I just got the hifizen Aleph-X PCBs and I have two questions. Does the Aleph-X have enough gain to be driven directly by a CD player or DAC, without a preamp? And, is it possible to use a passive volume control, say just put a 10K attenuator at input?
Depends on your player, but very likely yes.
Yes, but it wouldn't hurt to go for a little higher resistance on the pot.
Grey
Yes, but it wouldn't hurt to go for a little higher resistance on the pot.
Grey
I was using my Aleph X driven directly from a DAC. I had 500ohm switching attenuator at DAC's output. With 92dB speakers, I never run out of gain, but I was using 200k feedback resistor (instead of usual 100k).
My DAC won't drive 500 ohms properly as I can't fit larger DC blocking caps in the enclosure.
GRollins says to use over 10K. You are using lower. I'm confused.
GRollins says to use over 10K. You are using lower. I'm confused.
Need more information...............
By one of them or both............
One would need to know if your driving your Aleph X single ended and what the feedback resistor values are. You need to know the output level for the CD player. I believe its usually a couple volts RMS. The efficency of your speakers is a big factor and an Aleph X with 15 or 20 volt rails is going to require a pretty efficient speaker.
A passive volume control is not the best idea since the Amps feedback will not be symetrical. The series resistance from the output of the pot is part of the feedback resistor for a 10K pot the maximum resistance will be 2.5K which which gives a 12.5K resistance for the input feedback resistor for one side of the amp 10K for the other side if the input resistor is grounded for running the amp single ended. Using a larger pot will make this imbalance even worse and I haven't a clue why Mr. Rollins would reccomend it. Ask him, maybe there is a reason I don't know about.
Knowing the gain for the amp you are using now would be useful since the Aleph X doesn't have a large amount of gain and maybe considerable less than many amps. With the feedback resistor values Mr. Rollins can tell you what the gain is running the amp with the input single ended. I believe he was disscussing this mode of operation with some one the other day and has more experience with this amp than I do.😉
By one of them or both............
One would need to know if your driving your Aleph X single ended and what the feedback resistor values are. You need to know the output level for the CD player. I believe its usually a couple volts RMS. The efficency of your speakers is a big factor and an Aleph X with 15 or 20 volt rails is going to require a pretty efficient speaker.
A passive volume control is not the best idea since the Amps feedback will not be symetrical. The series resistance from the output of the pot is part of the feedback resistor for a 10K pot the maximum resistance will be 2.5K which which gives a 12.5K resistance for the input feedback resistor for one side of the amp 10K for the other side if the input resistor is grounded for running the amp single ended. Using a larger pot will make this imbalance even worse and I haven't a clue why Mr. Rollins would reccomend it. Ask him, maybe there is a reason I don't know about.
Knowing the gain for the amp you are using now would be useful since the Aleph X doesn't have a large amount of gain and maybe considerable less than many amps. With the feedback resistor values Mr. Rollins can tell you what the gain is running the amp with the input single ended. I believe he was disscussing this mode of operation with some one the other day and has more experience with this amp than I do.😉
I'll be driving it balanced. The balanced output of the DAC is 1.8V. I plan to build the Aleph-X for about 100W/channel, but I have not started building yet so no value is fixed. I was hoping for a balanced input impedance of not much less than 10K.
Look Prune, give it a shot with passive se drive use whatever pot you got 10k, 20k. At the most you won't achieve sonic bliss.
I don't remember exactly but the input sensitivity of the AX in its "regular" version (15V rails 5 amps bias one pair of 044 per side) was in the ball park of 2V RMS and the voltage gain is about 20 dB for 8 ohms so plenty of juice to run your speakers. The input imp. is no less than 10K
I don't remember exactly but the input sensitivity of the AX in its "regular" version (15V rails 5 amps bias one pair of 044 per side) was in the ball park of 2V RMS and the voltage gain is about 20 dB for 8 ohms so plenty of juice to run your speakers. The input imp. is no less than 10K
Where does the pot go?
"driving it balanced"
Ganged pots......... or what? Give the poor guy some specific advice.
So much for super symmetry......... I guess it would be sorta sorry semi symmetry
You sound like you know who with this post.
"driving it balanced"
Ganged pots......... or what? Give the poor guy some specific advice.
So much for super symmetry......... I guess it would be sorta sorry semi symmetry
You sound like you know who with this post.
