Frank,
The 2.2K was a honest mistake. I intended on using a 220K. I just changed the value to 500K, and I'll see what this does for the sound.
Hmmm, a mute switch, that is a good idea!
How does one determine what the effect on the bass would be? Is their a formula?
Thanks Again,
Bryan
The 2.2K was a honest mistake. I intended on using a 220K. I just changed the value to 500K, and I'll see what this does for the sound.
Hmmm, a mute switch, that is a good idea!
How does one determine what the effect on the bass would be? Is their a formula?
Thanks Again,
Bryan
Hi,
No preamp should be without one.
Certainly...
If only I could remember a single formula...2*Pi something along those lines....
Anyway, I'll look it up for you unless some gentle soul puts it here before me...
I'm an absolute disgrace when it comes to remembering formulae...
Cheers,😉
No preamp should be without one.
Certainly...
If only I could remember a single formula...2*Pi something along those lines....
Anyway, I'll look it up for you unless some gentle soul puts it here before me...
I'm an absolute disgrace when it comes to remembering formulae...
Cheers,😉
Frank,
That's why we spend all the money on fancy text-books!
2(PI)(R)(C) if I read correctly... That search feature does come in handy at times.
So, the preamp does sound MUCH better with the 500K leak resistor. The bass is now present!
I do, however, have some cosidderable humm, and a strange sound in one channel. Sounds like wind blowing, or leaves rustling. I have to admit that my wiring is not exactly perfect at this point. Ground lines near chokes, fillament power lines near chokes, chokes near chokes... I assume this is the source of a majority of the humm. Do you have experience with the other "wind" sound I hear, and if so what is the general cause?
My first choke is still buzzing quite nicely, any suggestions for a better make/model. It is currently the Hammond 20H 100mA 193C version, but I feel it may be best to sub it with something a little "better". Someone mentioned swinging chokes, any thoughts?
That's all for me today, time for bed😴
Thanks,
Bryan
That's why we spend all the money on fancy text-books!
2(PI)(R)(C) if I read correctly... That search feature does come in handy at times.
So, the preamp does sound MUCH better with the 500K leak resistor. The bass is now present!
I do, however, have some cosidderable humm, and a strange sound in one channel. Sounds like wind blowing, or leaves rustling. I have to admit that my wiring is not exactly perfect at this point. Ground lines near chokes, fillament power lines near chokes, chokes near chokes... I assume this is the source of a majority of the humm. Do you have experience with the other "wind" sound I hear, and if so what is the general cause?
My first choke is still buzzing quite nicely, any suggestions for a better make/model. It is currently the Hammond 20H 100mA 193C version, but I feel it may be best to sub it with something a little "better". Someone mentioned swinging chokes, any thoughts?
That's all for me today, time for bed😴
Thanks,
Bryan
Hi Bryan,
The wind noise is most likely a noisey tube. Try swapping the tubes side to side to see if the noise follows the tube.
For your buzzing choke, try putting a small cap between the rectifier and the choke. Something along the line of .5 to 1uf. You will still get the benefits of the choke input but the small amount of capacitance reduces the voltage swing that the choke sees and could cut down on the buzzing.
Gary
Got to get to bed, Alarm goes off at 4:00am...
The wind noise is most likely a noisey tube. Try swapping the tubes side to side to see if the noise follows the tube.
For your buzzing choke, try putting a small cap between the rectifier and the choke. Something along the line of .5 to 1uf. You will still get the benefits of the choke input but the small amount of capacitance reduces the voltage swing that the choke sees and could cut down on the buzzing.
Gary
Got to get to bed, Alarm goes off at 4:00am...
Thanks, I'll try a small cap tonight and see how I get along with a reduction in buzz.
Will also try swapping the tubes, to track down that breeze!
About the small amount of DC at the grounds of the cathode reisstor and grid-leak resistor, and grid??? I measure 120-130 mV DC at these points...? Why would this be. Is this a problem?
I measure 0 VDC at the earth.
Thanks,
Bryan
Will also try swapping the tubes, to track down that breeze!
About the small amount of DC at the grounds of the cathode reisstor and grid-leak resistor, and grid??? I measure 120-130 mV DC at these points...? Why would this be. Is this a problem?
I measure 0 VDC at the earth.
