cs43122 tube output stage help - based on cdenhancer II design - diyAudio
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Old 12th January 2004, 06:58 AM   #1
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Default cs43122 tube output stage help - based on cdenhancer II design

Dear Diyers!

I am currently building a DAC using CS43122

http://www.cirrus.com/en/pubs/proDat.../cs43122-2.pdf

and I have come across a tube output stage here

http://www.ultranalog.com/cdenhancer/cdenhancer2.html

I am just wondering if I build the 3a5 version, do I need to readjust any commponent on the circuit?

Thanks in advance

Arthur
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Old 12th January 2004, 09:25 AM   #2
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For this dac, you may omit the capacitor from grid to ground. It has nearly no energy in the band to 100 kHz, after whicht the tranny (sowter 8650 recommended) will filter strongly enough.

This dac has 1.33Vrms output. Be aware that you obtain 2.66Vrms out instead of 2V rms. If you wish, you can put small resistor ladders to lower the input, or load tranny to work with the 3a5's Rp.

By making one of each leg of the differential stage a pot, you can fine-tune the harmonic distortion (provided you can measure it). 10 dB or more of hd reduction can thus easily be obtained.
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Old 12th January 2004, 02:35 PM   #3
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Thanks! Looking at the login name, I guess you must be the original author for that web page. Many thanks for your schematics and I must say that I have heard a lot of good review over the web.

>For this dac, you may omit the capacitor from grid to ground. It has nearly no energy in the band to 100 kHz, after whicht the tranny (sowter 8650 recommended) will filter strongly enough.

Do you mena the R7 = 150ohms?

>This dac has 1.33Vrms output. Be aware that you obtain 2.66Vrms out instead of 2V rms. If you wish, you can put small resistor ladders to lower the input,

Do you mean putting a number of resistors in series with R4, R2, R13 and R14?

> load tranny to work with the 3a5's Rp.

What do you mean by this?

>By making one of each leg of the differential stage a pot, you can fine-tune the harmonic distortion (provided you can measure it). 10 dB or more of hd reduction can thus easily be obtained.

Would an OCR be good enough to do this?

Thanks in advance

Arthur
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Old 12th January 2004, 03:27 PM   #4
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Hi,

Although for a different chip, you can find some more information here:

DAC

Cheers,
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Frank
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Old 12th January 2004, 04:16 PM   #5
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Quote:
Do you mena the R7 = 150ohms?
No, I mean C1, C2, C11 and C12.
Quote:
Do you mean putting a number of resistors in series with R4, R2, R13 and R14?
No, those are gridstoppers. By the way, I just remembered the 3A5's mu is 14, so 1.33 Vrms would work out to be exactly 2Vrms out. Great. Forget the whole argument.
Quote:
Would an OCR be good enough to do this?
Optical Character Recognition?

Seriously, I have no idea what you mean by this. But try the design without fine tweaking first, and work your way from there.

Thanks for the link Frank. I was experiencing deja-vu but didn't feel like searching
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Old 12th January 2004, 04:23 PM   #6
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Oh! Of course, you were talking about cpacitors! What was I thinking!
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Old 14th January 2004, 05:21 PM   #7
Raj1 is offline Raj1  United Kingdom
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HI Ackcheng,

just a tip or 2,

look carefully at how Remco wired up this stage on the lid of his cdp, the filament wiring is close to the edge of the lid, to help reduce hum. If you do build into a lid as Remco did it is a good idea to keep signal wiring length from dac chip to tube pins long enough for the lid to be raised high enough to permit comfortable working underneath - should there be a problem.

I don't know what type of caps Remco used in the PS, but I went for an all film cap power supply after staring with an electro supply - it's very detailed, but I now understand why some people prefer PIO caps or even electro's. The only problem with film caps is they tend to make the sound a bit 'hard' in comaprison to the relative bloated sound of electorlytics. Ofcourse it's a matter of taste, film caps offer tight realistic bass, and very well defined highs in fact they have more detail and resolution thean eny electrolytics I've ever tried. If you wish to try PIO's then I think Angela instruments have these at a reasonable price (albeit expensive if you think about it).
Let us know how you get on, damn thing makes the finest sounding cdplayer I've ever heard.

Thanks
Raja
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Old 14th January 2004, 09:41 PM   #8
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Default dug up some more porn

Click the image to open in full size.
Click the image to open in full size.

signal wiring is shielded everywhere (microphone cable).

Filaments are on a LM317 regulator.

PSU tranny is switched on by a relay, driven from the player's 'standby' signal inverted.

PSU is a blend of electrolythics, PIO and film (if you need some, I have reserves).

Apply a bleeder resistor (~ 47k) over the PSU. This is not in the schematic since I only learnt it by building 1200V amplifiers. The bleeder empties the PSU when switched off (those blue film caps do not leak AT ALL, I've had a blow from one 72 hours after turning off the player). It also helps keep the voltage over the choke constant and thus eases the sound.

During testing this is more convenient:
Click the image to open in full size.
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Old 15th January 2004, 03:39 PM   #9
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Thanks,

I am just wondering whether using this PSU would be a good alternative.
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Old 15th January 2004, 05:07 PM   #10
Raj1 is offline Raj1  United Kingdom
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Hi,

that psu may be a good alternative, but I think you can also get good results using the one that Remco used,

bypass the rectifiers in his ps (3a5 filament supply) with 0.1uf film caps, I used schottky's and I would say that the benefits of schottky's with bypassing are definatley worthwhile.

Also I used 3a5's from Tube-shop (not a plug), they supplied me with raytheon 3a5's from the 1950's.

Getting hold of an az1 may be a bit more tricky, i'd love an old meshplate version if I can get one. Finding a socket can be tricky too, i still haven't bought one. Although I haven't made comparisons with other rectifiers, I love the az1, sounds good and looks nice!

Also you can try putting a low impedance cap at the filament pins of the tube socket, I used a couple of 16v 100uf black gate fk's, they do make a difference. But be warned you start messing with the character of the setup, the sound becomes 'hard', well and good if that's what you're looking for........

By the way I don't know the technical implications of it but I have no resistors in series with the diff output either, sounds great. Haven't done any measurements to find out whats going on (would need to know how), further Remcos advice a friend of mine has given me a scope to keep - 30mhz dual trace.

The choke I used is from maplins in the UK very cheap but does the job well enough, only around 7 ukp!!! I suppose there may be benefits to using more exotic chokes, perhaps Ultranalog or Frank can enlighten us to any experience they may have had with more upmarket chokes in the psu?

Thanks
Raja
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