dac tube output stage..pls help.

[tone]

hi all,
need advice.
what would be the optimum Rload resistor for my dac tube output stage, im getting cracking sound from high level volume music, this is without the resistor,
i did try with 1M resistor, but distortions..

i have posted in digital section but not getting any advice..

>hope might get a reply from this forum..thanks.

>best regards,
>tone.

[bournville]

I am not familiar with this particular circuit, but I would suggest that if the output is fed into a SS amp then the resistor should be 50-100k and if into headphones then probably 10k or less. If the problem is overloading you could replace the resistor with a pot of the same value and take the output from the wiper.

However, if you are getting distortion and crackling I would also check the 1uf coupling capacitor, as it might be leaky and passing DC.

[dhaen]

Tone,

The purpose of the resistor is only to stop high voltage from appearing on the output. 1M will do. A bit lower is probably OK too, but if you go much lower you will start to "load" the previous stage.
I think that this design will not work well into a low impedance.

Cheers,

[James D.]

Fully agree with John's advice 1M to 500K should do the trick nicely...

ciao

James

[bournville]

If this amp is feeding into a main amp the chances are that the resistor is unnecessary, as in the main map the input will feed across a load resistor anyway, possibly a volume pot - only if there is an isolating cap will a load resistor here be useful.

As far as any distortion/cracking is concerned, I think that this will caused elsewhere in the circuit, possibly the coupling cap, dry soldering joints, even noisy anode resistors (seems to be two in parallel) possibly...

[tone]

hi all,thanks for the advice..

will do what u guys have advice, will get back to u all soon..

btw:feeding directly a Inverted Gainclone "Thorsten Circuit".

thanks again.

tone.

[fdegrove]

Hi,

Not a digital expert but I find this setup rather errr... odd.

At the input of the xformer you have I/V conversion, the xformer steps up 1:15, than you have the tube stage where you take the output from the anode?? This ends up again in a highish Zo...

Looks odd to me.

Cheers,

[jean-paul]

If this amp is feeding into a main amp the chances are that the resistor is unnecessary, as in the main map the input will feed across a load resistor anyway, possibly a volume pot - only if there is an isolating cap will a load resistor here be useful.

Real bad advice if one want to disconnect DAC/cdplayer and amp now and then....

Or if one touches the center of the RCA cable...


It will give a plop from here to Tokyo and possibly the ( if SS ) amp will be dead too afterwards.

Old design techniques weren't invented for fun.

Jean-Paul

[tone]

hi all,

1M resistor works.or should i use 500K?

hi bournville : u were right, the 1uf solen caps was leaking or something is wrong, replace the caps with new one..works fine..thanks.no more cracking sound.

Hi frank: what u would recommanded? i couldnt find any one tube for both channel circuit for the dac..so i use my preamp circuit for the dac.pls advice..thanks.

btw:it seem the dac is lack of bass, would a higher cathode caps helps>?

best,
tone.

[jean-paul]

1 M is OK. Maybe you could check some tube output stages on these sites. Don't forget that the TDA1541A puts out more current than other DAC chips !

http://users.podolsk.ru/boga/Images/DAC_Buffer.gif

http://www.ndh.net/home/kboehm/T-DAC-P2.htm

http://www.ahfartaudio.com/6021W2doc.htm

http://www.megabaud.fi/~jtolonen/ga/tubedac/part1.html

http://home.netcom.com/~wa2ise/radios/tubedac.htm