Thanks,
Bryan
Bryan -
If you're still looking for bass, you should try bypassing that cathode resistor. Don't be shy about sticking a big-*** cap in there. - Pat
If you're still looking for bass, you should try bypassing that cathode resistor. Don't be shy about sticking a big-*** cap in there. - Pat
Cathode by-pass is on my list of things to try, but before I can tailor the sound to my specific taste, I need to attack the humm, and various other noises....???
Hopefully once i neaten up my wiring and grounds, the humm/noise will not be an issue!
100uF big enough?
BK
Hopefully once i neaten up my wiring and grounds, the humm/noise will not be an issue!
100uF big enough?
BK
Hi,
The use of a cathode bypass cap will not change the frequency response of the stage as such.
It will increase the gain and lower the Zo of it but the cap will also introduce distortions due to its own non-linearity.
Cheers,😉
The use of a cathode bypass cap will not change the frequency response of the stage as such.
It will increase the gain and lower the Zo of it but the cap will also introduce distortions due to its own non-linearity.
Cheers,😉
Hey Guys,
So, I've neatened up some of the wiring, and I still have the HUMMMMM, and the "wind-like" sound. Tried changing tubes and the sound remains.
One thing I've noticed, when trying to play with the orientation of the chokes, is that when I touch the outer case of the choke, the BUZZZ increases in volume. Thoughts?
I still have not tried placing a cap before the choke.... guess I'll give that a go now and report back.
What does "tube-rush" sound like? Could this be the windy sound I am rhearing?
Thanks,
Bryan
So, I've neatened up some of the wiring, and I still have the HUMMMMM, and the "wind-like" sound. Tried changing tubes and the sound remains.
One thing I've noticed, when trying to play with the orientation of the chokes, is that when I touch the outer case of the choke, the BUZZZ increases in volume. Thoughts?
I still have not tried placing a cap before the choke.... guess I'll give that a go now and report back.
What does "tube-rush" sound like? Could this be the windy sound I am rhearing?
Thanks,
Bryan
Hey all,
One other observation...
When I was toasting my PS a week ago😱 , with the excessive voltage, one of the 12AX4 GTA's began to glow RED HOT right begore the fuse blew. I've since corrected the voltage and the wiring, but kept the same rectifiers in the circuit. Upon close inspection of the tubes, I noticed that on one side of the plate, where the two grey plates are joined, there is a small gap, which may be from warpage due to the excessive heat the tube was subjected to!
The tubes are RCA, on one side of the tube, the seam is straight and perfectly connected, and on the other side is this warpage??? Is this common to the tube, or is it likely due to damage during this event? I will sub in some Sylvania 12AX4 GTB's tomorrow to see if the HUMM/BUZZ/WINDY sound prevails, but in the interim would like to know if anyone thinks this could be causing problems...
Sorry for the impropper description of the components of this tube, but I've tried to describe to the best of my ability.
Any thoughts?
Thanks,
Bryan
One other observation...
When I was toasting my PS a week ago😱 , with the excessive voltage, one of the 12AX4 GTA's began to glow RED HOT right begore the fuse blew. I've since corrected the voltage and the wiring, but kept the same rectifiers in the circuit. Upon close inspection of the tubes, I noticed that on one side of the plate, where the two grey plates are joined, there is a small gap, which may be from warpage due to the excessive heat the tube was subjected to!
The tubes are RCA, on one side of the tube, the seam is straight and perfectly connected, and on the other side is this warpage??? Is this common to the tube, or is it likely due to damage during this event? I will sub in some Sylvania 12AX4 GTB's tomorrow to see if the HUMM/BUZZ/WINDY sound prevails, but in the interim would like to know if anyone thinks this could be causing problems...
Sorry for the impropper description of the components of this tube, but I've tried to describe to the best of my ability.
Any thoughts?
Thanks,
Bryan
Hey Guys,
OK, I've narrowed down the humm and noise problems.
What I have noticed is that with the inputs connected to the source, I have MAJOR humm, but when the inputs are disconnected, the hum is GREATLY decreased.
As it is now, I have the ground and signal wire as a twisted pair going to the pot. Then, the ground and signal wire travels to the tube, and the ground wire to the ground buss by the tube, both wires twisted.
Could it be the twisting that is causing the humm??? The wires are also quite long, but do not travel near any chokes/transformers....
Any ideas?
