Hi,
I intend using a SRPP circuit based on E182CC with a diamond buffer (to power my 8ohm headphones). The diamond buffer has an input impedance of ~1MOhm. I know that the cathode resistor needs to be matched to the load impedance etc., but general question:
Does anyone have experience in operating an E182CC-based SRPP with such high load impedance, does the SRPP "like" to play against such a load, what is important to take care of in such a setup?
Many thanks!
Robert
I intend using a SRPP circuit based on E182CC with a diamond buffer (to power my 8ohm headphones). The diamond buffer has an input impedance of ~1MOhm. I know that the cathode resistor needs to be matched to the load impedance etc., but general question:
Does anyone have experience in operating an E182CC-based SRPP with such high load impedance, does the SRPP "like" to play against such a load, what is important to take care of in such a setup?
Many thanks!
Robert
1Meg is so high that it's practically no load at all! You would probably be better to arrange the stage as a half-mu amplifier, rather than an SRPP. (e.g., the first stage of the Aikido http://www.tubecad.com/2004/AikidoAmp5.gif). After all, the SRPP is a power amplifier, whereas all you need is voltage gain.
If you actually try to optimise the SRPP for a 1Meg load you will find yourself calculating cathode resistors in the region of 80k! As a rule, the SRPP doesn't like loads that are much greater than the anode resistance of the triode being used. Or perhaps I should say that with large loads, it stops being an SRPP and becomes an actively loaded triode, and the idea of optimised cathode resistors no longer applies.
Hi Merlin,
many thanks for your reply!
Firstly, thanks for pointing out to me the rule that the SRPP doesn't like loads that are much greater than the anode resistance of the triode being used. You mean the resistor between the anode of the lower triode and the cathode of the upper triode? This is currently at 200ohm (there is no resistor to the anode of the upper triode).
Secondly, a bit more information on the intended usage: This SRPP circuit is the "I/V stage" of my DAC chip. In fact it is a current output DAC anyway, so the voltage gain I get from the SRPP is absolutely fine. I try to drive my headphones with it, and since they have an impedance of 5-14ohm (depending on frequency) I thought it would be a good idea to use a buffer after the SRPP to just provide enough current to the headphones (voltage is enough).
May I ask what you would recommend in this case? It would not be a good idea to drive such low impedance headphones directly with the SRPP, right...?
Many thanks
Robert
many thanks for your reply!
Firstly, thanks for pointing out to me the rule that the SRPP doesn't like loads that are much greater than the anode resistance of the triode being used. You mean the resistor between the anode of the lower triode and the cathode of the upper triode? This is currently at 200ohm (there is no resistor to the anode of the upper triode).
Secondly, a bit more information on the intended usage: This SRPP circuit is the "I/V stage" of my DAC chip. In fact it is a current output DAC anyway, so the voltage gain I get from the SRPP is absolutely fine. I try to drive my headphones with it, and since they have an impedance of 5-14ohm (depending on frequency) I thought it would be a good idea to use a buffer after the SRPP to just provide enough current to the headphones (voltage is enough).
May I ask what you would recommend in this case? It would not be a good idea to drive such low impedance headphones directly with the SRPP, right...?
Many thanks
Robert
You want a mu-follower/stage, they're practically immune to loads above a certain amount.
That light of a load, pretty any dual-triode tube will do. There's also hybrids: http://www.diyaudio.com/forums/blogs/geek/104-underappreciated-hybrid-mu-follower.html
How much voltage gain do you need?
Cheers!
That light of a load, pretty any dual-triode tube will do. There's also hybrids: http://www.diyaudio.com/forums/blogs/geek/104-underappreciated-hybrid-mu-follower.html
How much voltage gain do you need?
Cheers!
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Hi Gregg and Lars,
many thanks for helping me with this!
I think to fully understand this right I need to take a step back and would like to once more look at the full picture please:
I do not think that I need any voltage gain at all. My headphones are Ultimate Ears UE-10pro in-ear monitors with an impedance of 5-14ohm, depending on frequency. Probably due to being in-ear headphones, they have a high efficiency and play pretty loud. I do not have a scope, but when I put my multimeter over gnd and V+ on either left or right headphone output channel of my current amp, I measure no more than 35mV at listening levels that I would not want to exceed.
