Banned
Joined 2002
OK well I have been fighting this a few weeks now and have no clue how to help my self. Could it be a impedance problem Or ?
Note all equipment is working properly.
Ok scenario..
I have :
LG DVD player with digital out and RCA out with built in DAC..
Dual TDA 1541a's DAC
Tube Buffer that goes with the DAC witch uses 6DJ8's.
Aleph Mini A's
50K Alps Passive Pot.
First I’ll describe the problem and some things I have tried.
The tube DAC is suppose to go along with the digital to analogue DAC. It goes from Digital out on my LG to > DAC then from DAC analogue out > to tube buffer then to Passive Pot > mini A's.
LG > DAC > tube > Passive pot > mini A's
If this is like this i get no bass maybe a squeak or so.
If i go LG > DAC > Passive pot ? mini A's I get bas clarity but hardly any volume but good sound.
If I go LG > DAC> pot tube buffer > mini A's I get all bass no treble.
Now if i go I-Pod > tube Buffer > mini A's then I get clear sound bass treble and etc etc.
Any ideas what to do here. ?
I could post any info needed upon request..
Note all equipment is working properly.
Ok scenario..
I have :
LG DVD player with digital out and RCA out with built in DAC..
Dual TDA 1541a's DAC
Tube Buffer that goes with the DAC witch uses 6DJ8's.
Aleph Mini A's
50K Alps Passive Pot.
First I’ll describe the problem and some things I have tried.
The tube DAC is suppose to go along with the digital to analogue DAC. It goes from Digital out on my LG to > DAC then from DAC analogue out > to tube buffer then to Passive Pot > mini A's.
LG > DAC > tube > Passive pot > mini A's
If this is like this i get no bass maybe a squeak or so.
If i go LG > DAC > Passive pot ? mini A's I get bas clarity but hardly any volume but good sound.
If I go LG > DAC> pot tube buffer > mini A's I get all bass no treble.
Now if i go I-Pod > tube Buffer > mini A's then I get clear sound bass treble and etc etc.
Any ideas what to do here. ?
I could post any info needed upon request..
Banned
Joined 2002
Banned
Joined 2002
Hi Jason,
As you mentioned impedances, let me try to figure out some questions:
You mention the pot to be 50k. Depending on the way you connect it, are you maybe loading the tube buffer too heavily (so that it can't deliver enough current/voltage for larger amplitudes)?
Maybe because your DAC doesn't suffer from the pot impedance (due to higher current capability/lower output impedance, compared to the tube stage).
But this time, the maximum output level of the DAC might not be sufficient to drive the mini-A with larger voltage levels (not enough overall gain).
Might the pot form an RC filter with the input (capacitance) of the tube buffer, implementing a low pass filter?
Sure, because the iPod has a fairly low output impedance (try driving the speakers directly, you'll be surprised) and the pot doesn't interfere with the tube.
All in all, I'd say you really have a problem with impedance matching between the stages. Depending on your needs either a higher or lower pot value might help (try different cheap ones both before and after the tube buffer), but you should post the schematics before I could guess any better.
Ciao,
Sebastian.
As you mentioned impedances, let me try to figure out some questions:
You mention the pot to be 50k. Depending on the way you connect it, are you maybe loading the tube buffer too heavily (so that it can't deliver enough current/voltage for larger amplitudes)?
Maybe because your DAC doesn't suffer from the pot impedance (due to higher current capability/lower output impedance, compared to the tube stage).
But this time, the maximum output level of the DAC might not be sufficient to drive the mini-A with larger voltage levels (not enough overall gain).
Might the pot form an RC filter with the input (capacitance) of the tube buffer, implementing a low pass filter?
Sure, because the iPod has a fairly low output impedance (try driving the speakers directly, you'll be surprised) and the pot doesn't interfere with the tube.
All in all, I'd say you really have a problem with impedance matching between the stages. Depending on your needs either a higher or lower pot value might help (try different cheap ones both before and after the tube buffer), but you should post the schematics before I could guess any better.
Ciao,
Sebastian.
Banned
Joined 2002
what can i do to fix this ?Banned
Joined 2002
Hi,
I didn't realise you had already posted here, the posts above reflect some of what I posted on Chung's forum.
I still think the output impedence of that tube buffer is not sufficient to drive a passive pot without an additional gain stage.
Either way it's going to cost money, it's all to do with budget and what seems reasonable and affordable to you. Of course the need for extra expense is unfortunate, but perhaps not strictlty nesessary, if you choose to live with the SS output only.......
Thanks
Raja
I didn't realise you had already posted here, the posts above reflect some of what I posted on Chung's forum.
I still think the output impedence of that tube buffer is not sufficient to drive a passive pot without an additional gain stage.
Either way it's going to cost money, it's all to do with budget and what seems reasonable and affordable to you. Of course the need for extra expense is unfortunate, but perhaps not strictlty nesessary, if you choose to live with the SS output only.......
Thanks
Raja
Banned
Joined 2002
Raj1 said:
What are my options to fix this then ?
New thing :
If i turn the pot up when connected dac then pot then tube buffer then ( any power amp ) if it is a low volume there it so much bass no treble if i turn it up say half and alittle more i get treble bass and lots of gain if i go louder ( eek ) i get all the signal with trebble bass and hi gain.. HUMM>>
Banned
Joined 2002
HI,
Bottom line is this, there is no quick fix to your problem, you need another gain stage period.
Using a 50k pot requires a lower output impedence and more gain than the tube stage you have can provide.
Here are your options,
1) a solid state buffer after the tube stage. Though this obviously negates the sonic benefits of that simple tube stage
2) To somehow transformer couple the output of the tube buffer so that it can drive into low impedence loads. You could probably get away with a 10k passive pot after it then.
3) to use a tvc, so that the roll-off is not so extreme. This is my own prefered option, it is not cheap, and does not technically impress the more scientific amongst us, in terms of measurments and theories. Ping Kuei Yang Wang, he uses a system similar to your dac with a TVC, and can easily tell you what the shortcomings of your present setup are. He is busy though so getting a response is not always easy.
4) to use another tube gain stage.
Nelson has said it, it's the pot, it will work fine with most SS buffers before it, but with cap coupled tube stages like these you need an active gain stage or another of the options above...........
once you have decided on what you want to do, ask on the tubes or solid state forum about how best to achieve it. I am no expert, but have a little experience with various passive/active setups I have used.
Thanks
Raja
Bottom line is this, there is no quick fix to your problem, you need another gain stage period.
Using a 50k pot requires a lower output impedence and more gain than the tube stage you have can provide.
Here are your options,
1) a solid state buffer after the tube stage. Though this obviously negates the sonic benefits of that simple tube stage
2) To somehow transformer couple the output of the tube buffer so that it can drive into low impedence loads. You could probably get away with a 10k passive pot after it then.
3) to use a tvc, so that the roll-off is not so extreme. This is my own prefered option, it is not cheap, and does not technically impress the more scientific amongst us, in terms of measurments and theories. Ping Kuei Yang Wang, he uses a system similar to your dac with a TVC, and can easily tell you what the shortcomings of your present setup are. He is busy though so getting a response is not always easy.
4) to use another tube gain stage.
Nelson has said it, it's the pot, it will work fine with most SS buffers before it, but with cap coupled tube stages like these you need an active gain stage or another of the options above...........
once you have decided on what you want to do, ask on the tubes or solid state forum about how best to achieve it. I am no expert, but have a little experience with various passive/active setups I have used.
Thanks
Raja
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