I purchased a Nobsound NS-02D tube amplifier from amazon.de, which was specified to have 1*5Z3P 2*6N9P 2*EL34B tubes. However, it actually came with 1*5U4G 2*6SN7GT 2*EL34C tubes.
I found some information from a YouTube video where a version of this tube amp was tested. The mode (pentode, UL, or triode) wasn’t specified. Here are the test results:
I want to ensure I don’t push it too much. My speakers have a sensitivity of around 85-87 dB.
P.S. The tubes in my amplifier are from Psvane and include: rectifier 5U4G, preamp 6SN7GT, and power amp EL34C.
#5U4G 6SN7GT EL34C
#5Z3P 6N9P EL34B
#nobsound ns-02d
I found some information from a YouTube video where a version of this tube amp was tested. The mode (pentode, UL, or triode) wasn’t specified. Here are the test results:
- 2.77W into 4 ohms at 1% THD @ 1kHz
- 4.37W into 4 ohms at 2% THD @ 1kHz
- 3W into 8 ohms at 1% THD @ 1kHz
- 5.5W into 8 ohms at 3.3% THD @ 1kHz
I want to ensure I don’t push it too much. My speakers have a sensitivity of around 85-87 dB.
P.S. The tubes in my amplifier are from Psvane and include: rectifier 5U4G, preamp 6SN7GT, and power amp EL34C.
#5U4G 6SN7GT EL34C
#5Z3P 6N9P EL34B
#nobsound ns-02d
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I have Pro-Ject Primary E + Pro-Ject Box-Design Phono Box MM connected to the amp and to get louder sound I need to turn volume control past 12:00 clock position. It could be that coming signal is little low or power lacks. Speakers start to giving humming sound past 12:00 clock position without music playing. Usually I listen volume knob turn to 09:00 clock position. Only for experiment I have turned it past 12:00 clock position. I wonder is it because there is only 1W of power.
1. A complete and accurate schematic of your amplifier is needed.
2. If I remember correctly, that phono preamp, can not drive a long shielded cable from the preamp to the power amplifier.
More information from you might be helpful for troubleshooting purposes.
2. If I remember correctly, that phono preamp, can not drive a long shielded cable from the preamp to the power amplifier.
More information from you might be helpful for troubleshooting purposes.
This is the user manual:
Info from amazon.de:
Nobsound® Douk Audio HiFi EL34 Valve Tube Amplifier, Classic 2.0 Channel Stereo Single-Ended Class A Tube Amplifier, Power Amplifier 12W x 2
About this item
Product description
Basic technical parameters:
Rectifier: 5Z3P (Class J military level tube).
Preamp tubes: 6N9P × 2 (Class J military level tube).
Power tubes: EL34B × 2.
Rated output power: triode connected 8 W x 2 (default), standard connection 12 W x 2.
Frequency response: 20 Hz - 25 kHz.
Total power consumption: 115 W.
Output transformer: import Japanese Z11 0.35 mm (22 x 45/50), very important to provide sufficient power.
Total harmonic distortion: 1% (1 kHz).
Input sensitivity: 500 mV - 2000 mV.
Input impedance: 100 KΩ.
Output impedance: 4Ω, 8Ω, suit for about 10-100w 88db (>=) speakers
SNR: 88 dB.
Dimensions (W x H x D): 380 x 160 x 230 mm.
Weight: about 9 kg.
Product technology and materials
All tubes are military level.
Rectifier and voltage tube are Seventies Class J military level tube.
Special HIFI levels capacitors:
German WIMA red grade fever no electrodes capacity.
Cathode capacity: Philips audio-specific.
All high-precision metal film resistors rings.
CLC filter inductor.
Power output transformer is handmade.
Optimised routing and extremely low noise.
Package:
1 x tube amplifier.
1 x power cord.
Info from amazon.de:
Nobsound® Douk Audio HiFi EL34 Valve Tube Amplifier, Classic 2.0 Channel Stereo Single-Ended Class A Tube Amplifier, Power Amplifier 12W x 2
| Manufacturer | Nobsound |
| Brand | Nobsound |
| Number of channels | 2 |
| Output power | 12 Watts |
| Package type | Box |
- This is our Douk audio brand Nobsound, the most cost-effective EL34 tube amplifier, take it home and it will give you a big surprise.
