I listened to my F6 at the lower starting bias for a few weeks then increased it but I cannot remember exactly how much maybe .7 without any heat problems using the store 4U case. I really could not detect any difference in the sound though using the higher bias.
The old saying about tightening a bandsaw blade is to tighten it until it breaks then back off some and it will be just right.
In an amp bias it up slowly and monitor the heat sinks keeping them as suggested 55C and 65C on the pins is what is good advice to follow.
The old saying about tightening a bandsaw blade is to tighten it until it breaks then back off some and it will be just right.
In an amp bias it up slowly and monitor the heat sinks keeping them as suggested 55C and 65C on the pins is what is good advice to follow.
Are you using the 9.1V zeners and 10Kohm for R7, R8 (or 6.2V zener and 3.3Kohm as per ZM mod?)? Are you finding the bias is drifting up and down or quite stable?
At some point in the future replace them with either 5.6V or 6.2V Zener.
After the amp has warmed up for an hour recheck bias, the mosfets have a positive temperature coefficient so they will continue to climb higher in bias till the heatsink reaches thermal equilibrium.
I built mine from the last schematic from Mr Pass with the only change was the 9.1 Zeners Jim ,6L6, recommended. I did not notice any drift and have not had any problems. My advice is to just enjoy it.
Nothing to learn. Just clamp the part in and press the button. They're all over ebay. It's not a DMM though. It doesn't read voltage.
MEGA328 Transistor Tester Diode Triode Capacitance ESR Meter mos PNP NPN L C R | eBay
I just want to say I do not want to say who is right or wrong in this debate because my knowledge of electronics is just the basics. I do not want to step on any ones toes. I just can say the way I built it, it came to life, no magic smoke to try and put back in, did not notice any drift problems, and sounds fantastic. You can always change things for the better later.
Hi Mike
Yes that simple is automatic detection of components and
after push button and short time delay it's show internal structure
( great feature not available on others testers ) and values of component on screen.
For such price a must have tool on bench it's real deal modern technology 🙂
Folks:
I'd appreciate your thoughts on a preamp to pair with an F6 that I'm helping a friend to build. He's up for the F6 project but neither of us have the time to devote to build a preamp to pair with it, so I'm keeping an eye on comparable quality equipment offered on ebay and audiogon.
Because my friend is primarily a vinyl hound, he'll need a MM phono stage. His total budget for the preamp and phono preamp is $600 (US). We'd prefer a unit that combines both; otherwise, I'm inclined to have him buy the DB Systems DB-8, which will leave about $400 for a line stage.
Lately, I've been focusing my attention on conrad johnson gear for him. There is a Sonographe SC22 (a c-j subsidiary), PV7 and PF1 that are all in his price range. Have you any thoughts on pairing a c-j preamp with an F6? Alternatively, what would you recommend?
Regards,
Scott
I'd appreciate your thoughts on a preamp to pair with an F6 that I'm helping a friend to build. He's up for the F6 project but neither of us have the time to devote to build a preamp to pair with it, so I'm keeping an eye on comparable quality equipment offered on ebay and audiogon.
Because my friend is primarily a vinyl hound, he'll need a MM phono stage. His total budget for the preamp and phono preamp is $600 (US). We'd prefer a unit that combines both; otherwise, I'm inclined to have him buy the DB Systems DB-8, which will leave about $400 for a line stage.
Lately, I've been focusing my attention on conrad johnson gear for him. There is a Sonographe SC22 (a c-j subsidiary), PV7 and PF1 that are all in his price range. Have you any thoughts on pairing a c-j preamp with an F6? Alternatively, what would you recommend?
Regards,
Scott
Phono - Hagerman Bugle 2
Line - O2 Headphone amp.
You cannot go wrong with those two devices. And you'll be well under budget.
Stick them in a fancy case if you desire, the circuits are totally worth it.
Line - O2 Headphone amp.
You cannot go wrong with those two devices. And you'll be well under budget.
Stick them in a fancy case if you desire, the circuits are totally worth it.
Hi Scott,
My F6 isn't finished yet, but I have used a Sonographe SC22 on the M2 (similar gain
to the F6). I have a small listening space and the gain and power of the pair
was more than adequate. Also, I preferred its phono input to a cheapie Creek
phono preamp I had tried (feeding the SC22's linestage).
The switches on my SC22 have gotten noisy over the years and probably need
some work. (I've had it for over 20 years). The alps pot is still smooth and quiet.
