[Dev]

Hi there!

First, sorry for my poor english. I'm a russian guy

.

I just want to talk with you about a CMoy amp's, rather my version of this... It's my first headphone amp, and I take care of upgrade it from time to time.

Well, there is scheme of it

.

AD826 have 50mA at output and easy to use with different DC supplies (I use OPA2604 also and get some oscillation troubles, i guess it's power supply problems of this op. IMHO), like AD825.
So, I use my amp with Yamaha RH-5ma headphones (32Ohms, 98dB). Ñertainly, this phones are with out pretentions to output part of sound source, but I observing excelent improvement of sound quality, and I am happy

...

May be I naive but I just want to hear your opinions about this circuit. This is not hi-end yet

, so your advices, questions, comments and suggestions... Please, if you have it. I glad to meet with it

.

 

[eric343]

Why is there a 50ohm/.07uF R-C network at the output?

 

[Dev]

Well, all power amps have it

. In chemes it's call 'oscillation blocking comonents'.

I guess it also matcher by phones/wires (long ones usually, 2 meters) impedance...

I've install it two days later and, in general, not noted greatly difference, but sound become more balanced, IMHO.

 

[kerelybonto]

Äåâ,

Ó Âàñ åñòü ôîòîãðàôèè âàøåãî óñëèòåëÿ?

Âû õîðîøî ïèøåòå ïî-àíãëèéñêè. ß íå õîðîøî çíàþ ðóññêèé ÿçûê, ïîòîìó ÷òî ÿ èçó÷àë îí ñêîëêî ìåñÿöà.

Ãåë-Ôàé ïðèâåòñòâóåò âàñ!

êåðåëèáîíòî

 

[eric343]

umm... in english that means...?

 

[Budgie]

" Well, all power amps have it . In chemes it's call 'oscillation blocking comonents'. "

In North America we call this a "Zobel network", though how it got the name, I have no idea!

More Info:
http://www.trueaudio.com/st_zobel.htm

 

[kerelybonto]

It means:

"Three, three, three for my heartache and
"Four, four, four for my headaches and
"Five, five, five for my lonely and
"Six, six, six for my sorrow and
"Seven, seven for no tomorrow and
"Eight, eight I forget what 8 was for and
"Nine, nine, nine for a lost god and
"Ten, ten, ten, ten for everything
"Everything, everything, everything."

But that's just a rough translation, really more like a guess.

kerelybonto

 

[Dev]

kerelybonto
Wow, I very glad to see my own language there!

Thanks for praises to me. I've teached engllish in school and university, but it's small part of my english education - mainly I've teach english by myself

. So, compliment in this area is very important to me. Thank you again.
Òâîé ðóññêèé òîæå çàñëóæèâàåò âíèìàíèÿ, íóæíî ñêàçàòü. Ðîäíàÿ ðå÷ü äàæå íåñêîëüêî øîêèðîâàëà ìåíÿ

.
Well, I guess russian is suck and hard languauge to teach. Very little part of russian people knew their language really excellent with all nuances and hidden dangers

.
Ok, ok, it's offtopic. All, sorry me...

I've digital camera and new photos aren't a problem

. But I must to notify my amp is not as beautiful and cool as an amps presents here by members. Please wait, I post my photos tomorrow (I'm just is busy now).

Budgie
Yes, in Russia we call this the same. Zobel, I think, it is man's last name

.

To the question about it: the fact is that loudspeaker have complex impedance which have tendency to increasing until frequensy is growthing up. This Zobel net is to set impedanse flatness and canceling a "sand sound" effect on high-frequencies...

 

[Budgie]

I am looking forward to the pictures, Dev. And it is good to hear from someone in Russia. Maybe this will turn out to be a good place to practice your english! Much like you described with Russians, few Americans speak english, with skill. I think we all need to expand our use of language.

 

[Dev]

Thus the photos, rather, links to it:

http://dev.azz.ru/pic/hamp/devhamp_front.jpg
I use chassis of USSR amplifier kit for young radiofans, it's 10-15 years of old and have plastic top/bottom but metal front/rear side. I am use some deitals from that kit - is power switcher, led and pots (old paired variable resistors having a lot of "hiss" but it is unimportant).

First pot (left) is unconnected and only to hole closing

. It's grounded of course. Second (right) pot is volume control as usual.

