Hey Folks,
after a year or so of gathering parts (most via this forum) I am finally finished with my first First Watt amp...an F1. I figured I would start with the first of the series and go from there. This will be the first time i've started up an amp so the start-up and biasing process is new to me. Before I 'plug and pray' would anyone care to offer suggestions on last minute checks, double checks etc. ?
Also to clarify my understanding do i need to connect anything to the inputs to start the biasing procedure ? Any help and/or suggestions would be greatly appreciated.
Thanks, Daniel.
P.s. I am trying to post pics but with no luck.
after a year or so of gathering parts (most via this forum) I am finally finished with my first First Watt amp...an F1. I figured I would start with the first of the series and go from there. This will be the first time i've started up an amp so the start-up and biasing process is new to me. Before I 'plug and pray' would anyone care to offer suggestions on last minute checks, double checks etc. ?
Also to clarify my understanding do i need to connect anything to the inputs to start the biasing procedure ? Any help and/or suggestions would be greatly appreciated.
Thanks, Daniel.
P.s. I am trying to post pics but with no luck.
Hmmm...bias issues
Well the "plug and pray" approach thankfully did not result in smoke or fire. Unfortunately though I seem to be having issues setting the bias.
1)P1 only gives me a range of 18.5v to 19.1v across the drains relative to ground. Should be set at 13.8.
2)Drain of Q7 is a measly .575v instead of 3v relative to ground.
3)The voltage across r27-r30 is right where it should be at .59 v.
4)The gates of Q1 and Q2 are at 5.75v instead of the specified 7v.
Any help would be greatly appreciated.
Daniel
P.s. The chassis is an ebay surplus from China. Looks great from about 10ft away.
Well the "plug and pray" approach thankfully did not result in smoke or fire. Unfortunately though I seem to be having issues setting the bias.
1)P1 only gives me a range of 18.5v to 19.1v across the drains relative to ground. Should be set at 13.8.
2)Drain of Q7 is a measly .575v instead of 3v relative to ground.
3)The voltage across r27-r30 is right where it should be at .59 v.
4)The gates of Q1 and Q2 are at 5.75v instead of the specified 7v.
Any help would be greatly appreciated.
Daniel
P.s. The chassis is an ebay surplus from China. Looks great from about 10ft away.
Not enough positive voltage being applied to the Gates of
Q1/Q2. Make sure the zeners aren't conducting, or the caps
aren't leaking at the input, or the values of r5-8 are correct.
No way a functioning Q1 and Q2 will only show 5.75 when the
input bias network is driven by 19V, unless something is
drawing the current off the input.
😎
Q1/Q2. Make sure the zeners aren't conducting, or the caps
aren't leaking at the input, or the values of r5-8 are correct.
No way a functioning Q1 and Q2 will only show 5.75 when the
input bias network is driven by 19V, unless something is
drawing the current off the input.
😎
Thank you Mr. Pass
Good morning, and thanks for taking the time to respond. I am getting a reading of .75v dc across all 4 of the zeners. (?) The values of r5-8 appear correct. As for checking that the caps arent leaking at the input could i get a little play-by-play as to how to go about it ?
Thanks again Mr. Pass,
Daniel.
P.S. I am starting to think that I'm in over my head...
Good morning, and thanks for taking the time to respond. I am getting a reading of .75v dc across all 4 of the zeners. (?) The values of r5-8 appear correct. As for checking that the caps arent leaking at the input could i get a little play-by-play as to how to go about it ?
Thanks again Mr. Pass,
Daniel.
P.S. I am starting to think that I'm in over my head...
Doh !
Wow...you guys are good. Zeners are indeed backa@#wards. Now that i have them desoldered should i reinstall correctly, get new ones and install or leave them out entirely ?
Regards, Daniel.
Wow...you guys are good. Zeners are indeed backa@#wards. Now that i have them desoldered should i reinstall correctly, get new ones and install or leave them out entirely ?
Regards, Daniel.
Frankenstein lives...
Thank you Mr. Flemming. After switching the orientation of the zeners the amp now biases steadily at 13.8v . Before hooking this beast up to my C&C Abbys I have two more questions...
1) since i am not running balanced inputs do i need to make any allowances (ie jumpers) for this on the board ?
2) In reference to the differential voltage (50mV) seen by the loadspeaker , where do i take this measurement ?
Its a pretty cool world where people from all over the globe can colaborate and help one another via group buys, making PCB's, BOM's, and troubleshooting. A special thank you to Mr. Pass for sharing your visions and making all of this possible.
Regards, Daniel.
Thank you Mr. Flemming. After switching the orientation of the zeners the amp now biases steadily at 13.8v . Before hooking this beast up to my C&C Abbys I have two more questions...
1) since i am not running balanced inputs do i need to make any allowances (ie jumpers) for this on the board ?
2) In reference to the differential voltage (50mV) seen by the loadspeaker , where do i take this measurement ?
Its a pretty cool world where people from all over the globe can colaborate and help one another via group buys, making PCB's, BOM's, and troubleshooting. A special thank you to Mr. Pass for sharing your visions and making all of this possible.
Regards, Daniel.
Measure the offset across the speaker terminals, prefereably
with a load.
As to inputs, this design really likes balanced inputs. You should
make provision for them and try to use it that way in the
future.
😎
with a load.
As to inputs, this design really likes balanced inputs. You should
make provision for them and try to use it that way in the
future.
😎
What Ebay user did you get the chassis from I have run across some from Johnango they are new from china but more money than I would like to spend
as I am hoarding parts for an F1 as well.
Regards you all, Elwood
as I am hoarding parts for an F1 as well.
Regards you all, Elwood
Thanks again Mr Pass,
Im getting 30mv across the right channel speaker terminals and 45mv across the left terminals. The amp has amazing depth to the soundstage but is surprisingly bass shy with my Abbys. (?) I'll run it in for a while today and see if it fills out. Paired with my 24v Aikido i dont seem to be getting enough gain.
Elwood, the amp chassis came from "biglawhk". They are pretty cheap but the shipping is almost a deal killer. I elected to wait 3-4months for ground shipping to make it more reasonable. Air freight is almost the same price as the chassis.
Regards, Daniel.
Im getting 30mv across the right channel speaker terminals and 45mv across the left terminals. The amp has amazing depth to the soundstage but is surprisingly bass shy with my Abbys. (?) I'll run it in for a while today and see if it fills out. Paired with my 24v Aikido i dont seem to be getting enough gain.
Elwood, the amp chassis came from "biglawhk". They are pretty cheap but the shipping is almost a deal killer. I elected to wait 3-4months for ground shipping to make it more reasonable. Air freight is almost the same price as the chassis.
Regards, Daniel.
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