Newest Version
ty adeS!
But I'm looking for the latest Version 1.04. Your link points to V1.02. Ofc I could update it, but no need to reinvent the wheel.
ty adeS!
But I'm looking for the latest Version 1.04. Your link points to V1.02. Ofc I could update it, but no need to reinvent the wheel.
The F8 is populated and some testing done. The offset is -240mV. Turning the trimmer does almost nothing. I tried both ways, using a 200R trimmer alone or Sonal's suggestion of using a 1K trimmer and two 150R SMD resistors. Pretty much the same results. Turning the trimmer causes the offset to vary but then return to -140mV~. Something else is off somewhere. I may try to create a Spice file and see if I can replicate it.s
It plays sine and Square waves fine. A slight overshoot but it looks fast.
It plays sine and Square waves fine. A slight overshoot but it looks fast.
Attachments
Nice fast work Terry. I hate it when the trimmer doesn't have an effect. My recent problems with large offset that wouldn't change on Quasi was fixed after Aksa said to delete a resistor and change values on others. So I think something must be off in the concept. Good luck.
Maybe Mr Mile can take a look at this again, but it seems to me having the offset trim as part of the feedback loop is not going to work as that is exactly why it seems to move then self correct back. DC offset needs to be done on the DC bias current going down 2k2 resistor feeding the diamond buffer. Replace one of the 2k2 with a 500R pot (wiper connected to one end) and a 2k resistor. Bypass the old pot. That should fix it, I think. That's how I set up the DC offset correction on CFH7 and in the sim, the pot works to adjust the offset correctly. Just a suggestion of you want to try quickly.
Maybe Mr Mile can take a look at this again, but it seems to me having the offset trim as part of the feedback loop is not going to work as that is exactly why it seems to move then self correct back. DC offset needs to be done on the DC bias current going down 2k2 resistor feeding the diamond buffer. Replace one of the 2k2 with a 500R pot (wiper connected to one end) and a 2k resistor. Bypass the old pot. That should fix it, I think. That's how I set up the DC offset correction on CFH7 and in the sim, the pot works to adjust the offset correctly. Just a suggestion of you want to try quickly.
Last edited:
Try xrk sugestion from previus post, it's work on AX17 and BA1200... I use dc offset like in hiraga for F8 without test and can be wrong way to adjust offset.
There is no diamond buffer in VSSA just simetryc singleton input stage, F8 use diamond buffer.
Here's another feedback on the DC-offset circuitry to keep in mind, in general, any time a trimmer is used in an amp where its work is to adjust some sort of DC-bias/offset etc., its a good practice to make a fool-proof design from the beginning as 2 additional resistors is so much cheaper than expansive OP transistors, loudspeakers.
In the present design the center/wiper leg should be outfitted with two catch-up resistors, each resistor connected to the center leg, one resistor to one end of the trimmer, the other resistor to the other side of the trimmer.
In a similar fashion are trimmers in a Vbe multiplier put between base and emitter, but Never between base and collector, otherwise, in case the wiper goes loose the bias will spike risking frying the output stage.
In the present design the center/wiper leg should be outfitted with two catch-up resistors, each resistor connected to the center leg, one resistor to one end of the trimmer, the other resistor to the other side of the trimmer.
In a similar fashion are trimmers in a Vbe multiplier put between base and emitter, but Never between base and collector, otherwise, in case the wiper goes loose the bias will spike risking frying the output stage.
Yes, you are right - my eyes see the crossed wires and assume one thing but now see that the diamond buffer goes to another small signal complementary transistor whereas in VSSA it goes straight to the VAS/driver stage as their are 2 less transistors. I hope moving the trimmer to the 2k2 leg helps.
Thanks
Hy mr. Mille i have 4 pairs of 2sa1264 2sc3181 recovered from old amplifiers. What project do you recommend for these transistors? I want to make a stereo amplifier, two pairs per channel or a mono amplifier with four pairs. Thanks in advance and sorry for my english.
An externally hosted image should be here but it was not working when we last tested it.
F8 saga continues
Hi Guys,
OK, this is what I did. I pulled the trimmer and installed two 150R SMD resistors in its place. Then I pulled R5 and replaced it with a 25k trimmer. This allowed me to adjust the offset to zero. However, the offset is very rail voltage sensitive. A volt or two up or down of the rails makes a pretty noticeable difference in the offset. The offset also jumps around quite a bit with music playing. Maybe as much as +-40mVdc. Maybe this is just how diamonds respond, I don't know.
It sounds very good with no sign of oscillation. Once I get Mile's blessings, I will post some scope shots and modify the other channel so I can listen in stereo.
Blessings, Terry
Hi Guys,
OK, this is what I did. I pulled the trimmer and installed two 150R SMD resistors in its place. Then I pulled R5 and replaced it with a 25k trimmer. This allowed me to adjust the offset to zero. However, the offset is very rail voltage sensitive. A volt or two up or down of the rails makes a pretty noticeable difference in the offset. The offset also jumps around quite a bit with music playing. Maybe as much as +-40mVdc. Maybe this is just how diamonds respond, I don't know.
It sounds very good with no sign of oscillation. Once I get Mile's blessings, I will post some scope shots and modify the other channel so I can listen in stereo.
Blessings, Terry
Offset jumping around with music playing is not a real problem. That would happen on any amp. Offset is only measurable with zero input or input grounded, no?
Glad it plays music and sounds good. Strange how rail fluctuations cause offset changes. Unless rail fluctuations were asymmetric.
Glad it plays music and sounds good. Strange how rail fluctuations cause offset changes. Unless rail fluctuations were asymmetric.
Not true. Most of my amps vary only slightly while playing music. On this amp I see a jump in offset just by playing a sine wave.
The rails are symmetrical.
+/-50mV offset fluctuacions is ok without DC servo... can you post scope measurements?
Regards