| rbroer |
Built this the last week; it's a variation of Jocko's simple I/V, using all generic unmatched parts, larger bias currents, and the R4 upstream of C3.
This is used in a non-oversampling cd player with Kwak-Clock version 3 and TDA1541A-S1.
I have adjusted Vc(Q3) with pot R6 to 10.0 Vdc
Ve(Q3) is adjusted with pot R3 to 0 Vdc, and readjusted after a few hours. It doesn't change much over time, within +/-1.0mV.
Current source Q1 is about 23mA, of which 6mA flows into R4, 17mA through Q3 and 15mA through current sink Q4.
All bjt's have hfe of ca. 300-400 measured with multimeter.
Since I didn't measure Vbe on Q3 and Q2 I ended up with different R3 values; ca. 5.6k and 22k.
I suppose one could select to get the lowest R3 value, that is, have some moderate current flowing into Q2.
The sound ?
Well my previous I/V was a LM6172 opamp driving a J309 jfet biased by few mA, Riv between +V and fet's drain.
Later I replaced the J309 by a BS170 mosfet which has higher transconductance, hence less "correction" to be done by opamp on fet's gate to keep output voltage compliance of 0V.
The latter sounded more sweet, treble got more transparant.
Just last week I replaced the BS170 with a BC547B and it sounded a little better again, so I decided to built this circuit.
Got an improvement again; sounds like treble is more free and transparent and basses seem to be driven by some "mass".
This circuit can be universally used for other current output DAC's;
use pot R6 to get the wanted Vce on Q3.
To use it with Philips DACs like the TDA1543 and TDA1545A with DC voltage on output, replace Q2 with LED's, zener, or diodes to get stay within the valid DC compliance range.
I do have some SA970's and SC2240's to try, which might sound better...but even with generic parts it sounds pretty good.
Have fun, |
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| Nicke |
Nice to see someone else tried Jocko´s circuit.
I have tried a similar in a DAC with PCM63´s,but with 2SA970´s & 2SC2240´s.
I have put a capacitator in parallell to R4 as a filter and all is followed with a simple JFET follower(2SK170).
It sounds really good,better then the previous analog stage which was the usual opamp style.
Nicke |
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| Kuei Yang Wang |
Hi,
| quote: | Originally posted by rbroer
I do have some SA970's and SC2240's to try, which might sound better...but even with generic parts it sounds pretty good.
[/B] |
You may wish to consider cascoding both the current source (load)transistor AND the current conveyor transistor and to use a lot of voltage in the "+B"....
BTW, the same principle of course works great with valves too....
Sayonara |
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| Ric Schultz |
Try replacing the LEDs with three signal diodes. Try fixed resistors instead of pots once you have figured out the value needed. Try changing the 10K bias resistors (currently used on LEDs) to 20K and putting them to the opposite power supply rail instead of to ground. If you do any of these mods, let us know what you hear. To me LEDs and pots are extremely non-linear (noisy and distorted).
Ric Schultz |
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| rbroer |
Cascoding:
Yes, I've been thinking to make the constant current source a little better by cascoding, but, higher B+ are hard to find in cd players (this is not a standalone DAC). Dunno if there will be audiable gains though.
A next version shall use a SA970 as CB, so I can cascode the current sink with a J111 fet.
What is the benefit of cascoding the current conveyor transistor ?
Then the cascode transistor will have the "problem" of a variable collector voltage.
LEDs & pots:
Really ? In fact I did some measurements last week, comparing how different LEDs and three 4148 change their voltage with increasing current. Red was best, green next, yellow changes a lot, like the three diodes. As a reference for a BJT CCS I suppose the steadier, the better.
Many other inmates seem to be using them.
But I'll compare LED/diodes on the pcb version I'll be using on a cd player with the TDA1543 (this was just a quick prototype).
A hunch tells me you already know the outcome Rick ?
Indeed those resistors on the LEDs can be connected to the opposite rail. One can even save a resistor by connecting the upper LED in series with 18k and next in series with the lower LED.
Happy new year to y'all. |
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| Kuei Yang Wang |
Hi,
| quote: | Originally posted by rbroer
Cascoding:
Yes, I've been thinking to make the constant current source a little better by cascoding, but, higher B+ are hard to find in cd players (this is not a standalone DAC).
|
For a higher +B simply build an external supply and while you are at it also make seperate suppies in the same case for clock and DAC, leaving only servo and uP powered from the internal supplies.
| quote: |
What is the benefit of cascoding the current conveyor transistor ?
Then the cascode transistor will have the "problem" of a variable collector voltage.
|
The changes in collector voltage change the transfer curve of the Transistor. If you "nail down" this voltage via a cascode you much reduce this effect. Same goes for FET's and Valves.
If you then use a suitably high voltage cascode transistor (or better FET, Valve!?) you can use a very high Supply Voltage which increases headroom and helps to keep the modulation of the Collector/Emitter or Drain/Source Voltage in percent of the absolute voltage small.
My Final Gambit would then be a suitable output transformer driven by the cascode and directly into a suitably low load...
I do agree on the pot's (but that should be self evident), on the LED Front, why not use a TL/LM431 instead, it costs more than LED's or diodes but is best in the context and for a DIY Unit....
Also, feed references NOT via resistors but via current sources, J-Fet "constant current diodes" or selected J-Fets tend to work fine...
Later T |
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| tschrama |
Hee.....this IV-stuff just keeps coming back.. great ... I use a very simple IV stage with 1 BJT, 1 diode, 1 cap and 3 resistors.. and it works just fine..... better than passive IV with just a resistor I think.. but how about this one .. DC to 10MHz.... better put some LP in it somewhere..nice output of 2Vrms too .. and low distortion.. but propably needs very good supply... all simulated offcourse (if you know me ;) )...
best of new years greetings,
Thijs |
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| AMT-freak |
@tschrama:
Your I/V-stage seems to be fed by a voltage source w/ series resistor... Hm. Why don't you use a current source in the simulation?
@Nicke:
Could we have a look at your circuit?
Happy new year! |
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| Nicke |
| quote: | Originally posted by AMT-freak
[B
@Nicke:
Could we have a look at your circuit?
[/B] |
It is almost the same as Jocko published but without the coupling cap.
And it is followed with a JFET source follower.
I don´t want to publish yet,because I got some clues from Jocko in a private email to him and it is his decision to publish it.
If you read the whole thread you could figure it out myself.
