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Old 11th April 2013, 11:22 AM   #901
gk7 is offline gk7
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Quote:
Originally Posted by masag1 View Post
... "Hiraga 8 Watt" from Klaus Scherm, Germany.
He changed drivers and output trans, and made a tricky setup with current sources for the input Jfets.

sounds great, and was successful at the poweramp shootout at the german "Frickelfest" ...
Is there a schematic available ?
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Old 11th April 2013, 04:40 PM   #902
dadod is offline dadod  Croatia
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Originally Posted by Telstar View Post
Hiya,

I decided to build an headphone amp based on the Monstre circuit.

My starting point was the one published by kk-pcb.
Since I wanted much less gain (and lower distortion) I had to touch the feedback resistors. Therefore I chose slow and low-gain driver transistors (the fairchild pair with only 4Mhz Ft) and also added a little compensation on them. I hope this wont make the amp oscillate.

The input jfets are not matched which I have in my scrap bin, likewise for the BC. One heatsink per channel will be used, good up to about 10W.
The two resistors R14 and R15 are just to reduce the power dissipation of the output transistors within the dissipation alu available.

My goal was to keep a nice harmonic spectrum (mostly 2nd and third) and plenty of power/current to drive eventually even orthos, and without using exotic transistors.
I wont start building it before a couple of months, since I have other stuff on schedule, but the simulation looks promising.

PSU will be the regulated sigma22 which I use on most of my headphone amps, with 80-120VA transformer.
You can try this pre/headphone amp, mostly very low 2nd and third harmonic and no global feedback.Current conveyor as a voltage amplifier
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Old 13th April 2013, 06:18 AM   #903
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I've chosen Le Monstre as my first attempt at a DIY Class A amp. This thread has given me many ideas to try...
One thing is for certain: I will try this with a capacitance multiplier. The original supply is absurd.
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Old 13th April 2013, 06:24 AM   #904
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Originally Posted by iaxxaxxai View Post
One thing is for certain: I will try this with a capacitance multiplier. The original supply is absurd.
Yes. And add considerable buffer capacitance to the multipliers' regulated outputs.
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Old 13th April 2013, 06:27 AM   #905
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Thank you, I will certainly do so. I realize much capacitance is required.
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Old 13th April 2013, 06:29 AM   #906
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I ordered some Sanken transistors from MCM. If I am LUCKY, they won't be fake. If I am unlucky... well, I ordered some other transistors too, from other places, so we'll see what works best.
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Old 13th April 2013, 05:25 PM   #907
Vostro is online now Vostro  South Africa
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@Telstar

Hi I haven't read this thread, but came across your post.
The TAD C2000 is a preamp I like, its similar-ish to your post.

So I thought Id just post it for info.

Regards,
It may not be of help, again just for interest.
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Old 13th April 2013, 05:32 PM   #908
Telstar is offline Telstar  Italy
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Quote:
Originally Posted by Vostro View Post
@Telstar

Hi I haven't read this thread, but came across your post.
The TAD C2000 is a preamp I like, its similar-ish to your post.
It is very interesting, i saved the schematic.
Most of its japanese transistors are unobtainium nowadays I think but it shows well where they needed to compensate.
Do you know how high were the rails?
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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 13th April 2013, 05:36 PM   #909
Telstar is offline Telstar  Italy
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Originally Posted by dadod View Post
You can try this pre/headphone amp, mostly very low 2nd and third harmonic and no global feedback.Current conveyor as a voltage amplifier
I read your thread, it's a good circuit, albeit a bit complicated, and it's not really related to the Hiraga 8W.
I have a long list of preamps/headamps to try, maybe one day i'll build yours too
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Old 13th April 2013, 07:10 PM   #910
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Default Fake 2SC2837?

Uh oh, it looks like I probably got a fake 2SC2837 here. It's hard to tell in the photo, but the top looks like it was sanded and relabelled. Doesn't have the right numbers - no O, P, or Y rank. When tested with an Atlas transistor tester, it gave an hFe of 20. Datasheet says 50 should be minimum. I got 4 of them and they all look like this and all test with an hFe ~20.

I got some 2SA1186 from the same supplier and they appear genuine and all test with hFe ~120, which is right in the range specified by the "P" rank that they have marked on them. If they're fake, at least they're more well done than the pathetic 2837s I got...

These came from MCM. I realize ordering from them is a roll of the dice. I've gotten transistors from them before with mixed results.
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