Hi,
A Normal CD-Player has around 2V Output, so to match that you need a little less than a gain of 4, or 12dB.
Well using the 6N16B your gain in SRPP will be around 20..25, so your output voltage from this circuit will be around 11V at full level from CD, probably more.
So, I guess you GOT gain/buffer, just like "way too much".
With the tubes and supply voltages used I am not surprised you get distorted sound.
The SRPP with the kind of tubes you selected cannot really work well in this application. So I guess you need a different circuit or a tube with much, much less gain.
Ciao T
A Normal CD-Player has around 2V Output, so to match that you need a little less than a gain of 4, or 12dB.
Well using the 6N16B your gain in SRPP will be around 20..25, so your output voltage from this circuit will be around 11V at full level from CD, probably more.
So, I guess you GOT gain/buffer, just like "way too much".
With the tubes and supply voltages used I am not surprised you get distorted sound.
The SRPP with the kind of tubes you selected cannot really work well in this application. So I guess you need a different circuit or a tube with much, much less gain.
Ciao T
Thorsten, thanks for your insights.
I actually took this design from Lukasz Fikus, who uses it with exactly these tubes on exactly the same machine (Behringer SRC2496). Only difference is that my B+ is a bit lower than his, and therefore I was forced to choose another operating point.
If SRPP is a bad choice for this tube (so contrary to Lukasz' findings), what other design would be more appropriate for the 6N16?
Thanks
I actually took this design from Lukasz Fikus, who uses it with exactly these tubes on exactly the same machine (Behringer SRC2496). Only difference is that my B+ is a bit lower than his, and therefore I was forced to choose another operating point.
If SRPP is a bad choice for this tube (so contrary to Lukasz' findings), what other design would be more appropriate for the 6N16?
Thanks
Hi,
First, I don't want to comment too much on Luksas'z "hobbyist" approach and I most certainly strongly applaud his enthusiasm and work for the community. But many of the circuits presented on his site are not always what I would choose or recommend in the given situation and may have certain drawbacks when used in "typhical" audio systems (his system hardly is that).
SRPP is not inappropriate for this (or any) tube.
But if you use the tube you use in SRPP as illustrated, then you get a gain that is EXTREMELY high for an Analog Stage to go with the DAC you have and a normal system.
The DAC in the Behringer unit outputs already enough voltage to overload most amplifiers WITHOUT needing any added gain, so the result is not particularly pretty as you found.
In fact, with around 20V RMS output voltage from the 1V the DAC chip can deliver, we are looking at nearly 60V peak peak from a tube stage that only runs on 140V. This will not be a particularly low distortion and may severely stress the input stages of the amplifier following on.
You may wish to read my 1999 Article on the subject of of DAC's and tube stages in general. The 6N16B is quite similar to the ECC88/6N23/6922 I used in that article.
http://www.fortunecity.com/rivendell/xentar/1179/theory/vasfda/vasfda.html
I do have an updated version of this article that I have submitted for publication in an on-line DIY Mag, but publication is still outstanding, so I guess you will have to make do with the above for now.
These days I personally use a commercial product ("upgrade module") that I designed to be in essence a tube version of the LC Audio Zap-Filter, with the ability to interface correctly with any DAC out there and to produce an output voltage of around 2V instead of the above circuitry though.
Ciao T
First, I don't want to comment too much on Luksas'z "hobbyist" approach and I most certainly strongly applaud his enthusiasm and work for the community. But many of the circuits presented on his site are not always what I would choose or recommend in the given situation and may have certain drawbacks when used in "typhical" audio systems (his system hardly is that).
SRPP is not inappropriate for this (or any) tube.
But if you use the tube you use in SRPP as illustrated, then you get a gain that is EXTREMELY high for an Analog Stage to go with the DAC you have and a normal system.
The DAC in the Behringer unit outputs already enough voltage to overload most amplifiers WITHOUT needing any added gain, so the result is not particularly pretty as you found.
In fact, with around 20V RMS output voltage from the 1V the DAC chip can deliver, we are looking at nearly 60V peak peak from a tube stage that only runs on 140V. This will not be a particularly low distortion and may severely stress the input stages of the amplifier following on.
You may wish to read my 1999 Article on the subject of of DAC's and tube stages in general. The 6N16B is quite similar to the ECC88/6N23/6922 I used in that article.
http://www.fortunecity.com/rivendell/xentar/1179/theory/vasfda/vasfda.html
I do have an updated version of this article that I have submitted for publication in an on-line DIY Mag, but publication is still outstanding, so I guess you will have to make do with the above for now.
These days I personally use a commercial product ("upgrade module") that I designed to be in essence a tube version of the LC Audio Zap-Filter, with the ability to interface correctly with any DAC out there and to produce an output voltage of around 2V instead of the above circuitry though.
