Wahab this is a bit tiresome. I repeat, 75 sets of this amplifier have been sold, and most built. The 1k pot adjustmrnt range is fine. The other comments you passed earlier on are also nonsense - the same point you raised applies to most VFA's - and it is not an issues.
The correct thing to do is get Joel's amplifiers working - not modify them and especially when we have not found the root cause.
The correct thing to do is get Joel's amplifiers working - not modify them and especially when we have not found the root cause.
Ok - you should be able to dial this out with the offset adjust pot. You may not be able to completey dial it out until we have found the other problem.
Will you post up the marked up schematic again?
Since you have surely a file in a simulator do a test with the pot at 330R, 300R, and 250R.
At 330R Iq is 80mA, at 300R it is 208mA, 554mA at 250R, at 0R it is 14A wich suggest that the 33R resistance in serial with the pot is totaly useless.
The other point was the current path from ground through R11, then R28/R29, then Q9/Q11 emitters/collectors and then through Q7/Q6 bases/emitters and R30/R31.
Theses two current paths are not limited and that s why Q11 was destroyed in Wesseling build, if the amp work flawlessly at start this doesnt matter much but if the DC conditions are faulty then excessive current can flow in this path.
This doesnt apply to VFAs because the emitters of the input stage are loaded by a current source, not by resistances as low as 15R..
Q11 wouldnt have burnt if said limitaton was implemented, so i guess that you have to sort out everything out of a non optimaly designed sheme, as said if something goes wrong it will be more difficult to service the things.
bonsai,
I've just been auditing your thread so this is just a general question that I think would apply to any amplifier. Where you have the 1K adjustable pot would there be any advantage to having a fixed resistance of lower value and then a lower value adjustable pot so that the adjustment would be finer rather than having the entire swing of a 1K pot? I don't know if there is a common resistance that the pots end up at so I'm just curious if a smaller adjustment range with a fixed resistance wouldn't be more precise to adjust. Thanks in advance for your answer.
I've just been auditing your thread so this is just a general question that I think would apply to any amplifier. Where you have the 1K adjustable pot would there be any advantage to having a fixed resistance of lower value and then a lower value adjustable pot so that the adjustment would be finer rather than having the entire swing of a 1K pot? I don't know if there is a common resistance that the pots end up at so I'm just curious if a smaller adjustment range with a fixed resistance wouldn't be more precise to adjust. Thanks in advance for your answer.
I have to order some parts form mouser, especially fuses - one week break, or more.
When I adjusted 1k pot to obtain 40ma in positive rail the current will not stabilize, current rises rapidly and takes out the fuses. A few times I could dial it back before the fuses popped but I couldn't hold the the current at even 20ma or less..
So I'm thinking I likely installed something wrong or caused an issue during the first start up..
so far, I removed Q6,7,12,13 and all PN and NP junctions are intact..
I plan to remove all the transistors and test them..
Bonsai, thanks for all your help.. I don't want to take up to much of your time so I would like to find the issue before I power up again..
When I adjusted 1k pot to obtain 40ma in positive rail the current will not stabilize, current rises rapidly and takes out the fuses. A few times I could dial it back before the fuses popped but I couldn't hold the the current at even 20ma or less..
So I'm thinking I likely installed something wrong or caused an issue during the first start up..
so far, I removed Q6,7,12,13 and all PN and NP junctions are intact..
I plan to remove all the transistors and test them..
Bonsai, thanks for all your help.. I don't want to take up to much of your time so I would like to find the issue before I power up again..
Andrew,
My offer still stands if you cannot get the ebay SNAFU sorted. To be clear, I would buy the PCBs and have them shipped to myself. This only costs 32.49 USD, including shipping. Then I would ship them to you via USPS, this costs 16.00, so your total would be 48.49 USD, excluding any fees you have to pay on your end when you pick it up.
BTW, I did not find your email in your profile, maybe I'm not looking in the right place.
Regards,
Richard
Most likely its a bad semi-conductor...... assuming no wrong value, wrong polarity or other similar issue.
THx-RNMarsh
THx-RNMarsh
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Joel, make sure R36 and R37 are 150 ohms and R27 and R28 are 120 ohms (110 or 150 ok for testing the amp boards out).
If R27 and R28 are the original 15 ohms you would have serious problems with R36 and R37 at 150 ohms.
If R27 and R28 are the original 15 ohms you would have serious problems with R36 and R37 at 150 ohms.
