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    Heartbeat-like thumping in speakers? ST-70 > PAS-3

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    DC92


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    Heartbeat-like thumping in speakers? ST-70 > PAS-3 Empty Heartbeat-like thumping in speakers? ST-70 > PAS-3

    Post by DC92 Fri Jan 29, 2021 11:35 am

    I've run my system for years; however, this phenomenon is new. I run an ST-70 into a PAS 3. If I run the 70 straight out, the thumping disappears. So it's either in the RCA connectors to the PAS 3 or it's in the PAS 3 somewhere.

    I don't know a better way to describe it than like a heartbeat pulse but it's a repeated pattern . . . like . . .Baa ba ba ba . . . Ba ba ba ba . . . but the tone of a heartbeat . . .

    Any experiences with such a thing? Even if I disconnect everything but the ST-70 the thump happens. And while it generally happens to the right (stage left) speaker, it does occasionally happen to left (stage right) speaker.

    It's a maddening sound. Like the tell-tale heart or something . . .

    Thanks!
    peterh
    peterh


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    Heartbeat-like thumping in speakers? ST-70 > PAS-3 Empty Re: Heartbeat-like thumping in speakers? ST-70 > PAS-3

    Post by peterh Fri Jan 29, 2021 2:01 pm

    DC92 wrote:I've run my system for years; however, this phenomenon is new. I run an ST-70 into a PAS 3. If I run the 70 straight out, the thumping disappears. So it's either in the RCA connectors to the PAS 3 or it's in the PAS 3 somewhere.

    I don't know a better way to describe it than like a heartbeat pulse but it's a repeated pattern . . . like . . .Baa ba ba ba . . . Ba ba ba ba . . . but the tone of a heartbeat . . .

    Any experiences with such a thing? Even if  I disconnect everything but the ST-70 the thump happens. And while it generally happens to the right (stage left) speaker, it does occasionally happen to left (stage right) speaker.

    It's a maddening sound. Like the tell-tale heart or something . . .

    Thanks!
    If your PAS is a non-X it has a small DC at it's output. That could affect the input of the ST70 as it
    has dc to the input tube grid.

    Try a small cap in series ( 0.1 would do just fine) between the PAS and the ST70. The most
    convenient point is probably in the PAS right at the output posts.

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    Bob Latino
    Bob Latino
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    Heartbeat-like thumping in speakers? ST-70 > PAS-3 Empty Re: Heartbeat-like thumping in speakers? ST-70 > PAS-3

    Post by Bob Latino Fri Jan 29, 2021 2:56 pm

    DC92 wrote:I've run my system for years; however, this phenomenon is new. I run an ST-70 into a PAS 3. If I run the 70 straight out, the thumping disappears. So it's either in the RCA connectors to the PAS 3 or it's in the PAS 3 somewhere.

    I don't know a better way to describe it than like a heartbeat pulse but it's a repeated pattern . . . like . . .Baa ba ba ba . . . Ba ba ba ba . . . but the tone of a heartbeat . . .

    Any experiences with such a thing? Even if  I disconnect everything but the ST-70 the thump happens. And while it generally happens to the right (stage left) speaker, it does occasionally happen to left (stage right) speaker.

    It's a maddening sound. Like the tell-tale heart or something . . .

    Thanks!

    Usually a repetitive thumping noise is caused by one or more power supply capacitors that are not doing their job. Try replacing the power supply capacitors and any associated resistors in the B+ power supply. In general this noise is called "motorboating" because sometimes it does sound like a motorboat. It may also be a sound that repeats at regular intervals (as in your case).

    Bob

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    DC92


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    Heartbeat-like thumping in speakers? ST-70 > PAS-3 Empty Re: Heartbeat-like thumping in speakers? ST-70 > PAS-3

    Post by DC92 Sat Jan 30, 2021 5:02 pm

    peterh wrote:
    DC92 wrote:I've run my system for years; however, this phenomenon is new. I run an ST-70 into a PAS 3. If I run the 70 straight out, the thumping disappears. So it's either in the RCA connectors to the PAS 3 or it's in the PAS 3 somewhere.

    I don't know a better way to describe it than like a heartbeat pulse but it's a repeated pattern . . . like . . .Baa ba ba ba . . . Ba ba ba ba . . . but the tone of a heartbeat . . .

    Any experiences with such a thing? Even if  I disconnect everything but the ST-70 the thump happens. And while it generally happens to the right (stage left) speaker, it does occasionally happen to left (stage right) speaker.

    It's a maddening sound. Like the tell-tale heart or something . . .

    Thanks!
    If your PAS is a non-X it has a small DC at it's output. That could affect the input of the ST70 as it
    has dc to the input tube grid.

