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Post by k2col on Apr 1, 2008 16:30:33 GMT
senj - I can't answer your question, except to say that the K501's 120ohm impedance will be no problem for the MB45 and that Mike and others have commented that it's a remarkably good budget amp. Obviously spending more gets you more, but if you can pick up an MB45 for £40, then spend a tenner on new caps you'll be laughing.
Also, should you decide to upgrade later and sell the MB45 then I expect you'd get your money back quite easily.
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Deleted
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Post by Deleted on Apr 1, 2008 18:09:09 GMT
Just a thought, from someone who would be taking instruction, why not use something basically good but cheap e.g. NAD 3020 in series 20 or 3020A or 3020B (not 3020e/i as they were slimline and might limit options), and turn it into "built to standard" rather that "built to price". There are loads of them around, both working and not, they tend to sell for around £50. ?
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rickcr42
Fully Modded
Rest in peace my good friend.
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Post by rickcr42 on Apr 2, 2008 15:37:57 GMT
I'm using ATH-500s which are 62ohms I think, and I get a low level of background hiss, although its soon lost amongst the music. Over time I'll try other headphone & amp combinations (the Doudou group buy is tempting me, but I think I'll try new phones first) as I'm fairly content for the time being. try some series resistance.You need to balance eliminating the noise with maintaining a good damping factor so probably the best way would be to use a rheostat connetion dual pot (one section for each channel so tip/ring) in series with the cans to "dial in" the proper value that gets rid of the noise and retains good sound then without moving the knob remove it from the circuit,measure the value of the "resistor" and then solder in two one watt hand matched L/R resistors of that value. ...... and DO report back if you try this either way it goes
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Post by senj on Apr 2, 2008 22:14:05 GMT
I thought of that too; simply increase the overall resistance of the circuit. Maybe we could come up with an ideal resistance total. Isn't the amp 2W per channel? or is that split?
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Deleted
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Post by Deleted on Apr 2, 2008 22:51:51 GMT
senj
You could try replacing the resistors feeding the headphone jacks with resistors of different values, but in pairs . Immediately below the orange capacitors, and above the headphone jacks on the LHS of photo DSCF0127 . Try pairs of resistors in different values up to 120 ohms. e.g. 47,68, 82,100,120 ohms. Those 1% metal film resistors are quite cheap at your local electronics parts store. Unfortunately, your photo isn't quite clear enough in that area to be certain what value the existing resistors are. SandyK
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rickcr42
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Rest in peace my good friend.
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Post by rickcr42 on Apr 2, 2008 23:41:52 GMT
Don't do it man.
At these values the thermal noise of the resistor is totally below the threshold of audibility so metal filmsresistors are not essential
BUT I if there is a worse sonic butcher than a cheap metal film resistor I have yet to hear it.If you use MFs use a good one or you are better off with a carbon film on the SQ.Remeber,this is a series connected part so everything has to go through it before reaching your cans so can have an impact on the ultimate tone/sonics
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Post by senj on Apr 3, 2008 11:54:01 GMT
So what do i do exactly? Try matching all four with new values? They are currenty 10.5 Ohms each.
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Post by PinkFloyd on Apr 3, 2008 11:57:09 GMT
Let me strip my old girl and do a few experiments with these resistors........ give me a couple of days...... I'll be back.
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Deleted
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Post by Deleted on Apr 3, 2008 12:55:07 GMT
Rick Those existing MF resistors have CHEAP already painted all over them. He will simply be replacing like with like ! It's not as if this ancient design was ever a REAL contender in the SQ stakes, and is never likely to be anything more than a competent headphone amplifier. The use of higher quality resistors at that location is almost certain to be masked by deficiencies elsewhere, except for one deficiency that Mike neatly sidestepped by his choice of plugpack. SandyK
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Post by PinkFloyd on Apr 3, 2008 23:22:15 GMT
Rick Those existing MF resistors have CHEAP already painted all over them. He will simply be replacing like with like ! It's not as if this ancient design was ever a REAL contender in the SQ stakes, and is never likely to be anything more than a competent headphone amplifier. The use of higher quality resistors at that location is almost certain to be masked by deficiencies elsewhere, except for one deficiency that Mike neatly sidestepped by his choice of plugpack. SandyK Have you ever heard an MB-45 Sandy? yes or no? If not I'll gladly send mine over to the land of OZ.... you may be quite impressed
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Post by senj on Apr 4, 2008 0:00:40 GMT
See what difference some high quality resistors make Pinky. Pretty please.
