Thanks mate - I'll increase the cap and see if it helps.
Also ordered some of this - could be useful, too!
eBay Australia: Buy new & used fashion, electronics & home d?r
Also ordered some of this - could be useful, too!
eBay Australia: Buy new & used fashion, electronics & home d?r
That shielding should, at the least, be good enough to find out if there is benefit to be had with blocking the humfield or moving the transformer.
Hi there - I will chip in to the conversation.
I bought this kit as well...
I measured frequency response of this DAC and it appears to start rolling off from around 10kHz down to -8db by 14.5Khz. Later I bypassed one of the transformers and I got ~+2db starting at 8kHz to 18kHz, rather strange...The supplied transformer clearly cannot handle frequencies above 12kHz.
The coupling transformer seems to also pick up magnetic interference from toroidal PS transformer that results in significant hum. Changing the position of PS transformer reduces the hum but not completely. This effect disappears with the removal of coupling transformers.
Don't run to remove your signal transformers yet! - bypassing them with passive I/V significantly increases overall noise level. My recommendation is to replace coupling transformers with better quality ones.
Some hum and buzz is still present after bypassing the transformers. My guess is that it is due to smallish filtering caps in HV PS. On my board there are two 22uf 400V filtering caps after the voltage regulator (looks like LT1084CT), will try to change to at least 47uf or larger...
There are better and cheaper DAC boards out there...
I bought this kit as well...
I measured frequency response of this DAC and it appears to start rolling off from around 10kHz down to -8db by 14.5Khz. Later I bypassed one of the transformers and I got ~+2db starting at 8kHz to 18kHz, rather strange...The supplied transformer clearly cannot handle frequencies above 12kHz.
The coupling transformer seems to also pick up magnetic interference from toroidal PS transformer that results in significant hum. Changing the position of PS transformer reduces the hum but not completely. This effect disappears with the removal of coupling transformers.
Don't run to remove your signal transformers yet! - bypassing them with passive I/V significantly increases overall noise level. My recommendation is to replace coupling transformers with better quality ones.
Some hum and buzz is still present after bypassing the transformers. My guess is that it is due to smallish filtering caps in HV PS. On my board there are two 22uf 400V filtering caps after the voltage regulator (looks like LT1084CT), will try to change to at least 47uf or larger...
There are better and cheaper DAC boards out there...
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I modified the DAC board and completely removed signal coupling transformers. It is quite simple really: remove transformers, remove R4 & R5 (LIN, RIN), remove RL4 & RR4 and replace with 300R, solder bypass wire on the transformer signal contacts. That's it. We got DAC with passive I/V via 300R resistor to the ground going straight to tube grids (we leave 1K series resistor in place). No more humming, I measure flat frequency response and low noise level.
Great to see someone else has worked on this board.
Since this thread was started I’ve also made a few changes.
I took out the telephone(!) transformers, they were rubbish and probably radioactive!
Kevin from K&K audio helped me locate a good replacement: Lundahl LL1530 (datasheet attached).
Also, changed R4 to 2k – the gain was just way too much + changed the pulse (isolation transformer) to LL1572.
Another thing, put some mumetal between the toroid and the pcb, helps a lot with the buzz.
Interesting to see your suggested to remove the transformers between the dac and the SRPP – what are they actually there for in the first place?
Since this thread was started I’ve also made a few changes.
I took out the telephone(!) transformers, they were rubbish and probably radioactive!
Kevin from K&K audio helped me locate a good replacement: Lundahl LL1530 (datasheet attached).
Also, changed R4 to 2k – the gain was just way too much + changed the pulse (isolation transformer) to LL1572.
Another thing, put some mumetal between the toroid and the pcb, helps a lot with the buzz.
Interesting to see your suggested to remove the transformers between the dac and the SRPP – what are they actually there for in the first place?
Speaking of SRPP and Lundahl for I/V, this might be interesting:
http://www.diyaudio.com/forums/digi...s-valve-output-stage-lundahl-transformer.html
http://www.diyaudio.com/forums/digi...s-valve-output-stage-lundahl-transformer.html
It's a Chinese design - turn good ideas into crap.
Coupling transformers are used to isolate digital circuitry from analog, including common rails. This method SIGNIFICANTLY reduces noise, interference, and distortion. Proper implementations cost thousands. Passive resistor I/V method is an excellent cost effective solution. In this case it sounds a lot better than "audiophile" transformer.
I quite like the sound with the Lundahl transformers - but it is tempting to try your idea and remove them altogether, the wiring on the transformers was a tedious and painstaking task, I might leave them in case I'm unable to put them back.
Did you change R4 at all?
Did you change R4 at all?
