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 Post subject: Hiraga MC pre-preamp
PostPosted: 27 Dec 2011, 00:29 
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Location: Australia
Now I have built one successful moving coil pre-preamp I consider myself an expert (haha). The one I built is the Le Pacific jFet based phono preamp. Scouting around has found this Hiraga gem http://www.bonavolta.ch/hobby/fr/audio/prepre.htm.
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The low noise transistor pairs he has specified (2SB737R) are no longer available but the SSM2220 is from rs-components for AU$11.00 each (you need two). I have ordered the parts and intend to try this different pre-pre.

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 Post subject: Re: Hiraga MC pre-preamp
PostPosted: 28 Dec 2011, 04:11 
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Joined: 22 Oct 2009, 08:47
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Location: Denmark
Hi i have built one too, it work like a gem. I had the same problem with the transistors ,i ha used bc560 fore mine.
Basicli you can use any type,it should have an ultra lov noise level.
I glued the transistors together so they have the same temperature,just remember to adjust the offset at the input
and you vill be fine
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Billede0017.jpg

Attachment:
Komponentplacering.pdf

nkdk


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 Post subject: Re: Hiraga MC pre-preamp
PostPosted: 28 Dec 2011, 07:31 
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The SSM2220 should work but you must swap the differential PS voltages over and any electrolytics must be turned upside down. I'll try it with the SSM2220 and see how it goes. The Le Pacific MC phono pre-pre was very successful.

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 Post subject: Re: Hiraga MC pre-preamp
PostPosted: 05 Jan 2012, 06:04 
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Location: Australia
Quote:
.........I consider myself an expert (haha)


expert - pfft. MASTER in all things perfboard - love it
mark - why the SSM2220 - the BC560 is an 'equivalent' for the 2SB737R - and less than $1AUD?

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 Post subject: Re: Hiraga MC pre-preamp
PostPosted: 05 Jan 2012, 07:17 
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Because these babies are a perfectly matched pairs on the one substrate. Ultra-low noise and are cute little chips. I have the parts, just need the time. Probably will be an assault on batteries again.

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 Post subject: Re: Hiraga MC pre-preamp
PostPosted: 12 Jan 2012, 07:04 
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Jean Hiraga has this "thing" with ridiculously large caps and running everything on big wet cell batteries. My batteries may not be big wet cells but I have found at work (Jaycar Electronics) we have 1F caps. Problem is they are only rated 5.5V. I will put two in series on a 100K 1W resistor ladder to give a rating of 11V at 500,000uf. So each 6V rail will have a 500,000uf cap across it with a 100K ladder across each cap and a 400K ladder across the total supply.

This will ensure that the +/- 6V from the battery pack provides a balanced and perfect +/-6V and there is 500,000uf of cap across each rail. This is now getting ridiculous: a bi-polar, substrate matched pair driven by two banks of batteries with a total of 1F of capacitance.

The real funny part is where I have promised the purchaser of my two stage tube phono preamp with RIAA equalization and JFet Le Pacific MC phono preamp a chance to swap (for a price) to the Jean Hiraga MC preamp. His Dynavector MC cartridge and high-end TT should allow us to decide the better MC stage. You never know the much simpler jFet design may win out.

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 Post subject: Re: Hiraga MC pre-preamp
PostPosted: 22 Jan 2012, 00:16 
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Drilling is complete and now so is the PS for the preamp. The small buttons are 1F 5.5V caps. I have had to put two in series to handle 6V. There is a total of 1F of capacitance across the batteries. The smaller caps are 0.47uf and 220uf low esr. The preamp section will be built on the front of the veroboard.
Attachment:
MCPSI.jpg
Attachment:
MCPSII.jpg


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 Post subject: Re: Hiraga MC pre-preamp
PostPosted: 22 Jan 2012, 00:56 
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I'm going to use 0.47uf PIO caps for output caps. The cct. specifies 1.5uf this looks too big. The MC preamp will be working into 47K so I can see the need for bigger caps. Other MC preamp cct. use 0.47uf so it must be OK. Any comments?

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 Post subject: Re: Hiraga MC pre-preamp
PostPosted: 22 Jan 2012, 13:49 
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Looking at the original circuit, the output impedance looks to be around 2kΩ. Driving an amplifier with an input impedance of 47kΩ means that the low end roll off frequency with the 1.5µf output capacitor is about 2.2Hz and the bias excursion recovery time is about 368ms. Lowering the capicator to 0.47µf moves the low end rolloff to 6.9Hz and lowers the bias excursion recovery time to 115ms. I personally think this is a good trade.

I typically don't like to let my bias excursion recovery times to exceed 150ms. Of course, this doesn't matter if you're driving a solid state input that doesn't draw excessive input current, but if you're driving a tube amp it's important. I say go ahead and make the change. You'll probably never hear it.

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 Post subject: Re: Hiraga MC pre-preamp
PostPosted: 22 Jan 2012, 15:53 
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Matt: Thanks all good news. I have already soldered one in and I hate mods after the fact. One DIYer raised the fact that the Russian PIOs I am using have a magnetic and not a non-magnetic outer casing. I tried the cap with a magnet and sure enough the magnet stuck. Do you think this will adversely affect the sonic performance of the cap. Could it be a blessing by offering better shielding to the cap?

One more question: MC cartridges usually see a 100 ohm load at the preamp. From the schematic above this is not obvious but the transistors do form part of the input impedance. Do you think the MC cartridge will see 100ohms?

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