Why don´t you try the published circuit to start with?
I am very satisfied with my I-V stage.
A last hint:Look at Nelson´s SU-SY patent. |
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| jkeny |
Rudolf,
How does the sound compare to your similar circuit with irf610 on 36v rails?
Can the CCS be done with simple jfet & resistor?
John |
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| rbroer |
jkeny:
Dunno, never used the IRF610 since inmate Dave from downunder compared it to BJT, and latter sounded and measured better.
After all suggestions I've come up with a version I'll try next (still enjoying the 1st version though);
I added a PNP cascode on the current conveyor to keep it's Vce pretty constant and as a bonus it creates more Vce voltage headroom on Q5 since it's referenced to negative rail.
I have cascoded current sink Q7 with Q6 since this one will be "seeing" the output voltage swing.
I1 ~ I4 are constant current sources made of jfets with resistor.
I'll be using 2SA970´s & 2SC2240´s
bias Q3, Q5 = 15mA
Vce(Q5) = 19V,
Ve(Q5) = 11V,
Vc(Q5) = -8V (+/-3V signal swing)
Any suggestions for a "bigger" Q5 ?
I may add the Borbely follower with two 2SK170 BL's
Regards, |
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| sonnya |
When using 2SC2240/SA970 at currents above 7mA you will operate them outside there linear range.
Pretty good transistor with good hfe linearity is parts like BC807/817 SMBT06/56(1 - 70mA) or BC846/847/848/849/850/856/857/858/859/860 (100uA - 8mA)
Sonny |
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| sonnya |
i did post some wrong info about 2SC2240 and 2SA970. The 2240 can easyli be used up to around 30mA but the complementary 970 starts rolling off at around 10mA.
I have a suggestion :
Design a complementary I/V stage. Does not have to use more than 4 BJT's in the active stage.
pro's :
Lower input impedance the half of a single BJT.
DAC see's a constant impedance. |
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| Nicke |
It works great with 5 mA through each stage also...
Perhaps it sounds better with more,but I haven´t tried that yet.
I think that 2SA970 & 2SC2240 is rated at 0,3 W so about 10 mA should work without problems with 15 V rails.
Nicke |
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| tschrama |
Sonnya,
check the other I/V thread ... there you can the my efforts in designing complementary I/V stage. .. simulated great!
That other guy ;) found a way optimize the canceling of the 2nd harmonic distortion, allthough he says it not a slightly different way and makes it look like something bad... |
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| Kuei Yang Wang |
Hi,
| quote: |
I have a suggestion :
Design a complementary I/V stage. Does not have to use more than 4 BJT's in the active stage.
pro's :
Lower input impedance the half of a single BJT.
DAC see's a constant impedance. |
Well, in that case, why not use a transconductance cell on a chip ("diamond transistor") like the OPA660? There you have already perfectly matched transistors on one chip, a buffer and can be run open loop. I think AD also has a transconductance Op-Amp (743? not sure) where the transconductance node is available externally and that can be used open loop thusly....
Of course, that replaces all that lovely discrete stuff with a chip and a few resistors but it will sure sound better AND measure better than all that cludge, but it would go against the DIY Spirit. Anyway, these days it is VERY HARD to make discrete designs that are even competetive against competent implementations of the right type of chip, but that's just me.
Sayonara |
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| tschrama |
Hi Kuei Yang Wang,
very interesting ... please could you make a simple example schematic...
gr,
Thijs |
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| sonnya |
| quote: | Originally posted by tschrama
Sonnya,
check the other I/V thread ... there you can the my efforts in designing complementary I/V stage. .. simulated great!
That other guy ;) found a way optimize the canceling of the 2nd harmonic distortion, allthough he says it not a slightly different way and makes it look like something bad... |
Yes i have read it. Add a folded cascode as you mentioned instead of your caps in the collectors. When modifyed this circuit could easely work with PCM1738... I know i know this is not part of this thread.
By the way. Use Switchercad III from linear tech. with this simulator you won't get fantastic distortion levels.
My circuit measure around -92dB based on the modified Jocko circuit first posted from Rbroer but with theoreticly current sinks and sources!
if i interchange them with fet's or BJT the numbers get 10dB higher. |
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| Kuei Yang Wang |
Hi,
| quote: |
please could you make a simple example schematic...
|
Not off-hand, but it really should be obvious from the Datasheet. Here the basics for the OPA660.
You connect a 270 Ohm resistor for biasing from pin 1 to the negative rail.
You decouple the negative and positive rail (pin 4 negative and Pin 7 positive) well and according to RF principles to ground, supply +/-5V.
You connect pin 3 via 100 Ohm to ground and pin 2 to the current input from the DAC. You place the required I/V conversion resistor on pin 8 and link pin 8 via a 100 Ohm resistor to pin 5.
Buffered output is from pin 6 via a 51 Ohm Build out resistor.
This has no lowpass, I would recommend a 62nF capacitor to ground on the output, this forms with the 51 ohm build out resistor a 50KHz 1st order lowpass, sufficient if the DAC is operated with 4 Times oversampling or more. You could make the Filter 2nd Order by paralleling the I/V resistor with a suitable value capacitor. The requirements for filtering for non oversampling operation are controversial, many people have their own ideas, as do I.
With -4mA Peak current from a TDA1541 the I/V conversion resistor should be sized so that the typhical output Voltage compliance is not exceeded or a +2mA compensating current should be injected into the TDA1541 Output. This is done easiest by using a 2k4 Resistor from a Well filtered +5V supply via a further 100ohm/1,000uF Filter section.
In this case the compensating current is used we have +/-2mA full scale peak current out of pin 8. To get 2.8V Peak (2V RMS) we thus need a 1k4 resistor, nearest standard value is 1k5 so we use that from pin 8 to ground. For a 50KHz 2nd Order lowpass we use a 33nF capacitor on the output and a 1nF capacitor in parallel to our 1k5 I/V conversion resistor.
I would feel that shunt regulating the +5V and -5V supplies via TL431/LM431 Shunt regulators is highly desirable.
L8er T |
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| tschrama |
Got it, thanks!
Nice interesting datasheet... I always love those simplified circuit diagrams.. Maybe use BUF634 instead of the 'onboard buffer' and connect direct to your favorite headphone :cool:
gr,
Thijs
PS
I'm still trying to make a perfect, ultra low noise, super fast V/I convertor (1-2mA max)at here at my work (Phd student). Wouldn't this opa660, with emmitor degeneration do this job? |
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| Pedja |
| quote: | Originally posted by Kuei Yang Wang
I think AD also has a transconductance Op-Amp (743? not sure) where the transconductance node is available externally and that can be used open loop thusly....
|
AD743 is quite conventional opamp, but AD844 is most likely what you are thinking about.
