Re: Re: New born
Hi,
I finished twin balanced f4 yesterday evening. I couldn’t bear the tension, couldn’t wait till the weekend.
First impressions: fantastic! Deep stage. Very clean sound and very good resolution. Finally I can listen with real pleasure music difficult to reproduce before. I discovered new sounds, details, backgrounds absent before.
Gentlemen, chapeau bas, here is a genius: Mr. Nelson Pass!
Remembering problems I had with reaching super symmetry at one of variations of exceptionally simple SOZ (thermal problems with potentiometers and probably hidden cold solders), I was afraid about f4 symmetry – a lot of electronic parts. Now is okay, I don’t know what will be with higher levels of input signals, now my f4’s are driven by DAC only. But symmetry is perfect even in spite of accidental parts I collected. For instance all 12 IRFP240 are matched by myself for 30mV (from bunch of 30 pieces), IRFP9240 are better: I got 12 matched for 20mV. Low power resistors are 1%, no-name. C1 and C2 capacitors are accidental (Philips, 105oC).
Only Q1 and Q2 have been professionally matched (all for 8.8-9.7 mV). I would like to thank Mr. Erno Borbely who properly decipher my intentions and perfectly realized my order.
I would like to thank Nelson Pass for his design, Ian Studley for Peter Daniels boards and all of you for advices.
What next:
I must replace old PS capacitors (8 years of work at SOZ), I discovered one of them is slightly swelled causing a little hum (one of supply voltages disappears much faster).
And build pre-amp.
Best Regards,
Andrzej
Andrzej Sochon said:
Hi,
I finished twin balanced f4 yesterday evening. I couldn’t bear the tension, couldn’t wait till the weekend.
First impressions: fantastic! Deep stage. Very clean sound and very good resolution. Finally I can listen with real pleasure music difficult to reproduce before. I discovered new sounds, details, backgrounds absent before.
Gentlemen, chapeau bas, here is a genius: Mr. Nelson Pass!
Remembering problems I had with reaching super symmetry at one of variations of exceptionally simple SOZ (thermal problems with potentiometers and probably hidden cold solders), I was afraid about f4 symmetry – a lot of electronic parts. Now is okay, I don’t know what will be with higher levels of input signals, now my f4’s are driven by DAC only. But symmetry is perfect even in spite of accidental parts I collected. For instance all 12 IRFP240 are matched by myself for 30mV (from bunch of 30 pieces), IRFP9240 are better: I got 12 matched for 20mV. Low power resistors are 1%, no-name. C1 and C2 capacitors are accidental (Philips, 105oC).
Only Q1 and Q2 have been professionally matched (all for 8.8-9.7 mV). I would like to thank Mr. Erno Borbely who properly decipher my intentions and perfectly realized my order.
I would like to thank Nelson Pass for his design, Ian Studley for Peter Daniels boards and all of you for advices.
What next:
I must replace old PS capacitors (8 years of work at SOZ), I discovered one of them is slightly swelled causing a little hum (one of supply voltages disappears much faster).
And build pre-amp.
Best Regards,
Andrzej
No room for more biasing higher than 1.5 Amps ?
Sensible practice is placing output devices on the sink and checking for a short one-by-one.
(the state of Oregon is located above California, Pacific time zone, 10 hour difference with central european time. Means Woody likely still hits the sack earlier than some in this time zone)
Sensible practice is placing output devices on the sink and checking for a short one-by-one.
(the state of Oregon is located above California, Pacific time zone, 10 hour difference with central european time. Means Woody likely still hits the sack earlier than some in this time zone)
jacco vermeulen said:
Hi Jacco,
My heatsinks are as you see at my avatar, approx. 245(H) x 200(W) mm, so there is a lot of space for additional MosFets or higher biasing, but the heatsinks are no black. MosFets are located on two opposite side heatsinks walls, front and back walls are free and are separated by oak wood. I set 260mV bias and after 2 hours of listening music I got 61C, so I think it is better to go down to 250 mV and make top cover more ventilated. And blacken side walls.
Best Regards,
a.
Bias point
Hello Andrzej:
I too struggled with the bias setting. I originally set the bias at 250mv when the amp was cold. I let it run for an hour or so and checked the setting, it had drifted to +-300mv. The amp was too hot to hold for more than a few seconds. I reset the bias to 200mv with the amp warm, it seems to be fine now. I think I can could raise the bias a bit but I am not sure if what the advantage would be.
I am making a pre amp right now and once completed I will be able to decide if the bias needs to go up a bit.
A novice question for the group:
What would be the minimum bias setting and what are the indicators of it being set too low?