For this reason I thought that I would not need voltage gain but would be best served with a power amplifier that focusses on current, not voltage. Would you agree to this?
I intended to use my E182CC SRPP stage for this, but have been told that this is not a good idea with such a low load impedance of ~8ohm. Would you confirm this?
So my idea was to use a buffer "in between" that could supply the headphones with the required current, but now the buffer's high input load impedance is the problem...
Thank you,
Robert
many thanks for helping me with this!
I think to fully understand this right I need to take a step back and would like to once more look at the full picture please:
I do not think that I need any voltage gain at all. My headphones are Ultimate Ears UE-10pro in-ear monitors with an impedance of 5-14ohm, depending on frequency. Probably due to being in-ear headphones, they have a high efficiency and play pretty loud. I do not have a scope, but when I put my multimeter over gnd and V+ on either left or right headphone output channel of my current amp, I measure no more than 35mV at listening levels that I would not want to exceed.
For this reason I thought that I would not need voltage gain but would be best served with a power amplifier that focusses on current, not voltage. Would you agree to this?
I intended to use my E182CC SRPP stage for this, but have been told that this is not a good idea with such a low load impedance of ~8ohm. Would you confirm this?
So my idea was to use a buffer "in between" that could supply the headphones with the required current, but now the buffer's high input load impedance is the problem...
Thank you,
Robert
Ah,
Then you need balanced to unbalanced unity gain to start with.
I´d suggest a 1:1, (10k:10k transformer with primary termination) followed by volumecontrol then a onestage triodeamp( 1/2 182CC) with output transformer ca 5k:8 ohm. Otherwise your diamond buffer could be used.
An E182CC White-follower after the input transformer might also work.
Then you need balanced to unbalanced unity gain to start with.
I´d suggest a 1:1, (10k:10k transformer with primary termination) followed by volumecontrol then a onestage triodeamp( 1/2 182CC) with output transformer ca 5k:8 ohm. Otherwise your diamond buffer could be used.
An E182CC White-follower after the input transformer might also work.
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Lars has some good ideas here, it's worthy to check them out
(Hey Lars, the forum's been fixed from the crash and permissions fubar, if you haven't been back)
Cheers!
Hi Lars and Gregg,
many thanks for helping me!
So after the DAC's differential voltage out I'll start out with the 10k:10k transformer with primary termination. I don't need volume control (it's done digitally in the player). And then after this input transformer I have four choices according to your suggestions:
-> mu-follower (taking the signal from the anode) -> headphones
-> one-stage triode amp with output transformer 5k:8 ohm -> headphones
-> one-stage triode amp -> diamond buffer -> headphones
-> E182CC White-follower
Correct? Counting on your experience and expertise, what would you say gives the best results sonically, what option would you choose?
Many thanks,
Robert
many thanks for helping me!
So after the DAC's differential voltage out I'll start out with the 10k:10k transformer with primary termination. I don't need volume control (it's done digitally in the player). And then after this input transformer I have four choices according to your suggestions:
-> mu-follower (taking the signal from the anode) -> headphones
-> one-stage triode amp with output transformer 5k:8 ohm -> headphones
-> one-stage triode amp -> diamond buffer -> headphones
-> E182CC White-follower
Correct? Counting on your experience and expertise, what would you say gives the best results sonically, what option would you choose?
Many thanks,
Robert
1st won´t work without a diamond buffer and will be close to but probably better than the 3rd.
Can´t tell which one sounds best as this up to the user to decide.
If I where to build I would go for #2.
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Hi Lars,
great, many thanks for your recommendations - I admit I also like the version with the transformers best and am very pleased by your confirmation I would expect that this can be quite superior sonically to the other choices.
Please allow one more question to the amp stage "between" input and output transformer: so a one-stage triode amp with an E182CC would mean that one valve would handle both channels, left and right, correct? I really love the E182CC, but would have expected that there are solutions with one valve per channel that would be better, just for reasons of channel separation, physical separation of components, reduced interference etc....? Now that we already have moved away from the SRPP idea that was based on my E182CC, the optimum solution for this amp stage between the two transformers does not necessarily have to be based on E182CC, we can choose whatever is best here. Is there something that you could think of as an even better / optimum solution?
