I don't know what 'Zobel error' you mean, but it's one thing to identify a PCB version from a photograph via obviously missing parts, another thing to answer questions about the circuit without a schematic.
i hear on abouy year 2000 in seller shop this amp and quite good,,i just wonder if there is any diy amp bettering this amp with same price at this time
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'.
So the schematic doesn't match the board. Not encouraging. And the instructions for changing the sensitivity are incomplete.
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
I tested with Lm49710 and OPA2134 and for me OPA2132 sounded a bit more balanced. Also TL071 was not bad. For all 3 disconnect the compensation 3.3pf capacitor.
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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47uF is the bootstrap. 100uF is the DC servo integrator. 220uF will be B+ decoupling and there should be two of them, one per rail.
I change LM391 or TL071 to OPA134 or NE5534, or in the recent good old days LME49710. Whether it really helps is another question, but my customers expect it.
I change LM391 or TL071 to OPA134 or NE5534, or in the recent good old days LME49710. Whether it really helps is another question, but my customers expect it.
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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1. If you use OPA134, none apart from removing the 3p3 capacitor. If you use LME49710 you may also need 100nF between pins 4 and 7.
2. In a stock 405 chassis there are no RCA sockets at all, but the input ground is connected to chassis ground via 10R on the PCB as a ground lift.
2. In a stock 405 chassis there are no RCA sockets at all, but the input ground is connected to chassis ground via 10R on the PCB as a ground lift.
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OPA1641 seems to be very appreciated in another projects based on QUAD405 topology.