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Old 9th June 2015, 07:30 PM   #1
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Default Magnum IA 170 ....

Well ... for once it seems that schematics are nowhere to be found but i am open to suggestions

I have my thing about these amplifiers and i think that are horrible designs but that is just my opinion Opinion that may originates from the conditions that these amplifiers appear before my bench ...

Usually burned beyond recognition Been Lucky enough to have one in my shop that transformer was on fire much before the original fuse blow so i have a slight idea about the parts installed on the board

Obviously a pair of tip 2955-3055 railed at 50+50 volts promising 70WPC with 4 transistors for both ch screwed on the bottom in general doesn't look very safe .

In order to repair one i need to reverse engineer some parts like the thermal protection and some other small details .... In reality that doesn't look much of a trouble and it can be done .

What really troubles me and i dont seem to be able to understand and its the point that i need help is that in the left ch the transistor that does Vbe duty is a NPN transistor while on the other ch the Vbe is a PNP transistor . In the first place i thought that this was done ...wrong by a previous repair then i checked with my Magnum and i found that this is factory made and also correctly printed in the pcb likewise ...

Any body can share something on this ?

Kind regards
Sakis

I could comment more about the mistakes i have have found of those like poor choice of headphone jack or pcb design that actually shorts when not n use resulting 330R drop resistors to actually boil to all those that i have seen but this will not help much at this point ...There is other small things like that ...
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Old 10th June 2015, 08:07 AM   #2
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70 views and no answer ...I dont expect much .... but this still remains weird

Kind regards
Sakis
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Old 10th June 2015, 08:26 AM   #3
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sorry

I had experience only with mosfet based Magnums (basically ditto from Hitachi app. papers) ;

I have no sch. for IA170
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Old 10th June 2015, 08:35 AM   #4
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Fine with me Zen but please dig in your head what might be the concept behind 2 different vbe one NPN for the one ch and PNP for the other ch ...

Kind regards
Sakis
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Old 10th June 2015, 09:09 PM   #5
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Hi Sakis. You may be in luck here. The designer apparently, may be Colin Wonfor who has a thread active here now and goes by the handle of Root2. Perhaps he can assist or suggest who could?
SECA Kit By Colin Wonfor
Magnum IA70 integrated amplifier.
The title IA70 should probably be IA170, as he referred to in the second link.
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Last edited by Ian Finch; 10th June 2015 at 09:24 PM.
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Old 10th June 2015, 10:00 PM   #6
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website and contact details: Magnum - Colin Wonfor
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Old 11th June 2015, 06:56 AM   #7
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OK lets see
this is the message i ve send

Could you please care to comment around the concept of having a NPN Vbe multiplier on the one ch. of the IA170 while a PNP on the second ? Thanks
Sakis
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Old 11th June 2015, 06:58 AM   #8
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I may as well sent him some pictures of the amplifiers arrived before my bench with all kinds of smell coming from them

( trafo / diodes / resistors produce a variety of smell when burned )
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Old 11th June 2015, 08:02 AM   #9
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Colin was pretty quick
Answer :
Hello Sakis,
Simply No I do not understand why you are contacting me, this product was based on my designs, but I resigned from the Magnum before this product was made so I have no circuit diagrams at all.

Sorry

Colin
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Old 11th June 2015, 10:21 PM   #10
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Yes Sakis, I guessed that was possible but Colin must assume that every interested person knows his background and has followed his C.V meticulously, so should not ask him about that model. Well, he has commented publicly on the design before and he could at least refer you to the ex-manufacturer or those responsible for the changes.
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IA170 started as a Oberon Amp Quickie has one of these, the original design was fitted with a MOS FET power stage.You say you have TI parts in the output can you read the numbers please. This could be a BK Electronics mod has the MOS FET's became rare, Tony changed the design to save money.
Best Col
So "I do not understand why you are contacting me" I think, is a bit too dismissive in the DIY spirit. If it really is as simple as the floor sweeper or storeman making whatever changes seemed to work and cost less, you probably have your answer right there. I would not expect that much thought and design effort was used and what you have is yet another fine example of British audio cottage industry practice. It was "re-designed" in the UK and so it burns up in Greece or Oz and probably burns down buildings in Brazil. 'figures....
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