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In Reply to: RE: best lundahl to use with pcm63 and tda1541a posted by AlexanderKonyarov@yahoo.com on June 02, 2009 at 06:47:04
With DAC chips like the PCM63 that have a unipolar current output and bipolar power supplies, and have, therefore, no DC bias on the current output, you can use pretty much any transformer that fits your need for output voltage level. I prefer the sound of the cobalt amorphous strip core transformers like the LL1636 and LL1674.
With either voltage or current output DACs with differential output stages and unipolar power supplies, you have to take care to exclude the flow of DC "offset" current through these transformer's primary windings unless the windings are symmetrical and the magnetic field resulting from current flow can be canceled by counter-directional flow.
For differential voltage output DACs, you probably don't need more than a 1:1 transformer, such as the LL1544A or the LL1690. I don't have much design experience with voltage output DACs (we prefer current output DACs), but the issue of current flow in the primary is the issue if you are to avoid coupling capacitors.
Kevin Carter
K&K Audio
www.kandkaudio.com
thx for reply
I like to know If you tried LL1674 as a step up passive out stage with pcm63 dac and tda1541a dac
what were results
anything specific for pcm63 and tda1541a setups
can you post how Is correct to use LL1674 with pcm63 dac and tda1541a
I have never seen only transformer output to tda1541a
I have never tried a transformer output for either of these DAC chips.
Kevin Carter
K&K Audio
www.kandkaudio.com
I've got excellent results with LL1674 as a 1:8 with both pcm63 and tda1541a,
no coupling capacitors, the bass is great
thx
would you post your connection of transformer with both pcm63 and tda1541
the circuit diagram is shown in the data sheet for LL1674
What I/V-resistor value did you use on the 1541? Still it must have had some DC on its output, did you measure it?
Brgds
Lars
40 ohm, it was four 1541a running in parallel
humless
because I am still not sure about buying LL1674 (I got to pay bit more than Euro 200 for a set which Is a serious buy) would you please be kind to provide your output diagrams of tda1541 and pcm63 dacs
Sasha, I am using standard configurations, exactly as shown in the old DAC tech papers, you can google it easily, also I can draw a sketch and scan it but I don't know how to send it to you, what is your fax number or email?
I would buy LL1674 for the tube line state output, it is a relatively large transformer with 22 v RMS primary(!!!), also for the current output DAC duties as I-V converter it has relatively low ratio (1:8), the volume will be on a low side, I ended up with another gain stage. While I am completely satisfied with the performance of LL1674 it might be overkill for the current output DAC.
If you insist on metal glass - I heard here that LL1678 for the DAC I-V purpose showed surprisingly good results, the DCR is much better as well, you can go with 1:16 single ended or even try the differential (balanced) configuration 1:16+16 (btw, highly recommended, worth every cent you spend on extra tube, I assume you don't go with passive I-V conversion).
In the past I tried 8347 and found that high ratio is very appropriate for the I-V conversion.
With LL1678 you can always lower resistor value (across primary) if you will feel overloading or realize a DC offset. With LL1678 the cost will be much lower too.
It will be a great investment for future transition to vinyl record player with MC cartridge (no kidding).
Actually I was lucky with absence of DC offset in both of my pcm63-based dacs. In case of tda1541- I have 4 DACs running in parallel, the (possible) DC offset can be closer to zero because of averaging.
HL
thx humless
my E-mail Is my nickname
I would like to use only step up transformer with resistor I/V - no output buffers, lamps and etc
do you have a schematic with only resistor and maybe capacitator and step up transformer which you tried with pcm63 and tda1541
OK, I will send it, you can use passive I-V conversion but transformers must be installed in the amp (not in the DAC :) then you can run long cables, also there is a caveat - the transformer approach works best with no-feedback tube amps, in general with simple circuit (=poor filtering) one can get interference noise in feedback amps, it will be unbearable if you use DAC like tda1541 in a non-oversampling mode. The latter works surprisingly good with NFB SET amp,
Effect of transformer-based I-V conversion on sound can be marginal, the I-V conversion might be not the weakest point in the chain, let us move discussion of your setup off the web
HL
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