- Rated output power: triode connected 8Wx2 (default) / standard connection 12Wx2
- Output impedance: 4Ω, 8Ω, suit for about 10-100w 88db (>=) speakers
- Rectifier tube: 5Z3P (Class J military level tube) / preamp tubes: 6N9P × 2 (Class J military level tube) / Power tubes: EL34B × 2
- Dimensions (W x H x D): 380 × 160 × 230 mm / Weight: about 9 kg
Product description
Basic technical parameters:
Rectifier: 5Z3P (Class J military level tube).
Preamp tubes: 6N9P × 2 (Class J military level tube).
Power tubes: EL34B × 2.
Rated output power: triode connected 8 W x 2 (default), standard connection 12 W x 2.
Frequency response: 20 Hz - 25 kHz.
Total power consumption: 115 W.
Output transformer: import Japanese Z11 0.35 mm (22 x 45/50), very important to provide sufficient power.
Total harmonic distortion: 1% (1 kHz).
Input sensitivity: 500 mV - 2000 mV.
Input impedance: 100 KΩ.
Output impedance: 4Ω, 8Ω, suit for about 10-100w 88db (>=) speakers
SNR: 88 dB.
Dimensions (W x H x D): 380 x 160 x 230 mm.
Weight: about 9 kg.
Product technology and materials
All tubes are military level.
Rectifier and voltage tube are Seventies Class J military level tube.
Special HIFI levels capacitors:
German WIMA red grade fever no electrodes capacity.
Cathode capacity: Philips audio-specific.
All high-precision metal film resistors rings.
CLC filter inductor.
Power output transformer is handmade.
Optimised routing and extremely low noise.
Package:
1 x tube amplifier.
1 x power cord.
1. I have sent email to douk audio and requsted electrical schematic
2. The cable is short 0.5m and have shielding (brand clicktronic)
The combination is turntable-phono preamp-integrated tube amp. Could be that signal is too weak for input of amp. Also could be that the amp only has 2x1W of power. Overall it is not big problem and like to listen to it, but printing that it works 2x8W triode is false information.
2. The cable is short 0.5m and have shielding (brand clicktronic)
The combination is turntable-phono preamp-integrated tube amp. Could be that signal is too weak for input of amp. Also could be that the amp only has 2x1W of power. Overall it is not big problem and like to listen to it, but printing that it works 2x8W triode is false information.
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There are this ready made unit and DIY kit in the amazon.de. You can find in the attachment the DIY kit electrical schematics, but I think it's in ultra linear connection type. Maybe this will show us why it lacks the power or input sensitivity? Why the effect that to get 80-90dB volume knob is past 12:00 clock?
Lets see if I can get the proper schematics later on.
Lets see if I can get the proper schematics later on.
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You already have the amplifier, Right?
The best way to see if you will like Triode Wired EL34s or not, is to do one of the easiest modifications in the world.
Before doing any modifications to any tube amplifier, make sure the amplifier is working correctly.
EL34, pin 3 is Plate, pin 4 is Screen.
Note:
If the EL34 sockets are on a PCB, you have to locate the screen traces and wire that goes to B+. Most likely, the screens are connected together to the same B+,, so you have to cut out a small section, and remove it, of the screen PCB traces that go to the screen B+ point. Connecting the 100 Ohm resistors from pin 3 to pin 4 is easy, do it right at the tube socket pins.
By scraping the PCB traces that is on either side of the cut, you can restore the amplifier by soldering a wire across the small missing trace section.
Get two 100 Ohm resistors.
Disconnect each EL34 screen from their B+ point.
For triode wiring, connect a 100 Ohm resistor from pin 3 to pin 4 on the EL34 sockets.
If the amplifier is Ultra Linear, remove the wires on the PCB that come from the output transformer UL taps, and insulate those UL wires with shrink tubing. The wires from the output transformer that connects to pins # 4 is the UL taps of the transformer.
When the mod is done . . . Listen! (do not spend anymore time wondering, only with real Triode wiring can you know the results).
Everyone's speakers are different, room size is different, room reflectivity is different, listening position to speaker distance is different, and music tasts are different. That means the needed power is different too.
Generalization:
If you are wondering if you are driving an amplifier too hard . . . you have ears . . . you will hear distortion if it starts clipping.
