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Limberpine
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41 minutes ago, Limberpine said:

Welp, I turned off every circuit in the house except the one that the stereo system is on and the buzz still persists. What's weird is that my SET amp doesn't have the buzz, it has a dull hum up close, but all of my push pull amps have this same buzz. 

 

Video attached of the sound from 3ft away from the speaker. Headphones are helpful to hear it, because of taking the video from my phone. 

 

My Leben CS300 has a similar hum, though, I think, not as loud. I have learned to live with it, as it is caused by the 'topology' (the architecture, the way the components are laid out inside the amplifier.) This topology creates the 'magic' of the amp, but it is impossible to change, and it is also the reason why 'measuring' will not result in finding anomalies. Also, the more efficient the speakers are, the more you can hear the hum. Klipsch speakers are very efficient...

 

The quote below is about the CS300 Leben, but I think your humming amp is having the same characteristics/topology.

Here is my source and citation, I put the crucial phrases in bold lettertype.

 

(...) I asked to check, why there is a slight mains hum audible (you can hear a 50Hz noise, and its multiplications 100Hz, 150Hz, especially in one channel). This was not the flaw of my unit – I heard something like that with all other CS-300 listened to. With normal use, with 89dB or less efficient loudspeakers, it was somewhere in the background, and did not interfere with music. The same thing was with headphones – AKG, which I used with all the Leben versions, have 62Ω impedance, quite low, so they did not pose any problems. But the HD800 are high impedance headphones - 600Ω – and they are not so forgiving, any error, any noise or hum can be heard immediately – just like with high efficiency loudspeakers. And with them, this hum was annoying. Mr. Waszczyszyn, like any scientist, systematically searched for the reason, and found out, that there is no choke in my unit, but only resistors, what increases noise slightly, and that the hum is a result of the chosen topology, with one channel closer to the power supply than the other. So it cannot be helped without reworking the whole amplifier. And I did not want to do that, because we could maybe improve on this one aspect, while destroying everything else, because architecture of elements is a part of the “magic” coming from years of experience. And I am sure Mr. Hyodo knew what he was doing. Well – this was probably a part of the compromise. There is nothing we can do with the loudspeaker output, but with the headphone output it is a different story. It was enough to solder a few resistors to the headphone socket, and that was it. Their values must be chosen experimentally, as it will depend on the impedance and efficiency of our headphones. At first the values were chosen too big, and needed to be adjusted, but now I can tell, that there is no hum at all! And no noise. This is the reason I recommend this simple trick to everyone – it is cheap and effective. Probably in the future I would like to see better resistors there, like Vishay, but for now, I am happy.

source: http://highfidelity.pl/@main-135&lang=en

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2 hours ago, MeloManiac said:

It was enough to solder a few resistors to the headphone socket, and that was it. Their values must be chosen experimentally, as it will depend on the impedance and efficiency of our headphones. At first the values were chosen too big, and needed to be adjusted, but now I can tell, that there is no hum at all! And no noise. This is the reason I recommend this simple trick to everyone – it is cheap and effective. Probably in the future I would like to see better resistors there, like Vishay, but for now, I am happy.

source: http://highfidelity.pl/@main-135&lang=en

So, should I look into placing some resistors across the speaker wire connects on the crossover? Would that help? 

 

But, Yeah, I guess I will learn to live with it.....for now.....

 

Thanks for your help! 🙂

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Your hum issue continues to be on my mind. The thing is that the Dynaco ST70's topology is quite symmetrical (compared to the asymmetrical topology of the Leben CS300).

So I found this information about it elsewhere, and it comes from Bob Latino, who has a great reputation related to ST70 tube amps. 

Your hum may be caused by not incorrect bias. You should be able to check this on your own. This may have been metioned earlier on in this thread, but I heaven't read all 8 pages....

https://dynacotubeaudio.forumotion.com/t2723-st70-hum-problem 

 

Quote:

New to the forum.... Gifted an ST70 w/KT88s, VTA w/12AT7s. Amp is dead quiet with no input cables. When preamp connected, no hum at minimum volume, moderate hum starting about ⅓ on volume, louder as volume is turned up. Balance control moved to the left, hum on left channel disappears, to the right, hum remains. As soon as it is moved towards the center, hum on both channels. When a record is played, volume is equal from both speakers (AR2a). Rolled 12AT7s and got hum with balance full left or right. Also need instructions on how to bias as no documentation was received.... (Gregg)

Hi Gregg,

If your VTA ST-70 is quiet with no input cables OR with the input cables connected to your preamp and the preamp on at minimum volume then the amp is not at fault .. It is your preamp that is at fault.

