Kohm! impedance seen by DAC is that you connect to it!... and it should be as low as possible. go to google.com, search, read.
sorry, really NO OFFENCE kimk, but it isn't thread about basics of electronics but about choosing best possibe transformer for PCM1704 DAC so it is rather question for experienced people in this area.
So please lets back to the topic and leave this unnesessary basics polemic.
Anyone got some additional experience with some Lundahl/Sowter/Jensen/Other trafos with PCM1704?
datasheet say that OUTPUT IMPEDANCE of DAC chip is 1Kohm! impedance seen by DAC is that you connect to it!... and it should be as low as possible. go to google.com, search, read.
sorry, really NO OFFENCE kimk, but it isn't thread about basics of electronics but about choosing best possibe transformer for PCM1704 DAC so it is rather question for experienced people in this area.
So please lets back to the topic and leave this unnesessary basics polemic.
Anyone got some additional experience with some Lundahl/Sowter/Jensen/Other trafos with PCM1704?
I know you are looking for subjective recommendations, but have you contacted the manufacturers for recommendations. The 'Law of Diminishing Returns' must apply at some point in the choices available.
Whenever I get done screwing around with my V out dac I'll be looking for the same info you are looking for. I'm seriously hooked on trafos now.
I hope you get more input, I'll be watching.
Best, Bill
Whenever I get done screwing around with my V out dac I'll be looking for the same info you are looking for. I'm seriously hooked on trafos now.
I hope you get more input, I'll be watching.
Best, Bill
I'm sorry! Marek, on these will not help you, in the title outside the discussion. I'm very sorry! I really do not intend to offend! If offended, please forgive me!
Thanks again for your follow through to teach! On google, I know how to use it!
I do not want you to think I am tough, so, wish you a great time!
Thanks again for your follow through to teach! On google, I know how to use it!
I do not want you to think I am tough, so, wish you a great time!
Bill,
Yes I contacted with Lundahl distributors (kandkaudio and jacmusic) and they can't help me with as simple and basic thing as inductance of windings... also contacted directly with Lundahl - no answer at all...
The same with Jensen-transformers.
Exeption is Sowter which recomended mi use one of theirs DAC destinated trafos which are already known by me.
Bill, you need a slighty diffrent trafo than me - Vout DAC wants to see very high impedance so you need 1:1 trafo with rather high DCR and impedances. I think 10k:10k trafos will be excelent. I heard positive opinions about Jensen transformers.
Kimk,
I'm not offended! I hope that I didn't offend you.
Regards
Not slightly different, a totally different animal. There is more to it than meets the eye, even with Vout dac chips. Inductance is very important with both configurations.
It might be that Sowter is the only manufacturer willing to deal with the offset problem. I haven't seen it mentioned in the limited research I have done on using trafos with current out dacs.
It might be that Sowter is the only manufacturer willing to deal with the offset problem. I haven't seen it mentioned in the limited research I have done on using trafos with current out dacs.
Yes,
It seems that Lundahl is directed to diffrent market (studio equipment).
Yes current output DACs with output trafos are very rare even in DIY.
I think I will try Lundahl because I think they are more technically advanced than Sowter (thats only my impresion).
I will buy LL1931 because it is based on innovative Colbalt amorphous core, reltively big and windings are made with hiQ Cardas copper wire, DCR of primary i very low (hope that doesn't mean very low inductance..)
If if won't work then I'll decide to use Sowter.
It seems that Lundahl is directed to diffrent market (studio equipment).
Yes current output DACs with output trafos are very rare even in DIY.
I think I will try Lundahl because I think they are more technically advanced than Sowter (thats only my impresion).
I will buy LL1931 because it is based on innovative Colbalt amorphous core, reltively big and windings are made with hiQ Cardas copper wire, DCR of primary i very low (hope that doesn't mean very low inductance..)
If if won't work then I'll decide to use Sowter.
My measuring technique was the following: I connected a 10000 pF 2.5% foil capacitor parallel to one secondary. I fed one primary (there are 4 of them) through a 1 k resistor from a signal generator. I measured the voltage at the secondary and searched for the peak. The peak frequency was about 240-250 Hz. The primary inductance is Lsec / n^2 that is about 170 mH.
1 H (sometimes written as Hy or Henry) is 1000 mH. I measured the secondary inductance (the winding with more turns) by using a known capacitor and measuring the resonace frequency. I coupled the test signal into the primary, but this has of no importance, I could have coupled the test signal into the secondary, as well. I calculated the primary inductance from the secondary inductance and the turns ratio, it resulted in 0.17 H (170 mH). I think these values are realistic.