Pedja |
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| Elso Kwak |
| quote: | Originally posted by Kuei Yang Wang
Hi,
Not off-hand, but it really should be obvious from the Datasheet. Here the basics for the OPA660.
L8er T |
Hi Thorsten, congratulations, you just constructed a current feedback amplifier but without the usual feedback resistor.
This whole thread seems to explore and reverse-engineer and possibly improve the circuit by Jocko.
I strongly disagree with you Thorsten that a discreet circuit would be worse than integrated. Why on earth would Jocko use four dozens of transistors on his IV-board if he was satisfied with a simple AD844?. BTW that is real current feedback amplifier.
I constructed as a first attempt to a discrete design a circuit as in the OPA627 datasheet and it sounded a lot better than the original.
The whole idea of the IV-converter seems to circle around the input impedance of the IV-converter as the output of the DAC chip has limited compliance. What does that mean?
Well to qoute from Horowitz:
"<B>Ideal current-to-voltage converter</B>
Remember that the humble resitor is the simplest I-to-V converter. However it has the disadvantage of presenting a nonzero impedance to the source of input current; this can be fatal if the device providing the input current has very little compliance or does not produce a constant current as the output changes" [due the current]
The transresistance configuration can be used that is a opamp with non-inverting input grounded and the current going to the inverting input. A feedback resistor is connected between the output and the inverting input. The opamp does not need to be IC-type. It works very well with a discrete opamp. This is the configuration I am using with cascoded JFET's.
Now for Jocko and many others feedback seems to be a ugly F-word so I asume Jocko is using a current feedback configuration without the feedback resistor just as you do Thorsten.
As for the offset there are ways around Jocko wrote. I see some IC's on Jocko's board and suspect these are servoamps for offsetcountermeasure. A full complementary circuit would also be a asset.
In the datasheet of the AD844 it is explained that the current feedback amplifier has some advantages over a normal voltage feedback amplifier as a IV-converter. This is too technical to repeat or explain here but has to do with phase margin and stability. Also in fig. 28 of the datasheet is a simplified schematic in which the first part is almost excactly the scheme by Thijs. (the other part is the double diamond outputbuffer, LH002 style) I have been using the AD811 and OPA603 current feedback amplifier during some years in my DAC. After reading the Pooge Chronicles by Walter Jung and Hampton Childress. Also tried the AD844. Thereafter I switched to my discrete circuit as it sounded superior to the IC-currentfeedback amps. See Sonny Andersons thread.
http://www.diyaudio.com/forums/show...a+AND+amplifier
(SCM.zip)
His circuit is similar to mines.:cool:
Of the three transistor configurations possible the common base amplifier (input goes to the emittor) has the lowest inputimpedance. This happens to be the inverting input of the current feedback amplifier.
With the transresistance configuration a virtual ground at the inverting input is created.:cool: |
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| Pedja |
Hi Elso,
Sorry, but I want to ask you, what is the (current) feedback without the feedback? No feedback, no current feedback. Simply. But signal goes to emitter. That is not feedback at all. That is common base. The result is buffered DAC’s current output, and its voltage compliance is not critical afterward. That is all. And not every current feedback monolithic opamp can serve for this purpose. But OPA660 and AD844 can.
However, it is little dubious if cfb opamp like AD844 is really useful this way as it’s inverting input impedance is 50 Ohms (non-feedbacked, typicaly, according to datasheet, SPICE model actually shows 65 Ohms), generally low, but higher than we would like. Btw, OTA’s emitter of OPA660 has some 7 Ohms input impedance.
Pedja |
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| Kuei Yang Wang |
Hi,
| quote: |
Hi Thorsten, congratulations, you just constructed a current feedback amplifier but without the usual feedback resistor.
|
Actually, Burr Brown constructed (and manufacturerd) the device, so congratulation for that to them.
And congratulations to you for my newest favourite oxymoron, namely:
"a current feedback amplifier but without the usual feedback resistor"
BTW, I did not construct ANYTHING LIKE what you say, but it sounds good. Congratulations.
| quote: |
This whole thread seems to explore and reverse-engineer and possibly improve the circuit by Jocko.
|
I don't know about "the circuit by Jocko", but I do have in my little black book copies from Audio in the earlier part of the 80's of the last century which show the same principle as discussed here and if I may be so bold, much better implemented than anything I have seen in this thread.
| quote: |
I strongly disagree with you Thorsten that a discreet circuit would be worse than integrated.
|
I know you do.
I also wish you a good time selecting dynamically matched complementary transistors (and matched at least a few MHz so this whole shebang really works) and to minimise parasitics in the layout. I for one have long given up discrete solid state circuits, in the basic area where I need them to work I find the right IC's applied competently outperfom OBJECTIVELY AND SUBJECTIVELY ANY discrete circuit presented to me.
But that's just me and I have only been playing this game for two decades, so WTFDIK.
| quote: |
Why on earth would Jocko use four dozens of transistors on his IV-board if he was satisfied with a simple AD844?.
|
Beats me. But IIRC he prefers oversampling too. Maybe an innate prefernce for the complex over the simple.
It takes all sorts.
| quote: |
I constructed as a first attempt to a discrete design a circuit as in the OPA627 datasheet and it sounded a lot better than the original.
|
Please qualify your remarks by saying:
"To me, in my system and based on my personal preferences and prejudices it sounded better."
Or if that is not correct state the "rahmenbedingungen" (cornerstones may be the best contextual translation of rahmenbedingungen). unqualified remarks assert usally superiorty that does not exist even in subjective terms, never mind the type of subjectivism usally falsely peddled to us as objectivism (see Hume).
| quote: |
Now for Jocko and many others feedback seems to be a ugly F-word so I asume Jocko is using a current feedback configuration without the feedback resistor just as you do Thorsten.
|
Feedback is feedback.