To bias an older 12AT7 driver board VTA ST-70 see below .. NOTE - The older VTA amps with the 12AT7 driver tubes have the bias pot's rotation in reverse > clockwise rotation will DECREASE bias level and counterclockwise rotation will INCREASE bias level.

Get your multitester and set the range for 0 to 2 volts DC. CONNECT THE SPEAKERS. Place the GZ34 rectifier tube and just the LEFT EL34/KT88 output tubes in their socket. Turn on the amp. Allow the amp to warm up for a minute and check to see that the EL34 and GZ34 tubes light up properly. Measure the bias on the LEFT output tubes by placing the BLACK NEGATIVE probe anywhere on the chassis and the RED POSITIVE probe in the hole marked “Biaset 1.56 v”. With a small screwdriver adjust the FRONT LEFT bias adjuster on the driver board closest to the front left tube. Turn the adjuster CLOCKWISE TO REDUCE BIAS and COUNTERCLOCKWISE TO INCREASE BIAS. Set the bias for .400 volts if you are using EL34 or KT77 tubes OR .500 volts if you are using KT88 or 6550 tubes. Now place the positive probe in pin 4 (which is on the opposite side of the power take off socket) and use the BACK LEFT bias adjuster to measure bias on the LEFT REAR output tube. Set it the same as the front tube. Turn off the amp. (Note - on some amps the REAR output tube's bias measuring point may be on a different front tube socket pin) Plug in the two RIGHT channel EL34/KT88 tubes, turn on the amp and repeat the bias procedure as outlined above on the RIGHT channel tubes. Now go back to the left channel tubes and notice that the bias is now a little LOW. ADJUSTING BIAS ON ONE TUBE HAS A SLIGHT AFFECT ON THE OTHERS. Go back and forth between all output tubes until all tubes have the proper bias.

Bob [Latino]

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37 minutes ago, MeloManiac said:

Your hum issue continues to be on my mind. The thing is that the Dynaco ST70's topology is quite symmetrical (compared to the asymmetrical topology of the Leben CS300).

So I found this information about it elsewhere, and it comes from Bob Latino, who has a great reputation related to ST70 tube amps. 

Your hum may be caused by not incorrect bias. You should be able to check this on your own. This may have been metioned earlier on in this thread, but I heaven't read all 8 pages....

https://dynacotubeaudio.forumotion.com/t2723-st70-hum-problem 

 

Quote:

New to the forum.... Gifted an ST70 w/KT88s, VTA w/12AT7s. Amp is dead quiet with no input cables. When preamp connected, no hum at minimum volume, moderate hum starting about ⅓ on volume, louder as volume is turned up. Balance control moved to the left, hum on left channel disappears, to the right, hum remains. As soon as it is moved towards the center, hum on both channels. When a record is played, volume is equal from both speakers (AR2a). Rolled 12AT7s and got hum with balance full left or right. Also need instructions on how to bias as no documentation was received.... (Gregg)

Hi Gregg,

If your VTA ST-70 is quiet with no input cables OR with the input cables connected to your preamp and the preamp on at minimum volume then the amp is not at fault .. It is your preamp that is at fault.

To bias an older 12AT7 driver board VTA ST-70 see below .. NOTE - The older VTA amps with the 12AT7 driver tubes have the bias pot's rotation in reverse > clockwise rotation will DECREASE bias level and counterclockwise rotation will INCREASE bias level.

Get your multitester and set the range for 0 to 2 volts DC. CONNECT THE SPEAKERS. Place the GZ34 rectifier tube and just the LEFT EL34/KT88 output tubes in their socket. Turn on the amp. Allow the amp to warm up for a minute and check to see that the EL34 and GZ34 tubes light up properly. Measure the bias on the LEFT output tubes by placing the BLACK NEGATIVE probe anywhere on the chassis and the RED POSITIVE probe in the hole marked “Biaset 1.56 v”. With a small screwdriver adjust the FRONT LEFT bias adjuster on the driver board closest to the front left tube. Turn the adjuster CLOCKWISE TO REDUCE BIAS and COUNTERCLOCKWISE TO INCREASE BIAS. Set the bias for .400 volts if you are using EL34 or KT77 tubes OR .500 volts if you are using KT88 or 6550 tubes. Now place the positive probe in pin 4 (which is on the opposite side of the power take off socket) and use the BACK LEFT bias adjuster to measure bias on the LEFT REAR output tube. Set it the same as the front tube. Turn off the amp. (Note - on some amps the REAR output tube's bias measuring point may be on a different front tube socket pin) Plug in the two RIGHT channel EL34/KT88 tubes, turn on the amp and repeat the bias procedure as outlined above on the RIGHT channel tubes. Now go back to the left channel tubes and notice that the bias is now a little LOW. ADJUSTING BIAS ON ONE TUBE HAS A SLIGHT AFFECT ON THE OTHERS. Go back and forth between all output tubes until all tubes have the proper bias.

