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Old 26th November 2007, 03:59 AM   #51
Pars is offline Pars  United States
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Default rbroer's stage in a Rotel RCD-855

Sorry to raise this old of thread from the dead

Finished up the prototype for a discrete I/V stage in my Rotel RCD-855 CD. This player uses the standard Philips late '80s/early '90s chipset (SAA7210 / SAA7220B / TDA1541a). It sounds really good, much better than any opamps I have rolled through this player. I really wanted to compare it to a G08 or something at a head-fi meet last weekend, but hadn't gotten in enough listening/testing yet, so wound up not going.

Mods include:
  • Shottky PSU diodes (11DQ10 player, 31DQ10 o22)
  • Tentlabs XO on a PFM Flea board (modified design with 2 PSU sections, one for the XO, one for the 74HC logic), with /2 direct DAC clocking
  • Tread board taking ~25Vdc down to 18-20Vdc for the Flea
  • home layout of an amb o22 PSU for the discrete stage (I needed a smaller board than the o22 at 3.5" x 6.5")
  • rbroer's less simple I/V for TDA1541a, modified to use 2SA970/2SC2240 transistors, FET buffer per cetoole's I/V stage (I removed this for the time being, works but needs redesign), and muting relay (not put in yet)
  • home-etched double-sided PCBs (I used tinnit for the first time on these, works pretty well)

Thanks to Rudolf for designing and sharing this!

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Old 3rd December 2007, 08:14 PM   #52
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Nice work Pars!

I've been thinking about trying a discrete I/V for my tda1541a dac. Trying to figure out whether rbroer's "less simple" is the most recent one he designed for the tda1541a, or is the "super pair" the more recent evolution?

What is your voltage output and Zout?
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Old 3rd December 2007, 11:34 PM   #53
Pars is offline Pars  United States
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Thanks for the comments!

From what Rudolf told me via email, he is still using this one... not sure if he ever built any of the others in that thread or not. In mine I'm currently using 1.5K I/V resistors and 1nf caps... I have not measured the output but it might be a touch hot; I may try 1.3k instead. As far as Zout, ??? not sure.

Chris
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Old 3rd December 2007, 11:39 PM   #54
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hi pars,

will u considerate use 1:10 step up transformers for IV. I was testing for this & hope to collect some comment!

thx

thomas
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Old 4th December 2007, 03:00 AM   #55
Pars is offline Pars  United States
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Well, I guess I would consider anything, but transformers weren't high on my list for I/V use.

Regards,

Chris
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Old 5th December 2007, 01:13 AM   #56
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hi pars,

sorry for my bad english,

U said --
transformers weren't high on my list for I/V use.

is it means not good or not suitable for IV area that use transformers to do so.

thx

thomas
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Old 5th December 2007, 02:22 AM   #57
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Hi Chris,

What I was inquiring about was whether the "less simple" I/V stage is a gain stage such that one can get say 2V output like a standard digital source...or do you need a gain stage in addition to the discrete I/V? I am only familiar with the traditional 33Rish passive I/V + tube gain stage for the 1541a.

Also, by Zout I mean the output impedance. I'm currently using a TVC volume control and would like to keep the impedance below 1k ohm if possible. I imagine with an SS stage like this it probably isn't an issue.

Thomas - I interpret Chris's response to mean that transformer I/V would not be his #1 choice.

BTW Thomas, I am enjoying your v2 twin 1541a dac but have completely bypassed the cs8414 and am feeding the dac signal pins directly with a synchronous reclocking board that receives left justified signal from squeezebox transport and then converts them to i2s and resynchs them with tent 11.2896 clock. The master clock is in the dac. The resolution and soundstage have improved dramatically.
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Old 5th December 2007, 04:11 AM   #58
Pars is offline Pars  United States
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Riotubes: I guess it is a gain stage in the sense that it takes the 2mA current from the DAC, moves it while trying to keep the input impedance that the DAC sees very low, and runs it through the I/V resistor (in my case 1.5K ohms) resulting in approximately 2Vpp (I guess) output. No additional gain stage is required, although a buffer stage might be if you were to run long ICs. The design is based on Jocko's I/V stage, and is a transimpedance amplifier (I guess that is the term normally used).

As far as its output impedance (Zout), would this in effect be the I/V resistor (1.5K?). Or is it the I/V resistor in parallel with the impedance of Q6, etc.? The schematic is in the 2nd or 3rd post of this thread. The only resistances that I adjusted were for the current sources in order to run the 2SA970/2SC2240s below 10mA (actually, more like 9mA max).

thomas: I guess I'm not sure what you are asking? Are you asking if this stage could be used with an output transformer? I suppose it could be... you would probably want to omit the DC servo, etc. in that case, and possibly put an output capacitor in if the transformer is sensitve to DC.

You are lucky you don't have to try to understand my (nonexistant) Chinese... your English is quite good compared to that.
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Old 5th December 2007, 05:37 AM   #59
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hi riotubes,

do U hd interest to try the final version of DAC. they use project D-1 to test & was only 5% different between project D-.

if u like to try. give me your address & I will free to provide one set to to try.

pars,

I understand wha U mean. Yes, it must rating several ma.

this is my prepare 1:10 nano amorphous IV step up transformers.

can use in 1541a DAC.


take a look first. it still under testing!

thomas: I guess I'm not sure what you are asking?

Do U see Audionote DAC 5?, it se transformers couple for IV. most people use sowter DAC transformers( IV ) & some said was very god & some was said not good. I thought reason was cause by sowter IV trans can onl ratin very low ma or cannot rating an DC. I cause saturate of the core & performance was not good. but I am not sure.

Are you asking if this stage could be used with an output transformer?
yes, 1541 use trans couple for IV. I suppose it could be... you would probably want to omit the DC servo, etc.

yes, 1541a was quite hot & rating higher ma than nowsdays chips, t must desig higher ma passing in OPT.

in that case, and possibly put an output capacitor in if the transformer is sensitve to DC.
yes, U can use this method, but I was worry performance was block or said Bottle neck was capactor.

You are lucky you don't have to try to understand my (nonexistant) Chinese... your English is quite good compared to that. many thanks, nice to discuss to U too.


thx

thomas



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Old 5th December 2007, 05:56 AM   #60
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hi pars,

I trust Sowter 's quality. probably your method ( add one small cap in front of the transformer)

pls remember this transformers must shield to lower noise!.


U can considerate use this, this sowter was my reference & compare material.

thx

thomas

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