What I propose does not include ANY form of feedback, not even local degeneration. Not knowing "Jocko's Circuit" I shall not speculate about what it is and what it not is. I do know what the circuit I propose is however and it does not include feedback in the I/V conversion..
| quote: |
As for the offset there are ways around Jocko wrote. I see some IC's on Jocko's board and suspect these are servoamps for offsetcountermeasure.
|
Well, I prefer to do without servos. I have in purely subjective sonic terms (though my sample size in these investigations considerably exceeds the number one it is not large enough to allow statistical significance at a .05 level) always found servos on the liabilities side of the balance sheet.
| quote: |
A full complementary circuit would also be a asset.
|
I am proposing to use one. And indeed one that due to the special process used is truely complementary, unlike ANY discrete circuit based on so called "complementary" types, selected for equal Ft and Beta (or transconductance, treshold voltage and Ft in FET's) or not. So what is your problem. Apart from the fact that the suggestion came from me, that is?
| quote: |
After reading the Pooge Chronicles by Walter Jung and Hampton Childress. Also tried the AD844. Thereafter I switched to my discrete circuit as it sounded superior to the IC-currentfeedback amps.
|
Again, you fail to sufficiently qualify your remarks. I personally prefer to use a combination of transformers and valves for I/V conversion (incorrigable reactionary is me). But what holds true for me is not the universal truth.
Sayonara |
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| Elso Kwak |
Hi Pedja and Thorsten,
I meant the <B>topology</B> of the current feedback amplifier of the course. The AD811 has 14 Ohm inputresistance on the inverting input and the OPA603 30 Ohm according to the datasheets.
I tried to make clear the similarity between Jocko's circuit, Thijs's & Rudolf's schematic, OPA660 and common current feedback topology. Apparently it is not appreciated by all:eek:
Thorsten I am surprised by your reaction. Just before you left the AudioAsylum you wrote that "most" solid state was fatally flawed.
http://db.audioasylum.com/cgi/m.pl?...flawed&session=
Now the right IC's are OK?;) |
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| Elso Kwak |
| quote: | Originally posted by Elso Kwak
of the course. ;) |
Please read instead "of course".
And it is LH0002 style buffer.;) |
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| Kuei Yang Wang |
Hi,
| quote: |
Thorsten I am surprised by your reaction. Just before you left the AudioAsylum you wrote that "most" solid state was fatally flawed.
|
Yup, I made clear MOST. Certain modern IC's are indeed "alright", few if any discrete circuits are, for the simple reason of severe dynamic mismatches between active components.
Sayonara |
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| Pedja |
Hello Elso,
Opamp’s open-loop input impedance is important if you could use it in open loop. AD8009 also has low inverting input impedance (8 Ohms, available only in SO package though), but the question is how to use it (and AD811, AD8001, OPA603) without the feedback. You only have their final (voltage) output available for connection. The only way to use them as I/V is to use them like classic opamp. Or I am wrong?
Again, that no_feedback approach can be meaningless if feedback doesn’t shorten bandwidth, and cfb doesn’t (… and if bandwidth is what we need here ;) ).
Pedja |
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| Elso Kwak |
Hello Pedja,
I only used the AD811, AD844, OPA603 and my own discrete opamp in the transresistance configuration. I.e with feedback applied. {Non-inverting input grounded and the current going to the inverting input. A feedback resistor is connected between the output and the inverting input. }
With the TDA1543 you can connect Vref to the non-inverting input of the opamp just as in the datasheet. You can even null the offset at the output by adjusting the resistor from Vref to ground but I found the sound better without the resistor.
I am not sure it will work without feedback. Maybe it works with the OPA660. Kuei Yang Wang, is your schematic a <B><I>working</B></I> circuit?
As said earlier I am not against feedback. :) |
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| rbroer |
Hi Elso,
I had been using opamps for I/V like most others, and much preferred the LM6172 as least evil above others like OPA2604, AD811, LM6181, AD797, OPA627, AD828, AD826, AD825, etc. etc.
About 1.5 years ago I made a real big step forwards using circuit shown; applied it to TDA1541 and TDA1543 cd players.
Didn't use opamps as I/V anymore since then.
The common base circuit is another step forwards and to quote Droopy "I'm happy".
If the Thorsten proposed circuit SOUNDS better, I'll use it, it is minimalistic enough for my DIY activities.
So, if anybody could send me a few OPA660's, I'll try it, compare it to my current common base circuit and post the results.
In the mean time, I started this thread to let other DIY know they can get good sound from a very simple discrete circuit, using generic parts and sounding so much better than the opamp I/V circuit used in many cd players and dacs.
As always, I'll try to pick up as much hints and suggestions as possibe, to complete my quest to audio nirvana...
:deer: |
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| Kuei Yang Wang |
Hi,
| quote: |
Kuei Yang Wang, is your schematic a <B><I>working</B></I> circuit?
|
If Burr Brown writes accurate application notes - yes. You can simply check their app note for the common base circuit, it's pretty much electronics 101.
As said, I would not use this type of circuit myself for any number of reasons, however if anyone wants a zero feedback, fully complementary I/V converter using the OPA660 is the best bet, plus you get your own buffer on chip too, so it is a single chip soplution for a feedback free I/V conversion.
Yet I too have not much against feedback,if applied apropriatly and in apropriate circuits, again, it is not WHAT you do that matters, it is HOW you do that matters.
Sayonara |
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| jkeny |
Now I'm interested - in building this I/V stage with OPA660 - simple enough even for me - can anybody advise on how a TDA1545 with about 3.3V Vref can be connected - I'm not very fluent in circuitry but followed T's description of circuit for 0V Vref (TDA1541)
John |
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| Kuei Yang Wang |
Hi,
| quote: | | Now I'm interested - in building this I/V stage with OPA660 - simple enough even for me - can anybody advise on how a TDA1545 with about 3.3V Vref can be connected - I'm not very fluent in circuitry but followed T's description of circuit for 0V Vref (TDA1541) |
This will not be so straightforward. First of all, the common mode Voltage of the TDA1543 will cause offset and the voltage compliance of the OPA660 ios too limited. It would require an unusual arrangement of Powersupplies to start with, namely +8.3V/-1.7V, then the base (pin 3) needs to be connected to Vref. This will ten give 3.3V DC offset on the output, requiring a coupling capacitor or some other form of DC nulling. Sounds like a lot of hassle..
Sayonara |
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| jkeny |
| quote: | | This will not be so straightforward. First of all, the common mode Voltage of the TDA1543 will cause offset and the voltage compliance of the OPA660 ios too limited. It would require an unusual arrangement of Powersupplies to start with, namely +8.3V/-1.7V, then the base (pin 3) needs to be connected to Vref. This will ten give 3.3V DC offset on the output, requiring a coupling capacitor or some other form of DC nulling. Sounds like a lot of hassle.. |
Oops, that's a shame - I was looking forward to trying it out - maybe I can use LM431's to set power supply voltages to 8.3/-17V and use back to back elctros on output (or would film caps do the job?)
