I see often a 1M on input and one on the output and it's a safety resistor if something goes wrong. In my case is it needed /or the 10K that goes to gound are they there for same reason? (but the one on the output seems to be on wrong side of cap?! In earlier schematics of this pre i've seen it have been 100K.
A high value resistor to ground on the far side of a coupling cap is a ground leak resistor. It avoids clicks when plugging things together. The value is not critical. Too low and it loads the previous stage unnecessarily. Too high and the voltage takes too long to stabilise after switching on. 100k-1M are about right, unless electrolytics are used.
10k seems low to me for reference resistors. Also on the output side it would make more sense if they were on the output side of the coupling cap. I would move the output side ones...looks like you could manage that under the pcb if you were concerned about aesthetics.
As to value I would change them to 1M. 1/4 watt should be fine.
As to value I would change them to 1M. 1/4 watt should be fine.
Can you explain what you mean with that?
I'm gonna exchange the BC caps with only film caps so it's gonna be 4x10uF MKP and after 10K 4x10uF MKP more.. This are also gonna be bypassed with 2x high quality Audyn cap plus 1,5uF that is left over. Total is gonna be 83uF film/mkp.
Any thoughts bout that? Is 100K leak resistor over caps still ok/ good value? In my MC100 KT88 there is one for each cap but they are 470uF...
Let's see if there is some time over today to do any mods (bias, leak resistor n so on) I'll report as soon as possible.
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Electrolytics leak, so need smaller ground resistors. They also tend to be larger values, so need smaller ground resistors unless you are patient.
83uF with 100k will give you a time constant of 8.3 secs, so the output voltage should be stable(ish) from about 25 secs after switch on. I assume you have carefully calculated what coupling cap values you need?
83uF with 100k will give you a time constant of 8.3 secs, so the output voltage should be stable(ish) from about 25 secs after switch on. I assume you have carefully calculated what coupling cap values you need?
-To be honest. I've read on the internet that if you have a tube rectifier you should never go over 100uF total. In varies datasheets for tube rectifier it usually are somewhere between 4-47uf what i've seen.
I have not done any calculation
Didn't even know you could calculate that? Please share. This is what i want to learn. And also how to calculate that leakresistor? Is 25 sec to long? What would you recommend?
I think many reading this thread that are like me would learn alot. Thanks everyone for sharing your knowledge. I would 5-10 years ago sit in front of the pc till i found my answer (like i did when i built speakers) but with a little daughter i just can't spend so much time anymore doing that. So very many thx for helping me out.
Those film PSU cap values look OK, its just clunky to use so many film caps on a PSU, really there is nothign wrong with good quality electrolytics for this chore, I prefer Nichicon or Panasonic.
For the bleeder resistor I would start with using at least 10K in value probably more, 100K should do OK. Just make sure they are not glowing hot. That is the most critical piece.
A good arrangement might look like
CLCRC with first C being Film cap, Choke, ~40uF worth of capacitance, 10K R, ~40uF worth of capacitance.
If it were me I would start with good quality electrolytics like Nichicon VZ or PW series. 47uF is plenty, you could go to 100uF for the third "C".
For the bleeder resistor I would start with using at least 10K in value probably more, 100K should do OK. Just make sure they are not glowing hot. That is the most critical piece.
A good arrangement might look like
CLCRC with first C being Film cap, Choke, ~40uF worth of capacitance, 10K R, ~40uF worth of capacitance.
If it were me I would start with good quality electrolytics like Nichicon VZ or PW series. 47uF is plenty, you could go to 100uF for the third "C".
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Only the last part when i was talking about the one that is connected between +/- on the last 47uF in the PSU.
I measured voltage with 250ohm = 0,91 vs 0,95 so 3,6 vs 3,8mA... I guess 180ohm next step =)
Also the 4p pcs /1M is in place before 330ohm /after last caps with 4pcs 10k removed. I sneak peaked on aikaido or was it audio note m77 that have same so i think i did right
Also 0,47uf removed and 330ohm in place s.c "gridstopper" i learned
Let's listen
I measured voltage with 250ohm = 0,91 vs 0,95 so 3,6 vs 3,8mA... I guess 180ohm next step =)
Also the 4p pcs /1M is in place before 330ohm /after last caps with 4pcs 10k removed. I sneak peaked on aikaido or was it audio note m77 that have same so i think i did right
Also 0,47uf removed and 330ohm in place s.c "gridstopper" i learned
Let's listen
You are now talking about the one in PSU? Is 3W ok? The one "bleeder" over the cap is 100K now.
-now the tubes start to heat up more then to fingerwarm, actually pcb start to be warm too
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Excellent!!!
You will make this preamp sing beautiful music soon!
I would not tinker any more and just listen for a while.
Max, please tell us exactly what is the listening configuration now? We have been talking about and suggesting so much. What is the current state of your preamp?
Also, more importantly, we have left this subject largely ignored. What power amp are you using with this preamp? You mentioned a KT88 amp but is that the one?
Merry XMas!
Carl
You will make this preamp sing beautiful music soon!
I would not tinker any more and just listen for a while.
Max, please tell us exactly what is the listening configuration now? We have been talking about and suggesting so much. What is the current state of your preamp?
Also, more importantly, we have left this subject largely ignored. What power amp are you using with this preamp? You mentioned a KT88 amp but is that the one?
Merry XMas!
Carl
Bass amp is Behringer iNuke 3000 and a Behringer DCX 2496 as active crossover. Cut off is approx. 180hz.
Speakers are home made with (one speaker) - 2pcs Seas L22 8" bass. SB acoustics sb17 and the dimpledome. 29rdc. Transmissionline. Weight 73 kg/ 200 pounds?! Looks little like von schweikerts new vr-4.. Crossover is of high quality (copperfoil, audyn cap plus caps )
Don't have pic on those this minute.
Speakers are home made with (one speaker) - 2pcs Seas L22 8" bass. SB acoustics sb17 and the dimpledome. 29rdc. Transmissionline. Weight 73 kg/ 200 pounds?! Looks little like von schweikerts new vr-4.. Crossover is of high quality (copperfoil, audyn cap plus caps )
Don't have pic on those this minute.
Current state?
It's playing music!! Removing those caps on input + those 10k plus lowering cathode resistor to 250 ohm (choke have to come later) and the 330ohm on input made a huge difference. Suddenly there is plenty of low bass but fast and hard. Sound is very open and almost scary dynamic! Gain is higher now, 10 o'clock before is maybe around 8 now...
When i'm done with cathode resistor i can draw a new schematic.
I already calculated that 8x10uf filmcaps is gonna have room so they were ordered yesterday. (I have 3pcs already) yes a bit bulky
Also about to order some Rike s caps Pio for coupling.
- not sure about value. 2,2 or 3.3uf??
It's playing music!! Removing those caps on input + those 10k plus lowering cathode resistor to 250 ohm (choke have to come later) and the 330ohm on input made a huge difference. Suddenly there is plenty of low bass but fast and hard. Sound is very open and almost scary dynamic! Gain is higher now, 10 o'clock before is maybe around 8 now...
When i'm done with cathode resistor i can draw a new schematic.
I already calculated that 8x10uf filmcaps is gonna have room so they were ordered yesterday. (I have 3pcs already) yes a bit bulky
Also about to order some Rike s caps Pio for coupling.
- not sure about value. 2,2 or 3.3uf??
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