Easy-to-build I/V stage

[LBHajdu]

Why not use the Nelson Pass I/V stage from the D1?

 

[Ric Schultz]

Pass IV stage

Yes, I am not only aware of the Pass I-V stage but have tried it. I am concerned by the possiblility of high distortion with the mosfet circuit and also highish noise from the mosfets. That is why I want to try the lower impedance, lower noise and possibly lower distortion bipolar route(soundwise, I really like FETS). The only way to know which circuit sounds best is to try different ones. And tweek them, of course.

So, any suggestions on using the bipolar circuit with a PCM 1738?

Ric Schultz

 

[borisov57]

I would connect emiter of q1 to common voltage of DAC ( 2,5 V in your case), so you would have the same voltage on q2 emiter. Look in the datasheet, if common pin can handle q1's current. Otherwise you could connect it through buffer.

 

[LBHajdu]

Sorry Ric I have no suggestions. I would however be interested in a more detailed review of the pass i/v stage. I have been getting many reviews that say the high end is somewhat rolled back.

Let me throw out another “Easy-to-build I/V stage” I found online:

 

[woody]

Are the resistor values,the type tube used and the voltage
for the tube available?

 

[fdegrove]

I/V

Hi,

That outputstage is the one from SDS Labs Tube DAC.

You can take a look at it here:

Tube DAC

Cheers,

 

[tschrama]

OK,

This must be it... my final I/V stage ... for now

The Vbias should be done acording to your favorite method (led, diodes, CCS, caps etc).

Some optimisation could be doen on the resistor values to increase ease of Voffset adjustment etc..

How about this one Jocko Homo? Agree that this could be worth those 4 PCM1702 I got?


gr,
Thijs

 

[halojoy]

Great! - tschrama

OK,
This must be it... my final I/V stage ... for now.
The Vbias should be done acording to your favorite method (led, diodes, CCS, caps etc).
Some optimisation could be doen on the resistor values to increase ease of Voffset adjustment etc..
Agree that this could be worth those 4 PCM1702 I got?
Thijs

Thanks, tschrama

Best one so far
of "Easy to build" and without exotic IC or expensive parts.

(Could be done more complicated , with parts only the chosen few can find/afford .
But who wants to see such designs? )


/halojoy - knows what circuits he likes

Here is the circuit - for all to see:

 

[tschrama]

Thanks Halojoy,

What Iq do you suggest? 5mA, 10mA?

gr,
Thijs

 

[Nicke]

OK,

This must be it... my final I/V stage ... for now

Why don´t you try Jocko´s I-V stage ?
It sounds really good

Nicke

 

[halojoy]

Thanks Halojoy,
What Iq do you suggest? 5mA, 10mA?
Thijs

What current.
Must depend on Peak input Current.
What is the peak out current of the DAC?

BC550/BC560 has low noise operation at 0.1-0.4 mA
and Good Bandwidth, speed at 2mA-5mA

0.4mA-2.0mA is a Good Compromisse, often used in Audio Amplifiers

---------------------

John Curl, the designer, once answered me in a post,
at AudioAsylum
where I had mentioned something about Current.

John Curl said: "Current Is Good"

This quote has been ringing in my head since then.

Current is good!

And judging of other great Amplifier Designers work
with Class A in mind,
I would have to agree: "CURRENT is GOOD!!!!"

The transistor will hold a temperture which is more
indepedent from surrounding temp.
It warms itself.
And the operation point is far from that unlinear
performance, in the "turn on" region.
--------------------------------------------------------

So your suggestion 5-10 mA might be a good choice,
especiall as voltage only is 15V.
Will give about 75-150mW operation.

 

[LBHajdu]

Here is a thread I started for trying to balance Jocko i/v stage so it can be used with an AX amp, take a look : A nice dac to complement the Aleph-X.

Leve

 

[halojoy]

Here is a thread I started for trying to balance Jocko i/v stage so it can be used with an AX amp, take a look : A nice dac to complement the Aleph-X.

Leve

Yes, I have already seen that, LBHajdu

And also downloaded (saved) the circuit, too

halojoy - adds one more circuit-picture to his collection

 

[Tieftoener]

Attention: tschrama!!

tschrama:

The Vbias should be done acording to your favorite method (led, diodes, CCS, caps etc).

Pardon my stupidity... but how on earth can you bias those wierd values (i.e. -9.62V, 9.54V) with diodes/LEDs??? I would have a hard enough time doing it with 1% resistors... Please help

Also - I'm confused about voltage bias using a CCS? Again pardon me - I'm a fresh out of school EE (although, I know that I'm of no such caliber to actually be called an engineer... )

I'd really like to build your last posted I/V stage in this thread - I've got all the BC BJTs sitting at home waiting for their new home...