Whether the amplifier is single ended, or push pull, when you hear distortion, it is clipping, no oscilloscope required.
When you hear distortion, turn the volume control down a little bit.
Getting full output power from an amplifier depends on:
Amplifier input sensitivity
Amplifier maximum output power capability
Signal source voltage to the amplifier
Amplifier maximum gain, with the volume control turned max clockwise.
Volume controls affect the amplifier gain, they do not control the maximum output power Capability of the amplfier.
Instead, the power supply and output stage determine maximum power Capability.
Sometimes CDs and Vinyl are recorded at low levels; if there is not enough amplifier gain, it will never put out its maximum power, even if the volume is fully clockwise.
A high level recording, and a signal source that has lots of output voltage, will make the amplifier clip with the volume control at 9:00, 12:00, or 3:00.
As you can see, there are lots of variables.
You will figure it out for your particular system.
Happy Mods, and Happy Listening!
Many of those Chinese amplifiers that look identical, have many different topologies and circuits.
The output stage may be Pentode mode, and have global negative feedback
The output stage may be Ultra Liner mode, and have No global negative feedback
The output stage may be Triode wired mode, and have not global negative feedback
It is all about the maximum output power capability, distortion at medium power levels, damping factor, and amplifier gain.
The best way to see if you will like Triode Wired EL34s or not, is to do one of the easiest modifications in the world.
Before doing any modifications to any tube amplifier, make sure the amplifier is working correctly.
EL34, pin 3 is Plate, pin 4 is Screen.
Note:
If the EL34 sockets are on a PCB, you have to locate the screen traces and wire that goes to B+. Most likely, the screens are connected together to the same B+,, so you have to cut out a small section, and remove it, of the screen PCB traces that go to the screen B+ point. Connecting the 100 Ohm resistors from pin 3 to pin 4 is easy, do it right at the tube socket pins.
By scraping the PCB traces that is on either side of the cut, you can restore the amplifier by soldering a wire across the small missing trace section.
Get two 100 Ohm resistors.
Disconnect each EL34 screen from their B+ point.
For triode wiring, connect a 100 Ohm resistor from pin 3 to pin 4 on the EL34 sockets.
If the amplifier is Ultra Linear, remove the wires on the PCB that come from the output transformer UL taps, and insulate those UL wires with shrink tubing. The wires from the output transformer that connects to pins # 4 is the UL taps of the transformer.
When the mod is done . . . Listen! (do not spend anymore time wondering, only with real Triode wiring can you know the results).
Everyone's speakers are different, room size is different, room reflectivity is different, listening position to speaker distance is different, and music tasts are different. That means the needed power is different too.
Generalization:
If you are wondering if you are driving an amplifier too hard . . . you have ears . . . you will hear distortion if it starts clipping.
Whether the amplifier is single ended, or push pull, when you hear distortion, it is clipping, no oscilloscope required.
When you hear distortion, turn the volume control down a little bit.
Getting full output power from an amplifier depends on:
Amplifier input sensitivity
Amplifier maximum output power capability
Signal source voltage to the amplifier
Amplifier maximum gain, with the volume control turned max clockwise.
Volume controls affect the amplifier gain, they do not control the maximum output power Capability of the amplfier.
Instead, the power supply and output stage determine maximum power Capability.
Sometimes CDs and Vinyl are recorded at low levels; if there is not enough amplifier gain, it will never put out its maximum power, even if the volume is fully clockwise.
A high level recording, and a signal source that has lots of output voltage, will make the amplifier clip with the volume control at 9:00, 12:00, or 3:00.
As you can see, there are lots of variables.
You will figure it out for your particular system.
Happy Mods, and Happy Listening!
Many of those Chinese amplifiers that look identical, have many different topologies and circuits.
The output stage may be Pentode mode, and have global negative feedback
The output stage may be Ultra Liner mode, and have No global negative feedback
The output stage may be Triode wired mode, and have not global negative feedback
It is all about the maximum output power capability, distortion at medium power levels, damping factor, and amplifier gain.
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Thanks for info and advices.
I got the electrical schematic for this Nobsound NS-02D. If someone could take a look at this and tell if the design is valid?
I got the electrical schematic for this Nobsound NS-02D. If someone could take a look at this and tell if the design is valid?
