I bought a very cheap tube amp from aliexpress (great deal)
2017 New Nobsound Handmade Stereo Single ended Class A Headphone Amp HiFi 6P1 Vacuum Tube Integrated Amplifier Black-in Amplifier from Consumer Electronics on Aliexpress.com | Alibaba Group
It's almost unavoidable to get into an issue with chinese amps. I have a problem with the bass getting all distorted at high volumes. I am a complete beginner in tube amps. My first modded amp with success is my Little Bear P7. I know how to solder. I have no schematics of the amp (seller doesn't want to give some). The amps is a AOSIBAO 6p1/6v6 tube amp with 5z4 power tube and 6H8C tubes.
It sounds pretty good at low volume (more soundstage than my LB7).
I opened the amp up and all I could see is a bunch of carbon 2W 240K resistors and
2x 450V 22uF KMG capacitors
2x 50V 220uF NXB capacitors
2x 25V 100uF LXV capacitors
4x 0.22uf 400V red vishay film capacitors
2x 450V 150uF big blue caps ??? I doupt those are the right values written.
I was planning on upgrading all those caps for better nichicon and panasonic caps (prefer panasonic caps to nichicon btw) to see if they magically fix the issue.
2x Nichicon UPW2W220MHD 0.22uF 450V
2x Panasonic EEU-FR1H221 220uF 50V
2x Nichicon UFG1V101MPM (35V) 100uF
4x Panasonic ECW-FE2J224J 0.22uF (630V)
(Any better suggestions?)
So does can anyone know how to fix this issue ? I have researched a lot and all I found is that i maybe need a coupling cap at the input jack to lower the lower frequencies. The question again is to find the right capacitance to fix that issue even if that is the problem.
I'm a true audio lover and I really appreciate any help I get.
Thanks in advance !
2017 New Nobsound Handmade Stereo Single ended Class A Headphone Amp HiFi 6P1 Vacuum Tube Integrated Amplifier Black-in Amplifier from Consumer Electronics on Aliexpress.com | Alibaba Group
It's almost unavoidable to get into an issue with chinese amps. I have a problem with the bass getting all distorted at high volumes. I am a complete beginner in tube amps. My first modded amp with success is my Little Bear P7. I know how to solder. I have no schematics of the amp (seller doesn't want to give some). The amps is a AOSIBAO 6p1/6v6 tube amp with 5z4 power tube and 6H8C tubes.
It sounds pretty good at low volume (more soundstage than my LB7).
I opened the amp up and all I could see is a bunch of carbon 2W 240K resistors and
2x 450V 22uF KMG capacitors
2x 50V 220uF NXB capacitors
2x 25V 100uF LXV capacitors
4x 0.22uf 400V red vishay film capacitors
2x 450V 150uF big blue caps ??? I doupt those are the right values written.
I was planning on upgrading all those caps for better nichicon and panasonic caps (prefer panasonic caps to nichicon btw) to see if they magically fix the issue.
2x Nichicon UPW2W220MHD 0.22uF 450V
2x Panasonic EEU-FR1H221 220uF 50V
2x Nichicon UFG1V101MPM (35V) 100uF
4x Panasonic ECW-FE2J224J 0.22uF (630V)
(Any better suggestions?)
So does can anyone know how to fix this issue ? I have researched a lot and all I found is that i maybe need a coupling cap at the input jack to lower the lower frequencies. The question again is to find the right capacitance to fix that issue even if that is the problem.
I'm a true audio lover and I really appreciate any help I get.
Thanks in advance !
I'm a true audio lover and I really appreciate any help I get.
Thanks in advance !
Do your headphones have the recommended impedance for the amp?
Being hard or easy to drive is about sensitivity. You need to know what impedance the headphone amp is looking for on its output jack.
My 6F3 amp that I bought from Aliexpress last year does have output transformers that seems to be identical to the picture on your web link. The weight is about 500 grams each and the iron width is 60mm (75mm between the holes on the brace). This is a standard size for a 2-3W single ended transformer with reduced low frequency response. If you have the most common 2-way bookshelf speaker type, efficiency is about 85dB only: 3W is not enough to drive them at full volume without distortion. If you like music at high volume you must add a separate active subwoofer and drive the tube amp trough a crossover to cut the bass frequencies.
My amplifier also had a background hum issue due to improper heater wiring, that I solved by a complete rewire. Maybe your amplifier has a similar issue, and the headphone output has been designed with excessive attenuation to mask the hum. Changing the output resistors that are going to the headphone to reduce the attenuation may solve the issue. To get a better answer a schematic is needed, you may trace it from the circuit.