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Post by PinkFloyd on Apr 4, 2008 0:33:20 GMT
See what difference some high quality resistors make Pinky. Pretty please. WILL DO MAN.
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Deleted
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Post by Deleted on Apr 4, 2008 0:48:19 GMT
Mike Thanks, but I don't have enough time to listen to the modded SC as it is. When I do find time for serious headphone listening, I much prefer my discrete Class A preamp. Actually, I prefer to listen via speakers for a far more involving experience, and relaxation. (family permitting !!!) BTW, I have seen you express similar sentiments on several occasions. Did I miss where you mentioned the speakers you listen to ? Alex
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leo
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Post by leo on Apr 4, 2008 0:50:01 GMT
That modded SC amp kicks Ass!
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leo
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Post by leo on Apr 4, 2008 0:51:12 GMT
The big classA that is
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Deleted
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Post by Deleted on Apr 4, 2008 0:52:30 GMT
I suggest that Mike uses the el cheapo variety first to find the most suitable resistor value, then try a high quality one of similar value. Some of these HQ resistors are too good to use for playing aroud with. Soldering and unsoldering etc. may alter their precision ? SandyK
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leo
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Post by leo on Apr 4, 2008 0:52:33 GMT
Must start a thread on that beast soon
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Post by PinkFloyd on Apr 4, 2008 0:57:23 GMT
Thanks, but I don't have enough time to listen to the modded SC as it is. Well PLEASE stop pontificating on amps you've never heard Alex.... it's MOST annoying! Stick to what you know and let the rest of us who have heard them comment on them..... fair enough? ;D
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Deleted
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Post by Deleted on Apr 4, 2008 1:09:39 GMT
Leo Are you still able to do a comparison between the 15W/Ch. Class A and those valve amplifiers at the next meeting? BTW, have you tried a temporary plug in setup for headphones with the Class A? TBH, I never tried using headphones with the Class A, only with the Class A preamp. Although the original Silicon Chip design did cater for headphones. Alex
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Post by PinkFloyd on Apr 4, 2008 1:14:49 GMT
Just as as I suspected Sandy..... you've NEVER seen one, let alone heard one ;D
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leo
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Post by leo on Apr 4, 2008 1:16:25 GMT
Leo Are you still able to do a comparison between the 15W/Ch. Class A and those valve amplifiers at the next meeting? BTW, have you tried a temporary plug in setup for headphones with the Class A? TBH, I never tried using headphones with the Class A, only with the Class A preamp. Although the original Silicon Chip design did cater for headphones. Alex I've not compared it direct yet but will do as soon as theres another meet up. Everytime I mention SC amp I do mean the big classA Sounds F*****g great as a headphone amp too IMO. Next project for me is to build another but convert to a pre and headphone amp
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leo
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Post by leo on Apr 4, 2008 1:18:22 GMT
Just as as I suspected Sandy..... you've NEVER seen one, let alone heard one ;D Come on now, you know our Alex, he wouldn't even wipe his arse on one let alone listen to it
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Deleted
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Post by Deleted on Apr 4, 2008 1:19:33 GMT
Yes, you are correct. I have never heard the QED MB-45. However I have constructed and listened to amplifiers using the LM1877,LM377 and LM379 . I even used an SQ, logic steered, surround system using the LM379s for several years.
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Post by PinkFloyd on Apr 4, 2008 1:46:16 GMT
EDIT: BANG out of order on my part
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leo
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Post by leo on Apr 4, 2008 1:59:49 GMT
Get em out for the lads eh ;D
I stick to modding others stuff to my liking, its bad enough P*****g about trying to find a case never mind racking the brains to come up with something original
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