If the top 6N9P ever shorts, or if the bottom 6N9P ever opens . . . the 0.47 250V coupling cap will have close to 400V across it. Ouch, cap; Ouch EL34.
I always use 600V or 630V coupling caps.
Some caps leak a very small current, and that puts a slight positive voltage across the EL34 grid and 270K grid resistor (changes the total tube bias voltage and increases the tube current).
The following comments on EL34 operating modes are relative to each other. All have their own validity, and should be tried if possible:
The EL34 is operating in native Pentode mode.
Highest gain, highest power out, highest distortion.
But the lowest damping factor.
Unless the output transformer has an Ultra Linear tap, you can not wire the EL34 for Ultra Liner mode.
Medium gain, medium power out, medium distortion.
But a medium damping factor.
You can disconnect the screen from its B+; then connect a 100 Ohm resistor from screen to plate. That puts the EL34 in Triode Wired mode.
Lower gain, lower power out, lower distortion.
But the highest damping factor.
Something that is easy to modify and try.
290VAC from the power transformer secondary is 410V peak. The only voltage drop is the 5Z3 rectifier, and it is not much, especially before the EL34 tubes warm up; or in the case of one or two EL34 going "open".
450V caps would give a slight voltage margin, but for me . . . I would use 500V caps for the B+. What you have will probably be OK, but I am a stickler for having safety margins on specs, and for reliability, including other part(s) failures, like rising B+ when EL34 tubes fail or go weak as the years pass.
B3 is almost certainly there to raise the voltage on the 6N9P filaments. You would need two 100 Ohm resistors from B3 to the two ends of the 6N9P filament secondary. Elevation is necessary, because the top 8N0P cathode is at about 1/2 of B2 voltage.
If you operate the 220V transformer from 230V or 240V mains, the B+ voltage will be high, and the tube filament voltages will be high.
The amplifier will probably operate for a long time as it is, but If I were to use that topology and build from scratch, I would use the recommendations above.
Happy Listening!
I always use 600V or 630V coupling caps.
Some caps leak a very small current, and that puts a slight positive voltage across the EL34 grid and 270K grid resistor (changes the total tube bias voltage and increases the tube current).
The following comments on EL34 operating modes are relative to each other. All have their own validity, and should be tried if possible:
The EL34 is operating in native Pentode mode.
Highest gain, highest power out, highest distortion.
But the lowest damping factor.
Unless the output transformer has an Ultra Linear tap, you can not wire the EL34 for Ultra Liner mode.
Medium gain, medium power out, medium distortion.
But a medium damping factor.
You can disconnect the screen from its B+; then connect a 100 Ohm resistor from screen to plate. That puts the EL34 in Triode Wired mode.
Lower gain, lower power out, lower distortion.
But the highest damping factor.
Something that is easy to modify and try.
290VAC from the power transformer secondary is 410V peak. The only voltage drop is the 5Z3 rectifier, and it is not much, especially before the EL34 tubes warm up; or in the case of one or two EL34 going "open".
450V caps would give a slight voltage margin, but for me . . . I would use 500V caps for the B+. What you have will probably be OK, but I am a stickler for having safety margins on specs, and for reliability, including other part(s) failures, like rising B+ when EL34 tubes fail or go weak as the years pass.
B3 is almost certainly there to raise the voltage on the 6N9P filaments. You would need two 100 Ohm resistors from B3 to the two ends of the 6N9P filament secondary. Elevation is necessary, because the top 8N0P cathode is at about 1/2 of B2 voltage.
If you operate the 220V transformer from 230V or 240V mains, the B+ voltage will be high, and the tube filament voltages will be high.
The amplifier will probably operate for a long time as it is, but If I were to use that topology and build from scratch, I would use the recommendations above.
Happy Listening!
Thanks for looking into it. At this schematics can it be verified that, which mode is used pentode, UL or triode? What about the Psvane tubes used in this amp (rectifier 5U4G / pre 6SN7GT / power EL34C)? Are they compatible with this circuit?
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The schematic shows the EL34 screens are connected to B1. That puts a relatively constant voltage on the screen; that is Pentode Mode.
The schematic does not show any UL tap on the output transformer, you will have to check that for yourself. Without that tap, you will not be able to operate your amp in UL.