Cheers,
Dennis
My F6 isn't finished yet, but I have used a Sonographe SC22 on the M2 (similar gain
to the F6). I have a small listening space and the gain and power of the pair
was more than adequate. Also, I preferred its phono input to a cheapie Creek
phono preamp I had tried (feeding the SC22's linestage).
The switches on my SC22 have gotten noisy over the years and probably need
some work. (I've had it for over 20 years). The alps pot is still smooth and quiet.
Cheers,
Dennis
Jim:
The O2 is an interesting suggestion; customized to better suit my friend's situation, it'd be about $150 (plus shipping). Lacking RCA outputs is a minor aggravation. Also, it's missing any source selection capability and, though my friend will largely rely on his turntable, he may need more than one input. Still, well worth consideration.
The Bugle2 is also an option. I have a tricked-out FryKleaner (the original version) and have long been a fan of Jim Hagerman. We'll have to compare the DB-8 to the Bugle2; on the cosmetic front, they're neck and neck (i.e., functionally ugly).
Dennis:
Comforting information. Minor parts replacements on a c-j aren't out of the question. And it's hard not to love the warmth of the c-j house sound.
Thanks for the suggestions!
Regards,
Scott
I have completed a single Channel F6 Build.
R7 & R8 = 5K 1/2W Resistor (10K in parallel)
Zener = 6.2V (500mW)
Bias is very stable.
Cold Start = 0.5V in R2
30min = 0.6V in R2
DC offset = 0V
After reaching Heatsink equilibrium(30min) its stays in 0.6V and 0V offset +/- 0.5mV for so many hours.
Cheers.
R7 & R8 = 5K 1/2W Resistor (10K in parallel)
Zener = 6.2V (500mW)
Bias is very stable.
Cold Start = 0.5V in R2
30min = 0.6V in R2
DC offset = 0V
After reaching Heatsink equilibrium(30min) its stays in 0.6V and 0V offset +/- 0.5mV for so many hours.
Cheers.
just a general question - do u guys think its good engineering practice to have the PCBs parallel to the heatsinks like this ? The boards and all the components (caps!) on them are subject to all that heat and arguably, needlessly so.
This kind of construction probably makes a lot of sense for low bias amps but for full on class A - i wonder?
Note that I am using the same but can't help but notice that nelson's production amps are all laid out perpendicularly to the heatsinks....
This kind of construction probably makes a lot of sense for low bias amps but for full on class A - i wonder?
Note that I am using the same but can't help but notice that nelson's production amps are all laid out perpendicularly to the heatsinks....
Yeah I've thought about it. Either way it's going to get hot because of the hot air inside. My guestimate is there's probably a 5 degree difference between the way Nelson does it and the way we do it.
Probably electrolytic caps are the only thing that might be somewhat affected (shortened life).
Nelson doesn't really have any choice as his heatsinks have the extruded/cast bracket.
I'm not overly worried about it. It's easy to replace caps every 5 years if required (many Firstwatt amps don't even have electrolytic caps)
If it is a concern of any builder a small quite computer fan will make a big difference in heat inside the case. A little movement of air makes a lot of difference. I do not understand exactly why but most builders are afraid of a small fan as they are a snake.
Listen to most new computers and the noise level is a non issue.
I made the mistake on my 2nd build of buying heat sinks that are inadequate and the temperature rose to 70C quickly before I cut it off. I installed a fan and presto another build that runs 55C. I understand if the fan quits I will have failure but we are diy'ers. Install some more mosfets if it happens, fix the fan and life is good again.
Listen to most new computers and the noise level is a non issue.
I made the mistake on my 2nd build of buying heat sinks that are inadequate and the temperature rose to 70C quickly before I cut it off. I installed a fan and presto another build that runs 55C. I understand if the fan quits I will have failure but we are diy'ers. Install some more mosfets if it happens, fix the fan and life is good again.
I made the same mistake. I also noticed that even one fan makes a significant difference in temperature, however I ended up using a few since the noise is really insignificant when you take into account all the crap going on around my apartment.
I hope some builder on a budget notice this post if the cost of adequate heat sinks is keeping him from building a Pass amp. You can use a smaller case or smaller heat sinks if you design your build with a fan. I would rather not have one but it is certainly not a problem to use one if you want to. Zen Mods baby sitter is another option. It is a platform with a fan in it that the amp sets on that can be used with any amp. Easy to find information about this on this site.