Hello:
I own an out of warranty Willsonton R8 tube amplifier using KT88 tubes and everything is stock. This amp has a triode and ultralinear mode. I'm connecting it to Polkaudio RTi A7 speakers as well as some Klipsch RP-600.
Very happy with the sound but the other day I cranked up the volume to see what else it can do and the result was not pleasant. In triode mode, when I go past 10 o'clock on the volume scale it starts to distort in the louder sections, or the peaks. The distortion comes in the form of loud pops or crackling, kinda like the sound that tends to blow speakers, like a dirty pot at high volumes. This happens in both channels equally.
When I switch to ultraliner mode everything sounds clean, no popping or crackling. Went all the way to 12 o'clock in this mode and continues to be clean.
I've contacted Willsenton support and they responded quickly asking what speakers I have. Nothing past that so I was wondering if the knowledgeable people on this forum have any ideas what might be the cause. I sure hope it's not the output tubes, or God forbid, the output transformers. I'm not sure if I ever tried to go that loud before so I have no idea is this issue was always there or developed over time. One thing is for sure, both channels start to pop at the same point equally bad.
Can anybody that has this amp with stock tubes KT88 tried to crank the volume in triode mode and see if they experience the same thing?
I've attached a schematic for your review. I'm somewhat knowledgeable and I can take measurements if needed. Not sure how far Willsenton support is willing to go so I'm on my own.
Thanks
I own an out of warranty Willsonton R8 tube amplifier using KT88 tubes and everything is stock. This amp has a triode and ultralinear mode. I'm connecting it to Polkaudio RTi A7 speakers as well as some Klipsch RP-600.
Very happy with the sound but the other day I cranked up the volume to see what else it can do and the result was not pleasant. In triode mode, when I go past 10 o'clock on the volume scale it starts to distort in the louder sections, or the peaks. The distortion comes in the form of loud pops or crackling, kinda like the sound that tends to blow speakers, like a dirty pot at high volumes. This happens in both channels equally.
When I switch to ultraliner mode everything sounds clean, no popping or crackling. Went all the way to 12 o'clock in this mode and continues to be clean.
I've contacted Willsenton support and they responded quickly asking what speakers I have. Nothing past that so I was wondering if the knowledgeable people on this forum have any ideas what might be the cause. I sure hope it's not the output tubes, or God forbid, the output transformers. I'm not sure if I ever tried to go that loud before so I have no idea is this issue was always there or developed over time. One thing is for sure, both channels start to pop at the same point equally bad.
Can anybody that has this amp with stock tubes KT88 tried to crank the volume in triode mode and see if they experience the same thing?
I've attached a schematic for your review. I'm somewhat knowledgeable and I can take measurements if needed. Not sure how far Willsenton support is willing to go so I'm on my own.
Thanks
Attachments
Not sure if this info matters but it happens on all frequencies at the same volume level. I tried a 20KHz tone, since I don't hear that anymore, and it started popping loud right around the 10 mark in triode mode. In ultralinear I went all the way to the max and no popping at all.
But it works great in ultralinear mode.
The TR/UL switch is a relay. I will hard wire it as TR is the default relay position anyway. Will post the results soon.
The TR/UL switch is a relay. I will hard wire it as TR is the default relay position anyway. Will post the results soon.
I have hardwired the relay and it has the same problem.
Any other advice on what else it could be? The fact that it happens on both channels equally leads me to believe that the issue has been there since new.
Any other advice on what else it could be? The fact that it happens on both channels equally leads me to believe that the issue has been there since new.
I took some measurements using my phone with db meter app and the distortion in triode mode starts at around 80db at a distance of about 10 feet (3 meters).
I have a 60w pp amp with U/T where the max is around 90% before clipping. I don't know much about output transfer design but mine has R: 180 ohm while your is 1K. I thought I read somewhere that the voltage between pin 3 and 4 is around 5V. If yours is big different, then that may be the caused.
Check this forum for more info
https://forums.stevehoffman.tv/threads/willsenton-r8-and-r800i-805-or-845-news-and-views.1107931/
Check this forum for more info
https://forums.stevehoffman.tv/threads/willsenton-r8-and-r800i-805-or-845-news-and-views.1107931/
Thanks for the info. I will read the tread.
I measured between pin 3 and 4:
Not sure if this info helps.
I measured between pin 3 and 4:
- triode: positive 1.62 - 1.65 volts from minumum volume to about the time it starts to distort at which point it goes up and down from 1.6 to over 2.1 volts fluctuating quite a bit, popping and crackling at higher voltages.
- ultralinear: negative 1.24 volts steady until around 11 o'clock. Around 12 o'clock it starts to fluctuate going into positive 2 volts very briefly. I kinda hear somewhat of a distortion at that point but more like a traditional distortion, not a pop or crack like in triode mode.
Not sure if this info helps.
Output power in triode connection is typically at least 3dB lower than in UL or pentode connection. It would be helpful to determine whether the output stage or the driver stages are clipping first. Requires scope and disconnecting the feedback from the transformer secondary. This needs to be done with resistive loads to protect your amp and speakers.
