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Old 18th February 2013, 02:14 AM   #71
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Location: Jackson,michigan
You also need to find out what the maximum peak voltage is to your sound card and then design your voltage dividers around that value.
At first I though that 1v p-p as about what mine is, but, I later found out that 4Vp-p was the true maximum for my onboard sound system using the Realtek ALC 892.

I also have a GINA24 sound card it can handle an even higher voltage so I will have to adjust for this should I decide to start using it.
I have posted an update about this and I now employ some output buffers to minimize the loading errors on the voltage dividers and a 4X gain stage to account for my original error of voltage levels.

jer
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Old 18th February 2013, 04:46 AM   #72
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Here are some OPT's for a reasonable prices.

Weber Transformers and Chokes Order Form

jer
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Old 18th February 2013, 10:45 AM   #73
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Quote:
Originally Posted by owenhamburg View Post
I think so too, how should I do this best?

My scope does not like > 300 V AC, and says things like it will die in it manual.

It looks like about 100 V is the maximum input that can be displayed.

My multimeter only 600 V AC.

I guess a potential divider into a ADC and optical the computer is the easiest?

Regards

Owen
Owen,

If you want to measure your transformer(combination) you should use a 1:10 probe for your oscilloscoop. Not only you have 10 times less voltage on your scoop but also less capacitive load for the transformers. Next step is to add a 80pF capaciter and see what is happening (1:10 probe + 80pF = Stax headphone load)

Measure between 0 and + phase and later on between 0 and - phase ( there could be a differance between them)

Martin
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Old 18th February 2013, 05:34 PM   #74
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Quote:
Originally Posted by esltransformer View Post
If you want to measure your transformer(combination) you should use a 1:10 probe for your oscilloscoop. Not only you have 10 times less voltage on your scoop but also less capacitive load for the transformers. Next step is to add a 80pF capaciter and see what is happening (1:10 probe + 80pF = Stax headphone load)
Measure between 0 and + phase and later on between 0 and - phase ( there could be a differance between them)
Martin
Thankyou all on the measurement tips, little will happen tonight or tommorow as I am busy on other things, (that make money) but this said I will read and try all the things you guys said for measuement. I will get my self that ADC as I can see msyself making use of it more than once.

The load of stax headphones is very interesting information, that I was wondering how I could simulate as I have plans to do do tests and dont want to distroy the headphones.

Good ways to measure impedance would also be useful, esltransformer (Martin) I guess its just measure the current and voltage on the input and output of the transformer?

Regards

Owen
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Old 18th February 2013, 05:54 PM   #75
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Quote:
Originally Posted by owenhamburg View Post
Thankyou all on the measurement tips, little will happen tonight or tommorow as I am busy on other things, (that make money) but this said I will read and try all the things you guys said for measuement. I will get my self that ADC as I can see msyself making use of it more than once.

The load of stax headphones is very interesting information, that I was wondering how I could simulate as I have plans to do do tests and dont want to distroy the headphones.

Good ways to measure impedance would also be useful, esltransformer (Martin) I guess its just measure the current and voltage on the input and output of the transformer?

Regards

Owen
Indeed, A & V
I use a serie resistor of 10 Ohm and measure the voltage drop of this resistor and secondly the voltage drop of the transformer. I use always the same voltage drop of this serie resistor so I know that the transformer has always the same current.
All measurements I put in a spreadsheet and do some calculation on it and then make a graph.

If you use a (digital)voltmeter be sure that it is a true rms meter also for 20KHz!

Martin
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Old 19th February 2013, 04:59 PM   #76
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Default Just a little post to keep things in one place.

Dear all,

My stax headphone sockets came in the post today

An interesting site showing some stax models and some schematics.

I have attached the schematic of the SRD-5 so it does not get lost.

Regards

Owen
Attached Images
File Type: jpg SRD-5-1.jpg (99.0 KB, 115 views)
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Old 19th February 2013, 05:52 PM   #77
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Very cool site!!

Lots of great info, Thanks for the link!!

I still don't see why the charged so much for these things!!! He,he,he,he

If you are using Google Chrome you can easily translate it as it is all in Japanese.

