Hey everyone!
so, after some days at 90% (and some smiles dure to the already fabulous sound) I adjusted yesterday evening to 600mV. After hours of waiting till thermal equilibrium is reached, i was happy with an offset around 0.5/mV and 597mV/595mV source voltage... So quite nice I think...
Today I just wanted to be clear and measured the offset/bias when starting from cold. So... I don't know, maybe thats normal or my thermistors have something but at the beginning the voltage at the source resistor goes up to ~740mV (????) and I have an offset of 2 and 13 mV. After one minute its already at 675mV and 6/7mV... now it slowy decreases... after 15minutes i have 619mV and 5/3mV and after 45 minutes i am at 603mV and 3.3/ 0.1mV.
So is this normal?
Hope you can help me! All the best,
Philip
so, after some days at 90% (and some smiles dure to the already fabulous sound) I adjusted yesterday evening to 600mV. After hours of waiting till thermal equilibrium is reached, i was happy with an offset around 0.5/mV and 597mV/595mV source voltage... So quite nice I think...
Today I just wanted to be clear and measured the offset/bias when starting from cold. So... I don't know, maybe thats normal or my thermistors have something but at the beginning the voltage at the source resistor goes up to ~740mV (????) and I have an offset of 2 and 13 mV. After one minute its already at 675mV and 6/7mV... now it slowy decreases... after 15minutes i have 619mV and 5/3mV and after 45 minutes i am at 603mV and 3.3/ 0.1mV.
So is this normal?
Hope you can help me! All the best,
Philip
That is also normal, i think. Thats part of the process to reach thermal equilibrium. If you blow directly to the thermistor you can make the voltage to climb. Thats why we tweak the bias after an hour or 2. And you have to Adjust with fully assembled chassis. In mine, i close everything and wait a few minutes wile observing. I then Adjust bias to the desired voltage and offset. I do this repeatedly until i get the results i want. Thats a slow process but a very rewarding one. Mr. Nelsson said in the last BAF that this process is really important and thats why DIY is a good option compared to some comercial products.
Have in mind that i am only a new DIY audio hobbist. Wait for the more solid opinions.
BR
Have in mind that i am only a new DIY audio hobbist. Wait for the more solid opinions.
BR
heats the amp up to final operating temperature more quickly.
Does no harm at all.
It is common in Thermistor compensated controls.
Soooo, to bad, I was to early... I just realized that there is a very very quiet 50Hz (europe) buzz I can hear on one of my speakers BUT only when i connect both inputs 
When I connect only one, it doesn't depend which one, I hear nothing! Also when I set both inputs to ground I can hear nothing. When i connect both I hear a buzzing on one of the two speakers. Also I hear that buzz on the same speaker when I change the inputs...
Does someone have an idea?
to see if the problem comes from the preamp (DCB1) I just checked with my old amp, i cant hear a noise there...
When I connect only one, it doesn't depend which one, I hear nothing! Also when I set both inputs to ground I can hear nothing. When i connect both I hear a buzzing on one of the two speakers. Also I hear that buzz on the same speaker when I change the inputs...Does someone have an idea?
to see if the problem comes from the preamp (DCB1) I just checked with my old amp, i cant hear a noise there...
Soooo, to bad, I was to early... I just realized that there is a very very quiet 50Hz (europe) buzz I can hear on one of my speakers BUT only when i connect both inputs
Does someone have an idea?
to see if the problem comes from the preamp (DCB1) I just checked with my old amp, i cant hear a noise there...
You might try putting a 10 ohm resistor from the rca jacks to ground. May even work just using one channel.
Rush
hm, so i added the resistors (12 Ohm...)
View attachment 588408
i can still hear the buzz
The 10~12 ohm resistor should be in series with ground wire, amp ground and RCA ground. You are trying to break the ground loop by adding the small resistance. In the picture I believe you have just loaded the RCA signal to ground with the 12 ohm resistor. That is of no use.
The board has a signal to ground load resistor, don't need to add one at the RCA.
Rush
Soooo, to bad, I was to early... I just realized that there is a very very quiet 50Hz (europe) buzz I can hear on one of my speakers BUT only when i connect both inputs
Does someone have an idea?
to see if the problem comes from the preamp (DCB1) I just checked with my old amp, i cant hear a noise there...
Looks like you need some hum breaking resistors. See here for an explanation and further posts, and read David Joffe.
Ah, i see!
So this is my loop (with the blue line):
And i add the resistor there (red) and remove the blue. I will try this in the evening. I think this goes in hand with the discussion in the build-thread of the F5.
post 429:
http://www.diyaudio.com/forums/pass-labs/188691-illustrated-guide-building-f5-43.html
Still, I don't know why I am the first one with this problem in connection with the DCB1
So this is my loop (with the blue line):
And i add the resistor there (red) and remove the blue. I will try this in the evening. I think this goes in hand with the discussion in the build-thread of the F5.
post 429:
http://www.diyaudio.com/forums/pass-labs/188691-illustrated-guide-building-f5-43.html
Still, I don't know why I am the first one with this problem in connection with the DCB1
Read about HBRR & HBRL in the paper authored by D.Joffe.Soooo, to bad, I was to early... I just realized that there is a very very quiet 50Hz (europe) buzz I can hear on one of my speakers BUT only when i connect both inputs
Does someone have an idea?
to see if the problem comes from the preamp (DCB1) I just checked with my old amp, i cant hear a noise there...
He explains all in the problem of loops in stereo systems.
Putting the added resistance into the wrong part of the loop will make the hum louder rather than quieter.
Be very careful with inserting any added resistance into grounding/Earthing wiring.
You MUST NOT increase the impedance of the Safety Earth under any circumstances.
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yes break the blue connection and insert the added resistor between the two. a value between 1r0 and 100r should do the job of attenuating the loop current. It does not eliminate the interference current. It only reduces it.Ah, i see!
So this is my loop (with the blue line):
View attachment 588473
And i add the resistor there (red) and remove the blue. I will try this in the evening. I think this goes in hand with the discussion in the build-thread of the F5.
post 429:
http://www.diyaudio.com/forums/pass-labs/188691-illustrated-guide-building-f5-43.html
Still, I don't know why I am the first one with this problem in connection with the DCB1
You should also break the black connection and insert a similar resistor into the other channel's reference link.
I suggest you make these resistors as low as you need to make the Hum inaudible, or a bit bigger.
AndrewT said:
hm.... so I did as suggested and added the 12Ohm resistor. For that I removed the connection of the the blue cable (see post 15272) and the rca outside connection and added there the resistor in series. the blue cable then goes to the pcb (F5 V3 boards) and then there over the gnd connection to the psu gnd. (i used the wiring andrew suggested in the buildguide, see post 401 http://www.diyaudio.com/forums/pass-labs/188691-illustrated-guide-building-f5-9.html#post3161231).
to bad, the hum got louder, so i think this was the wrong place
but as far as I understand this is exactly as mentioned in the pdf of Daniel and as in my drawing.By the way, now including those resistors I even hear a hum when I only connect one rca between DCB1 and F4
