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Reisong A10: Technical review.

StepheK said:
KT77 = EL34 as far as power use, it's a direct swap just like a 6CA7 is. KT88 is not suited for this amp. It would technically work but it would be VERY under biased and the amp down't have the power transformer nor the output transformers to deal with the wattage generated by a KT888 biased up correctly
Click to expand...
That’s what i thought. Thx.
 
I install a switch : with and without feedback. I want to check the (positive ?) effect of this feedback.
No capacitor bypass of R204 --> Less gain & less distortion.
 
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Last version. It will stay like this.
I'll try SRPP with an external breadboard.

Actually i build a 300B SE. Pics to come.

IMG_20240927_184119218.jpg
 
StepheK said:
To follow up with the work I did on the big sister amp, the Boyuurange/Reison A50, a viewer had a new in the box A12 dropped shipped for me to review and possibly modify it etc.

I'm going to post this spoiler, it's a hot mess.

Massive distortion was visible on an analog scope and running a THD vs power sweep showed me that what I was seeing on the analog scope was reality. It goes into hard stop, square wave producing clipping at 1/2 the rated watts and crosses the 1% THD mark at 0.015W. It is making 6-7%+ distortion at 1W and it goes past 10% before 2W. The cheap little Nobsound 6P1 out of the box performs better than this. With my DIY >$20 mods it destroys the A12 at almost 1/2 the price.

I go into more detail in the review video and I'm hopeful in future videos I can find a resolution to whatever is causing these problems. It's a shame, as I had high hopes for this little amp, and it has what you would think it takes be a decent performer, 12AX7 driver into a SEUL EL34. But it's clearly a swing and a miss out of the box.

TL;DR at this point I would not recommend buying one of these with the expectation of goodness out of the box or just basic tube rolling. I'm sure this will be controversial, but the numbers don't lie.

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Hi StepheK

Why was a 3V signal supplied to the amplifier?
The problem with distortion is that the amplifier only accepts 700 mV, but the video says that a 3V input signal was supplied.With different tuning options, I got 1.5 V of the input signal, while the final power did not change, but the gain decreased.
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A10 and A 12 have different input tubes, although they are similar. The Russian tube 6N2P has a different internal resistance, from this and other resistance ratings.
 
pashka said:
Hi StepheK

Why was a 3V signal supplied to the amplifier?
The problem with distortion is that the amplifier only accepts 700 mV, but the video says that a 3V input signal was supplied.With different tuning options, I got 1.5 V of the input signal, while the final power did not change, but the gain decreased.
///////////////


A10 and A 12 have different input tubes, although they are similar. The Russian tube 6N2P has a different internal resistance, from this and other resistance ratings.
Click to expand...
Huh? These Audio analyzer suite power vs THD sweeps start at .01VRMS and stop when the output hits 10%. At no point does the power start going back down as the input signal is increased. And FYI that 3V on the scope is a peak to peak signal, which is 1Vrms. And yes, once the amp starts clipping (It's max power limit), driving more power in doesn't give more power out. It just turns the sine wave into a square wave.

It's not like the only test I did was blast an input signal way past clipping as the test.
 
StepheK said:
Huh? These Audio analyzer suite power vs THD sweeps start at .01VRMS and stop when the output hits 10%. At no point does the power start going back down as the input signal is increased. And FYI that 3V on the scope is a peak to peak signal, which is 1Vrms. And yes, once the amp starts clipping (It's max power limit), driving more power in doesn't give more power out. It just turns the sine wave into a square wave.

It's not like the only test I did was blast an input signal way past clipping as the test.
Click to expand...
Thanks for your work, Stephe!
@StepheK : what is the calculation formula for the UL resistor (R106 & 206) ? What should be its nominal value ?
What does this resistor do and what effect does it have on the sound?
Thanks
 
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At the very beginning, while waiting for spare parts, I wrote down what I changed in the amplifier from what was there and one day I got just a magical sound. I could not tear myself away from any music, even the one I do not listen to.
The music flowed naturally and naturally, full presence and some kind of magic, it was so realistic and captivating sound. Then I installed new parts and everything disappeared.
I tried for a long time to find what the problem was,
and it turned out that the cathode resistor then stood at 330 ohms,
but when I changed it to 250 ohms, this was the problem.
 

I've browsed through many forums from different parts of the world and saved all the information. This is my first experience with a tube amplifier and an attempt to do something better understanding what you're doing. I decided to talk to the GPT chat. Here's my dialogue and advice:​

​

Modification and Optimization of Reisong A10 for Better Soundstage and Realism​

1. Optimization of the Input Stage (V1, V4 - 6N2P-EV)​

Anode Resistor (R103, R203)​

  • The current value is 75kΩ, which slightly reduces gain and provides a softer sound.
  • Suggested value: 100kΩ – 120kΩ (e.g., Allen Bradley or Vishay Dale).
  • Power rating: 0.5W – 1W is sufficient.