I'd appreciate any explanations you can offer...

 

[jwb]

Well, I quite seriously doubt that he is biasing his base to exactly -9.6267V. Probably he just typed that in off a calculator or something. Looks to me like the best way to get a stable, quiet bias would be to use a LM329 reference from the rail. That would put Q2 at about -8.1V and Q5 at +8.1V. Adjust R5 and R3 to get the desired current for a given bias voltage.

 

[tschrama]

You are right Tieftoener, such voltages can not be pratically be achieved with diodes and LEDs only.
I made my remark because some time ago there was a thread(s) as to how to accomplish very stable low noise voltage sourches. I've seen ellaborate configurations with CCS, shunt regs, lots of capacitance, diodes or LEDs (?) ... well ..etc...

If you use good power supply it can be as siple as a potmeter with a small cap across the middle pin and ground .. The approximation of Vbias can be calculated if you have choosen a Iq for the stages, this will determine the voltage drop across the resistors, keep in ind the base/emitter drop of about 650mV: well you figure that out offcourse. The circuit is sensitive for bias voltages so keep your scope and voltmeter at hand to check everything.

Goodluck,


greetings,
thijs

 

[Tieftoener]

Thanks guys (particularly tschrama) - you rock

Now I have a project for this weekend...

I don't have a scope though Still searching ebay and used/refurb dealers for a nice one with a good price.

Lucky me - I just ordered a Tektronix TDS2012 for work and a B&K 4017A function generator . I gave my boss a few options for recommendations, and he just told me to get the best. I should have had the foresight to put an Agilent scope on my list too... Who knew he'd go for broke?!?

I'm stuck to using my SpectraLAB program on my SB live! card (I know, I know... but I can't afford a Lynx Studio card at this point - a few loans to pay off first). Just make sure to run it in 48kHz sampling... and results are good enough for prototypes. I just need a way to be able to accept higher voltage than a darn 2Vrms audio input for my ADCs on the Live! card...

Anyhoo - wish me luck this weekend We'll see how far I can get with my DMM...

Regards,

 

[Jocko Homo]

"Why don´t you try Jocko´s I-V stage ?"

Because they don't have the full schematic.

Anyway, the one that you all have is very close. Like the man said......try it.

The point of this was to show you how you can get really great sound without a lot of parts, and no feedback. And to get you guys thinking on how it works so that you can come up with the full version just like Nicke did.

Make sure that you have a very good PSU. This design has no feedback.....(because it is not needed, Elso.......), and the sound will suffer with a poor supply.

IOW, no three-terminal regulators.

Jocko

 

[Tieftoener]

I'm such a dork

Hey Jocko!!

I've never talked to you really, but it's a pleasure to finally meet you online. I've been avidly reading your posts for the last several months, and can't thank you enough for your valuable explanations and advise.

I never did get to testing tschrama's ckt, although, I did get one channel built up in a breadboard... I do need to add a driver stage to it yet also.

Jocko - I, unlike many here, am trying to build some circuits for experimentation... just like you I totally agree that building it and measuring results are totally different than a darn simulator! (like, try simulating a 4th order L-R active XO, and then measure a mock-up real-life example... after you measure the knee of that curve, you'll find its not actually a butterworth squared Q, and your corner freqency will be off... and... you'll be banging your head up and down on your lab table, or wall

Anyhoo, I do have every intention of building up your circuit Jocko - all in good time. I just haven't gotten around to ordering the BJT's for yours yet, and the budget is wearing a little thin this month. I will build it... (and they will come - sorry, lame)....

I will build it and measure it and compare it to tschrama's. The poor DACs in my Denon deserve even better than my mod'ed opamp stage. I wish I had more time in the day

 

[Oli]

Is discrete transistor I/V conversion an option at +/-5(five) Volts

Hi everyone!

(Hi Elso - This thread seemed more appropriate for a discussion of my I/V conversion)

I have been recently looking at op-amp I/V conversion for my single ended output AD1865N-K project. I am currently using the internal opamps and attempting to shunt HF to ground in the form of a first order filter (To cut a long story short.. I am loading the input of the opamp with capacitance- making it unstable!)

I am looking at my options... I only wish to use +/- 5 (five) Volt supplies.

Can Jocko's zero feeback discrete I/V converter be adapted - I would love to give it a try?

How can I first order filter with an opamp for my AD1865N-K.

Your thoughts please...