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Old 7th April 2012, 10:30 PM   #1
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Default Oriel Z1, my headphone amp, or...

... how to try to make a business and finally spend a lot of money and get a good fun, no business
I want to share my experience.

The idea was to develop endless quality amp for private purpose.
I've went the long way trying something.
My end point for this moment is amplifier based on the following rules:
- semiconductor-based amp with negative voltage feedback
- constant open loop gain in audio range
- A-class output stage
- short and exponentially decreased harmonics spectrum
- differential input
- separated smps's for l/r channels
- ascetic but modern user interface

This amp has the following features controlled with menu:
- Differential or single-ended input
- 0 or 12 dB pre-gain
- Selectable AC- or DC-coupling
- Ground lift
- Selectable output impedance (0.1, 10 or 100 Ohms)
- Selectable output stage bias current (30, 130, 220 or 350 mA)
- Disconnectable DC Servo loop

THD is (very pessimistically) less than -120 dB@25 Ohm, 3V rms
No any traces in audio spectrum associated with multiple smps's or control board with high current display. I don't show the spectrums because my measurement system (E-MU 1212m) doesn't feel the difference with or without Z1

A volume control is based on logarithmic step current mode attenuator (equivalent resistance is 3KOhm) with inverting buffer. Relays are special ruthenium Coto 2342. (see LSCM_attenuator)

All signal commutations are with Coto 2342 relays.

A power amplifier is a composite amplifier. (see HA_PA)
Output step response (Rload=50Ohms, 16Vp-p):
Click the image to open in full size.

A power supply is a multichannel switching mode power supply based on Traco converters.

The amp is controlling by microprocessor board with Osram matrix LED display readable from 3 meters. A user control is two Alps encoders.

Despite the highest objective characteristics, I would like to say a few words on the subjective characteristics.
The sound of amp is light, dynamic and very detailed. Particular attention is drawn to the ability to accurately reproduce large compositions, without any hint of dirt or innuendo. In church choirs individual voices are understandable. Orchestral tutti is so vivid and deep that you are forced involuntary shudder. The sound of the snare drum - it seems that it has sounded in the room next to you. Fans of harp will be encouraged by the energy and rich tones.

I'm listening to it with Denon D7000 and my own DAC (pcm1704 based).

Enjoy.

Meet Oriel Z1, it is made in Russia.
Click the image to open in full size.

Amplifier PCB
Click the image to open in full size.

Back side
Click the image to open in full size.

Open cover
Click the image to open in full size.
Attached Files
File Type: pdf LSCM_attenuator.pdf (51.8 KB, 64 views)
File Type: pdf HA_PA.pdf (55.7 KB, 77 views)
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Old 8th April 2012, 06:17 PM   #2
Telstar is offline Telstar  Italy
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Quote:
Originally Posted by Electrovoicer View Post
A power supply is a multichannel switching mode power supply based on Traco converters.
Why?
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"The total harmonic distortion is not a measure of the degree of distastefulness to the listener and it is recommended that its use should be discontinued." D. Masa, 1938
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Old 8th April 2012, 06:30 PM   #3
Nisbeth is offline Nisbeth  Denmark
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Looks very nice. One question: What is the socket that you are using for DC in?

/U.
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Old 9th April 2012, 05:24 AM   #4
rjm is offline rjm  Japan
Richard Murdey
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Thanks for sharing the design.

I like it, it's very Russian:

i.e. "whimsically overboard"
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Last edited by rjm; 9th April 2012 at 05:28 AM.
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Old 9th April 2012, 09:10 AM   #5
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Quote:
Originally Posted by Telstar View Post
Why?
because classic linear power supply with similar characteristics (regulation, output impedance, impedance vs. frequency) has 10x size, 30x weight and 2x price
There is only one problem - how to cook smps in right way due to switching noise. But proper filtering and placement bring the win.
Three isolated regulated DC/DCs (two for L/R channels, one for digital part) allow me to find optimum grounding scheme.
Another useful thing - the quality of primary power supply is not so important as with the classic linear power supply.
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Old 9th April 2012, 09:14 AM   #6
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Quote:
Originally Posted by Nisbeth View Post
Looks very nice. One question: What is the socket that you are using for DC in? /U.
Thank you.

It is WEIPU connectors the waterproof connectors stand out
Chinese, but very good quality comparable with Amphenol/Tyco/etc.
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Old 9th April 2012, 09:19 AM   #7
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Quote:
Originally Posted by rjm View Post
Thanks for sharing the design.

I like it, it's very Russian:

i.e. "whimsically overboard"
I hope I understand you, thank you.

Be careful with values in composite amp. On schematics you can see only approximated values, which are not guarantee the stability of circuit. In other words, I show only design idea. This design very depends on "parasitic" pcb elements and topology.
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Old 9th April 2012, 04:57 PM   #8
qusp is offline qusp  Australia
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very nice and very nice choice of parts, panasonic pps around multifeedback loops in the center, I use these caps and love the result. i'm quite interested in the linear post regulation PSU schematic if possible?

nevermind I found the reed relays at digikey

but i was actually mistaking the relay part you mention as being a bank of Wima film caps haha. the ones i'm interested in are the smaller coto part 1042; actually i found them just now too, but only the PTH version, do you have a part number and supplier for the SMD version you apear to have used?

Last edited by qusp; 9th April 2012 at 05:12 PM.
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Old 9th April 2012, 07:25 PM   #9
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Quote:
Originally Posted by qusp View Post
very nice and very nice choice of parts, panasonic pps around multifeedback loops in the center, I use these caps and love the result. i'm quite interested in the linear post regulation PSU schematic if possible?

nevermind I found the reed relays at digikey

but i was actually mistaking the relay part you mention as being a bank of Wima film caps haha. the ones i'm interested in are the smaller coto part 1042; actually i found them just now too, but only the PTH version, do you have a part number and supplier for the SMD version you apear to have used?
hello, thank you!

panasonic PPS are in DC servo integrator thanks to low dielectric absorption and excellent AC performance.

I use two types of Coto relays - 2342 for attenuator/input commutation and 9903 for output circuits/ground lifting which you have seen as Wima caps

All the components in this unit you can find in Digikey and Mouser...

Surprise : there is no linear post regulators in analog part, only proper filtering after dc/dc but it doesn't interfere to reach the necessary characteristics
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Old 10th April 2012, 12:20 AM   #10
rjm is offline rjm  Japan
Richard Murdey
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Quote:
Originally Posted by Electrovoicer View Post
Surprise : there is no linear post regulators in analog part, only proper filtering after dc/dc but it doesn't interfere to reach the necessary characteristics
Well, this is strictly the correct way I would say. No point in using a regulator.

By the way, how difficult was it to get the circuit to run stable, and how did you check?
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