I will drive it balanced. I don't understand why using a balanced volume control would destroy the symmetry.
To rephrase my question, I want to find out what value balanced pot/attenuator would be best (while trying not to have a too low value as I can't drive it).
To rephrase my question, I want to find out what value balanced pot/attenuator would be best (while trying not to have a too low value as I can't drive it).
Get a dual ganged linear 100K or 50K. The 10K input impedance will give you law faking sort off log pot when connected to the wiper of the pot for its output. Passive preamps reqiuire short low capacitance interconnects and really don't have the dynamics of a buffered pot.
"I don't understand why using a balanced volume control would destroy the symmetry."
It won't ......... my post was about driving it single ended which what Grataku was recommending and I thought you were doing originally. You have to give enough information to get a useful answer..........
Maybe Grey is the one to help you. He will probably look at your post tommorow. I think I am just confusing you. BTW I see you're Canadian.
"I don't understand why using a balanced volume control would destroy the symmetry."
It won't ......... my post was about driving it single ended which what Grataku was recommending and I thought you were doing originally. You have to give enough information to get a useful answer..........
Maybe Grey is the one to help you. He will probably look at your post tommorow. I think I am just confusing you. BTW I see you're Canadian.
Prune, what Fred is getting at is that a balanced input buffer would be better. I remember someone once posted an highly black-box-version X-preamp without input buffer. 😉 I am sure that someone will produce that if you ask him nicely.
Fred, where in my post did I say he should be driving it SE?
I may have thought, like you did, that he was using a SE dac which maybe more common.
Fred, where in my post did I say he should be driving it SE?
I may have thought, like you did, that he was using a SE dac which maybe more common.
Just one wasn't enough huh
Now your confusing me! I don't know exactly what circuit you are refering to. In all honesty and no joke,Grey is working on a couple of X preamp circuits and maybe he has an idea. Really, I not trying to be funny or rude.
Now your confusing me! I don't know exactly what circuit you are refering to. In all honesty and no joke,Grey is working on a couple of X preamp circuits and maybe he has an idea. Really, I not trying to be funny or rude.
Re: Just one wasn't enough huh
Er, thanks for your replies, but I hope the proximity of these two statements is just a coincidence, for the implication otherwise is offensive at best.
As for short low capacitance interconnects, I have such. Do you mean for between a passive preamp and the A-X? I was thinking of having the volume control in the A-X enclosure (with a bypass option).
Is there any possible problem with using the setup you suggest, as in negative effects on sound? And how to choose between 50K and 100K?
Fred Dieckmann said:
Er, thanks for your replies, but I hope the proximity of these two statements is just a coincidence, for the implication otherwise is offensive at best.
As for short low capacitance interconnects, I have such. Do you mean for between a passive preamp and the A-X? I was thinking of having the volume control in the A-X enclosure (with a bypass option).
Is there any possible problem with using the setup you suggest, as in negative effects on sound? And how to choose between 50K and 100K?
Prune,
don't let Fred's negative attitude get to you. He just loves politics much more than he likes engineering. Particularly he likes to put the seed of doubt in one's head. However he often stops short of providing a solution for the "big" problem he's hinting at. Anyway enough about that.
If the output impedance from your dac is too high with respect to the input impedance of the AX with long interconnects you can alter the freq response. Whatever is in between the dac and the amp will act as a tunable low pass filter (tuned by the volume control pot). Unless we are talking studio lenght cable and huge impedance mismatch the effect will be very small. Introducing a pre amp in the circuit will probably make a more audible difference than a slight impedance mismatch.
If you can't sleep look for a buffer circuit (that ideally is a gain 1 voltage amplifier with very low output impedance and no sonic signature) to put inside your dac box following your volume pot, which will be dual ganged one per channel.
I think by the time you are done with your high power AX you'll probably be dying to listen to it so just try the connection and see what it sounds like. 😉
don't let Fred's negative attitude get to you. He just loves politics much more than he likes engineering. Particularly he likes to put the seed of doubt in one's head. However he often stops short of providing a solution for the "big" problem he's hinting at. Anyway enough about that.
If the output impedance from your dac is too high with respect to the input impedance of the AX with long interconnects you can alter the freq response. Whatever is in between the dac and the amp will act as a tunable low pass filter (tuned by the volume control pot). Unless we are talking studio lenght cable and huge impedance mismatch the effect will be very small. Introducing a pre amp in the circuit will probably make a more audible difference than a slight impedance mismatch.
