Tubed CCDA I/V Amp for TDA1541(A) - diyAudio
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Old 4th January 2010, 09:40 PM   #1
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Default Tubed CCDA I/V Amp for TDA1541(A)

What about this approach? A Constant Current Draw Amplifier with positive feedback instead of the usual cathode decouple cap to raise the amplification.

Click the image to open in full size.

It seems nearly everyone is using Mr. Fikus Lampizator circuit, which again is an old circuit that I think Mr. Torsten Loesch was one of the first to use for a TDA1541 DAC.
The SRPP circuit. The one I here present has higher amplification and lower output impedance with same use of tube flavour.

Last year I started a thread with some vague ideés and I think SY was closest to the circuit I for the moment are testing at my testbench. common-grid I to V converter

Actually, this could be the first amplifier part in a good phonostage, which uses passive RIAA EQ in between. Again, John Broskie at Tubecad has inspired me
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Old 4th January 2010, 11:49 PM   #2
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Thumbs up Work in progress

I have corrected some errors on the schematic above. Please update your browsers.
Now there is also the component values I use ftm. (exept I use ECC803S ftm) Gridstoppers could be what you have and you can also lower the output cap to 1uF which then gives -3dB at 15 Hz. Output impedans is 580 ohm teorethical. Anyway it should be low enough for a normal amp after.

Pictures below reveals my hacking of a beatiful phono kit from John Broskie and Tubecad when testing my idée above. I have longed to get time to do such a phonostage and when John presented this kit this autumn, I bought a PCB and saved some time.
Now it seems I have to do a dedicated PCB for my DAC

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

How does it sound?
Well, after my last bragging with the sucess of the old Jocko I/V converter I maybe should be more careful with my judgements (it worked really well though)
But this time, believe me, I am over the top. This is the biggest leap forward of them all on this DAC. I hear the music in a totally new way. I listen to all my old CD's I know really well, most of them from the -80's and -90's, and sometimes it now reveals character and motion to the music I never thought was on the CD.
When it comes to measuring my laptoop is broken so I have to use my M-Audio external card on some other computer in the house and try to set up a descent test rig. But so far I use my ears and the scope to listen and look at -60dB 1khz (testfile fromPedja Rogic's site) The distorsion is low and the hiss ... isn't much of. I never thought that it could be that silent with tubes but I had my thoughts because this concept for the phono amp was also very silent when it should.

What next?
There is -66mV over the paralelled Allen Bradley resistors. I maybe will test with something there but I really don't think it's necessary.
Test rig and some FFT first of all.

Please feel free to ask or comment. I can take it
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Old 5th January 2010, 12:44 PM   #3
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Thumbs up Monologue continues

Hi all
Didn't get much sleep this night. After some late breakfast and a lot of Coffé I'm back in business again.

So, I was awake this night fiddling with FFT tests and even though the sound was superb there is more distortion with the tubes and probably because of the -66mV at the TDA's output then with OP's and zero volts.

K2 is:
-60dB at 0dB 1khz sample from CD (Pedja Rogic) vs.
-84dB with OP's. Different OP's showed no or little difference.
-66dB i got with Jocko's simple I/V converter. I just have to test that one. In the simple form it's very sensitive to adjust and I'm not into having the time and eager to further develop that circuit, now that I have found that my tubecircuit really get me near what I'm after.

Distortion with -60dB 1khz sample was more then 40dB below for all upper multiples on all measurings. I thought it was wit the -60 dB i should see the most differences because of the small voltage on the I/V resistor. Maybe someone can explain? In the meantime ... more empirical work has to be done.

I'm starting to document all this on my homepage if someone in the future want's a more relaxed reading then the brainstorming such thread as this is

Brainstorming use to have a group of several people throwing idées?
O Brothers where are thou?
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Old 6th January 2010, 08:43 PM   #4
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Thumbs up New CCD injecting

Going further with this one.

A JFET CCS a'la Pedja solved the -66mV issue and got all available bits on the track.
I have today worked with a homepage for this project. Among other stuff there is FFT graphs of this circuit with and without the CCS injector.

Be my guest.
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Old 6th January 2010, 10:12 PM   #5
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Interesting work!