There's R4 and R5 220R resistor on DAC side - remove it. On the SRPP side there are two R4 47k resistors - remove and replace with good quality 300R resistors, those will be your I/V resistors (Also remove C3 output filtering caps - they are not necessary)
I think it is better to put those I/V resistors on SRPP side rather than on the DAC side for better ground reference.
Now the DAC sounds really good.
OK I'll try it out - sheesh those Lundahl transformers and Z-Foil 220R resistors were not cheap! I hope it works OK.
I have also removed the transformers, sounds much better! Note there is a thread (in French) in which a group of fellow DIYers have also had good success doing the same:
Réalisation DAC NOS AD1865 SRPP
I still have a small amount of hum/buzz - funny thing is, if I connect the RCA output GND to the chassis ground (where the mains earth is connected) then there is no noise at all. Does anyone have an RC Parallel circuit I could implement? I recall reading that this is the best method of connecting signal GND to mains earth....
Réalisation DAC NOS AD1865 SRPP
I still have a small amount of hum/buzz - funny thing is, if I connect the RCA output GND to the chassis ground (where the mains earth is connected) then there is no noise at all. Does anyone have an RC Parallel circuit I could implement? I recall reading that this is the best method of connecting signal GND to mains earth....
Sounds like ground loop issue. I assume you have connected GND on the board PS to your mains ground.
No, my high voltage transformer has a ground wire, but it is on the primary side of the transformer - this is connected to the mains earth. I have nothing connected to the gnd terminal block at the psu section of the pcb. I'll test out connecting the gnd terminal to mains earth and report back.
ClefChef - you are correct, I connected the GND to the mains earth, silence! Thanks for the assistance, the sound really is fantastic. I've also swapped out the output capacitors for some 1uF K73-16 Russian caps, not a noticeable difference, yet, but the bass roll off is unchanged as my power amp has an imput impedance of 100k.
How do we calculate the vrms output of the DAC?
According to this site:
DAC End 2 - the AD1865N-K with single ended vacuum output stage
The vrms output of the ad8165 dac w/220R resistors is 127mV, what factor do we multiply this by given the SRPP is a 6DJ8 medium mu stage?
How do we calculate the vrms output of the DAC?
According to this site:
DAC End 2 - the AD1865N-K with single ended vacuum output stage
The vrms output of the ad8165 dac w/220R resistors is 127mV, what factor do we multiply this by given the SRPP is a 6DJ8 medium mu stage?
Hello
Greetings to all the forums I am a new user and if somebody can help me on my DAC ad1865 coupling transformer srpp from raindrop hui. I doubt if my chip is original or not, and I pick up a new one. Are chip with gold writing is original ad1865n-k
AD1865N K AD1865 18bit Audio DAC Upgrade Audionote IC | eBay
Greetings to all the forums I am a new user and if somebody can help me on my DAC ad1865 coupling transformer srpp from raindrop hui. I doubt if my chip is original or not, and I pick up a new one. Are chip with gold writing is original ad1865n-k
AD1865N K AD1865 18bit Audio DAC Upgrade Audionote IC | eBay
My recollection is, that a triode based SRPP will have a voltage gain equal to half the triode's mu. For the 6DJ8 having a specified mu of 33, the voltage gain would be 16 to 17. If we multiply 127mVRMS x 16, the fullscale output voltage should then be approximately 2VRMS.
Ken - that is spot on. I did some more reading on the data sheets and this particular circuit, I think (in this circuit) the 6cg7 is more similar to the Chinese 6n11. With the 6cg7, I get cathode volts of 2.5v, plate current of 5ma and plate voltage of 100v (a bit low I know).
Using the 6CG7 rather than 6DJ8 gets around half the gain I guess, so the SRPP is probably only giving out around 127mV*(mu/2) = 127mV*11 = 1.3vrms, not bad given how loudly music is recorded these days.
My own home brew DAC's I/V and analog output consists of a single resistor. The fullscale signal amplitude is only 200mVRMS, which is then directly connected to my power amp without any preamp unit or volume control. The resulting sound is usually loud enough to suit me (my speakers have 93dB sensitivity) and, depending on the CD, it can sometimes sound a bit too loud. I have it configured this way because this gives me the most transparent, realistically natural reproduction I've yet heard from my system. So much so that, for now, it's worth the inconvenience of having no volume control.
I'm quite close to reaching the 'no volume control' conclusion myself.
My speakers are 90dB, however my 15W push pull power amp has a sensitivity of 3.5v, so it doesn't seem to be 'driven' as well without a pre/grain stage.
What topology power amp are you using, Ken?
My speakers are 90dB, however my 15W push pull power amp has a sensitivity of 3.5v, so it doesn't seem to be 'driven' as well without a pre/grain stage.
What topology power amp are you using, Ken?
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