Knowing the primary inductance, one can calculate the highest allowable source resistance for a given lower cutoff frequency. Let's say we need fc=10 Hz. The corresponding time constant T is about 16 ms. From the equation T = L / R we get R = 10 ohms (approx). If we connect the I/V resistor across the primary, this is the highest resistance we can use. Since the primary has some resistance itself, it has to be included in the previously calculated total R resistance, and the external I/V resistor should be less by this value.
If the I/V resistor is connected across the secondary, its value is R * n^2, in our case 10 * 16^2 = 2.56 kohm (less the resistance of the secondary).
I am curious if there is any audible difference between using a 10 ohm I/V resistor across the primary or using 2.56 kohm across the secondary. Anybody has some experience regarding this?
Knowing the primary inductance, one can calculate the highest allowable source resistance for a given lower cutoff frequency. Let's say we need fc=10 Hz. The corresponding time constant T is about 16 ms. From the equation T = L / R we get R = 10 ohms (approx). If we connect the I/V resistor across the primary, this is the highest resistance we can use. Since the primary has some resistance itself, it has to be included in the previously calculated total R resistance, and the external I/V resistor should be less by this value.
If the I/V resistor is connected across the secondary, its value is R * n^2, in our case 10 * 16^2 = 2.56 kohm (less the resistance of the secondary).
I am curious if there is any audible difference between using a 10 ohm I/V resistor across the primary or using 2.56 kohm across the secondary. Anybody has some experience regarding this?
do not touch amorph. cores souns like oversampling...
try to stick with old types of cores?
and You will need low res buffer before the trans. anyway
try to read jensen papers PDF docs how to implement the interstage
for propper groundings, and loading...
it will be better to find model with 2 independent primrys an 2 ind. sec.
you wil have more opportunity to make CT or not, parallel sec. and so...
if You want directly from the DAC, bare in mind DC resistance of prim...
cheers
try to stick with old types of cores?
and You will need low res buffer before the trans. anyway
try to read jensen papers PDF docs how to implement the interstage
for propper groundings, and loading...
it will be better to find model with 2 independent primrys an 2 ind. sec.
you wil have more opportunity to make CT or not, parallel sec. and so...
if You want directly from the DAC, bare in mind DC resistance of prim...
cheers
Oshifis,
Thanks for your calculations.It looks quite correct.
I think this is a mistake. turns ratio is a relation of secondary turns to primary turns (without square) so :
44H/16=2,75H
don't say that - I've just ordered LL1931 cobalt amorphous core...
Have you compared amorph based trafos with those with MU core? what types and in what aplication?
Thanks for your calculations.It looks quite correct.
I think this is a mistake. turns ratio is a relation of secondary turns to primary turns (without square) so :
44H/16=2,75H
don't say that - I've just ordered LL1931 cobalt amorphous core...
Have you compared amorph based trafos with those with MU core? what types and in what aplication?
why? I think it is possible.
datasheets of selected models contains something like this (example from LL9226 datasheet):
"Primary no load impedance @ 0 dBU, 50 Hz, all in series:3 kΩ typically"
If this is no load impedance (load on secondaries is infinite) we can assume trat trafo is just a ferrite bead with some inductance, so:
Z=2*3,14*f*L => L=z/(2*3,14*f)
so
L=3000/2*3,14*50=9,55H
this is summary inductance od 4 primary windings so each primary 2,39H
Note that every primary of LL9226 has DCR only 5ohm, secondary of LL1678 has 375ohm...
datasheets of selected models contains something like this (example from LL9226 datasheet):
"Primary no load impedance @ 0 dBU, 50 Hz, all in series:3 kΩ typically"
If this is no load impedance (load on secondaries is infinite) we can assume trat trafo is just a ferrite bead with some inductance, so:
Z=2*3,14*f*L => L=z/(2*3,14*f)
so
L=3000/2*3,14*50=9,55H
this is summary inductance od 4 primary windings so each primary 2,39H
Note that every primary of LL9226 has DCR only 5ohm, secondary of LL1678 has 375ohm...
Inductance is proportional to the number of turns squared. Inductance ratio is proportional to the turns ratio squared. I will measure the inductance of one primary winding, just to be absolutely sure about the 170 mH. Result will follow soon...
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