OK, I've narrowed down the humm and noise problems.
What I have noticed is that with the inputs connected to the source, I have MAJOR humm, but when the inputs are disconnected, the hum is GREATLY decreased.
As it is now, I have the ground and signal wire as a twisted pair going to the pot. Then, the ground and signal wire travels to the tube, and the ground wire to the ground buss by the tube, both wires twisted.
Could it be the twisting that is causing the humm??? The wires are also quite long, but do not travel near any chokes/transformers....
Any ideas?
Try swapping out interconnects for a different pair. You might also try running a wire between preamp ground and source chassis. Sometimes, this is enough to break up any ground loops...if they are the cause of the hum.
Heads Up
Bill Perkins (PEARL) has just reposted a revised version of his replication of the GE 12B4 datasheet.
http://www.pearl-hifi.com/06_Lit_Archive/04_Tube_Data/Tubes_GE/GE_12B4_Data.pdf
dave
Bill Perkins (PEARL) has just reposted a revised version of his replication of the GE 12B4 datasheet.
http://www.pearl-hifi.com/06_Lit_Archive/04_Tube_Data/Tubes_GE/GE_12B4_Data.pdf
dave
Hi Guys,
A few quick questions....
I have cleaned up the wiring, and fixed a ground loop, and the humm is down quite dramatically. With the volume at normal listening levels, it is hard to hear near the speaker, but as I increase the volume, the humm is noticable. I think a lot of this may be due to very long input wires, which span over 3 feet. I'll try to shorten these, and isolate/shield to determine if this may be the problem.
What I did notice was that when I run the 12b4A's at 33mA, I hear a lot of "hiss", but when I bring it down to around 23mA, the hiss is greatly decreased. Is it possible that the sound I hear is from running too much current through the tubes?
Also, if I connect the output to the amp when the preamp is powered up, I get a loud pop from the speakers, and then all is quiet. No noise if I unplug the output while the preamp is on. Any ideas as to the cause of this?
With the PS, I am using two 12AX4's, in a hybrid full wave configuration. The transformer is 190-0-190. Each leg of the AC HV has a 1n4007 with the cathodes connected and grounded to the first cap of the LCLC filter (similar to the diagram earlier in this post). The PS is then grounded from the first cap to earth. I currently do not have the CT grounded, as when I do this, the voltage is decreased by half from the rectifier. Is it correct to leave the CT unattached as I currently have it?
Any ideas and assistance is appreciated,
Thanks,
Bryan
A few quick questions....
I have cleaned up the wiring, and fixed a ground loop, and the humm is down quite dramatically. With the volume at normal listening levels, it is hard to hear near the speaker, but as I increase the volume, the humm is noticable. I think a lot of this may be due to very long input wires, which span over 3 feet. I'll try to shorten these, and isolate/shield to determine if this may be the problem.
What I did notice was that when I run the 12b4A's at 33mA, I hear a lot of "hiss", but when I bring it down to around 23mA, the hiss is greatly decreased. Is it possible that the sound I hear is from running too much current through the tubes?
Also, if I connect the output to the amp when the preamp is powered up, I get a loud pop from the speakers, and then all is quiet. No noise if I unplug the output while the preamp is on. Any ideas as to the cause of this?
With the PS, I am using two 12AX4's, in a hybrid full wave configuration. The transformer is 190-0-190. Each leg of the AC HV has a 1n4007 with the cathodes connected and grounded to the first cap of the LCLC filter (similar to the diagram earlier in this post). The PS is then grounded from the first cap to earth. I currently do not have the CT grounded, as when I do this, the voltage is decreased by half from the rectifier. Is it correct to leave the CT unattached as I currently have it?
Any ideas and assistance is appreciated,
Thanks,
Bryan
Glad to hear that you are making progress.
Do you have bleeder resistors after the output caps? Check for DC voltage on the ouputs. If you have large caps and large bleeder resistors it may take a long time to get the output side of the caps back down to ground after powering up the preamp.
When using a bridge configuration you do not connect the center tap to ground. This will roast the output transformer as it shorts out half of the secondary.
From your description it sounds like the first cap in the power supply is connected to ground. This is not a good idea if you have the far end of the power supply connected to the single point ground. You would be much better off if the only ground connection in the power supply was at the last cap. Go back and look at the schematic of the 85 line stage in group 3 of this posting string. Note how the power supply is connected to the single point ground at the output end only. This keeps the charging currents in the first cap/choke/rectifiers out of the ground scheme. No need to run the charging currents anywhere near the signal ground.