    Try a small cap in series ( 0.1 would do just fine) between the PAS and the ST70. The most
    convenient point is probably in the PAS right at the output posts.



    Thanks for this. I am running a non-X, but I recently just by-passed the tone controls.

    I apologize for my own ignorance here, but could you elaborate on this:

    "Try a small cap in series ( 0.1 would do just fine) between the PAS and the ST70. The most
    convenient point is probably in the PAS right at the output posts."

    I'm not sure what you mean by "small cap in series." The RCA connectors are what are connecting the PAS and the ST70. And by "output posts," do you mean the female connector for the male RCA inserts?

    Thanks!

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    DC92


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    Post by DC92 Sat Jan 30, 2021 5:06 pm

    Bob Latino wrote:
    DC92 wrote:I've run my system for years; however, this phenomenon is new. I run an ST-70 into a PAS 3. If I run the 70 straight out, the thumping disappears. So it's either in the RCA connectors to the PAS 3 or it's in the PAS 3 somewhere.

    I don't know a better way to describe it than like a heartbeat pulse but it's a repeated pattern . . . like . . .Baa ba ba ba . . . Ba ba ba ba . . . but the tone of a heartbeat . . .

    Any experiences with such a thing? Even if  I disconnect everything but the ST-70 the thump happens. And while it generally happens to the right (stage left) speaker, it does occasionally happen to left (stage right) speaker.

    It's a maddening sound. Like the tell-tale heart or something . . .

    Thanks!

    Usually a repetitive thumping noise is caused by one or more power supply capacitors that are not doing their job. Try replacing the power supply capacitors and any associated resistors in the B+ power supply. In general this noise is called "motorboating" because sometimes it does sound like a motorboat. It may also be a sound that repeats at regular intervals (as in your case).

    Bob


    Thanks for this, Bob. I'll study this to see what components those are exactly in the PAS-3. By the way, I've noticed that it's not consistent. For example, it can switch rhythm and speaker. And it can go awhile without making the sound. I can turn off the system, too, and then start it back up, and the sound will disappear for however long, but it always returns at some point. It just starts up with no real rhyme or reason. I don't know if that info makes any difference, but thought I'd add it.

    As always, I appreciate your advice and council!
    audioregenesis
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    Post by audioregenesis Sat Jan 30, 2021 7:25 pm

    What instructions did you follow when you bypassed the tone controls? Proper instructions should include the addition of a 1.0uF coupling capacitor to prevent excessive DC voltage from appearing at the output of the PAS. Power amplifiers, like the ST-70, which are not AC coupled at the input, may become unstable if too much DC is present. A stock PAS (non X) will exhibit about 100mV of DC at the output, which the ST-70 will tolerate, however, bypassing the tone controls without including the capacitor will elevate that to about 800mV, which can be a problem for the ST-70.
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    DC92


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    Post by DC92 Sat Jan 30, 2021 9:16 pm

    audioregenesis wrote:What instructions did you follow when you bypassed the tone controls? Proper instructions should include the addition of a 1.0uF coupling capacitor to prevent excessive DC voltage from appearing at the output of the PAS. Power amplifiers, like the ST-70, which are not AC coupled at the input, may become unstable if too much DC is present. A stock PAS (non X) will exhibit about 100mV of DC at the output, which the ST-70 will tolerate, however, bypassing the tone controls without including the capacitor will elevate that to about 800mV, which can be a problem for the ST-70.

    I followed curcioaudio's directions .

    Refer to figure 1 and proceed with the following steps.

    We will begin with the Left Channel.

    4. Refer to figure 1 and connect a jumper from terminal 4 to terminal 6 on the foil
    side of PC-5.

    5. Connect another wire jumper from terminal 6 to terminal 7 of PC-5.

    6. De-solder the wire connected to terminal 3. You will find that it is connected to
    the center lug of the Left Treble Control and once desoldered from PC-5 terminal 3, you may cut it at the connection to the Left Treble control.

    Next we will make the same changes to the Right Channel.

    7. Refer to figure 1 and connect a jumper from terminal 11 to terminal 13 on the foil
    side of PC-5.

    8. Connect another wire jumper from terminal 12 to terminal 13 of PC-5.

    9. De-solder the wire connected to terminal 10. You will find that it is connected to
    the center lug of the Right Treble Control and once desoldered from PC-5 terminal 10, you may cut it at the connection to the Right Treble control.