Bob [Latino]

This was not previously mentioned in the rest of the thread. Thanks! 

 

I have never set the bias on the St-70, the last tube amp tech I had check it out, reset it with the newer tubes I got for it. I'm running a NOS GZ37 and new Tung Sol El-34s and NOS RCA 7199 blackplates, in that amp right now. I will admit its a bit daunting to me to take this bias adjustment on, cause I don't want to ruin anything, but I also want to learn more about all of this, so I will find some time to try out what Bob Latino suggests

 

The ST-35 doesn't have bias pots and James Burgess PP 45, this is what James told me There are no bias adjustments. It is set up so the AC(signal) balance of the phase inverter can be adjusted.  This is only necessary when changing/replacing the 6SN7 tubes. 

 

All the tubes in the James Burgess are NOS and close matched. 

 

I listened to the PP 45 last night and ignoring the noise, the sound was divine. 

 

Thanks for your thoughts and help!

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Non metallic small screwdriver or insulated. If you do, mark the position before you begin so you can return. Warmed up first

 

One of those brand model has an auto biasing circuit or part put in them afterwards but, manually maybe better.

If it works.

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  • 6 months later...
  • 2 weeks later...
On 4/2/2021 at 2:44 AM, MeloManiac said:

Does anybody know how these new types of light, mostly energy saving, like dimmable LEDs and fillament lamps affect the electrical circuit and ultimately the sound quality?

 

Unfortunately, it is not just "lights" that affect the electrical circuits in a home. Any appliance, motor (fan), freeezer, fridge, HVAC, etc can affect the electric circuit in your home and introduce "hash" (RF junk) into your audio system. Dimmers usually have a switching MOSFET circuit and that will introduce buzzes, clicks and other junk back into the house circuitry. 

 

The "quietest" type of light would be a good old incandescent type bulb. It is just a resistance filament, so it is quiet by nature. Flourescent, LED, CFL, Neon, etc type lights are noisy and can introduce humm / buzz into the house circuitry easily. 

 

To help attenuate these types of noises, I have had good luck with Tripplite ISO-BAR power conditioner / surge protecters. 

 

They are high quality and get great reviews. If you try a Tripplite unit, ensure it has the "isolated filter banks", not all the Tripplite units have them, but most do. 

Tripplite ISO-BAR-4 ULTRA.jpg

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On 11/12/2021 at 1:48 PM, Curious_George said:

 

Unfortunately, it is not just "lights" that affect the electrical circuits in a home. Any appliance, motor (fan), freeezer, fridge, HVAC, etc can affect the electric circuit in your home and introduce "hash" (RF junk) into your audio system. Dimmers usually have a switching MOSFET circuit and that will introduce buzzes, clicks and other junk back into the house circuitry. 

 

The "quietest" type of light would be a good old incandescent type bulb. It is just a resistance filament, so it is quiet by nature. Flourescent, LED, CFL, Neon, etc type lights are noisy and can introduce humm / buzz into the house circuitry easily. 

 

To help attenuate these types of noises, I have had good luck with Tripplite ISO-BAR power conditioner / surge protecters. 

 

They are high quality and get great reviews. If you try a Tripplite unit, ensure it has the "isolated filter banks", not all the Tripplite units have them, but most do. 

Tripplite ISO-BAR-4 ULTRA.jpg

I now have 2 powervar Powe conditioners/isolation transformers now. Would you still suggest this tripplite iso bar knowing that I have these? 

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On 10/29/2021 at 3:46 PM, Limberpine said:

Finally some semblance of order in my room. Got the component racks finished and in place last night. Fun fun! 

20211029_124454.jpg

 

BTW, when I ported my LaScala's, I discovered that putting wheels underneath the speaker to bring them up off the floor improved the low-end quite a bit in my room. You may want to experiment with 4 pieces of wood in each corner and see if that affects anything. Mine are raised about 4" off the ground. 

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