Cheers!!

jer
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Old 22nd February 2013, 05:44 PM   #78
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Quote:
Originally Posted by owenhamburg View Post
The SRD-5 and SR-3 that I got at a good price from ebay arrived today and I am pleasantly surprised how well they work in their original state. From what I have learnt already I can without doubt improve the SRD-5, and it should immediately have its capacitors replaced as although they don't do much work, and will have little effect on the sound, but they are older than me and could blow at any time.
The capacitors arrived today by post for the SRD-5, and other components for the potential divider, (so measurement can start) and some resistors and capacitors to adjust my Lambda drivers.

So I set up my Quad 303.

I have just been listening to :

Tchamantché by Rokia Traoré
Stairway To Heaven by Rodrigo Y Gabriela
Malka Moma Dvori Mete by Chet Nuneta

and I am very pleased.

The hum is gone and the sound is exceptionally good, bettering all my experiments so far. Subjectively it is better than the too bright high notes I had with my previous experiments.

Its getting close to optimization time and being critical, rather than just being happy it sounds good.

So lets start with what I don't like:

(a) In the circuit in the SRD-5 the bias that charges the electrostatics is driven direct from the mains in an asymmetric way, with no decoupling transformer, so plugged in one way it generates hum, and one way not (German plugs can be plugged in swapping live and neutral, something I have found most hifi/musical people dislike but most consumers have no problem with) I will at least partially solve this my moving the plug to the IEC type.

(b) The SRD-5 plugs are not Stax plugs but have been replaced with high quality 240 degree din plugs with screw plugs. (now its confirmed they are screw locked Din plugs as I found a 240 Din plug in my stocks) I am unsure I can be bothered to change this in the short term as they don't look too dangerous and my Stax plug will be difficult to attach as safely to a cable.

(c) Their is some pickup from the cable. (did not notice it before as was too much hum)

(d) I suspect theirs still some supersonic oscillation that I can perceive but not hear, this needs to be confirmed by measurement, the capacitors responsible for this are very small ceramics that I have not yet replaced yet)

(e) The SRD-5 box is too small to put in another circuit board.

(f) The polyester capacitors I intended to use for the bias supply are just a little to big to fit in the gap between the PCB and the transformer. I had to use the backup electrolytic capacitors for the power supply. I am convinced I could make a better bias power supply, using transformer decoupling and a lot more filtering after the voltage multiplier, but on the good side it is surprising how slowly the volume decreases when you unplug the SRD-5 from the mains.

I am convinced that although I now feel the Stax SR-3 / SRD-5 is the best pair of headphones I have ever had, I am not yet confident the Bass is as good as it can be, judgement can wait though as the headphones are new and my opinion can wait till after I have built the measurement tools and received the new Analogue to digital converter.

The Stax Lambda (which I started this thread about) has a Stax plug so I have not connected it to the SRD-5, and I think that my experiments will focus on this soon but not quiet yet, I suspect I will wait until I start customizing the Stax electret driver which should arrive some time soon and adding a bias circuit. I am also seriously considering building a direct drive amplifier but measurements will happen first.

Regards

Owen
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Old 22nd February 2013, 06:19 PM   #79
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Little picture of the Stax SRD-5 and SR-3
Attached Images
File Type: jpg srd5.JPG (37.7 KB, 76 views)
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Old 23rd February 2013, 02:19 AM   #80
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Quote:
Originally Posted by esltransformer View Post
First i have to tell that the original Stax transformer in the SRD-7 has a 1:60 step-up. Mine has 1:50.
A esl transformer is a push-pull transformer so it has a + and - fase. In fig. 1 you see that the Stax transformer has not equal fase response for the high frequencies. This is one of the reasons i would like to have a better transformer. Secondly i would like to have a transformer with very low losses. Third i like a transformer-esl combination wich is easy to drive with any amplifier so impedance should be high even at 10Hz or 20kHz

I use for my headphone 500V polarisation. I not use a 1 Ohm resistor but a 0.47 Ohm, i just use a 1 Ohm for measurements. Adding a series resistor is not good for the low frequency response and also give more distortion.
The next stage of my tweaking the home made driver will start soon, thank you for giving me some advice on the resistance range.

The current circuit on the SRD-5 has 4 Ohm in series and 30 Ohms in parallel with the low tension in the transformer. But I guess their designs had to work with Amplifiers designed for 16 Ohms, and compromise on sound for universality and not breaking amplifiers?

The capacitor, in parallel with the headphone is not understood my me? Why is it like that? AM I right with my first guess that it was making the speakers have a low pass filter, the more I think about it this explanation it seems wrong, and since the headphones behave like a very non ideal capacitor why add more capacitance to the high tension?

Regards

Owen
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