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Old 28th January 2005, 05:55 AM   #1
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Richard Murdey
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Default Phonoclone Update

It was brought to my attention recently that the 47 Labs Phonocube uses an OP27G as the front end op-amp.

I'd always held out for the AD797, but although the OP27 is has about five times the voltage noise, its low bandwidth and slow slew rate would make it a much easier beast to implement.

It seems that every few months something comes up regarding this project that has me scribbling out layouts at all hours of the day. So it is that I've come up with a new layout for the phonoclone that has separate voltage regulation for the input and output op-amps. It has the requisite 25 parts per channel and I'm confident that its pretty close to the Phonocube design. The layout, however, still looks too complex to be a good match.

More info :

http://www.geocities.com/rjm003.geo/.../diy_pho4.html
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Old 28th January 2005, 06:24 AM   #2
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Default OP27 output stages

Shown in the attached image is the output sections for the Analog Devices OP27, the TI OP27 and the LT1007.

The LT1007 appears to be a different, but I'm curious about the two OP27s. The TI schematic shows two pnp transistors for the output Q45,46, while the AD schematic shows a complimentary pnp, npn set.

I'm quite ignorant of transistor circuits. Are the two OP27 schematics equivalent? Is one a typo? If the schematics are correct, given the choice is one arrangement preferable to the other?

thanks

-rjm
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Old 28th January 2005, 06:33 AM   #3
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Default Re: OP27 output stages

Quote:
Originally posted by rjm
Shown in the attached image is the output sections for the Analog Devices OP27, the TI OP27 and the LT1007.

The LT1007 appears to be a different, but I'm curious about the two OP27s. The TI schematic shows two pnp transistors for the output Q45,46, while the AD schematic shows a complimentary pnp, npn set.

I'm quite ignorant of transistor circuits. Are the two OP27 schematics equivalent? Is one a typo? If the schematics are correct, given the choice is one arrangement preferable to the other?

thanks

-rjm
Hi rjm,
Hey that's funny the TI OP27 is using all NPN transistors. (Not PNP as you wrote erroneously)
First time I see a second sourced part with a different simplified schematic.



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Old 30th January 2005, 09:19 AM   #4
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Default Another Layout

Here's another layout. Its the same circuit as above, but with a simpler arrangement. The power rails are now on the outside, with the regulator and bypass caps on the four corners. The signal grounds all connect to the central bulge of the ground tab.

-rjm
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Old 30th January 2005, 01:46 PM   #5
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Default and lastly (for now)

- Expanded to square shape.

- Narrowed the center ground trace, so the signal runs under the IC. This removed the need to bridge over traces, everything is now a simple single sided layout.

- Added a little more room for larger capacitors.

-rjm
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Old 30th January 2005, 08:19 PM   #6
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Default Re: and lastly (for now)

Quote:
Originally posted by rjm
- Expanded to square shape.

- Narrowed the center ground trace, so the signal runs under the IC. This removed the need to bridge over traces, everything is now a simple single sided layout.

- Added a little more room for larger capacitors.

-rjm
Just had a look at the layout and this design uses two single opamps per channel and you have 2 regs per opamp = 8 regs for one stereo phonoclone!
So maybe you should separate the psu section so we can only use 2 regs for all opamps? just a thought
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Old 30th January 2005, 08:50 PM   #7
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Richard,

wending your way around the world? BC->Scandinavia -> now Japan?

Keep up the good work

dave
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Old 30th January 2005, 08:51 PM   #8
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Default Re: Re: and lastly (for now)

Quote:
Originally posted by maxw
Just had a look at the layout and this design uses two single opamps per channel and you have 2 regs per opamp = 8 regs for one stereo phonoclone!
So maybe you should separate the psu section so we can only use 2 regs for all opamps? just a thought
One of the tricks to get the most out of opamps is to use lots & lots of regs.

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Old 31st January 2005, 03:58 AM   #9
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Default Phonoclone Circuit

It on the web page, but for easy reference I'll copy it to this thread.

Parts list for one channel:

R1 47R (Denon DL103, set equal to cartridge impedance)
R2 6k8 (Denon DL103, 75dB gain, calculate for desired cartridge/gain)
R3 680R
R4 680R
R5 33k *
R6 220k *
R7 33k
R8 47R

C1 3.3 nF (WIMA MKP) *
C2 10 nF (WIMA MKP) *
C3 4.7 F (Black Gate non-polar)

U1 (OP27 for 75dB)
(OP37 for 90dB)
U2 OP27 ?

* RIAA values, match to 1%.

also needed, 2 each LM78xx and LM79xx regulators, and eight low-impedance filter capacitors, 47-220 F .

and the appropriate power supply
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Old 31st January 2005, 04:08 AM   #10
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maxw:

People who've spent the money on a low-output moving coil cartridge to use with the Phonoclone probably won't get too worried at the prospect of 8 voltage regulators. In this instance I think they should be considered a necessary part of the amplifier circuit, rather than an optional part of the power supply.

However if you want to, for example, use a battery power supply, or just for the hell of it, attached is what it would look like sans regulators.

-rjm
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