Front side is without signatures cause I inverted it underside and make hole to phones output jack - in his place was hole to the third pot (it's usual to amplifiers - volume, balance and tone controls). I've idea to free-hand's write signatures like "volume, power, phones" by permanent marker

.

http://dev.azz.ru/pic/hamp/devhamp_front_r_and_cd.jpg
My amp (it have not name yet) from right perspective and with cd on top

.

http://dev.azz.ru/pic/hamp/devhamp_front_and_rh-5ma.jpg
Amp and my Yahama RH-5Ma headphones. I've tweaked it by deplacing foam-rubber filler between capsule and soft ear pincushion, so now holes is look funny...

http://dev.azz.ru/pic/hamp/devhamp_inside_top.jpg
Well, inside part of amp

. All elements are take seats as hanging. PCB board in center it's just to putting opamp, I've take it from kit described above (russian chips have the same pin demensions). One 8-lead mini-DIP AD826 placing on another PCB side via mini-DIP panel. PCB paths are not used except one to grounding...

All components are russian, except 9V E-block battery, electrolytic capacitors and wires (using professional instrumental cabel)

. Crimson elements are 1/8W and 2W resisitors (resistors also two green blocks at lower-left corner near with pot). Blue blocks at upper-right corners (power supply part there) are MKT like type caps (small black elco is under theirs). Elements between battery and upper MKT are Zobel mica plus two metal-paper caps.

RCA inputs are not attached to chassis and dangling overboard

.

So inner life of my amp is not beautifull, I'm noticed you

.

http://dev.azz.ru/pic/hamp/devhamp_inside_back.jpg
Described above things but other viewing angle.

http://dev.azz.ru/pic/hamp/devhamp_without_head.jpg
Just amp without top cover.

http://dev.azz.ru/pic/hamp/devhamp_inplace.jpg
And amp's daily place

. Source (Sony cdp-ce335 carousel exposed post-DAC tweak (1-order passive low-pass filter instead of 3-order active and AD826 buffer (my favor opamp

))) connected by 0.6m Nordost Black Knight cable.


Heh, probably I must interpret some russian inscriptions to you.
1. CD on amplifier: "Agata Kristi" is not an Agatha Kristie detective master woman, it's just russian rock-pop band and their album called "Guile and love".
2. Text on heart-shaped picture post card is "I love you". My girl-friend's gift

.

So I think photos of my CMoy amp will be stand out of other photos in your collection

.

 

[Tomo]

Hey,

You use Zobel Network at the output. I do that too sometimes. I use 1pF for it. I haven't seen people use these. I think it's a good idea.

As for cramming stuffs in the case, maybe clean up is in order

But then it works so it's fine.

(Me? I do circuit OK. But my biggest problem is "UGLY" casing. Sometimes, when my amp is "turned on," it can be "threatening.")

Tomo

 

[Dev]

Here, in Russia, Zobel network is using often in amp models I've seen. Generally speaking amps DIY making and commerce of it (brand's and technical done models too) isn't very popular here.

But my tech belief found it (Zobel) interesting

.

I use 1pF for it
One picofarad? But it is very small cap to working in Zobel net, I guess...

I have modulated phones impedance-Zobel work in some loudspeaker design softwares (they might to generate impedance curve even independently, just by getting the inductivity of loud inductor. "LspCad" software, for example) and decided what exactly 0.07uF cap value (or some deflection of it) will make headphones driver impedance flat. At the same time resistor value have not a fundamental importance...
So, in that way I've understand reason of putting 0.07uF cap in Zobel net by russian headphones-amp makers

.

 

[AssafL]

Is that a chocolate bar on top of the amplifier? Must keep chocolate warm and soft

 

[AssafL]

On a more serious note:

1. I would guess Zobel networks are more of a necessity in Loudspeakers due to dips in crossover response. Headphones are high impedance and (usually) should not require a Zobel.

2. Looking at your diagram: Isn't the ground impedance a bit on the high side? As well as frequency dependant? Perhaps an Op-Amp ground, or even better: two 9 Volt batteries with center ground?

Assaf.

 

[Tomo]

Ok ok,

I just call it Zobel because it "looks" like it. It probably doesn't do what "Zobel" should be doing for headphones.

I insert Zobel-like circuit to terminate the amplifier at high freq. 1pF will become a short around 1MHz or so and the impedance drops to the resistor value. This protects the amp from oscillation at high freq. This I found extremely useful. But I care really little about crossover blahblah etc so I keep the capacitance real small so that corner freq stay well beyond audio freq. (but not big enough so that oscillation at RF doesn't occur.)

This RF killa application works real well. It is completely transparent for our ears. I tested with my wideband highspeed opamp which cause TVI when near TV and pluging and unpluging the input sockets. (It was dead stable if I didn't mess with sockets already so essentially I had to work hard to make the opamp oscillate.) After installation of the RF killa or Zobel-like circuit, TVI simply no longer exists even if I unplug or plug the amp during the listening sessions.

Tomo