F5 Voltage question
Hi Guys,
I have just built an F5 and it biases up OK with no or very little DC offset once warmed up, and sounds very good with no issues.
However i noticed that when measuring the DC supply to the Amp PCBS i get +21.5v/-21.5v on both my PCBS (I run them as a monoblocks pair)
The offload PSUS give 24.5v (when not connected to the amp PCB and all PSU parts are the same values as papas design except i used smaller value bleeder resistors cuz that's all i had to hand !)
i was under the impression that most people got from 23.5 v to 24v on there creations?-- just wondering if this is an issue-- but it dosent sound like it when listening to music.
thanks boys
johnny
Hi Guys,
I have just built an F5 and it biases up OK with no or very little DC offset once warmed up, and sounds very good with no issues.
However i noticed that when measuring the DC supply to the Amp PCBS i get +21.5v/-21.5v on both my PCBS (I run them as a monoblocks pair)
The offload PSUS give 24.5v (when not connected to the amp PCB and all PSU parts are the same values as papas design except i used smaller value bleeder resistors cuz that's all i had to hand !)
i was under the impression that most people got from 23.5 v to 24v on there creations?-- just wondering if this is an issue-- but it dosent sound like it when listening to music.
thanks boys
johnny
Since you have one channel working I assume you know the biasing routine. But just in case here is what I have found works best after having done this numerous times.
Biasing should always start with the pots set to zero and and making small turns. You alternate the two pots in the direction that increases bias and keeps DC offset down. You need 3 multimeters connected to the two resistors and the speaker terminals, so you can keep an eye on all three numbers. Set it to about 400mv first and leave it for an hour and then set it to where you want it.
Incidentally if this doesn't work, I would recheck the soldering on the board. My f5 after about a year of flawless operation suddenly started fluctuating bias on one channel. I replaced all the semis on the board as well as the pots. No luck. Finally I just reheated every solder point on the board and that fixed it.
Thanks for your responses.
Yes, I was able to bias the right channel with that procedure.
On the left channel, P1 and P2 run out of turns at about 0.13V across R11 and R12.
I have desoldered, measured, and replaced P1 and P2. They are 5Kohm trimmers as they should.
Any ideas on what to do next?
Yes, I was able to bias the right channel with that procedure.
On the left channel, P1 and P2 run out of turns at about 0.13V across R11 and R12.
I have desoldered, measured, and replaced P1 and P2. They are 5Kohm trimmers as they should.
Any ideas on what to do next?
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Here's the link to 6L6's excellent build thread where he had the same problem.Although he was able to bias higher than you have.Hope it turns out to be as simple as changing the resistors.I had to do the same on my F5T build.
http://www.diyaudio.com/forums/pass-labs/188691-illustrated-guide-building-f5.html
http://www.diyaudio.com/forums/pass-labs/188691-illustrated-guide-building-f5.html
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Hi there, having condemned the F5 in previous posts as it really didn't like my far less than sensitive B&W DM683s, I'm now considering building another pair for quite a different application.
I've already got an Aleph 4, which at 100W / Channel is a meaty beast and I'm not giving it up for no-ones money.
I'm considering building a tri-amp active speaker - based on the Wilmslow Audio Prestige Platinum, you will see thread of its build also in these pages.
So, I need 6 x capable amplifiers.
I've already got 2 x D White Hi Quality MOS-FET 100W amps. Not as good as any of the Pass offerings but still very good. I was considering giving them the duty of driving the bass driver (ie Sub 400Hz).
The mid driver (400Hz - 3800Hz) I'm going to give to the Aleph 4.
OK, both those amps are 100W, the tweeter (3800Hz - 40kHz) needs only 10W or so which I thought the F4 or F5 would handle nicely.
Anyone got any thoughts on my thoughts ?
I've already got an Aleph 4, which at 100W / Channel is a meaty beast and I'm not giving it up for no-ones money.
I'm considering building a tri-amp active speaker - based on the Wilmslow Audio Prestige Platinum, you will see thread of its build also in these pages.
So, I need 6 x capable amplifiers.
I've already got 2 x D White Hi Quality MOS-FET 100W amps. Not as good as any of the Pass offerings but still very good. I was considering giving them the duty of driving the bass driver (ie Sub 400Hz).
The mid driver (400Hz - 3800Hz) I'm going to give to the Aleph 4.
OK, both those amps are 100W, the tweeter (3800Hz - 40kHz) needs only 10W or so which I thought the F4 or F5 would handle nicely.
Anyone got any thoughts on my thoughts ?
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I assume you have two transformers rather than a split primary for 110V (parallel) or 240V (series) operation; you will need a soft start of some description.
I concur with 6L6, Keep It Simple (KISS).
AndrewT's suggestion is also a good one, but only recommend if you have lots of experience dealing with the main supply, defiantly not for novices.
As a follow up.
I have a few soft starts and always use series connected resistors in the limiting positions.
I vary between 3 off 20r 5W and 7 off 20r 5W depending on the VA of the transformer.
With any of these I could substitute a power NTC for any single resistor. The more NTCs the better the soft starter.
If I could afford it, I would use CL60 exclusively in my relay bypassed softstarters, but they are just too expensive compared to my 10r and 20r 5W resistors.
I have a few soft starts and always use series connected resistors in the limiting positions.
I vary between 3 off 20r 5W and 7 off 20r 5W depending on the VA of the transformer.
With any of these I could substitute a power NTC for any single resistor. The more NTCs the better the soft starter.
If I could afford it, I would use CL60 exclusively in my relay bypassed softstarters, but they are just too expensive compared to my 10r and 20r 5W resistors.