I advise to avoid the capacitor change, it will probably be ineffective. On a similar china-sourced amp I got earlier, iI had to change the output transformer with another one 4 times bigger (and with much better winding arrangements). Further improvement has been reached by reworking the 6H8C input and the global feedback. With the original transformers, I had to keep it at minimum to avoid oscillations.
My amplifier also had a background hum issue due to improper heater wiring, that I solved by a complete rewire. Maybe your amplifier has a similar issue, and the headphone output has been designed with excessive attenuation to mask the hum. Changing the output resistors that are going to the headphone to reduce the attenuation may solve the issue. To get a better answer a schematic is needed, you may trace it from the circuit.
I advise to avoid the capacitor change, it will probably be ineffective. On a similar china-sourced amp I got earlier, iI had to change the output transformer with another one 4 times bigger (and with much better winding arrangements). Further improvement has been reached by reworking the 6H8C input and the global feedback. With the original transformers, I had to keep it at minimum to avoid oscillations.
is this a line amp? if so, this is a spin off from the marantz 7 line amp topology that originally used the 12ax7's....
those pentodes were wired common cathode triodes and cascaded to give high open loop gains, then overall negative feedback is used to lower the overall gains, suitable for line amp duty...
i made a similar line amp using the 13FM7, these are real triodes....
Edit: i saw the picture after second attempt and i see that it was a single ended amp, if wired as pentode, give higher gains, but wire it as a triode and the sound is more enjoyable...did that came with the schematics...
those pentodes were wired common cathode triodes and cascaded to give high open loop gains, then overall negative feedback is used to lower the overall gains, suitable for line amp duty...
i made a similar line amp using the 13FM7, these are real triodes....
Edit: i saw the picture after second attempt and i see that it was a single ended amp, if wired as pentode, give higher gains, but wire it as a triode and the sound is more enjoyable...did that came with the schematics...
I would sell it on ebay to recover part of the cost, and thus not modify anything ( keep original) Then i wold buy a proper pushpull amp in the powerclass you need. If it should drive speakers you need more then 10w depending on speaker. As usual, there is no free lunch, good stuff will cost.
Transformers are expensive and larger ones are more expensive. Too small transformers will cause bad bass which you already discovered. Same goes for other components, larger tubes cost more and needs more power supply, which costs more.
Transformers are expensive and larger ones are more expensive. Too small transformers will cause bad bass which you already discovered. Same goes for other components, larger tubes cost more and needs more power supply, which costs more.
Dunno… maybe that's the solution — we don't have a schematic (or do we?) and the original complaint is, “when I play it loud it badly distorts”.
Well, if you connect anything from a 32 Ω to a 600 Ω set of headphones to the output thru a dropping resistor, to get it "loud", you'll have to be running the thing near full range output. Which, necessarily, is also where clipping of various forms starts.
The 2 easy solutions would be …
№ 1 — lose the dropping resistors
№ 2 — use the lowest impedance headphones too.
№ 2 — use the lowest impedance headphones too.
If — of course — there are no dropping resistors, then just using the lowest impedance headphones will get the volume up. More watts to the tin cans.
It would have been nice to see the actual schematic. With the assortment of tubes indicated, it looks to be push-pull, driven by a valve phase inverter, running class A, most likely.
Which brings up another thought — if it is running Class B at its upper range of output, it quite easily could explain the unmistakeable distortion. Where the two suggestions above continue to make sense.
GoatGuy
fixed the issue
Changed the caps for better ones with lower ESR, changed tubes, changed coupling caps, added some 240K resistors in series to the early stages of the power delivery.
Done ! Issue fixed !
The 3 resistors each channel at at the output jack need to stay there.
The amp is fine it just comes with crappy tubes and it uses wrong value capacitors.
Like the coupling caps, it had 4x 0.22uf 450V. Changed it to 4x 0.47uf 630V panasonics and the bass it lacked came back.
I hope this helps anyone who buys this amp and want to fix these issues.
I can now get the amp at 90% knob volume without any signs of distortion.
Thanks to all for your suggestions !
Changed the caps for better ones with lower ESR, changed tubes, changed coupling caps, added some 240K resistors in series to the early stages of the power delivery.
Done ! Issue fixed !
The 3 resistors each channel at at the output jack need to stay there.
The amp is fine it just comes with crappy tubes and it uses wrong value capacitors.
Like the coupling caps, it had 4x 0.22uf 450V. Changed it to 4x 0.47uf 630V panasonics and the bass it lacked came back.
I hope this helps anyone who buys this amp and want to fix these issues.
I can now get the amp at 90% knob volume without any signs of distortion.
Thanks to all for your suggestions !
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