Hi everybody! And Happy new 2016 in advance!
I'm the happy owner of a diyed kondo m7 (single 5687) and I'm very happy with the sound, unfortunately it has a lot of gain for my 300b single ended amp (Lux-Diyhifisupply). The gain is so high that I cannot hear music at low volume as the Tocos carbon pot channel mismatch makes that while one speaker sounds at a reasonable low volume the other doen't sound at all.
I was about to order a shunt attenuator (basically on price and convenience considerations) but I read that it was not suitable for all the configurations and that it needed low source impedance.
This is my question: My Cd has got an output impedance of aprox. 100 ohms and the preamp an output impedance 35k ohms. Is a shunt attenuator (100db attenuation) a viable option for this step? Should I opt for a ladder one instead?
Thanks in advance for your help!!!
Raul
I'm the happy owner of a diyed kondo m7 (single 5687) and I'm very happy with the sound, unfortunately it has a lot of gain for my 300b single ended amp (Lux-Diyhifisupply). The gain is so high that I cannot hear music at low volume as the Tocos carbon pot channel mismatch makes that while one speaker sounds at a reasonable low volume the other doen't sound at all.
I was about to order a shunt attenuator (basically on price and convenience considerations) but I read that it was not suitable for all the configurations and that it needed low source impedance.
This is my question: My Cd has got an output impedance of aprox. 100 ohms and the preamp an output impedance 35k ohms. Is a shunt attenuator (100db attenuation) a viable option for this step? Should I opt for a ladder one instead?
Thanks in advance for your help!!!
Raul
Apart form the above figure which seems entirely wrong i cannot see any issue you may have with a shunt attenuator. 100db of max attenuation also sounds wrong - most attenuators go to -60db which is more than sufficient.
What really matters is the value of the series resistor and the number of steps. If your system has excessive gain more steps can be advisable. A series resistor of 10k is pretty much standard as even the weakest sources can drive it. The design being shunt usually indicates higher losses which in your case seems to be desirable.
Hi Analog_sa! thanks for your help. I found the info about the preamp output impedance here Home built line stage "Well, the single 5687 version of the M7 has unbypassed cathode resistors, so the output impedance will be quite high, in the region of 35kOhms. Far from ideal for your purposes." And the attenuation I got it from a friend of mine that has a ladder attenuator and 100 db of attenuation for a similar gain diyed M7 preamp (12Ay7 variety).
Regards,
Raul
Regards,
Raul
You should definitely not believe everything people write on the net
Output impedance of your pre should be around 2k. Either way, how is this connected to the impedance of the attenuator? You intend using it before the grid of the tube and not at output, right? What is the output impedance of the pre is just unrelated to your query.
Thanks again. I was throwing data around just in case it was necessary (my knowledge of electronics is quite limited to say the least). Yes, it's going to be connected before the grid. Glad to know that a shunt attenuator is feasible in the context of this kit, a ladder attenuator (4 poles) is more expensive and difficult to build (which I try to avoid, because it's a friend who is going to take charge of it). Again, your help has been invaluable.
Best wishes for the new year!!!
Raul
Best wishes for the new year!!!
Raul
The Source has to drive the Cable and the Receiver.
The Receiver should have some RF (radio frequency) filtering on it's input.
The RF filter and the cable capacitance will load the Source.
You can calculate the HF attenuation of the cable connection from
F-3dB = 1 / { 2 Pi R C }
eg.
2m of 60pF/m cable
470pF of Receiver filtering
2k ohms Output Impedance of Source
F-3dB = 1 / {2 Pi 2k (120pF+470pF) } = 1/2/3.14/2000/590 * 10^12 = ~134kHz
That last term (*10^12) converts F to pF and back again.
If you use a short cable you have less capacitive loading. If you use a high capacitnace filter you have more capacitive loading. If you use a high Source Impedance you have more high frequency roll-off.
Fortunately most RF filters have some series resistance and that reduces the HF roll-off while preserving the required RF roll-off.
The Receiver should have some RF (radio frequency) filtering on it's input.
The RF filter and the cable capacitance will load the Source.
You can calculate the HF attenuation of the cable connection from
F-3dB = 1 / { 2 Pi R C }
eg.
2m of 60pF/m cable
470pF of Receiver filtering
2k ohms Output Impedance of Source
F-3dB = 1 / {2 Pi 2k (120pF+470pF) } = 1/2/3.14/2000/590 * 10^12 = ~134kHz
That last term (*10^12) converts F to pF and back again.
If you use a short cable you have less capacitive loading. If you use a high capacitnace filter you have more capacitive loading. If you use a high Source Impedance you have more high frequency roll-off.
Fortunately most RF filters have some series resistance and that reduces the HF roll-off while preserving the required RF roll-off.
Andrew, risking annoying you with my blantant lack of grasp... I don't think my preamp (which is a diyed Kondo) has nothing like a Radio Frequency Filter. Here is the schematics
Simple 5687-based preamp - diyparadise. By "receiver" do you mean the "preamp"? The output of my CD is a tube module with an max impedance of 100ohm (I guess that means a low magnitude) Does it help?
Again, thanks for your contributions. And bear with me, Changing a lightbulb is the only thing electronics-related that I can do with some ease.
Regards,
Raul
Simple 5687-based preamp - diyparadise. By "receiver" do you mean the "preamp"? The output of my CD is a tube module with an max impedance of 100ohm (I guess that means a low magnitude) Does it help?
Again, thanks for your contributions. And bear with me, Changing a lightbulb is the only thing electronics-related that I can do with some ease.
Regards,
Raul
That sch does not show an RF input filter.
I suggest you fit one.
1k in series with the signal and then a 330pF to 1nF grounding capacitor. MKP, or NP0/C0G, would do nicely.
This goes before the vol pot.
And just to confirm
Receiver is the bit of equipment that receives a signal from another bit of equipment.
I suggest you fit one.
1k in series with the signal and then a 330pF to 1nF grounding capacitor. MKP, or NP0/C0G, would do nicely.
This goes before the vol pot.
And just to confirm
Receiver is the bit of equipment that receives a signal from another bit of equipment.
Hello Andrew,
I think I am writing posting here a question, probably in the wrong thread, I suppose. It is because i see many hard rated audio engineers online here. pardon me for this wrong posting, if my question doesn't match the thread.
I am using tda7313 as a preamp and want to attenuate the output signal to feed my amplifier whose input is at 60Kohm. I need about -14 db cut between preamp and amplifier. Can i go for a L type attenuator? And is there a need to match the impedance of preamp (output load resistance = 2K, output resistance = 75ohm) to amplifier (input resistance of 60K)?
I think I am writing posting here a question, probably in the wrong thread, I suppose. It is because i see many hard rated audio engineers online here. pardon me for this wrong posting, if my question doesn't match the thread.
I am using tda7313 as a preamp and want to attenuate the output signal to feed my amplifier whose input is at 60Kohm. I need about -14 db cut between preamp and amplifier. Can i go for a L type attenuator? And is there a need to match the impedance of preamp (output load resistance = 2K, output resistance = 75ohm) to amplifier (input resistance of 60K)?
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