Thorsten TDA1541A ECC88 output stage

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IDM
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Thorsten TDA1541A ECC88 output stage

Post by IDM » Tue Feb 14, 2012 12:33 pm

Dear All,

I have been using Thorsten's choke loaded ECC88 stage couple to my TDA1541A DAC chip. The only difference with the attached circuit diagram is that I used single 75 ohm Holco metal film resistors for the I/V.

Thinking that there might be good reason for using Thorstens more complex stage I finally got round to rebuilding the stage as per the attached schematic.

The result was positive with regard to detail and also helping to get the individual instruments and voices to sit better in their own space. However, it is far less relaxing with more than a hint of sibilance.

The 47nf (polystyrene) capacitor is as I understand it to roll-off the response in the ultra-sonic region. The 330nf (metallised polyester) and the inductor I think are to boost the HF response, however I am not sure that I have that right. Resistors used were 0.5W carbon films.

Could someone please help me to better understand the circuit and help me to work out what to try altering first to get the response right in my system.

Many thanks,
Ian
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Mike H
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Post by Mike H » Tue Feb 14, 2012 6:47 pm

Picture's a bit small?

:D
 
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pre65
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Post by pre65 » Tue Feb 14, 2012 6:57 pm

Ian, there was a long thread about 1541 valve output stage by Richard a while ago.

Might pay you to read through it.

http://www.audio-talk.co.uk/phpBB2/viewtopic.php?t=3182

I built one with 6N2P to go with a 1541 DAC in a Marantz CD player and when the 1541 "green " DAC is finished it will be used with that.
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IDM
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Post by IDM » Tue Feb 14, 2012 7:35 pm

Hmm, not sure why the picture is so small! I had a tooth out today so not thinking too well and finding a way to get the file size below 250kb seems beryond me. Will try later.
Ian

IDM
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Post by IDM » Wed Feb 15, 2012 11:10 am

Thanks Phil,

Not sure why I didn't find that thread when I was searching the forum. Any road to cut a long story short I have built and tried that version of Thorsten's valve stage and was not overly impressed. Indeed that article on Fortunecity was I believe theoretical he had not built it. Thorsten discusses his best valve stage in this thread:

http://www.diyaudio.com/forums/digital- ... 41dac.html

The thread details the final circuit circuit I built using a simple 75 ohm resistor for I/V and no inductor or capacitor filters. This circuit was a substantial improvement on the Fortunecity one.

The circuit was rediscussed in 2011 in thi thread:

http://www.diyaudio.com/forums/tubes-va ... 1541a.html

As mentioned in my opening piece it was when I added the filters that I got both positive and negative elements to the sound. What I would like to understand is what values of which filter capacitors to tweak in order to roll-off the high frequency a bit.

Cheers
Ian

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Mike H
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Post by Mike H » Thu Feb 16, 2012 5:12 pm

IDM wrote:Hmm, not sure why the picture is so small! finding a way to get the file size below 250kb seems beryond me. Will try later.
Ian
Needs an image editor to not only reduce width & height (but keeping same aspect ratio) but also number of colours, GIF is max. 256 colours. Or just reduce size & save as JPG. Lines may be blurred though.
 
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IDM
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Post by IDM » Fri Feb 17, 2012 12:41 pm

Yes I tried that and got very blurred lines. you cansee the circuit better through the links though.

Cheers
Ian

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Mike H
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Post by Mike H » Fri Feb 17, 2012 2:25 pm

Couldn't find that circuit by those links. Mind you didn't spend too long on it TBH :D
 
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Post by IDM » Fri Feb 17, 2012 2:39 pm

The circuit is is in the firstlink post 9 (the first posting by Thorsten).

Since the first post I have been playing around with the circuit and am currently listening to the circuit as shown but without the 47nf cap. This seems less sibilant, though from my limited understanding of the circuit this is counterintuitive as I think that cap rolls off the HF response. Presumably to try and block the harmonic images?

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Paul Barker
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Post by Paul Barker » Fri Feb 17, 2012 3:34 pm

Image

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