    10. The tone controls are now removed from the circuit.

    11. Replace the bottom plate and top cover and secure with the four screws
    audioregenesis
    audioregenesis


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    Post by audioregenesis Sat Jan 30, 2021 9:48 pm

    The curcioaudio instructions, which have been out there quite a while, oddly, did not include the capacitor. It is quite important, and why it was included in the PAS 3X, which has the tone bypass feature incorporated into the special tone control pots. The audioregenesis tone bypass instructions mimic the way it happens in the 3X and, of course, include the capacitor in exactly the same way.

    http://www.audioregenesis.com/documents/PAS%20Tone%20Control%20Bypass.pdf

    At this point, it may be easier to just add a capacitor at the output jack of your PAS as peterh described, although I'd perhaps go little larger than .1uF to take better advantage of the now lower output impedance of the PAS, should you ever require it.
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    DC92


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    Post by DC92 Sat Jan 30, 2021 10:04 pm

    audioregenesis wrote:The curcioaudio instructions, which have been out there quite a while, oddly, did not include the capacitor. It is quite important, and why it was included in the PAS 3X, which has the tone bypass feature incorporated into the special tone control pots. The audioregenesis tone bypass instructions mimic the way it happens in the 3X and, of course, include the capacitor in exactly the same way.

    http://www.audioregenesis.com/documents/PAS%20Tone%20Control%20Bypass.pdf

    At this point, it may be easier to just add a capacitor at the output jack of your PAS as peterh described, although I'd perhaps go little larger than .1uF to take better advantage of the now lower output impedance of the PAS, should you ever require it.

    Do you know where I can find instructions for that? I don't quite understand intuitively what it means to " just add a capacitor at the output jack."

    Thanks again!
    audioregenesis
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    Post by audioregenesis Sat Jan 30, 2021 10:22 pm

    Basically all it means is adding a capacitor in series with the wires that connect to the output jacks. It can be as simple as unsoldering the wires at the jacks, solder one lead of the capacitor to the jack, and then solder the wire to the other end of the capacitor. Keep the leads of the capacitors short so everything is neat, compact and secure. The capacitors can be low voltage to keep the size down, and any good quality film capacitor will work well. Perhaps 0.22 - 0.47 should be fine.
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    Jampot


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    Post by Jampot Mon Feb 08, 2021 5:30 am

    I'm a bit late to this so perhaps the problem is resolved. Do you use power line network adaptors by any chance? I do and find that they induce mains borne noise similar to that you describe in my phono stage. No apparent interference on other inputs so it may become audible due to the increase in gain.

    Hope you get it sorted.

    Jim

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    DC92


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    Post by DC92 Mon Feb 08, 2021 10:05 am

    Jampot wrote:I'm a bit late to this so perhaps the problem is resolved. Do you use power line network adaptors by any chance? I do and find that they induce mains borne noise similar to that you describe in my phono stage. No apparent interference on other inputs so it may become audible due to the increase in gain.

    Hope you get it sorted.

    Jim

    Thanks for the response. I'm not sure I know what "power line network adaptors" are, so I doubt I've added them. I've not yet resolved the issue because it seems like I might need to order some stuff, so I swapped it out with my Hafler DH-101 for the moment.

    What do you the power line adaptors do for you? Thanks again for your input. This board is so good!
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    Post by Jampot Mon Feb 08, 2021 12:04 pm

    Here in UK, (and I'm sure on the other side of the pond too) we have available network adapters that utilise the mains wiring in the house to provide a connection to the broadband router. It helps to cover wifi black spots where otherwise internet access wouldn't be available in the house.

    The networking feature is a great success but the gadgets inject noise into the mains supply which in my case is audible when playing vinyl via a stand alone phono stage. In fact it was so annoying I moved the adapter to an outlet next to the hifi with a long cable to the router so it was conveniently to hand and could be switched off for a 'proper' listening session:-)

    Jim
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    DC92


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    Post by DC92 Tue Aug 31, 2021 3:09 pm

    audioregenesis wrote:Basically all it means is adding a capacitor in series with the wires that connect to the output jacks. It can be as simple as unsoldering the wires at the jacks, solder one lead of the capacitor to the jack, and then solder the wire to the other end of the capacitor. Keep the leads of the capacitors short so everything is neat, compact and secure. The capacitors can be low voltage to keep the size down, and any good quality film capacitor will work well. Perhaps 0.22 - 0.47 should be fine.

    Hi folks,

    So I added a 50V .47 cap from the connecting wires to the output jacks as per suggested by you all. Although without them, I didn't seem to have any issues (that issue in the OP seemed to have disappeared on its own) unless it was causing the issue with ST-70s rectifiers blowing out fairly quickly, with the added caps, the volume—at least in my initial impression—seems to be lower than it was before, and so I have to give it a pretty nice boost with the volume knob, up to and even past the volume boost.

    What should I notice with the new caps, if anything? I suppose I don't understand still what the caps are doing? Are the regulating power to the ST-70 in some way? If so, how?

    Thanks!


    Last edited by DC92 on Tue Aug 31, 2021 3:49 pm; edited 2 times in total (Reason for editing : Added new info.)

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