Ciao T
So your B+ is only 100V like the first message suggests ? You really don't want another Rk + Ri choking the tube, so I really wouldn't go for any series arrangement of tubes, SRPP included.
Why not try a simple common cathode stage with unbypased cathode and additional NFB ? The tube you've selected has mu = 25 and you only seem to need a gain of ~4. This way you'll get the most out of your avaliable B+.
BTW, what was that "300R to ground" your first message mentioned ? I assumed this was your load (= headphones) but it is now obvious it must have been something else. It wasn't Rk as you specified that already.
Why not try a simple common cathode stage with unbypased cathode and additional NFB ? The tube you've selected has mu = 25 and you only seem to need a gain of ~4. This way you'll get the most out of your avaliable B+.
BTW, what was that "300R to ground" your first message mentioned ? I assumed this was your load (= headphones) but it is now obvious it must have been something else. It wasn't Rk as you specified that already.
Hi,
Definitly worth trying first, don't you think? Easy, quick and if it works you can add a follower or work on other designs with other tubes that have less gain and so on...
Ciao T
Definitly worth trying first, don't you think? Easy, quick and if it works you can add a follower or work on other designs with other tubes that have less gain and so on...
Ciao T
Hi,
The DAC is specified to drive 600 Ohm. AKM's example schematics often SHOW the resistor (as 620R) so I would not loose sleep on that front.
Ciao T
The DAC is specified to drive 600 Ohm. AKM's example schematics often SHOW the resistor (as 620R) so I would not loose sleep on that front.
Ciao T
Hi,
I would remove the 620R (experimentally), I do not think it makes the DAC sound any better having it.
Yes. Some like this best, I tend to be among them. To make a Tube Cathode follower that is really better sounding needs some serious work and good powersupplies...
Ciao T
I would remove the 620R (experimentally), I do not think it makes the DAC sound any better having it.
Yes. Some like this best, I tend to be among them. To make a Tube Cathode follower that is really better sounding needs some serious work and good powersupplies...
Ciao T
I've done both now, and still in evaluation mode.
a) direct out from AKM4393 via Obbligato 6.8uF caps
b) AKM4393 --> voltage divider --> SRPP stage --> Obbligato caps
a has better positioning, while b is a bit warmer sounding. Not sure yet which I like more.
Quick question: Since I use the R+ and L+ outputs only on the DAC, I have 2.61 DC offset, which I currently do not block via any coupling caps before it goes into SRPP. DC is only blocked by the Obbligato's after the tube stage. Should I block DC already before (I have some Visaton 1uF around) the tube stage + after by Obbligato?
a) direct out from AKM4393 via Obbligato 6.8uF caps
b) AKM4393 --> voltage divider --> SRPP stage --> Obbligato caps
a has better positioning, while b is a bit warmer sounding. Not sure yet which I like more.
Quick question: Since I use the R+ and L+ outputs only on the DAC, I have 2.61 DC offset, which I currently do not block via any coupling caps before it goes into SRPP. DC is only blocked by the Obbligato's after the tube stage. Should I block DC already before (I have some Visaton 1uF around) the tube stage + after by Obbligato?
Hi,
Did you make sure to correct for the polarity inversion of the SRPP? Did you make sure to match levels closely?
If using an inverting Tube Analog Stage take the output from the R- & L- pins to preserve the correct polarity. Yes, I find both polarity and small level differences > 0.1dB < 0.5dB audible, at least insofar as it can severely skew blind preference tests, with preferences expressed for louder and correct polarity chains.
You can DC couple on the input, just take care to adjust the cathode resistor of the lower Tube in the SRPP to correct for the extra DC, which will otherwise lower the anode voltage.
You can improve the SRPP by making the upper Tube into a true CCS BTW, there are several ways.
You may also want to consider the Cathode Follower from my Article as option , instead to a stage with gain, if you feel you MUST have a tube to continue living... ;-)
Ciao T
Did you make sure to correct for the polarity inversion of the SRPP? Did you make sure to match levels closely?
If using an inverting Tube Analog Stage take the output from the R- & L- pins to preserve the correct polarity. Yes, I find both polarity and small level differences > 0.1dB < 0.5dB audible, at least insofar as it can severely skew blind preference tests, with preferences expressed for louder and correct polarity chains.
You can DC couple on the input, just take care to adjust the cathode resistor of the lower Tube in the SRPP to correct for the extra DC, which will otherwise lower the anode voltage.
You can improve the SRPP by making the upper Tube into a true CCS BTW, there are several ways.
You may also want to consider the Cathode Follower from my Article as option , instead to a stage with gain, if you feel you MUST have a tube to continue living... ;-)
Ciao T
In my hybrid design I used a SRPP stage and found it to be very clean sounding.
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