Thanks for the help
John |
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| ronjg |
I don't know how Jocko's circuit works. I just know that I have one in my CD player. I have never heard any CD player sound better.
Jocko sez it does not use feedback, cuz feedback is not needed.
Did anyone think of asking him about it?
/rg |
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| Nicke |
| quote: | Originally posted by ronjg
I don't know how Jocko's circuit works. I just know that I have one in my CD player. I have never heard any CD player sound better.
Jocko sez it does not use feedback, cuz feedback is not needed.
Did anyone think of asking him about it?
/rg |
You can look for a more simple version here:
Jocko´s I-V stage
It sounds great...
Nicke |
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| mevangel |
Hi Kuei Yang Wang,
| quote: | | With -4mA Peak current from a TDA1541 the I/V conversion resistor should be sized so that the typhical output Voltage compliance is not exceeded or a +2mA compensating current should be injected into the TDA1541 Output. This is done easiest by using a 2k4 Resistor from a Well filtered +5V supply via a further 100ohm/1,000uF Filter section. |
Can you give details for a newby as I am?
Using the OPA660, is it necessary to compensate the 2mA current?
What about using an LM234 as a current source?
Ciao.
Marco |
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| Kuei Yang Wang |
Hi,
| quote: |
Can you give details for a newby as I am?
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What do you mean, DETAILS? You have in essence the whole circuit in description, only need to draw it out. What more DETAILS?
Sayonara
PS:
1) Yes
2) No |
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| Pjotr |
| quote: | | Yet I too have not much against feedback,if applied apropriatly and in apropriate circuits, again, it is not WHAT you do that matters, it is HOW you do that matters. |
Fully agree. In fact there is no life without feedback. This holds for electronics as well. The debate about feedback in electronics is as old as there are electronic amplifying devices around. The large internal feedback of a triode was the reason for developing tetrodes and later on penthodes.
Concerning the IV stage with an op-amp: What counts is the slewing capability of the input stage without going into saturation and the open-loop corner frequency to handle the fast transients coming out of the DAC. Some BB app notes put a large cap directly at the output of the DAC to tame this. Unfortunately this impairs the noise gain of the amplifier.
Maybe a pair of J-Fets or even an ECC88 as the input stage of a discrete op-amp is better option for the input stage in an IV converter with “feedback”
;) |
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| mlloyd1 |
Hmmmm... Check out the Borbely Audio site's All FET DAC
mlloyd1
| quote: | Originally posted by Pjotr
.....Maybe a pair of J-Fets ... is better option for the input stage in an IV converter with “feedback”
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| apassgear |
I don't think is wise to start another thread on the same subject, so here is my question.
I'm replacing the CFB AD844 I/V originally proposed by Jung on his Pooge articles on the CDB650 CDP with the LM6181 CFB opamp.
Sure I'm doing somethig wrong so please give some advise.
The Dac connection is going to the inverting input of the opamp through a 220 Ohms and the feed back is a 1K Ohms. I also have a 47 Ohms resistor at the output to isolate cable capacitance.
The result is nice but with a lot of noise indeed.
What's wrong? |
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| apassgear |
| Just to give some more information. The stage has no low pass filter. And the load of the Opamp, besides de cable, is a 50K attenuator. |
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| Jocko Homo |
Why is it going through 220 ohms??????? And why no output filter?????
Just in case anyone cares.....I used the AD846 as an I/V before I came up wit the one you guys are trying to reverse engineer.
The reason why is that our dealers did not like the sound of the CFB I/V.
And while we are at it......................here is one more for you guys to ponder......mostly Elso [joke]........
On the op-amp I/V stages, I pumped a 1.8 mA current into the input to cancel out the unipolar current the '1541 puts out. And that current was servo controlled.
Jocko |
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| Kuei Yang Wang |
| quote: | Originally posted by Jocko Homo
On the op-amp I/V stages, I pumped a 1.8 mA current into the input to cancel out the unipolar current the '1541 puts out. And that current was servo controlled.
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AND?
:devily: |
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| Elso Kwak |
| quote: | Originally posted by Jocko Homo
Why is it going through 220 ohms??????? And why no output filter?????
Just in case anyone cares.....I used the AD846 as an I/V before I came up wit the one you guys are trying to reverse engineer.
The reason why is that our dealers did not like the sound of the CFB I/V.
And while we are at it......................here is one more for you guys to ponder......mostly Elso [joke]........
On the op-amp I/V stages, I pumped a 1.8 mA current into the input to cancel out the unipolar current the '1541 puts out. And that current was servo controlled.
Jocko |
Jocko, Not funny.
I know what's in your board. I will not spread the knowledge.
I have enough of pesting other forummembers!
I have enough of this hobby. Did throw my DAC against the wall. Bang, what a bad sound!!!
END OF STORY->
:dead: |
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| jean-paul |
| Cheer up, Elso ! There are more things in life than audio. |
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| tbla |
| keep it up.......a nice burgundy might help....:drink: |
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| Jocko Homo |
Too bad you didn't think so.
And I know that you do not know about this board that I am refering to: none were ever sold in Europe.
Repeat: The dealers did not like the sound of CFB op-amps as I/V stages. It died a quick death. Or the company would have.
Anyway.....for the rest of you........Thorsten are you listening........the "and" part should be obvious.
If you think about it long enough.
Jocko |
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| jean-paul |
Please give us the schematic Jocko. We really can't wait another year ;)
| quote: | | And I know that you do not know about this board that I am refering to: none were ever sold in Europe. |
I don't think this prevents information to be exchanged around the globe. You would be surprised what amount of ( handdrawn ) schematics float around on the web, but never the one I am looking for at that moment :D |
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| tbla |
do you sell those magic boards...?
:wiz: |
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| Jocko Homo |
This thread started back when I was on vacation, so I missed the bulk of it. I believe that something extremely close to it is up here.
Another thing to remember.......I made the board in one night.....it had to fit into the existing board space that the CFB design was in. I did just enough to make it work, in very little time, to save my company from massive dealer revolt. It was never "tweaked", and there is ample oppurtunity for such.
So unless I am wrong, there is a good starting point here already.