Cathode Resistor (R101, R201)​

  • Replaced 10kΩ with 1.2kΩ, which improved dynamics and microdetail.
  • Lowering this value further may lead to excessive gain and distortion.

Cathode Capacitor (C104, C204 - missing on the schematic)​

  • Adding 100µF – 220µF / 25V (preferably Nichicon, Elna, or Black Gate) can improve bass response and midrange clarity.
PS. THIS IS PARAMETRS FOR 6N2P EL WITJ ONE TRIOD IN USE NOT PARALEL >

2. Output Stage (V2, V5 - EL34) Optimization​

Cathode Resistor (R108, R208)​

  • Stock value: 500kΩ → replaced with 330kΩ, which provided a more balanced and magical sound.
  • Experimenting with 250kΩ – 330kΩ affects harmonic balance and overall texture.

Cathode Resistor for EL34 (R106, R206)​

  • Some suggest 2kΩ, but it depends on desired sound.
  • Suggested range:
    • Warm, full-bodied sound: 270Ω – 300Ω (higher bias, stronger bass).
    • Balanced, 3D soundstage: 330Ω – 360Ω (recommended).
    • High detail and airiness: 390Ω – 470Ω (cleaner but slightly thinner).

Bias Current for EL34 (Best Soundstage & Naturalness)​

  • Best balance: 55 – 60mA (Cathode voltage: 22V – 24V).
  • Detailed & airy sound: 50 – 55mA (Slightly less bass).
  • Warm & powerful sound: 65 – 75mA (More bass, slightly compressed stage).
Conclusion:
The best compromise is 330Ω – 360Ω for the cathode resistor with 55 – 60mA bias current for a natural, realistic, and immersive soundstage.

///////////////////////////////////////////////////////////////////////////////////////////////​

Modifications and Optimization of Reisong A10 for 3D Soundstage and Realistic Tone​

1. Input Stage Optimization (V1, V4 - 6N2P-EV in Parallel Mode)​

The 6N2P-EV tubes are wired in parallel mode, which affects the choice of resistor values for achieving the best sound balance.

Anode Resistor (R103, R203)​

  • Stock value: 75kΩ (reduces gain, softer sound).
  • Suggested values for best 3D sound and realism:
    • 33kΩ – 39kΩ (Vishay Dale, Allen Bradley, Amtrans).
    • 33kΩ → Warmer, denser sound.
    • 39kΩ → More air, detail, and spaciousness.

Cathode Resistor (R104, R204)​

  • Suggested values:
    • 1kΩ – 1.2kΩ
    • 1kΩ → Maximum transparency and openness.
    • 1.2kΩ → Slightly warmer and smoother sound.

Cathode Capacitor (Optional, Not Shown in Schematic)​

  • 100µF – 220µF / 16–35V(Elna Silmic II, Nichicon Muse).
    • If removed → more micro-detail, but thinner bass.
    • If added → wider soundstage and richer tone.

2. Output Stage Optimization (V2, V5 - EL34)​

Cathode Resistor for EL34 (R108, R208)​

  • Stock value: 500Ω → Produces soft, warm sound but lacks dynamics.
  • Experimentally tested values:
    • 330Ω – 360Ω (recommended).
    • 270Ω – 300Ω → More powerful bass, but slightly compressed stage.
    • 390Ω – 470Ω → More clarity, but slightly leaner bass.

Optimal Bias Current for Best Soundstage & Naturalness​

  • Best balance: 55 – 60mA (Cathode voltage: 22V – 24V).
  • Maximum detail & airiness: 50 – 55mA.
  • Warm & dynamic sound: 65 – 75mA (More bass but slightly less spaciousness).
Conclusion:
The best compromise is 330Ω – 360Ω for the cathode resistor with 55 – 60mA bias current, resulting in a natural, realistic, and immersive soundstage.

3. Additional Modifications for Improved Sound Quality​

Removal of R301​

  • Removing R301 (feedback resistor) resulted in a more open and dynamic sound.

Replacement of R302 (8.2kΩ → 4.3kΩ)​

  • Lowering R302 increased dynamics and improved clarity.

R101 Change (10kΩ → 1.2kΩ)​

  • Resulted in better micro-detail and more natural tone.

Optimizing R106 (2kΩ option)​

  • Some suggest using 2kΩ for improved midrange clarity, but the effect varies.