Thanks for the help
Hello Andrzej:
I too struggled with the bias setting. I originally set the bias at 250mv when the amp was cold. I let it run for an hour or so and checked the setting, it had drifted to +-300mv. The amp was too hot to hold for more than a few seconds. I reset the bias to 200mv with the amp warm, it seems to be fine now. I think I can could raise the bias a bit but I am not sure if what the advantage would be.
I am making a pre amp right now and once completed I will be able to decide if the bias needs to go up a bit.
A novice question for the group:
What would be the minimum bias setting and what are the indicators of it being set too low?
Thanks for the help
Re: Bias point
Hi,
As far as I understand voices on f4 Forum: lower bias may cause distortions at lower frequencies.
I think that for f4 approx 0.5 – 0.6A bias, Vds/Vgs voltages and temperature >50C define the best point at IRFP240/9240 characteristic curve resulting in optimal compromise between the largest output amplitude (large clipping margin) and lowest distortions.
The best formula for novices: proceed as close as possible to the Nelson Pass First Watt model F4 Operation and Service Manual:
“Output device bias is approximately .43 amps per device, which measures 200 mV across the .47 ohm source resistors....Cold, bias is adjusted low at 130 mV and readjusted as the amplifier warms up...The proper value is achieved after 1 hour with the heat sinks at about 50 deg C...”
So yours 200mV is perfect, now you can start to experiment observing bass at lower bias.
rgds, a.
SCD said:
Hi,
As far as I understand voices on f4 Forum: lower bias may cause distortions at lower frequencies.
I think that for f4 approx 0.5 – 0.6A bias, Vds/Vgs voltages and temperature >50C define the best point at IRFP240/9240 characteristic curve resulting in optimal compromise between the largest output amplitude (large clipping margin) and lowest distortions.
The best formula for novices: proceed as close as possible to the Nelson Pass First Watt model F4 Operation and Service Manual:
“Output device bias is approximately .43 amps per device, which measures 200 mV across the .47 ohm source resistors....Cold, bias is adjusted low at 130 mV and readjusted as the amplifier warms up...The proper value is achieved after 1 hour with the heat sinks at about 50 deg C...”
So yours 200mV is perfect, now you can start to experiment observing bass at lower bias.
rgds, a.
carpenter said:I'm off with a shoulder injury (strained rotater cuff).
I just like to hang with the men whenever I can...
Hi Carpenter,
wow, pain, I am sorry to hear that; can you walk and do typical daily activities or you stay in bed watching TV and surfing Internet. What happened? An accident? To small ax, to heavy transformer, too much
screwdriver operations during bias/offset experiments?
Wishing you a good health,
Andrzej
I have the first run of boards that Peter Daniel made for this project and am about to order the parts to do the stuffing. I know that the current BOM is a little different than when those boards were created...but has the circuit layout changed?
I apologize in advance for being lazy and not studying before asking my question, and thanks to any and all who respond,
C
I apologize in advance for being lazy and not studying before asking my question, and thanks to any and all who respond,
C
Andrzej Sochon said:
Thanks for the concern.
It's been 4 weeks, and I'm much better. Shoulder rotator cuff pain is truly awful, couldn't move my arm what-so-ever the first week. I felt as if I were in a straight-jacket. Quite claustrophobic! I'm so happy to be over the hump--there is light at the end of the tunnel... Hey, there's the silver lining: I got to spend a ton of time with you guys and my audio projects. I even hired my cousing to help me convert the rear porch into my new hobby room: John's DIY audio--no girls allowed
Unless they're on the internet, haha. 
Nice, There is nothing better than dedicated man space. Mine has the stereo, soldering bench, kegerator, and stash of assorted high octane homebrew beverages. No windows and concrete walls, but in the dark it all sounds better anyway.
Sorry to hear about your shoulder. Did you have to have surgery, or did they just put you on rest?
Sorry to hear about your shoulder. Did you have to have surgery, or did they just put you on rest?
carpenter said:
Thanks for the concern.
Hey, there's the silver lining: I got to spend a ton of time with you guys and my audio projects. I even hired my cousing to help me convert the rear porch into my new hobby room: John's DIY audio--no girls allowed
woodie .....
you're my Idol
DaveM said:Nice, There is nothing better than dedicated man space. Mine has the stereo, soldering bench, kegerator, and stash of assorted high octane homebrew beverages. No windows and concrete walls, but in the dark it all sounds better anyway.
Sorry to hear about your shoulder. Did you have to have surgery, or did they just put you on rest?
Now, that's what I call home away from home! Good job, Dave. Mine's little but cute (the hobby room, I say, the hobby room). 8 feet by 16 feet.
I'll bet that someone could start a thread on proper man-spaces. When mine's finished, I'll go first...unless someone beats me to the punch.
No surgery
just lots of rest and the standard rehab. I'm beginning to learn that carpentry is for the young and the restless.
