Build This MoFo!

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#1,285
MEPER said:
Just for my technical interest I asked what the weight would be for a 1 mOhm choke. 40 kg and price just below $1000 each (incl Danish tax). That would be the ultimate MoFo choke. I think not many chokes of this size exists in private homes.
The 20 mV DC I get (2.5A bias) with the 20 kg choke will probably not harm the performance of 15" woofer which handles frequencies below 180 Hz. But only 2-3 mV DC using the 40 kg choke is tempting.
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I got a message today from the transformer company that they had miscalculated the RDC so 8 mOhm is not possible. After recalculate and some optimization 70 mOhm was possible for the 20 kg choke. So I go with that and hope the "large" 70 mOhm RDC will ensure stable bias. It will be with output capacitors. I could have cancelled the order and got Hammond 193 instead but now I want to see how the big choke performs. The next step was a type UI 210A core where RDC would be approx. 32 mOhm and the weight is 55 kg. So I think Zen Mod was right that 10 mOhm RDC would be hard to reach for a 50 mH choke.
 
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#1,287
AKSA's Lender Preamp with 40Vpp Output
It uses daughter boards to allow you to fine tune the output for whatever amplifier you might be using.
I have built the Pass BA-3, ImPasse, and the Aksa for use with the MoFo and Pass F4 amps. All three are solid performers. From a price point the Aksa is the least expensive to build and probably the most versatile.
All are great sounding.
Enjoy
David
 
#1,292
xrk971 said:
If you want a very nice high current, low distortion choke that can provide the measured data shown a few pages above, do a search on eBay for a MOT part number "MD-803AMR-1". These measure about 67mH and 0.47ohm DCR.
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Coming late to this but always on the hunt for a bargain.

In the UK I have found some MOTs reference MD-803EMR-1. I take it that the specifications are unlikely to be significantly different to the US one above and could well suit this project?

Also if I can get hold of 4, would it be safe to assume that a slightly higher supply voltage to offset the additional dc resistance of two of these in series might be beneficial, or is little sonic improvement likely with double the inductance?
 

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#1,293
Little_Eddy said:
Coming late to this but always on the hunt for a bargain.

In the UK I have found some MOTs reference MD-803EMR-1. I take it that the specifications are unlikely to be significantly different to the US one above and could well suit this project?

Also if I can get hold of 4, would it be safe to assume that a slightly higher supply voltage to offset the additional dc resistance of two of these in series might be beneficial, or is little sonic improvement likely with double the inductance?
Click to expand...

Hi Mike

if that doesn't work out I have 2 hammond 159zc from the mofo you saw at Owston. They won't be doing anything as I'm concentrating on the pp amp. let me know if interested.
 
#1,299
Little_Eddy said:
Coming late to this but always on the hunt for a bargain.

In the UK I have found some MOTs reference MD-803EMR-1. I take it that the specifications are unlikely to be significantly different to the US one above and could well suit this project?

Also if I can get hold of 4, would it be safe to assume that a slightly higher supply voltage to offset the additional dc resistance of two of these in series might be beneficial, or is little sonic improvement likely with double the inductance?
Click to expand...

I don’t think you need more inductance than 50uH to 100uH - it serves to store energy to give a higher peak-peak outpt than available from the rail voltage.
 
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