Arne K
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Old 7th January 2010, 01:55 PM   #6
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have you tried - Pass D1 output stage - pedja ad844 out stage - Tollonen mu follower
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Old 7th January 2010, 06:20 PM   #7
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Default Studying

Hello samoloko

I have studied Pedjas work a bit and I like his attitude and work. The other ones I have to update myself on. It's the right time know when I'm into it. I think Pedja's approach is hard to beat (as he actually says ). I like it.

The thing is I have allways liked to build something with tubes, because I can. But I'm no freak who is afraid of SS. To combine these things ... me like . It took me 30 years of "thinking" and a lot of "armchair building" before I decided to actually try to build something at all (more then my first guitarr amp) and for a moment disregard all simulations on the PC and also don't listen to all "opinions" on the net for a while.

From that day it started to happend things. At last I now have "my own" tube design for a OTL headphone amplifier I'm very proud of.

The next larger project is this one. I once read a story on Internet of building a DAC with tubed output and was jealous on the guy which had that skill. This was at least 10 or 12 years ago. I can't recall but maybe it was this forums Torsten Loesch? (I can't recall his alias here)

Anyway I think that the SRPP circuit with 100 ohm I/V resistor that nearly everyone use (without compensate the offset over the resistor, so you miss the last bits at low levels) is the best sollution at all.

I really like my circuit because it's a better compromise (maybe subjective... OK). You need a good PSU though because the PSRR isn't the best but on the other hand this circuit is easy with the PSU because it draw a constant current and is not thugging or pushing at the Power supply feeding.

I also have a super reg shunted psu I will use in my final build. It's a DIY group buy that now will come to use. That one has to be tested and verified first though

Anyway, I'm having fun right now and thats the best part.
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Last edited by Radioman62; 7th January 2010 at 06:29 PM. Reason: typo
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Old 8th January 2010, 07:06 AM   #8
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would you tell what dac you are using
TDA1541A ?

till now I have tried DIY SRPP with 100 R I/V with Sheldon Stokes tube DAC (pcm63) and find out that this tube stage Is In no terms Hi FI - It Is slow, no highs, no details, no resolution, too tubed sound, not dynamic
but when I moved to Pass D1 out stage It was great Improvement

I really want to try mu follower out stage which have to be much better than SRPP - the gain of 2 times compared to SRPP can be compensated with lowering I/V value

Last edited by samoloko; 8th January 2010 at 07:09 AM.
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Old 8th January 2010, 04:51 PM   #9
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TDA1541A yes.

SRPP is not suitable as an I/V converter for this kind of DAC IMO.

For some reason it's very common used by the DIY community. Maybe because it works and there isn't much other tube schematics of other sollutions out there.
Most people seems to think it's good but you don't. Maybe you have discovered that the high output impedance from a SRPP is getting you problems with capacitances in the connection cable and maybe also the impedance of the amplifier connected after. Could be something you heard.

My schematic is simple but not to simple. A good working sollution with high amplification, pretty low output impedance, compared to the SRPP stage and also the elegant constant current draw of the circuit. You wont need anything more before your endstage.
You need good power supply though. Anyhow, money is no object in that case, is it . My circuit is just CRCRC filtered for the moment.

The sound is ... that kind of liquid feeling you get when listening to a good vinyl setup. The character of instruments and voices is that good I have to listen to all my old CD records again and find out that even the songs I didn't like that much before is joyfull because it's more life in it and the songs sounds different and allmost new. Tubesound? If you mean round wolly and warm, this is not. There is no color at all I think. There is only music ....

I'm over the top flying right now. But I'm not finished ... Last night I piggybacked another TDA1541A on top of the other, with the DEM clocks not shared but syncronised with a 100pF silver mica between the legs 16.
... Thats another story then this Tubecircuit though.
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Last edited by Radioman62; 8th January 2010 at 04:53 PM. Reason: typo and fiddling with the grammar of the english languish ;-)
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Old 9th January 2010, 09:22 PM   #10
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Exclamation Second approach updated on the schematic above

Hi
I discovered that the "injection" of positive feedback gives a pretty high raise (about 10dB) in k2 harmoic distortion together with the 3dB raise in amplification, which we really don't need.
Second approach gives less distortion and still near 2 volts RMS for the next amplifier, your endstage.
I have some more thoughts and are replying to Mr -ecdesigns- on that passive I/V resistor right here. Post #3076.
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