Elso:
The reason I "tweaked" you is because I believe that I read something like "Feeback seems to be a four letter word to Jocko".
No, it is not. But the sound that the '846 I/V yielded nearly cost us all our dealers. It did so many things right, but what it did that was wrong was something none of them would accept in a highly competitive market. Ergo, it needed to be fixed.....ASAP, and the fastest, and apparently best solution, was to rip apart an '846.
Or you can do what Thosten did......evolve the I/V into a CFB.
They both use a common-base input stage and current sources/mirrors out the wazoo.
The reason I don't just post it and say: "Here, build it" is so that you guys can learn to like a designer. I believe that I can be of much more help in getting you guys to work this stuff out on your own........furthering your understanding.......than I would by just selling surplus boards (which are gone, sorry......) accompanied with a poorly drawn hand schematic.
(Yes, along with no simulation software, I have no schematic capture software either. What a dinosaur I am.)
Jocko |
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| apassgear |
Well I read most of both threads again dealing with this I/V issues, trying to figure out whats going on. Quite frakly I feel naive when comming to design and more so within this seemingly esoteric arena.
My simple question was regarding the implementation of the LM6181 to this task, since what I can hears is realy nice, but of course I oppened the pandora box once again.
If there is not a straight awnser to my question and if Jocko continues to hold the "secret" (for some reason I don't understand) behind the non feedback I/V I will give a try to Kuei's open proposal for the use of OPA660 which might even be better than Jocko's esoteric design.
Still for appling the OPA660 I have some questions regarding the +2mA compensating current required. Is it mandatory? Reading Kuie's post it seems to me that that is an open question.
To summ up for what I'm looking for is the simplest I/V with the best sound available today to be applided to an oversampling TDA1541A. Rails could be anything.
Any suggestions???
Reader's Digest style please (TM)
Happy listening!!!
:) :) :) |
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| tschrama |
| quote: | | to be applided to an oversampling TDA1541A |
A oversampling TDA1541A, stock, or DIY? Could you tell someting about your circuit and components.
Regards,
Thijs |
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| apassgear |
| quote: | Originally posted by tschrama
A oversampling TDA1541A, stock, or DIY? Could you tell someting about your circuit and components.
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The CDP is a regular Magnavox CDB650 which was Pooged many years ago it has an SAA7210 decoder and SAA7220 Filter and a TDA1541A S1 DAC.
On the analog section had an AD846 (not shure, but it is a CFB opamp which was proposed originaly by Jung) keeping part of the original analog filter. Later I've been trying to replace it with an LM6181 CFB without any analog filtering.
The analog section PSU is using dedicated Jung/Sulzer super reg at (+)(-) 15V without the sensing option.
Hope I don't forget something important. |
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| apassgear |
| Here is a pic of the unit before trying to implement the LM6181 analog section. |
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| apassgear |
| Oopss... That was not the one I wanted to show, but this |
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| Peter Daniel |
| I just modified my Marantz CD-94 two days ago. I disconnected digital filter, so it's non oversampling now, changed and upgraded all electrolytics to Cerafine and HFQ, with ceramic bypasses at the pins. The output stage is using only first IC and I put OPA627 there in original config. Form output of OPA627, the signal goes directly to RCA jacks. I'm using 4.7 BG N for coupling, but I'm tempted to remove them. The resistors network at TDA1541 output was removed. It is still not finished yet (new clock and reclocker will be added, with new PS regulators) but as it is now, the sound is very good. |
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| apassgear |
I appreciate your input Peter...
Since I am not satisfied with the CDP sound, been trying different approches to this I/V analog section but with my limited electronic knowledge I get frustrated, besides I don't get straight answers from the many well experianced guys around here such as say "you can't do that with an LM6181 so try this" or "your getting into deep waters so follow this approach." which has been the gereral attidude on DIYaudio forums.
Well, frustrated or not I continue to work on this CDP (at my slow pace). To beggin with, I'm quite amazed at all what it can be get from the TDA1541A, it's such an overwelming sound I get from the new opamp (minus the noise of course) that I will like to continue with original oversampling setup, for the moment.
One interesting thing with this "new" approach with the LM6181 is that I decoupled the chips rails with only one 1uf film cap very very near the pins which might be contributing to the excellent sound I'm getting.
On trying to solve the noise (thinking it could be PSU related) I tryed further decoupling adding a ceramic cap at each point plus a MKS 4 0.01u across both rails at the chip.
I had never before try to use ceramic caps, the regular types. The result after this addition degraded the sound. |
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| apassgear |
Even though I will try non oversampling when the time comes I'ts my gut feeling that is better a digital filter than an analog low pass filter.
I'll do the non oversampling after I get the analog portion working and then figure out how to do the analog low pass.
What's your feeling regarding this two (different) filter approach? |
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| Peter Daniel |
| I will simply remove low pass analog filter. I don't think it's needed;) |
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| apassgear |
| Interesting, so no attempt to reduce the hall of mirrors, wide open, no digital or analog filtering. |
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| tschrama |
Hi Apassgear,
Thanks for your info and pics. I am not a real-pro-experienced-diy-freak like Peter but I would like to share my experience with you:
I have wonderfull results with a CS8412 / TDA1541A / single BTJ I/V /capacitor / to amplifier or direct (4mApp) into headphone. There's only 1 cap in the signal path, no low-pass filter, no oversampling. There's a snap, rythm and ambiance to the bass I've never heard before in my other DACs. The CS8412 has it's own regulator, like the TDA1541A, but the I/V stage (the single BJT) shares its +/-15V power supply with the TDA1541A, decoupled with 100hm/1000uF, running 13mA Iq each channel.
This setup has a assymetrical slewrate but I don't know wheter that actually mattters. Anayways, the discrete single BJT I/V stage can be made small enough to fit a 8 pin DIP package, just to give you another option.
Goodluck, regards,
Thijs |
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| apassgear |
Thijs,
Well that's a very minimalist TDA1541 and very atractive proposal for me and specially if it sounds as you say, this is what I'm looking at the end.
Did you make a dedicated PCB or is it a P2P setup?
Just to get an idea, is the BTJ connected similarly to Rbroer shema without the opamp? Grounded gate?
Why did you select a CS8412?
Thanks for your input hope to hear more from you.:) :) :) |
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| apassgear |
Coming back to my LM6181 I/V "stage".