Final Recommendations for the Best Sound Experience​

For a 3D soundstage and realism:

  • 6N2P-EV in parallel mode with 33kΩ – 39kΩ anode resistor & 1kΩ – 1.2kΩ cathode resistor.
  • EL34 cathode resistor 330Ω – 360Ω for balanced dynamics and air.
  • Bias current 55 – 60mA for optimal warmth and clarity.
For a cleaner and more detailed sound:

  • Increase EL34 cathode resistor to 390Ω – 470Ω.
  • Remove cathode bypass capacitor for more transparency.
For deeper bass and warmer sound:

  • Use 270Ω – 300Ω cathode resistor for EL34.
  • Add 220µF – 1000µF cathode capacitor for more body and low-end presence.
This summary covers the optimal modifications for Reisong A10 to achieve maximum realism, spatial depth, and transparency. Let me know if you need any refinements!
 

How Anode Current and Cathode Resistor Affect Sound in 6N2P-EV (Parallel Mode) Reisong A10​

1. The Role of Anode Current (Ia) in Sound Quality​

The anode current significantly impacts the soundstage, detail, and overall realism of the amplifier. Here’s how different anode currents affect sound:
Anode Current (Ia per triode)Sound Characteristics
Too low (below 3mA per triode, ~6mA in parallel mode)Collapsed soundstage, weak dynamics, "thin" and lifeless sound.
Optimal range (4 – 5mA per triode, ~8 – 10mA in parallel mode)Best balance: wide, three-dimensional soundstage, natural timbre, clarity.
Too high (above 6mA per triode, ~12mA+ in parallel mode)Increased harmonics but reduced microdynamics, possible distortion and harshness.
Optimal anode current for 6N2P-EV (parallel mode): 8 – 10mA per tube (4 – 5mA per triode).

2. How Anode Resistor (Ra) Affects Sound​

The anode resistor (Ra) sets the anode voltage and affects gain, linearity, and dynamics.
Anode Resistor (Ra)Effect on Sound
Too high (82kΩ – 100kΩ)Lower anode current → "colder" and more analytical sound, reduced dynamics.
Optimal range (33kΩ – 39kΩ in parallel mode)Balanced anode current → natural, deep soundstage, good airiness.
Too low (22kΩ – 27kΩ)Higher current → more warmth but risk of compression and loss of microdetails.
For 6N2P-EV (parallel mode), the recommended Ra is:
  • 33kΩ – 39kΩ for the best balance of three-dimensional sound and natural tonality.
  • Voltage drop across Ra should be around 140V – 160V for optimal operation.

3. The Effect of the Cathode Resistor (Rk)​

The cathode resistor sets the bias point, affecting dynamics, timbre, and openness of sound.
Cathode Resistor (Rk)Effect on Sound
Too low (330Ω – 470Ω in parallel mode)Higher gain, more dynamics, but possible loss of smoothness.
Optimal range (1kΩ – 1.2kΩ in parallel mode)Best tonal balance, natural warmth, open and airy sound.
Too high (2kΩ – 2.4kΩ in parallel mode)Lower gain, increased clarity, but risk of analytical or sterile sound.
For 6N2P-EV (parallel mode), the best cathode resistor is:
  • 1kΩ – 1.2kΩ → best three-dimensional sound, natural realism.
  • Cathode voltage should be ~1.5V – 2.5V for optimal biasing.

4. Measuring Anode Current and Biasing​

To ensure the tube is operating in its optimal range, measure anode voltage and current:
✔ Anode voltage (Va):
  • Should be 150V – 180V (if B+ = 300 – 310V).
✔ Anode current (Ia) calculation:
  • Measure voltage across Ra (anode resistor) and calculate:
Ia=VRaRaI_a = \frac{V_{\text{Ra}}}{R_{\text{a}}}Ia=RaVRa
✔ Cathode voltage (Vk):
  • Should be 1.5V – 2.5V for proper biasing.

5. Summary: Best Settings for 6N2P-EV (Parallel Mode)​

ParameterRecommended Value
Anode Resistor (Ra)33kΩ – 39kΩ
Cathode Resistor (Rk)1kΩ – 1.2kΩ
Anode Voltage (Va)150V – 180V
Cathode Voltage (Vk)1.5V – 2.5V
Anode Current (Ia, per triode)4 – 5mA (8 – 10mA total per tube)
These settings will give you the best balance of deep, three-dimensional soundstage, realistic tonality, and smooth but detailed sound.
Let me know if you need more details! chat GPT
 
Removing R301 (10Ω) in Reisong A10 Power Supply: Effects and Solutions

Question:​

I removed R301 (10Ω) in the power supply of my Reisong A10 as some people suggested. I would like to understand how this affects the amplifier and whether I should replace it with something else for better performance.

1. What Was the Purpose of R301 (10Ω)?​

This resistor was placed after the rectifier (5AR4) and before the first filter capacitor C301 (100μF). It had several important functions:

Ripple Reduction – It acted as a damper between the rectifier and capacitor, helping to reduce ripple. Inrush Current Limiting – It protected the rectifier from sudden current spikes. Noise Suppression – It reduced high-frequency ringing in the power supply.