I've made some more measurements and calculations and I believe it comes down to overdriving the amp. If you can bare with me and confirm if my calculations are right and if you think the amp performs as it should and there is nothing wrong with it.
Amp specs
Triode mode
sqrt(25w*8)=14v output at max volume. At 380mV input signal has a gain of 14/.38=37x gain.
Ultralinear mode
sqrt(45w*8)=19v output at max volume. At 380mV input signal has a gain of 14/.38=50x gain.
It looks like triode mode starts distorting at roughly half of the spec'ed power at 7.2v out of 14v, at half the volume. Ultralinear is clean all the way to maximum.
Is this to be expected and there is nothing wrong with the amp or is there something not right?
Thanks
Amp specs
- Input sensitivity is 380mV
- Input impedance is 100K
- triode mode: 25W+25W (doesn't specify if 4 or 8 ohm is used)
- ultralinear mode: 45W+45W (same as above)
Triode mode
sqrt(25w*8)=14v output at max volume. At 380mV input signal has a gain of 14/.38=37x gain.
- input of 380mV of 1KHz signal it starts to distort at 12 o'clock with an output of 7.2V
- input of 940mV of 1KHz signal it starts to distort at roughly 11 o'clock with and output of also 7.2v
- input of 2.1v (my DAC) of 1KHz signal is starts to distort at roughly 10 o'clock with an output of also 7.2V
Ultralinear mode
sqrt(45w*8)=19v output at max volume. At 380mV input signal has a gain of 14/.38=50x gain.
- input of 380mV of 1KHz signal - no distortion with an output of 16v
- input of 940mV of 1KHz signal - no distortion with an output of 18v
- input of 2.1V (my DAC) of 1KHz signal - no distortion with an output of 19v
It looks like triode mode starts distorting at roughly half of the spec'ed power at 7.2v out of 14v, at half the volume. Ultralinear is clean all the way to maximum.
Is this to be expected and there is nothing wrong with the amp or is there something not right?
Thanks
The B+ seems to be correct between pin 3 and 4. I am not pretty good with the measurement.
As [B]kevinkr[/B] mention, you may want to check where the clipping at the driver or output.
However, it's not surprised with the specs. Same as mine that the spec listed U: 60w and T:30w but mine start clipping at 45w and 20w where vol pot is at 90%. If you have the scope, mark down where the max for U and T, that's what I did on my amp.
As [B]kevinkr[/B] mention, you may want to check where the clipping at the driver or output.
However, it's not surprised with the specs. Same as mine that the spec listed U: 60w and T:30w but mine start clipping at 45w and 20w where vol pot is at 90%. If you have the scope, mark down where the max for U and T, that's what I did on my amp.
my first thought is also "What speakers are you using?" if your speakers are inefficient, they may push the amp to clipping in triode mode. Ideally, you'll want speakers that are at least 92dB efficient or better. the Polks are not particularly sensitive, but the Klipsch, at +94dB, should be relatively clear.
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I can't comment on possible issues with your amplifier, but I used a LM-216IA in triode mode (22w) with 85dB 1w/1m speakers and had no problems.
I've also used a set of Klipsch which are 95% efficient. Same thing once the output reaches 7V.
I also made a video so you can hear the pops. They don't sound like normal distortion to me but more like static. The link is at the bottom of the post.
Although I know I'm not supposed to, I disconnected the speakers and cranked the volume with 1KHz sine wave. The distortion was present in the same spot when connected to a scope so it has nothing to do with the speakers.
Connected the speakers back on and took some pictures on the scope. It turns out that the pops happen only between 7V and 12V output. 12v and above the popping is gone but you can still see that the wave is not accurate. The attached pics go with the video of me going up and down in volume.
Pictures
- 7Volts - That's when the popping starts and you can see the spikes
- 7Vto12V - That's obviously between the the 2 voltages on the output
- 12V&up - The sine wave after 12v and up
Hope this helps. I will provide the same info to Willsenton support but so far they stopped responding to my emails.
I also made a video so you can hear the pops. They don't sound like normal distortion to me but more like static. The link is at the bottom of the post.
Although I know I'm not supposed to, I disconnected the speakers and cranked the volume with 1KHz sine wave. The distortion was present in the same spot when connected to a scope so it has nothing to do with the speakers.
Connected the speakers back on and took some pictures on the scope. It turns out that the pops happen only between 7V and 12V output. 12v and above the popping is gone but you can still see that the wave is not accurate. The attached pics go with the video of me going up and down in volume.
Pictures
- 7Volts - That's when the popping starts and you can see the spikes
- 7Vto12V - That's obviously between the the 2 voltages on the output
- 12V&up - The sine wave after 12v and up
Hope this helps. I will provide the same info to Willsenton support but so far they stopped responding to my emails.
Attachments
Nop that's not normal. There's some squegging/instability. I would reduce the NFB by increasing the 33k FB resistor to see if it clears.