Wahab,
Ok - increasing the 33 ohms is a useful chsnge - but doing so while Joel has other unsolved issues will not help to uncover the root cause of his problem.
To your point about adding series resistance to the collector of the level shifter - there are lots (most in fact) VFA and CFA circuits where you have high voltage across a device and little or no current limiting in the event of a problem - eg a short. If the driver or pre- driver in a VFA goes short, it usually takes out other active devices around it. Further, the diamond configuration as shown in the nx and sx Amplifiers is well tried and tested - both in discrete audio form (many designs out there) and in IC form.
Secondly and many more importantly, a ressistance of 4.7 k in the collector of the level shifter will affect the slew rate. Recall in a CFA that the current on demand property requires that you can deliver high peak currents into the TIS node to support the higher slew rates.
Ok - increasing the 33 ohms is a useful chsnge - but doing so while Joel has other unsolved issues will not help to uncover the root cause of his problem.
To your point about adding series resistance to the collector of the level shifter - there are lots (most in fact) VFA and CFA circuits where you have high voltage across a device and little or no current limiting in the event of a problem - eg a short. If the driver or pre- driver in a VFA goes short, it usually takes out other active devices around it. Further, the diamond configuration as shown in the nx and sx Amplifiers is well tried and tested - both in discrete audio form (many designs out there) and in IC form.
Secondly and many more importantly, a ressistance of 4.7 k in the collector of the level shifter will affect the slew rate. Recall in a CFA that the current on demand property requires that you can deliver high peak currents into the TIS node to support the higher slew rates.
AndrewT,
Stanton replied to me and said there are no issues as far as he knows
He gave me the following link
100WX2 Ovation NX Current Feedback Amplifier PCB Set New Version 2 0 | eBay
Above was the subject of my PM to you (why doesn't your PM work - easy way to communicate!)
Stanton replied to me and said there are no issues as far as he knows
He gave me the following link
100WX2 Ovation NX Current Feedback Amplifier PCB Set New Version 2 0 | eBay
Above was the subject of my PM to you (why doesn't your PM work - easy way to communicate!)
I agree, 4.7 k will affect the slew rate to much, but 2.2 k will affect the SR less then 10% (in mine amp) and that could be good compromise.
I have checked my "Contact" options.
For some reason the Email option has disappeared and I cannot see it in the user CP.
I will contact Mods.
opened your link. "Buy it now"
reports
This is the same as has happened to me over ~6months.
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seems to be issue with your ebay id can you check below thread regarding this
Why do I Get This message: "item can't be purchas... - The eBay Community
Why do I Get This message: "item can't be purchas... - The eBay Community
My Ebay Buyer feedback from Sellers is exemplary.
I have never sold anything, so I don't have any Seller feedback.
I suspect they have blocked my username as a result of comments on this Forum, or they are blocking UK based buyers. Our trading regulations are quite strict in the way buyers are protected and maybe the Seller does not like that.
Bonsai,
when this is sorted, could you ask the Mods to remove these posts?
No problem as far as I can see ; I get as far as paying. Is that where the message occurs?
Surely but as implemented the VBEM yield the relevant Iq when the pot is at 307R, from here 1% variation, that is 3.07R, induce 10% Iq variation, so it s not easy to set the current.
The variation is 5% when using a 2K7 resistance as R21 as at 1K there s too much current flowing in the divisor (2mA) and this reduce the efficency of the VBEM.
As for Wesseling amp it almost work apparently but is difficult to service because once he try something the currents gets out of control, so here a few suggestions to help solve this issue.
First is to limit the OS max current with a 3V zener in parrallele with the VBEM the time it takes to fix this part, second are said limiting resistance in the IPS, from here he can manipulate the settings without much risks.
Not sure we are talking of the same part of the circuit, the drivers have nothing to do in the point i adressed, in your schematic it s Q9/Q11 who need those limiting resistances in their collectors.
As pointed by Dadod their influence is minimal as they are in serie with Q9/Q11 wich are current sources when seen from the TIS input, the 2K2 he suggest limit the current to 25mA in worst cases, that s 375mW for the transistors assuming a 50% duty cycle.
As said they are not strictly necessary but they improve the reliability, moreover when there s eventual faulty DC conditions that occur.
not R27? - 28 and 29
I measured and checked the color codes
R36&37 are both 150 ohms
R28&29 are both 115 ohms