2. What Happens When You Remove R301?​

✅ Pros:

  • Slightly higher B+ voltage (~2–3V increase), which may subtly affect tonal balance.
  • Less power loss, but not significant.
❌ Cons:

  • Higher inrush current, which can shorten the lifespan of 5AR4.
  • Increased ripple, especially with a 100μF first capacitor.
  • Potential high-frequency noise, affecting amplifier clarity.

3. Best Replacement for R301 (10Ω)​

Optimal solution – Use a choke instead of R301!This improves filtering and provides a cleaner power supply.

Recommended choke specifications:

  • 2–10H, 100–200mA, resistance 50–200Ω.
  • Example: Hammond 159P (10H, 125mA), 193H (5H, 200mA).
Benefits of a choke:
✅ Better dynamics and bass response.
✅ Lower noise and hum.
✅ Smoother operation of the rectifier.

4. Alternative Solutions If a Choke Is Not an Option​

If adding a choke is difficult, reinstalling R301 but with a different value can still improve performance.

Option 1: Increase Resistance

  • Instead of 10Ω, use 22–47Ω (2–5W, metal film). Effect:
    ✅ Reduces inrush current.
    ✅ Protects 5AR4.
    ✅ Slightly lowers ripple.
Option 2: Use an NTC Thermistor
For soft start and tube protection, use CL-90 (or similar NTC thermistor 47Ω/2A). Effect:
✅ Gradual startup.
✅ Protects diodes and capacitors.

Conclusion:​

1️⃣ Best choice – Replace R301 with a 5–10H choke for cleaner power and better sound.
2️⃣ If a choke is not feasible, use 22–47Ω (2–5W) for protection.
3️⃣ For smooth startup, an NTC thermistor (CL-90, 47Ω/2A) is a great option.

Removing R301 without replacement increases noise and shortens 5AR4 lifespan. A choke or resistor upgrade will significantly improve performance!
 
Of course, I was in a hurry to post the values that the chat advised me; this is not an ideal option, and on the same 6n2p you can drive it into different modes in different ways.
The GPT chat is not a bad teacher for beginners, he reads the circuit, he told me how to measure, how to calculate, and most importantly, he explained to me what happens to the sound by changing certain parameters of the circuit in different places.
 
The GPT chat is sometimes slow, if you look at the parameters he suggested for the 6n2p lamp that I posted, he's slow. 6n2p maximum anode current is 2.3 mA on one side. I told him about this and he admitted that he hadn't taken this into account and then changed the recommendations.Trust but verify.
 
Can someone suggest the best parameters in which the 6N2P tube will sound good?Anode current?Anode voltage?Cathode voltage for the A10 amplifier?
 
<gets up on soapbox>

A bit off topic, but as quoting chatGPT is becoming common practice (and with all due respect to the original poster): Folks, I beg thee... please give ample consideration to the fact that it's a large language model predictive engine, not an artificial intelligence. It can't think or reason... it simply knows to a very high degree of accuracy the most commonly-used/appropriate next word in any given sentence, given the billions of sentences it has been given to read.

As a result, it makes stuff up all the time because its job is *exactly* that: to make up sentences.

As a result, "trust but verify" becomes "every word needs to be verified".

And, to StepheK's point specifically appropriate for this forum: I'm pretty sure it has no ears.

<gets down off soapbox> :)
 
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If you look at different forums on setting up the BIOS on a 6n2p tube, you can find identical circuits but with different values for the anode and cathode resistors. This is my first experience with a tube amplifier. I played with the settings by changing the anode and cathode resistors, and eventually installed variable resistors and watched what was happening on the oscilloscope.
My problem is that the settings in my system are too complicated.
I have two A10 amplifiers working after an active crossover on the midrange and high frequencies, and it is very difficult to describe the changes in sound after changing certain resistor values. I can say that at first, changing the resistors on the anode and cathode of the 6n2p, I accidentally got into a mode where the sound became so mesmerizing that I could not tear myself away. It's good that I wrote down what the resistor values were and after various changes I returned to this random option.
When I buy equipment to measure the amplifier distortion and good speakers so that I can change the tube mode in real time and see what happens with harmonics and distortion and at the same time listen to what happened to the sound after the changes. Feedback in the amplifier for me is a dead sound.
The purchase of a tube amplifier prompted me to get a more realistic live sound, which is what I strive for.

The GPT chat or another one actually knows and helps with tuning, suggesting what needs to be changed and tried so that the sound changes and offers different options, after which it asks to tell you what happened with your sound.
I did not have much time for experiments, but this is a good assistant and can read the diagram that you upload to him as a photo. .Yes, this can really help for creativity and development, especially for beginners.

All the options that I posted that the GPT Chat offered me are an example.

The only bad thing is that IA can become a god for many in the future and a complete controller of your life, which is where we are being driven, complete control.
 
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