Quad 405-2 circuit query

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Snorbans
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#1 Quad 405-2 circuit query

Post by Snorbans »

Hello
I have been working through my Quad 405-2, following Nick DeSmiths notes, with some of Keith Snooks DCD mod 3 changes (I'm not inverting anything as my pre amp is already inverting) - adding the Tr1a/b change and new Tr2/3 transistors (there was no Tr4). The board is M12565 iss.7, the same as Keith Snook is modifying on his site.

Snook states 'with Tr2 changed to 2SC2547E and R23 removed and Tr4 replaced with ZTX753 ** and C11 replaced with a link there should be no need for C7 // R14 and C7 can be replaced with a wire link'. I'm a bit wary of this change (C7 with a link wire) as C7 is actually a resistor not a 330nf capacitor, a 3R3k resistor, R17 and 'C'7 are both 3r3k resistors. Looking at other photos this is true for all 405-2 boards. For the intended circuit I remove both resistors and replace one with a wire link, C7. Can anyone confirm this would be correct?, it would be a pain to blow anything up at this stage

Cheers
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Dave the bass
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#2 Re: Quad 405-2 circuit query

Post by Dave the bass »

Hi Snorbans.

Nick dS posts here under the user name of 'jack', hopefully he'll see your question and be able to answer it.

If not send him a PM, he's a helpful fella.
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#3 Re: Quad 405-2 circuit query

Post by Snorbans »

I will, thanks Dave
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jack
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#4 Re: Quad 405-2 circuit query

Post by jack »

I got the pm, thanks.

I haven't looked at this for many years, so bear with me for a day or so while I get my brain into gear and reread the relevant docs and have a peek inside that 405-2 (which is in store at the moment as I'm not using it).
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#5 Re: Quad 405-2 circuit query

Post by Snorbans »

Thanks for the offer to look Nick, I have attached an image from your notes, showing C7 as a resistor. C7 is also a resistor on some of the 405 boards yet all the circuit diagrams i have found show it as a capacitor, a 330pf capacitor. As I say I'm sure both the resistors, C7 R17, need to go, I just don't understand this aspect and find no discussion of the issue though it's a much discussed board. Possible minefield.
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Trek
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#6 Re: Quad 405-2 circuit query

Post by Trek »

Tubular capacitors, rare but true
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Nick
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#7 Re: Quad 405-2 circuit query

Post by Nick »

Quiet common for a 330pf

https://uk.rs-online.com/web/p/polystyr ... s/0113291/

And forgive my OCD, but the standard notation is either 3R3, which is a 3.3 ohm resistor, and 3k3 which is 3300 ohm. 3R3k is neither one thing or the other,
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jack
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#8 Re: Quad 405-2 circuit query

Post by jack »

Not forgotten this - just been busy
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