Yes I have tested them all since. They appeared to be ok. I actually made that mistake with the other channel, so it is not relevant presently. I will double check it when I get back to that channel.
P2 is 500 ohms. I let it warm, up last night for about an hour and the bias was virtually identical.
P2 is 500 ohms. I let it warm, up last night for about an hour and the bias was virtually identical.
I always find it near impossible to really get things across in emails. The worst part is when your words are mi-interpreted and someone gets offended or angry. Ahhh communication skills. One of my true weak points.
Is the lowest offset achieved when P2 is at its highest resistance or its lowest resistance?
And which polarity is the offset?
And which polarity is the offset?
P2 is to it's lowest setting and the Bias is Positive. I verified the value of R22 is 750R.
The long lead resistors are simply parts I changed out and didn't set close to the board, as I had a feeling I might be changing them again.
The long lead resistors are simply parts I changed out and didn't set close to the board, as I had a feeling I might be changing them again.
Hi Dave,
Can I suggest you isolate the Power FETs and measure the various voltages on the PCB (see my post #1490)to confirm all is OK with the main PCB before connecting the Power FETs ?
Best Regards
S K
Can I suggest you isolate the Power FETs and measure the various voltages on the PCB (see my post #1490)to confirm all is OK with the main PCB before connecting the Power FETs ?
Best Regards
S K
skseah said:
I remember reading that post. Sure seems like a smart way to double check everything.🙂
Perhaps you could discuss, in depth, how you arrived at those figures. I.e., where you take the measurements, math, etc.
Hi,
1. Connect the multimeter in line with the positive supply to measure the current drain by the PCB (i.e. without the Power FETs). The measured current should be around 11-12mA (LED 2.2mA + K170/J74 7-8mA, others 1mA). If the current is too high, your jfet, or TL431, diodes or zener may be reversed.
2. Use your probe from your multimeter to measure the voltage drop across each for the 2 10ohms resistors (R3 & R4). The voltage drop for each of them should be 70 to 80mV, i.e 7 to 8mA (70mV / 10 ohms).
3. Check the 10ohm resistor and C1/C2 point to see if the voltage is close to ground 0V.
4. Adjust P1 to full anti-clockwise, the voltage between 240 gate and 9240 gate (i.e. at R10 and R13, either side will do) should be >8.5V. Adjust P1 to full clockwise, the voltage between 240 gate and 9240 gate should not more than 7.5V. Keep the P1 full clockwise position which means that the bias is minimum. You can later adjust this to increase the bias.
5. At this stage, there is no need to adjust P2 for DC offset at output as there is no power mosfet and bias and the offset has to be adjusted with all that.
6. Then the pcb is ready to be mount on the heat sink and solder all the power mosfet. Make sure that 240 and 9240 is at correct position.
Best Regards
S K
1. Connect the multimeter in line with the positive supply to measure the current drain by the PCB (i.e. without the Power FETs). The measured current should be around 11-12mA (LED 2.2mA + K170/J74 7-8mA, others 1mA). If the current is too high, your jfet, or TL431, diodes or zener may be reversed.
2. Use your probe from your multimeter to measure the voltage drop across each for the 2 10ohms resistors (R3 & R4). The voltage drop for each of them should be 70 to 80mV, i.e 7 to 8mA (70mV / 10 ohms).
3. Check the 10ohm resistor and C1/C2 point to see if the voltage is close to ground 0V.
4. Adjust P1 to full anti-clockwise, the voltage between 240 gate and 9240 gate (i.e. at R10 and R13, either side will do) should be >8.5V. Adjust P1 to full clockwise, the voltage between 240 gate and 9240 gate should not more than 7.5V. Keep the P1 full clockwise position which means that the bias is minimum. You can later adjust this to increase the bias.
5. At this stage, there is no need to adjust P2 for DC offset at output as there is no power mosfet and bias and the offset has to be adjusted with all that.
6. Then the pcb is ready to be mount on the heat sink and solder all the power mosfet. Make sure that 240 and 9240 is at correct position.
Best Regards
S K
Well, Last night I swapped out the R22 for a slightly lower value. So, with 7K on R9 and 600R of R22, I was able to get 200mV of bias and zero DC offset. Unless there are concerns about these changes to the operation of the amp, I guess I am all set and up and running.
Thanks for all of the help.
DaveM
Thanks for all of the help.
DaveM
DaveM
Way to keep at it.
One of the reasons for me asking if the MOSFETS were matched is I have seen low 3.xx and some high 4.xx. P2, 500 ohms, is not much adjustment. In Nelsons service manual it states that all MOSFETS are matched for Vgs to .02V. Just something for others to keep in mind when using the r0 6/4/07 schematic and the banks of devices are not very closely matched. But then again all you have to do is make some adjustments like Dave did!
By the way was R8 22K or 27K?