Hope this helps,
Gary
Do you have bleeder resistors after the output caps? Check for DC voltage on the ouputs. If you have large caps and large bleeder resistors it may take a long time to get the output side of the caps back down to ground after powering up the preamp.
When using a bridge configuration you do not connect the center tap to ground. This will roast the output transformer as it shorts out half of the secondary.
From your description it sounds like the first cap in the power supply is connected to ground. This is not a good idea if you have the far end of the power supply connected to the single point ground. You would be much better off if the only ground connection in the power supply was at the last cap. Go back and look at the schematic of the 85 line stage in group 3 of this posting string. Note how the power supply is connected to the single point ground at the output end only. This keeps the charging currents in the first cap/choke/rectifiers out of the ground scheme. No need to run the charging currents anywhere near the signal ground.
Hope this helps,
Gary
Gary,
Thanks for the advice.
I do have a large bleeder resistor after the caps, 1M, and the cap is 1mF. I thought the problem may have been from some DC at the output. I will measure it during power-up, and see if it is being bled to ground. Would it be wise to decrease the value of the bleeder a bit?
I'll try the advice with the PS grounding. I will ground the PS fro the last cap, directly before the VR tubes. I'm curious to see if this makes a difference!!!
Any other thoughts of words of wisdom?
Thanks,
Bryan
Thanks for the advice.
I do have a large bleeder resistor after the caps, 1M, and the cap is 1mF. I thought the problem may have been from some DC at the output. I will measure it during power-up, and see if it is being bled to ground. Would it be wise to decrease the value of the bleeder a bit?
I'll try the advice with the PS grounding. I will ground the PS fro the last cap, directly before the VR tubes. I'm curious to see if this makes a difference!!!
Any other thoughts of words of wisdom?
Thanks,
Bryan
Hi Gary
At the schem of group 3 with 85 can I replace the BSSCCS with your pentodeCCS with EL84?
With the 85 how much gain do you have and Zout?
I'm building the same line stage with Bryan but I'm thinking to use a pentode CCS for anode load.
At the schem of group 3 with 85 can I replace the BSSCCS with your pentodeCCS with EL84?
With the 85 how much gain do you have and Zout?
I'm building the same line stage with Bryan but I'm thinking to use a pentode CCS for anode load.
Hey Guys,
Seems I may have figured out the problem with the "popping" noise when I power up the preamp.
I measured the DC voltage at the output during warm-up and shut off.
When I flip on the power, the DC raises (lowers) to about -30VDC, and then slowly evens out at 0VDC, where it fluctuates about between 0, an 1mV.
When I power off the unit, the voltage jumps again to -30 ish, and then raises to ground.
Any thoughts?
Thanks,
BK
Seems I may have figured out the problem with the "popping" noise when I power up the preamp.
I measured the DC voltage at the output during warm-up and shut off.
When I flip on the power, the DC raises (lowers) to about -30VDC, and then slowly evens out at 0VDC, where it fluctuates about between 0, an 1mV.
When I power off the unit, the voltage jumps again to -30 ish, and then raises to ground.
Any thoughts?
Thanks,
BK
Hi,
Bryan,
Have you put a bleeder resistor of, say, 100k in shunt with the output?
Also, to avoid thumps, leave everything connected, switch the preamp on with the mute switch engaged.
Wait for five minutes, then switch on the amp and have that warm up for another five minutes.
After that, disengaged the preamp with the volume at low level.
No turn on thump should occur if you adhere to this turn on sequence.
For turn of, first mute the preamp...In short run the sequence in reverse bar the stanby, warm up period of course.
Cheers,😉
Bryan,
Have you put a bleeder resistor of, say, 100k in shunt with the output?
Also, to avoid thumps, leave everything connected, switch the preamp on with the mute switch engaged.
Wait for five minutes, then switch on the amp and have that warm up for another five minutes.
After that, disengaged the preamp with the volume at low level.
No turn on thump should occur if you adhere to this turn on sequence.
For turn of, first mute the preamp...In short run the sequence in reverse bar the stanby, warm up period of course.
Cheers,😉
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