I removed the ceramic bypass caps and connected the DAC directly to the inverting input of the opamp still with the 1K FB resistor. I did not remove the 0.01u cap across both rails though.
To my surprize I got some AC noise through the speakers which was not present before and this is without any signal going through the CDP!!!
Feeding signal I got same noise as before.
Beats me!
Any suggestion? |
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| Jocko Homo |
Peter.....you really didn't say this did you:
| quote: | | I will simply remove low pass analog filter. I don't think it's needed |
You either need to borrow a spectrum analyzer.....or drive down to Texas to borrow mine.
Guido........Phred.......this one is yours......
Jocko |
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| Peter Daniel |
I think it was Phred who liked the sound of Scott Nixon's DAC. As far as I know, it doesn't use low pass filter.
And I remember when you said that both TDA1541/43 are ancient chips and non-oversampling can't be any good. It happens that I just tried both of them without digital filter and they are not any worse than my PCM1704 DACs. I can only blame myself for not trying it earlier;)
But, I also don't measure anything and rely only on my (and some friend's) ears. Maybe it's good, maybe not. |
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| Fred Dieckmann |
I have a low pass filter on mine. I had a talk with Scott and think you might get away without one in some cases. The high output impedance of the DAC's I to V stage (a resistor in this case) acts as a filter with the cable impedance to provide some filtering. Many amps and preamps also contain low pass filters at the inputs. In light of this you actually do have a low pass filter but at a pretty high frequency. I put low pass filters on the inputs of most analog circuits to suppress RFI noise at the input. I do it because it sounds better (and I know the engineering reasons why) So much for the objective versus subjetive debate on this one.
"But, I also don't measure anything and rely only on my (and some friend's) ears. Maybe it's good, maybe not."
Jocko and I listen to everything we design as well as circuits designed by others. That's how you make correlations between good sonics and good engineering pratices. Often, one hears sonic differences and then goes back to measure things to see what the technical reason might be. You can then pay attention to this part of the design on the next go around. It's kind of like the joke about the guys who goes to the doctor and says" It hurts when I do this." The doctor tells him "Then don't do that!" |
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| jean-paul |
| quote: | Originally posted by Peter Daniel
I will simply remove low pass analog filter. I don't think it's needed;) |
Playing with fire AFAIK. I don't have sophisticated equipment but my scope reveals RF garbage coming out with the filter removed. The filter is needed, especially when using SS amps without input filtering. In the case of tube gear the necessity is probably arguable. A friend of mine used the non os TDA1543 DAC with and without filtering on his 300B SE amp and wasn't able to hear any difference but kept the filter "just in case".
In my setup the difference is audible so I use filtering. I use 1 % polystyrene caps for this purpose as tolerance is critical in this setup. That also counts for the resistors used for I/V. |
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| tschrama |
Hi Assapgear, hi all, nice to hear from everybody again.
I also realize that NonOversampling could mean intermodulation distortion from the high frequency quantisation noise. Yet is does sound OK to me. I also build Scots DAC, but the TDA1543 looks bad on my scope. This picture of the noisy low-level signal on my scope keeps popping up when I trying to listen. I put 10nF (?) parralel to the output resistors to tame the HF-noise.
| quote: | Well that's a very minimalist
TDA1541 |
Hmmmm that's not a compliment is it? I wasn't trying to be mininmalistic. The DAC-board has 6 regulators and 16.000uF total capacitance on board, excluding the I/Vstage. I hope this makes it a little less minimalistic. However it is P2P wired.
| quote: | | Why did you select a CS8412? |
I got them cheap, they are easy to solder (P2P) and I use only a 44.1/16bit CD source so I don't need the CS8414.
The IV stage is jocko's published simple IV-stage but using resistors instead of CCS. 1 BJT, 1 diode, 3 resistors. Im sure Jocko's version will outperform mine. Both are build within a hour.
Regrads,
Thijs |
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| rbroer |
| quote: |
Jocko, Not funny.
I know what's in your board. I will not spread the knowledge.
I have enough of pesting other forummembers!
I have enough of this hobby. Did throw my DAC against the wall. Bang, what a bad sound!!!
END OF STORY->
|
Seriously Elso ?:bigeyes:
Well, I know the feeling.
I just moved and overall my soundstage improved, except for the lowest bass, it's missing now :bawling:
Last week I listened to a Sony DVP9000ES SACD player with the Vakuumstate board and low jitter clock upgrade.
It was very clear redbook is flawed; lacking too much microdetail in comparison.
Each time going back from SACD to the same album on redbook, it's quite obvious how much it's missing; goodies like ambiance, CD sounds it's in a hurry, soundstage, sweetness of treble, decay...
I'll keep my non-os TDA1541A-S1, Kwak-clock, synchronous reclocked, Jocko's common base (soon to be the "better" one as he hints and I've verified it with him) player, but know there's better out there, not in the circuits, but just more info in the data available to start with...
The end of the day, SACD has more potential. Note this V.S.E. upgrade takes the raw DSD signal stream, and it will not be available in all SACD players.
I also took the liberty (hope you don't mind Allan) to reverse engineer the V.S.E. circuit; it's very good.
Discrete Pooge regulators, but setup as shunt regulators (similar to LCaudio's zapfilter), fed by current sources with current sources for the LED references, fet buffer with dmos cascode and complementary darlington. DC servo to finish.
Cheer up Elso,
Maybe you should upgrade your turnable ? ;) |
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| janneman |
| quote: | Originally posted by apassgear
Coming back to my LM6181 I/V "stage".
I removed the ceramic bypass caps and connected the DAC directly to the inverting input of the opamp still with the 1K FB resistor. I did not remove the 0.01u cap across both rails though.
To my surprize I got some AC noise through the speakers which was not present before and this is without any signal going through the CDP!!!
Feeding signal I got same noise as before.
Beats me!
Any suggestion? |
If what you removed are the supply bypasses, most probably you got into oscillations territory. That would be there with and without input signal.
Jan Didden |
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| Jocko Homo |
Scott Nixon is a tube man.
I agree with J-P. Put some kind of LPF in front of that SS gear.
Either that, or a Jensen transformer.
Which might do wonders for than one reason.
Phred......your turn to supply the necessary links.
Jocko |
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| Pedja |
| quote: | Originally posted by Jocko Homo
Peter.....you really didn't say this did you:
"I will simply remove low pass analog filter. I don't think it's needed" |
But I think he did. And I think I know why he did it. I think I also do say the same.
