Sometimes you get this message if someone has given you a late pay or non-pay ding and the seller (Jim's) has excluded that whole class from bidding.
Joel it almost seems like your 0.33 ohm resistors are shorted out for some reason so you go from low bias to high bias and no control.
You would have a similar problem if the 33 ohm tie resistor between the driver emitters was high resistance ( say damaged during first problem).
Are all the OPS devices and drivers ok? As Bill_P asks, are both amps doing the same?
You would have a similar problem if the 33 ohm tie resistor between the driver emitters was high resistance ( say damaged during first problem).
Are all the OPS devices and drivers ok? As Bill_P asks, are both amps doing the same?
Can you also make sure that there are no shorts between the OPS devices and the heatsinks
Also, dump Question, the 0.33 Ohm resistors are 0.33 and not a much lower value?
Also, dump Question, the 0.33 Ohm resistors are 0.33 and not a much lower value?
One other thing- if the output was shorted to ground you could get this problem as well. Make sure your hookup wiring is ok.
Thanks, but shipping from the far east via the USA will attract double postage charges and run the doubled risk of attracting import charges and Value Added Tax.
One posting for cheap PCB from the Far East gets below the exemption limits and I should not have to pay DHL exhorbitant "doorstep" fees for something they have already been paid for, to deliver an international packet.
I saw you rfailed PM.
You could have used Email, but you sent a second failed PM.
I have never bought anything from Jim's, so I can't be a bad customer.
I do ask Members to check on Customer Support from Ebay dealers.
Jim's did attract comments from me in the long distant past, because his customer support appeared to be non existant.
He has changed and changed a lot, for the better.
I have not had to forewarn any Member about using Jim's since he changed his support for our Members.
I also made a comment on Jim's use of "copyright" protected names on his product.
If Jim's has deliberately barred a Member because of past comments on this Forum, then Jim's deserves more bad press.
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I have bought several kits from jims audio including NX pcb and never ever have issues with them.The products are excellent also they will ship it fast.The price is also very reasonable when you compare the quality of PCb they have.They have very good reputation in ebay I think they deserves it. Try to order from different ebay account and ship to your address.
From the indications of one of the builders i spoted another design error that can have , and had, deadly consequences, although this one is present in about all CFAs discussed in this site, and is prevented in most commercal vintage designs...
Where do you come with this stuff Wahab? There are no 'deadly consequences' with CFA. TI, ADI and any other semi supplier you care to name integrally make hundreds of millions of CFA amplifiers every year. And, the audio industry makes 100's of thousands of CFA power amplifiers a year also - maybe millions.
If you don't like CFA - that's ok but please don't poison this thread which is specifically about helping builders of the nx and sx-Amplifiers - both of which are CFA.
If you don't like CFA - that's ok but please don't poison this thread which is specifically about helping builders of the nx and sx-Amplifiers - both of which are CFA.
AndrewT , I emailed Stanton and asked him to look into it. hopefully we can get it clarified in the next few days.
If you can not design a good CFA, it does not mean everyone else can not either.
Ostripper, Bonsai, Dadod make some good CFA. Me too 😎
That has nothing to do with CFAs but with the fact that some basic analysis is not made in a few of thoses designs..
This can occur because the current path from ground to a rail voltage is limited by only 165R total resistance, in this case it could have been Q6 wich would had blown due to excess base current provided by Q11.
To prevent Q11/Q6 and Q9/Q7 being destroyed if there s faulty conditions or peaks a 4K7 resistance must be inserted in serial with Q11 and Q9 collectors.
In the old assymmetrical such design the equivalent of Q11/Q9 was sometimes destroyed when powering the amp, a problem that didnt exist with LTPs as this latter is inherently protected by its current source.
Let say that i m not much interested in designs that are device dependants and whose linearity is often mediocre given the component counts, Bonsai s is not the worse in this respect...
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Turns out 1 zobel connection wasn't connected
. But will this cause issue? Also, with the 11 ohm resistors in, I blew out(dead short between C & E) Q1 and Q4I now have 2 Zobel connections complete - I followed the wiring diagram as there seems to be a connector number mismatch if I go by the PS connection details page.
So now I'm testing amp 2 - with 1a fuses, the problem looks mirrored to amp 1, turning R6 I can't get stable 25mv across 33 ohm resistors. Then with ammeter in positive rail, turning R6, current will switch on at about 50ma but fuse blows trying to reach 300ma.
The 0.33 R's measure fine - 0.8 Ohms between Q1&Q2 Emitters , same for Q4&5
No shorts to heatsink, with Q1,2,4,5
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Joel,
you do not need to have the Zobel connected while you do not have a load. If you drive the amplifier hard at HF with the Zobel connected it will smoke - so I usually leave it unconnected until final wiring.
Have you measured the 33 Ohm resistors?
Can you measure between the output and GND
you do not need to have the Zobel connected while you do not have a load. If you drive the amplifier hard at HF with the Zobel connected it will smoke - so I usually leave it unconnected until final wiring.
Have you measured the 33 Ohm resistors?
Can you measure between the output and GND
Thanks!
I measured R5 - it is 33 Ohm
Also, I measure from base of Q12 to Base of Q13:
zero link + 1k + 1k variable + 15 + 33 + zero link - Measures about 2024
Turn R6 full and it's about 1000 ohms less.
568 Ohms - Looks right from what I see going through the feedback chain.
Okay Thanks for the PM. I'll examine the suggested voltages..
Is it correct that I don't need matched devices on the front end.. Just Checking
KSC3503 and KSA1381, I purchased from Mouser but the gain grades were different. Then I Purchased both transistors with matching gain grades from Joshvi - member on this site, and I got enough to built 3 of these amps..
The mouser units are D&E, the batch from India are all E - I only removed the mouser D's from the amp and installed them with the new E's.
Maybe I should try complete set of the New E's
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With R6 at 1k ohms the voltage is negative 0.6-0.7 wrt GND. Fuses stay intact
I removed C7, measures 68pf
Just doing a few checks before following the PM
I removed C7, measures 68pf
Just doing a few checks before following the PM
When the VBEM start to be on conduction a 30R variation of the pot (whose 60% of the range is useless) will increase the bias by 200%.
To allow a smooth setting of the bias the two attached resistances should be 2K7 for R21 and 560R for R20, any other values are inadequate for a 1K pot.
To allow a smooth setting of the bias the two attached resistances should be 2K7 for R21 and 560R for R20, any other values are inadequate for a 1K pot.