Way to keep at it.
One of the reasons for me asking if the MOSFETS were matched is I have seen low 3.xx and some high 4.xx. P2, 500 ohms, is not much adjustment. In Nelsons service manual it states that all MOSFETS are matched for Vgs to .02V. Just something for others to keep in mind when using the r0 6/4/07 schematic and the banks of devices are not very closely matched. But then again all you have to do is make some adjustments like Dave did!
By the way was R8 22K or 27K?
My gut was right, but it was hard to just leap and make the change assuming that I know what I am doing. The learning curve is steep for those with mechanical backgrounds. I ordered the parts to do both channels with Vishay's. Work was putting in a next day order to Mouser, so I should be able to get them both up and running tomorrow night. Yes!!
Thanks Carpenter for you support and advice. Nelson, this board and community have enabled me to accomplish something that I would never have been able to do on my own. I now have a Pearl phono, F-4 power amp, and a J-BOZ pre. Too Cool. Now on to cases and a
Thanks Carpenter for you support and advice. Nelson, this board and community have enabled me to accomplish something that I would never have been able to do on my own. I now have a Pearl phono, F-4 power amp, and a J-BOZ pre. Too Cool. Now on to cases and a
Hmmmm , would John Broskie's tube Aikido pre amps work well with the F4? It seems that they have a lot of voltage output, that could surely be raised to a point that it could drive the F4 full out.
http://glass-ware.stores.yahoo.net/newhardware.html
Seems that he and others have done similar setups to the F4 hooked to the Aikido. The Moskido is also pretty much on the same track..
How about using them with a balanced F4? can that be done with more boards?
http://glass-ware.stores.yahoo.net/newhardware.html
Seems that he and others have done similar setups to the F4 hooked to the Aikido. The Moskido is also pretty much on the same track..
How about using them with a balanced F4? can that be done with more boards?
Aikido + F4
Hello Mr Variac:
I have been thinking along the same track. I have done a bit of research and have not come across anything to steer me away from this line of thinking. My skills are not so good in the design part so I am hoping the Moskido or the Zen kido folks will be able to lead the way.
I suspect we will have a very fine marraige with the F4 and an Aikido pre amp. And think of the options for tube choices with the Aikido. This is going to be wonderful
Hello Mr Variac:
I have been thinking along the same track. I have done a bit of research and have not come across anything to steer me away from this line of thinking. My skills are not so good in the design part so I am hoping the Moskido or the Zen kido folks will be able to lead the way.
I suspect we will have a very fine marraige with the F4 and an Aikido pre amp. And think of the options for tube choices with the Aikido. This is going to be wonderful
Variac said:
seems that my email with few words is coming your way ....... in few minutes ...... if my dreky WiFi allow that ....
I heard SY's pre at the show, admittedly under the not-perfect conditions it sounded GREAT. I saw the insides and it has hardly any parts- only a handful of components... Knowing SY's philosophy, it will be very cheap to make- that's good for poor people like myself..
At the moment it ONLY works with a balanced setup so you need two F4's. Lucky I have them!!
Actually , it was thinking about Sy's pre and that's when I thought about the Aikido being another pre of interest- although much more expensive to make probably-especially for balanced..
Still, the Aikido has an established reputation as very very good...
At the moment it ONLY works with a balanced setup so you need two F4's. Lucky I have them!!
Actually , it was thinking about Sy's pre and that's when I thought about the Aikido being another pre of interest- although much more expensive to make probably-especially for balanced..
Still, the Aikido has an established reputation as very very good...
Your positive comments from the show, low parts counts, and balanced operation are all of interest.
Thanks Mark,
C
Thanks Mark,
C
Variac said:
Absolutely, that's been my plan all along - balanced Aikido linestage into balanced F4's.
In the Aikido, the first pair of tubes determines the overall gain(minus a small amount) while the second sets the output impedance. John B supplied this spec page which lists mosts of the possible tube combinations and the resulting gain/impedance output.
Since Nelsen P. has stated that 14V+ preamp output is necessary for full volume, just about any of the tubes listed with an input gain(not dB's) over 8-10 would work - assuming a standard 2V source output.
If you want an optimal ~600 ohm balanced output without using transformers, then 12AU7's run at 250V w/ resistors R15 of 79899 and R16 of 100k would yield and output of 601 ohms.
I guess if it isn't used with balanced amps then more gain is needed...
We, Mr. Moebius, please keep us informed on your final setup. It turns out that the Aikido isn't very expensive in fact..
Appropriately I think that SY is at the Triode Fest in Europe somewhere. Hope he gives us some info on his return..
We, Mr. Moebius, please keep us informed on your final setup. It turns out that the Aikido isn't very expensive in fact..
Appropriately I think that SY is at the Triode Fest in Europe somewhere. Hope he gives us some info on his return..