If you can't sleep look for a buffer circuit (that ideally is a gain 1 voltage amplifier with very low output impedance and no sonic signature) to put inside your dac box following your volume pot, which will be dual ganged one per channel.
I think by the time you are done with your high power AX you'll probably be dying to listen to it so just try the connection and see what it sounds like. 😉
Prune said:
I think the answer to this is very simple. Check what is the input to ground shunting resistor in your amp and repalce it by the same value switching attenuator (dual gang per channel).
In this way, adding a pot will not change anything in the input impedance of the amp and it should work fine.
In case you build a stereo amp and settle on 50K input impedance, this pot would be perfect for your application. I still have two of them left
http://www.diyaudio.com/forums/showthread.php?s=&threadid=3279&highlight=
Whoops........
I'm sorry it was very late and I stopped in mid sentence without finishing my thought....... I was in the process of saying that Peter had built this amp and maybe you could give him a call and see what results he has had with passive preamps and the AX. I honestly plead fatigue and really have should have just gone to bed instead of typing in my sleep. I often wonder if the misunderstandings on the forum are often the result of having a real time chat with someone half the way around the world. I am a terrible insomniac in the last few years and perhaps should watch TV instead chatting on the net at 3 in the morning. I gave up soldering in the middle of the night after a few interesting episodes with that unwise pastime.
Sorry for the misunderstanding. It does appear a rather cryptic post in the light of day. I had a wonderful visit to Vancover one summer in my childhood and will never forget the hospitality shown my family be our host and plan to return someday.
I'm sorry it was very late and I stopped in mid sentence without finishing my thought....... I was in the process of saying that Peter had built this amp and maybe you could give him a call and see what results he has had with passive preamps and the AX. I honestly plead fatigue and really have should have just gone to bed instead of typing in my sleep. I often wonder if the misunderstandings on the forum are often the result of having a real time chat with someone half the way around the world. I am a terrible insomniac in the last few years and perhaps should watch TV instead chatting on the net at 3 in the morning. I gave up soldering in the middle of the night after a few interesting episodes with that unwise pastime.
Sorry for the misunderstanding. It does appear a rather cryptic post in the light of day. I had a wonderful visit to Vancover one summer in my childhood and will never forget the hospitality shown my family be our host and plan to return someday.
Good idea!
"I think the answer to this is very simple. Check what is the input to ground shunting resistor in your amp and repalce it by the same value switching attenuator (dual gang per channel).
In this way, adding a pot will not change anything in the input impedance of the amp and it should work fine."
An excellent idea as well. See.... Canadians are smart people.
"I think the answer to this is very simple. Check what is the input to ground shunting resistor in your amp and repalce it by the same value switching attenuator (dual gang per channel).
In this way, adding a pot will not change anything in the input impedance of the amp and it should work fine."
An excellent idea as well. See.... Canadians are smart people.
"He just loves politics much more than he likes engineering. Particularly he likes to put the seed of doubt in one's head. However he often stops short of providing a solution for the "big" problem he's hinting at. Anyway enough about that."
I hate politics! A few hints and the joy of self discovery is much more satisfying than over specific advice and spoon feeding. It also allows a possible escape exit when things go awry!
🙄
I hate politics! A few hints and the joy of self discovery is much more satisfying than over specific advice and spoon feeding. It also allows a possible escape exit when things go awry!
🙄
Buffered passives
"Introducing a pre amp in the circuit will probably make a more audible difference than a slight impedance mismatch."
I don't know......... a buffer can be as simple as a couple of jfets. There
are many that feel driving cables with a low impedance improves bass,
dynamics and detail. I guess I am in this camp.
Make everything as simple as possible but not simpler.
With the number of pundants analyzing my post for subtext I am starting to feel like a politician. Come on folks, WYSIWYG.........
"Introducing a pre amp in the circuit will probably make a more audible difference than a slight impedance mismatch."
I don't know......... a buffer can be as simple as a couple of jfets. There
are many that feel driving cables with a low impedance improves bass,
dynamics and detail. I guess I am in this camp.
Make everything as simple as possible but not simpler.
With the number of pundants analyzing my post for subtext I am starting to feel like a politician. Come on folks, WYSIWYG.........
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