Many thanks again
Robert
great, many thanks for your recommendations - I admit I also like the version with the transformers best and am very pleased by your confirmation
I would expect that this can be quite superior sonically to the other choices.Please allow one more question to the amp stage "between" input and output transformer: so a one-stage triode amp with an E182CC would mean that one valve would handle both channels, left and right, correct? I really love the E182CC, but would have expected that there are solutions with one valve per channel that would be better, just for reasons of channel separation, physical separation of components, reduced interference etc....? Now that we already have moved away from the SRPP idea that was based on my E182CC, the optimum solution for this amp stage between the two transformers does not necessarily have to be based on E182CC, we can choose whatever is best here. Is there something that you could think of as an even better / optimum solution?
Many thanks again
Robert
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Lars,
great, many thanks!
One more question on the transformers: One can easily spend several hundreds or thousands of Euros (e.g. Audio Note) on quality transformers. For a first version of the amp (there's always room for further optimization and upgrades), can you recommend a manufacturer and maybe also suitable models for such input and output transformers that offer good quality at a decent price?
Many thanks
Robert
great, many thanks!
One more question on the transformers: One can easily spend several hundreds or thousands of Euros (e.g. Audio Note) on quality transformers. For a first version of the amp (there's always room for further optimization and upgrades), can you recommend a manufacturer and maybe also suitable models for such input and output transformers that offer good quality at a decent price?
Many thanks
Robert
Hey Robert,
ATRA0211 might be something to begin with
Frag Jan zuerst- Ask Jan first: Roehren und mehr
Go for a really good transformer, Lundahl LL1690, for the DAC. Buy from Benny Glass.
Aquablue Transformers
ATRA0211 might be something to begin with
Frag Jan zuerst- Ask Jan first: Roehren und mehr
Go for a really good transformer, Lundahl LL1690, for the DAC. Buy from Benny Glass.
Aquablue Transformers
Lundahl LL1690
Lars,
thank you so much for these recommendations, I really appreciate that!
I had a look at the data sheet for the Lundahl LL1690 at http://www.lundahl.se/pdfs/datash/1690.pdf and at the pin layout there, and am a bit confused:
I get L+, LREF and L- as well as R+, RREF and R- from the DAC chip. Where do I put the mid-rail reference voltages...?
Thanks again,
Robert
Lars,
thank you so much for these recommendations, I really appreciate that!
I had a look at the data sheet for the Lundahl LL1690 at http://www.lundahl.se/pdfs/datash/1690.pdf and at the pin layout there, and am a bit confused:
I get L+, LREF and L- as well as R+, RREF and R- from the DAC chip. Where do I put the mid-rail reference voltages...?
Thanks again,
Robert
Lundahl LL1570XL ?
Hi Lars,
I just discussed this issue with Benny Glass. He has recommended to use a LL1570XL instead (http://www.lundahl.se/pdfs/datash/1570_0xl.pdf) because this can deal with different ground levels, as you know my DAC also outputs the two different reference signals LREF and RREF that the LL1570XL can deal with. This would then be in the input side L- to pin 8, L+ to pin 6, 5 and 7 connected together, E1 and E2 connected together and LREF connected to it, and on the output side 2 and 3 connected together as + and 4 and 1 connected together as GND.
What do you think of this, is this what we need in this design that you have layed out before? I wonder though if this LL1570XL is of high enough quality...!!
Regards,
Robert
Hi Lars,
I just discussed this issue with Benny Glass. He has recommended to use a LL1570XL instead (http://www.lundahl.se/pdfs/datash/1570_0xl.pdf) because this can deal with different ground levels, as you know my DAC also outputs the two different reference signals LREF and RREF that the LL1570XL can deal with. This would then be in the input side L- to pin 8, L+ to pin 6, 5 and 7 connected together, E1 and E2 connected together and LREF connected to it, and on the output side 2 and 3 connected together as + and 4 and 1 connected together as GND.
What do you think of this, is this what we need in this design that you have layed out before? I wonder though if this LL1570XL is of high enough quality...!!
Regards,
Robert
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