You mean this one https://www.ebay.com/itm/321679308112 ? It has a number of the modifications suggested by Ludwig and Snook. It does not come with the components and the text is crazy. It looks like a clone of the Dada PCBs. It still has the high pass filter suiting the Quad ESL speakers but may need modification for speakers digging deeper in the bass.
This is certainly not a Dada board. For a start it is a transitional 405-1, not a 405-2, as seen by Tr5/6: and the Dada boards don't have regulators for the +/-15V supplies. The Dada boards were all developed from the latest Quad 405-2 schematic M12333.10.
I also don't know what 'highpass filter suiting the Quad ESL speakers' you are referring to, when the lower -3dB point of a Quad 405 is around 14 Hz (and it is specified as -1dB at 20Hz), or why this would need 'modification for speakers digging deeper in the bass', unless you're a 64' organ fiend (as I am myself), but I've commented before on this listing. It is not a 405-2; a 405 is not 80W but at least 100W into 8 ohms; it is not 'class A'; and it does not have 'dynamic biasing'.
I also don't know what 'highpass filter suiting the Quad ESL speakers' you are referring to, when the lower -3dB point of a Quad 405 is around 14 Hz (and it is specified as -1dB at 20Hz), or why this would need 'modification for speakers digging deeper in the bass', unless you're a 64' organ fiend (as I am myself), but I've commented before on this listing. It is not a 405-2; a 405 is not 80W but at least 100W into 8 ohms; it is not 'class A'; and it does not have 'dynamic biasing'.
Its not a 405Mk1 as it has provision for the hybrid SOA, N1 and N2 and assuming the schematic is reflected in the board it has the 2 transistor current source which was never fitted by Quad even in the later 405-2s, it also has the bias diode D6 again only fitted to the 405-2
Stuart
I’ve picked up a pair of the LJM boards which are labelled as : “ Quad 405 upgraded version 2019 “
Is there a general consensus as to the best drop in op-amp upgrade from the stock LM301AN. The stock op-amp has a small film bypass capacitor labelled 47nk100, also I have added a 1000uf across the op-amp power supply pins
Is there a general consensus as to the best drop in op-amp upgrade from the stock LM301AN. The stock op-amp has a small film bypass capacitor labelled 47nk100, also I have added a 1000uf across the op-amp power supply pins
Thanks! There are 3 caps on the amp boards, a 47 uf at the centre, is this the bootstrap? then a 100uf next to the op-amp, is this across the op-amp power supply? and there is a 220uf polymer type in the corner. Are any of these worth changing
Also, do you think the op-amp upgrade is worth the time and expense. Keith snook said it would make little difference
Also, do you think the op-amp upgrade is worth the time and expense. Keith snook said it would make little difference
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Sorry, i made a mistake on the 220uf cap. It states on the board that it should be 220uf, but the cap itself is marked as 150uf 16 volts. Have had a good look and there is only one of these caps on each board.
Also should the rca input ground be connected to the chassis, it is on the stock quad 405, but what about with the LJM clone boards
Also should the rca input ground be connected to the chassis, it is on the stock quad 405, but what about with the LJM clone boards
Thanks! Here's a pic to show the position of the three caps if it may help in any way:
If i swapped out the stock op-amp for the OPA134 or LME49710, what changes need to be made in the surrounding circuitry. Would you go for the opa134UA or opa134PA
Also, i am using a stock quad 405 enclosure in which the rca input ground is connected to the chassis, the negative speaker terminals are connected to the chassis, the speaker return cable is connected to the chassis via the bridge rectifier, the zero volts of the 50-0-50 volt power supply is connected to the chassis, as is the transformer ground, and the mains earth is also connected to the chassis. Do i need to break any of these connections
Thank you.
If i swapped out the stock op-amp for the OPA134 or LME49710, what changes need to be made in the surrounding circuitry. Would you go for the opa134UA or opa134PA
Also, i am using a stock quad 405 enclosure in which the rca input ground is connected to the chassis, the negative speaker terminals are connected to the chassis, the speaker return cable is connected to the chassis via the bridge rectifier, the zero volts of the 50-0-50 volt power supply is connected to the chassis, as is the transformer ground, and the mains earth is also connected to the chassis. Do i need to break any of these connections
Thank you.
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Any idea where i can buy either of these from, have tried cpc, farnell and rs components, but not available.
Only place i can find them is nikko electronics on ebay.
They seem to be old op-amps that are out of stock, especially the lme49710, are there any modern op-amps for the LJM quad boards
Only place i can find them is nikko electronics on ebay.
They seem to be old op-amps that are out of stock, especially the lme49710, are there any modern op-amps for the LJM quad boards
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