For those interested, I did measured TDA1543 DAC, powered by 6V and I/V converted by 1K resistors. THD is 0.08%, and IMD is 0.05%. As seen, figures are quite decent, but still notably worse (let us say 10x to 30x) than almost any commercial CDP. That is about distortion measurements. Was funny to make them, but more than it said something about the measured units, it said something about THD and IMD measurements themselves (again). Sorry, I do not have a way to measure TIM, but it anyway concerns unit following DAC and not the DAC itself.
Then:
Whatever you do with non-o/s you can not filter it “redbook successfully” unless you practically completely destroy the sound. So for the “legitimate engineers” it will always be incorrect (they will always prefer what they see at their spectrum analyzers to what they hear, if hear anything).
And when I am at TIM, my experience with low passing of the buffered gainclone reminds me it might be better to deal with the amp’s ability to resist to garbage (hmm, GC is SS?) than to bother with the redbook principles of filtering in digital.
For those still interested in non-o/s filtering may I suggest to look at the five filtering options for the non-o/s, five quite marginally visited pages at my site.
Pedja
Ps: …I saw the light! |
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| Peter Daniel |
| quote: | Originally posted by Jocko Homo
I agree with J-P. Put some kind of LPF in front of that SS gear.
Either that, or a Jensen transformer.
Which might do wonders for than one reason.
|
I tried transformers at the output of TDA1543. I didn't have Jensens, but Lundalh LL1570XL were within reach. Some people in my are do serious business by installing them at the output of CDPs for bettter sound. But when I instaled them in my DAC, it was not an improvement. A bit of the real essence of music was gone and I will never put them back again.
I also tried MSR860 diode in the PS (DAC circuit) of my Marantz CD94. And here I was for another surprise. While both MUR and MSR 860 worked great in the gainclone, in a CD player they simply messed up everything. The soundstage was gone, the top end dissapeared and everything was flat. I quicly reinstalled the original Philips supplied diodes.;) |
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| hifi |
1:1 transformer outputs should (IMHO) mainly be used with Vout dacs there they can do miracles, with Iout it would be more suitable with say 1:15 and use them fore voltage amplification.
/micke |
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| Peter Daniel |
| The Lundahl is 1:1 transformer and TDA1543 is Vout DAC. I used the transformer right after I/V resistor and coupling cap. It didn't work as I expected (miracle;). |
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| apassgear |
Thanks Jan for your input. Very welcomed.
If you read my previous posts you will notice that the ceramic caps were added to a 1uf film cap, which is arguably low in value but did sound apparently OK. Leads from the PSU are rather short, about 10 Cm (4"). The PSU +- 15V is dedicated to this stage and is the Jung/Sulzer type w/o sensing option. You can have a partial look at the posted pics.
So removing the cer caps I only went back to what I had which did not produce the humm, but...
Also you will read that when I added the cer caps I also added a MKS 4 0.01u across the both rails at the chips and this one was not removed. So this is the suspect now.
I have been concerned about DAC damage, you know, working with little experiance in this area, though I strap myself to ground, but testing some not well design output analog stages, so the question....
How easy is to damage the DAC through the output pins?
And taking this opportunity I have a silly question concerning the 14 bit caps that go along with the '1541 DAC. Are these reverse polarity?
Meaning if the leg that goes to ground is positive in relation to the connection to the pin? |
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| apassgear |
| quote: | Originally posted by tschrama
Thanks for your info and pics. I am not a real-pro-experienced-diy-freak like Peter but I would like to share my experience with you:
|
You may say so but to me you have covered considerably more ground than me, at leat on digital, , so all your comments and experiance are welcomed.
Yes, been minimalist it is a compliment from my poit of view so congratulations for your implementation and as I said I'm willing to try somethig like these in the near future.
Now I wait and see if these other guys shead some light on my twisted LM6181 CFB (I/V) analog stage, if they only took the boder to read my posts..... |
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| jean-paul |
| quote: | Originally posted by Peter Daniel
The Lundahl is 1:1 transformer and TDA1543 is Vout DAC. I used the transformer right after I/V resistor and coupling cap. It didn't work as I expected (miracle;). |
TDA1543 is Iout DAC chip. |
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| Peter Daniel |
| In that case I have to try it with TDA1541. This is all still new to me;) |
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| Jocko Homo |
Peter:
Never tried the Jensen 1:1 output trannies......only the 4:1 step-down input types. They have the advantage of having really good CMRR. Please note that their input and output types are not interchangeable.
I don't think either are very fond of DC offset, although I have no idea as to their B-I curves.
Perhaps that could explain some of your disappointment.
Jocko |
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| Fred Dieckmann |
Peter:
"I used the transformer right after I/V resistor and coupling cap."
Jocko:
"I don't think either are very fond of DC offset
Perhaps that could explain some of your disappointment."
How much DC offset is there on the other side of the coupling cap? You definitly don't want to put several volts of DC on the transformer winding.
Maybe I can get a job as an editor............. |
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| tmblack |
Do you feed this directly into your preamp or I would think some LP filter with gain?
Tom
EE |
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| mllum |
Can anyone post a schematic to show how Rudolf's schematic at the beginning of the post can be adapted to a differential current output dac like the ad1853 so that there can be a singe ended output?
Thanks in advance |
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| hollowman |
| quote: | Originally posted by rbroer
After all suggestions I've come up with a version I'll try next (still enjoying the 1st version though);
I added a PNP cascode on the current conveyor to keep it's Vce pretty constant and as a bonus it creates more Vce voltage headroom on Q5 since it's referenced to negative rail.
I have cascoded current sink Q7 with Q6 since this one will be "seeing" the output voltage swing.
I1 ~ I4 are constant current sources made of jfets with resistor.
I'll be using 2SA970´s & 2SC2240´s
bias Q3, Q5 = 15mA
Vce(Q5) = 19V,
Ve(Q5) = 11V,
Vc(Q5) = -8V (+/-3V signal swing)
Any suggestions for a "bigger" Q5 ? |
Questions about the folding-cascode "upgrade" to rbrorer's I/V -- and specifically with respect to its use with TDA1541A:
Are all Q's now 2SA970's & 2SC2240's?
What are the values for R1, R6 and R7 (are these best off as pots)?
Are the LED colors still green ... or will red work better ... or does it really matter?
For anyone who built the orignal and the folding-cascode "upgrade" ... how big of a sonic difference is there between the two?
Thx for any info you can provide. |
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