Kit building Quad 405 Clone

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Patrik Floding

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Joined 2005
Mooly,

Yes, C2 shunts AC components of the amp's output signal to ground, allowing any DC on the output to be corrected. However, any imperfect shunting will result in a signal on the inverted input -so it certainly is in the signal path.

Perhaps a re-design that removes C2 would be the best solution.

Good point about the ground for C2, although hopefully any ground Z will be a lot more linear than C2's non-linearity. C2 goes to signal ground, via input cabling back to the pre-amp, in parallell with the chassis, sinking the signal. (I wish this was cleaner.)

P.S: Seems I got you mixed up with the OP in an earlier posting. :blush: I must have been tired..
 
D

Dukanita

Member
Joined 2006
pcb

Hi
Does anyone have pcb drawing for aditional pcb located on speaker terminal. Here are triac SC141B (6A, 200V), 2N4992 Silicone bilateral switch, resistors and one bipolar.
Too, does anyone know where to find triac and 2N4992 and what are substitute for this parts. I try to find in my local store but nothing.
Thanks
Duka
 
Mooly

Mooly

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Joined 2007
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Mooly

Mooly

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Joined 2007
Paid Member
Certainly effective. I think they used this protection to gaurd against damaging their ELS speakers, which was the intended match for the 405.
That could be interesting, 50 volts DC up an ESL
They do not like it up 'em.
 

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JonLawes

Member
Joined 2008
RIGHT!

Worked it out (with help from a guy who knew what he was doing....)

I had some of the transistors the wrong way (they were the right way according to the screen printing...). So its fixed, just got to swap a wire on the power supply I built and case it and I have a 405 clone! :cool:

Many thanks for your help guys.
 
J

JonLawes

Member
Joined 2008
Haven't given it a proper workout yet; I want to build a posh enclosure and see how it compares to my genuine 306. I mounted the Power supply in a seperate box so when I make future amps I don't have to remake the supply. I would also like to make an iPod interface; digital stuff is closer to my ability.
 
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Patrik Floding

Member
Joined 2005
JonLawes said:
RIGHT!

Worked it out (with help from a guy who knew what he was doing....)

I had some of the transistors the wrong way (they were the right way according to the screen printing...). So its fixed, just got to swap a wire on the power supply I built and case it and I have a 405 clone! :cool:

Many thanks for your help guys.
Click to expand...

Good to hear!

I would try to make it easy to mod the amp, as there are a couple of very easy mods that really transform the sound.

Regards
 
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audiolabtower

Member
Joined 2008
Mooly said:
Certainly effective. I think they used this protection to gaurd against damaging their ELS speakers, which was the intended match for the 405.
That could be interesting, 50 volts DC up an ESL
They do not like it up 'em.
Click to expand...

the triac protection was for dc offset in the event of device failure. If the loudspeaker output went to more than plus or minus 5V DC the circuit would short circuit with the design objective to force the 4A rail fuses in the amp to blow and not your woofers.

The ESL57 protection was different and consisted of placing a component (early 405's resistor, later ones a link connecting zeners) in the pcb sockets to limit the op-amp output so the 405 output was 50W and the voltage swing could not arc over the original electostatics.
 
C

CopperTop

Member
Joined 2009
I just bought some Quad 405 ready-assembled PCBs off eBay (£25 the pair inc. P&P). They seem to be built to the Mk1 pre-production design i.e. to the original Peter Walker paper. (Why not the 405-2 seeing as the circuit is readily available?)

I wired one up with T1A fuses in the +/-50V supplies and connected my source (DAC) ground to the PSU star ground - not the dedicated source ground on the PCB. Mistake! The thing oscillated and blew out the tweeter on the (big but crap) speaker I was using - even though the PSU was ostensibly limited to 1A-ish.

With the DAC ground connected to the dedicated source ground it seems terribly well behaved, and I have briefly had a clean 100W into 8 ohms despite an improvised heatsinking arrangement. It has spurred me into writing some code to measure the THD & noise using a PC sound card. The noise performance is undoubtedly crap, but it would be fascinating to measure the improvements with the well-known mods to the op amp circuitry etc.

I mention all this because it seems as though what is really needed is a conventional DC protection crowbar circuit, plus a trigger based on high frequency nastiness. Has anyone come up with anything like this?
 
R

reddiesel

Member
Joined 2015
Hi im hoping that i can get some help with a chinese clone 405-2 from ebay im building its the one with the fuses on each side, and the plastic type output transistors, one of the boards works fine the other blows the fuses on the board when powered up, im not sure how to troubleshoot the fault ? i have 46v + and - supply , the boards were ready built and everything looks identical transistors and diodes the right way etc, can someone please give me some fault finding tips ? , this is a great site by the way.
 
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