Triode mode is easy to wire (and easy to return to pentode mode). Modify for triode mode, but only after you have used and listened to pentode mode for a while.
You may, or may not be surprised with the "sound" of triode mode.
The schematic does not show any UL tap on the output transformer, you will have to check that for yourself. Without that tap, you will not be able to operate your amp in UL.
Triode mode is easy to wire (and easy to return to pentode mode). Modify for triode mode, but only after you have used and listened to pentode mode for a while.
You may, or may not be surprised with the "sound" of triode mode.
Seems that there is 6h8c mentioned in user manual and it has 6sn7gt substitude.
Other hand also 6N9p is specs in amazon.de and in electrical drawings.
Atleast it's working as we speak.
I utilized AI ... Copilot and Gemini with the schematics. I asked is connection pentode, ultra-linear or triode? Depending if asked about whole circuit or the EL34-B part of it. It said that it is pentode or ultra-linear. It didn't say anything about triode. It's 2024 and AI is here, but do we trust it. Other hand is these imports from China what can hold anything inside of it. In the unit it reads Nobsound NS-02D, but no where in internet can it be found.
Copilot AI
Q. Is this el34 connection pentode, ultra-linear or triode?
A. The schematic diagram you provided shows the EL34 tube connected in a pentode configuration. This is identified by the screen grid (G2) being connected to a voltage source, separate from the plate (anode) and control grid (G1).
Q. Is this connection pentode, ultra-linear or triode?
A. The schematic diagram you provided shows the EL34 tube connected in an ultra-linear configuration. This is identified by the presence of screen taps on the output transformer, which are connected to the screen grids (G2) of the EL34 tubes.
Gemini AI
Q. Is this el34 connection pentode, ultra-linear or triode?
A. The EL34 tube in the diagram is connected in ultra-linear mode.
Here's how we can tell:
Q. Is this connection pentode, ultra-linear or triode?
A. The EL34 tube in the diagram is connected in ultra-linear mode.
Here's how we can tell:
Copilot AI
Q. Is this el34 connection pentode, ultra-linear or triode?
A. The schematic diagram you provided shows the EL34 tube connected in a pentode configuration. This is identified by the screen grid (G2) being connected to a voltage source, separate from the plate (anode) and control grid (G1).
Q. Is this connection pentode, ultra-linear or triode?
A. The schematic diagram you provided shows the EL34 tube connected in an ultra-linear configuration. This is identified by the presence of screen taps on the output transformer, which are connected to the screen grids (G2) of the EL34 tubes.
Gemini AI
Q. Is this el34 connection pentode, ultra-linear or triode?
A. The EL34 tube in the diagram is connected in ultra-linear mode.
Here's how we can tell:
- Grid 2 (G2) Connection: G2 is connected to a voltage divider network that includes resistors R1 and R2. This connection provides a partial negative voltage to G2, which is characteristic of ultra-linear operation.
- Screen Grid (G3) Connection: G3 is connected to a high voltage point through resistor R3. This ensures that G3 operates at a higher voltage than G2, which is also a key feature of ultra-linear operation.
- Plate (P) Connection: The plate is connected to the output transformer, which is typical for power amplifier circuits like this one.
Q. Is this connection pentode, ultra-linear or triode?
A. The EL34 tube in the diagram is connected in ultra-linear mode.
Here's how we can tell:
- Grid 2 (G2) Connection: G2 is connected to a voltage divider network that includes resistors R1 and R2. This connection provides a partial negative voltage to G2, which is characteristic of ultra-linear operation.
- Screen Grid (G3) Connection: G3 is connected to a high voltage point through resistor R3. This ensures that G3 operates at a higher voltage than G2, which is also a key feature of ultra-linear operation.
- Plate (P) Connection: The plate is connected to the output transformer, which is typical for power amplifier circuits like this one.
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Yesterday it said pentode or ultra-linear. Today it said pentode.
Well it's all the same. Atleast it plays with nice sound. I don't push it too hard. I believe that line input signal could be stronger then it would work better. I am considering a streamer for it. Wiim Pro Plus or Wiim Ultra.
Well it's all the same. Atleast it plays with nice sound. I don't push it too hard. I believe that line input signal could be stronger then it would work better. I am considering a streamer for it. Wiim Pro Plus or Wiim Ultra.
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