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Old 8th May 2003, 01:27 PM   #1
x-pro is offline x-pro  United Kingdom
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Default Simple MM only RIAA preamp

Hi all,

here is the link to the article (unfortunately, in Russian) I've published in 1999 in "RadioHobby" in Kiev about the original idea behing Creek Audio OBH-8 preamplifier. Since that time newer versions of this circuit are used in the current line of OBH preamps. However, this circuit is a good example of what could be done with few transistors. The sound of this circuit is good and it is very DIY friendly .

http://vlab.netsys.ru/audio/lpcor7.stm

It is single-ended class A with passive EQ. What else would you wish?

Technical Data of this preamp:

Gain - 90

SNR - better than 70 dB A-wtd ref 5 mV 1kHz input

RIAA deviation +/- 0.5 dB 50Hz-30kHz, -3 dB at 20 Hz

Max. output 5V RMS

Distortion for 1V output - less than 0.01% at 1 kHz

To prevent possible questions - it is my own design and the original publication was made with permission from Creek. The circuit is copyright of Creek Audio Limited (it is printed in the original article, unfortunately on the linked web site they cut the picture and lost it... .

Enjoy

Al
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Old 8th May 2003, 10:54 PM   #2
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Gain = 90 at 1 kHz?
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Old 8th May 2003, 10:58 PM   #3
x-pro is offline x-pro  United Kingdom
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Yes, 90 at 1 kHz.

Al
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Old 9th May 2003, 08:24 AM   #4
Werner is offline Werner  Europe
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Per-Anders probably misread it as

90dB

Thanks for sharing the circuit with us. It is interesting, although for sheer simplicity nothing beats a Pacific.

Click the image to open in full size.
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Old 9th May 2003, 08:47 AM   #5
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Hi X-Pro,
you mean about 40 dB.as input 3,5mV and output 300mV
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Old 9th May 2003, 09:14 AM   #6
x-pro is offline x-pro  United Kingdom
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2 Werner - yes, Pacific is simpler, however it does not have much gain and it's linearity is somewhat suspect . My circuit does have high enough gain and reasonably low distortion - even at 4-5 V RMS output, just before clipping, distortion are about 0.1-0.2% at 1 kHz. And this is using only one gain transistor Q1 - the rest are followers and a current source .

2 hsort - it is 90, or about 39 dB at 1 kHz.

Al
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Old 9th May 2003, 09:41 PM   #7
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Koinichiwa,

Quote:
Originally posted by x-pro
2 Werner - yes, Pacific is simpler, however it does not have much gain and it's linearity is somewhat suspect .
Linearity is arguable, though the harmonic structure of the Pacific is exemplary.

The gain is actually higher than 90, assuming the correct FET's are used. The 2SK170 @ 5mA has around 30mS (30mA/V) transconductance and operates into around 2k4 Loads. This gives a stage gain of 30mA*2.4k = 72. With 2 stages the overall gain becomes 5200 or 74db, of which a bit over 20db are lost in the passive RIAA EQ.

So the Pacific after accounting for the RIAA has around 60db Gain and around 0.15uV Ein (150nV Input Referred Noise) which makes it (marginally) suitable for medium output MC's without further Stepup or Pre-Pre. Output Impedance is around 2k. Not bad for a brutally simple circuit.

A friends Pacific runs fine and sounds VERY good. Originally it used 9V Block Batteries, when it stayed with me for a while (it drove a S&B TX-102 ever so much better than my Shindo copy Preamp) I converted it to using a 24V non looped switching supply, with better sound than we got from the batteries and no regular recharging!!!!

Quote:
Originally posted by x-pro
My circuit does have high enough gain and reasonably low distortion - even at 4-5 V RMS output, just before clipping, distortion are about 0.1-0.2% at 1 kHz. And this is using only one gain transistor Q1 - the rest are followers and a current source .
[/B]
Mebbe, but what does the harmonic structure of that circuit look like and what does it sound like? The original Creek phonostages sounded uninspiring.

Sayonara
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Old 17th May 2003, 10:00 PM   #8
Illusus is offline Illusus  Canada
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Default Konichiwa Thorsten-san,

I just finished building an "el Cheapo" for a friend (thank you for the advice). Even though I had to build it on a budget and skimp on a few components, it sounds fanastic, shockingly so.

I am in the middle of building a new turntable for myself. I want to build an intergrated pre, hardwired to the arm and interconnect. I chose the Pacific, because of it's simplicity it will allow me to keep the footprint small enough to fit into my arm base, plus I already have a boatload of the correct fets. I was wondering if you had any suggestions for the components to use(brands, models) in it's construction, cost is not much of an issue, but availability is, I hate hunting for parts and ordering from more than one or two sources.

Domo aregato,
Bart G.
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Old 17th May 2003, 10:11 PM   #9
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Default Re: Konichiwa Thorsten-san,

Koinichiwa,

Quote:
Originally posted by Illusus
I was wondering if you had any suggestions for the components to use(brands, models) in it's construction, cost is not much of an issue, but availability is, I hate hunting for parts and ordering from more than one or two sources.
We build the whole circuit hard wired, in a copprfoil clad wooden enclosure. We used Holco Resistors (sorry, no longer available as non-magnetic, current Holco's are NDFG), LCR 0.47uF Foil & Film Coupling Capacitors (plus MIT 2u2 PPMF "bypass" on the output) and LCR Polystyrene Cap's for the EQ. This Parts Mixture is true "UK Style" and most components are/where available from Radio Spares and/or Farnell.

Sayonara
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Old 17th May 2003, 11:49 PM   #10
Cobra2 is offline Cobra2  Norway
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Default BTW...

Have anyone tried this? comments?
I think it is from a Hafler Pre-Amp....

Arne K
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File Type: gif hafler riaa.gif (92.4 KB, 4608 views)
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