[plainbriny]

My previous amp is a DAC/AMP combo xDuoo TA-01, which is a great little hybrid amp using 12AU7 tube. I like it very much and it is powerful enough to drive my cans.

However, I always want to try a PURE tube amp. There are various options, but it would be better if I can build one from the kit! So after some search, I found one which uses 6n5p (6AS7/6080) + 6n11 (6DJ8/6922). The total cost with PCB, parts, transformer, potentiator, case etc (tubes excluded) is only a tiny fraction of other amps. This amp doesn't have brand, but they call it Qing Feng (Breeze Audio) E-100. You may also see assembled amp named Nobsound, I think they are the same thing, rebranded maybe.

The assembling is straight forward and can be done in several hours. But I spent some time figuring out how to assemble the case..


Edit June 6th: well, this kit is cheap but some of the components are wrong. For example, one of the 5W resistor is wrong (1.5K instead of 5.6K), cause extremely high temperature (from higher than expected current) and the PCB is smoked. I have desoldered them and will replace once the new resistors I ordered arrived.

I got the tubes locally, because they only provide Chinese 6n5p and 6n11. 6n5p is compatible with 6AS7(G) and 6080 (perhaps others), and 6n11 is compatible with 6DJ8 and 6922. My first combination is Thomson-CSF 6080WA and Mullard PCC189.



The box of CSF 6080WA is ridiculously huge....

This combination is very nice and c/p value is good. I have also tried some 12AU7 (with adapter) but the sound is muddy. Looking at the spec I found the resistance is much higher in 12AU7 and mu is lower, maybe that's why 12AU7 is not performing well in this amp. The first image is Sveltana 6H13C with Mullard PCC189, this combination is also good.

So far I am very pleased with this amp, and more mods to come. The only issue right now: it's too darn hot! (Edit: which might be due to the 5W resistor with wrong ohm value and thus causing higher than expected current and temperature. Will fix in the next couple days.)

June 6th: desoldered the wrong 5W resistor

The PCB is smoked since the current and power (heat) is several times of those of the adjacent one.

I also removed some other capacitors, to improve mid-high frequency response with a 2.2uF in stead of 0.1uF one. Ordered but not yet arrived.


June 8th update: the replacement parts arrived

The resistors were moved to the back side of the PCB, will be on the top after assembled.


Some capacitors replaced.


At first, I found that the the volume of left channel seems to be louder than the right, perhaps the wrong resistor (and current) did some damage to the other parts? I need to listen more to make sure. Update: After some cross testing, it seems to be the fault of 3.5 to 6.3 mm adapter. All is well now.

June 11 update: tried some means to lower the temperature. This has some effects, at least I can comfortably use the turning knob now.

Haven't applied thermal paste yet, should be able to decrease the temperature further.
However this limited the space for 6AS7/6H13C tubes...

June 26 update: rolled e88cc to dual 5654W (6ak5) with adapter, they are far exceeding my expectations, considering the price of 5654, this configuration is very cost-effective.

 

[GarageBoy]

I have the same kit and was missing the transistor for the power supply. Can you tell me what proper one is? I saw the part number on a schematic somewhere and was only able to find one on some shady eBay listing, and it runs really hot

 

[plainbriny]

The high voltage uses FGL40N120 (G40N1500 printed on the PCB), the low voltage one is LT1083 or LT1084.

The first one I built finally went wrong, with popping sounds randomly in the right side (maybe leaking capacitor?) so I order a second kit and reuse the case/transformer etc.
The first kit included LT1084, and the second kit comes with LT1083, both used.
I have replaced almost all components in the second kit, not necessary, just try to make it better.





using 3A instead of 2A, a bit overkill and can't even went through the holes...



My current tube combination is RCA 6080 and Russian 6n1p, works pretty well and not as hot as the first unit, perhaps because it's winter now?

 

[plainbriny]

One note about the unit I built: it is working very well with high impedance cans (DT990 pro 250 ohm and Q701 62 ohm).
It's interesting that despite the higher impedance, the volume scale is lower with DT990 than Q701, perhaps due to DT990 more closed than Q701?

But my 32 ohm In2uit T100 and Philips SHP2000 are TERRIBLE with this headphone amp.
The 32 ohm headphone sounds like it were covered, the sound is muddy and depressed.
However, I can hear some more details with In2uit T100, perhaps because its sensitivity is higher.
Tweaking with the output capacitors may be necessary to make it working with 32 ohm cans, but right now I mainly use the high impedance cans.

 

[GarageBoy]

Yeah, the high impedence source will cause the sound to be flabby. That's the price of otl. I should give mine a run again, it's simply the board mounted on an aluminum channel, no chassis

 

[mateusfig]

I bought this kit also. Im trying figuring out the right transformer for it. The informations suplied by the sellers seems wrong. I'm about to buy a hand manufactured transformer (toroidal or EI) but I'm afraid. These are the information provided by the seller:
0v---150v / 0.5A
0v---9v / 1A

0,5A for 150v seems too much for these tubes. I don't know if the voltages are the right ones as well.

Anybody could help me on this?

 

[GarageBoy]

Not sure if it's right, but the other ebay sellers call for a similar transformer - 0.5 amps gives you a little bit of room

 

[mateusfig]

The high voltage uses FGL40N120 (G40N1500 printed on the PCB), the low voltage one is LT1083 or LT1084.

The first one I built finally went wrong, with popping sounds randomly in the right side (maybe leaking capacitor?) so I order a second kit and reuse the case/transformer etc.
The first kit included LT1084, and the second kit comes with LT1083, both used.
I have replaced almost all components in the second kit, not necessary, just try to make it better.





using 3A instead of 2A, a bit overkill and can't even went through the holes...



My current tube combination is RCA 6080 and Russian 6n1p, works pretty well and not as hot as the first unit, perhaps because it's winter now?

Please, could you tell me the RIGHT transformer ratings (current and voltage)?

 

[rattoko]

Please, could you tell me the RIGHT transformer ratings (current and voltage)?

For high voltage side, each channel draws about 50 ma, so total circuit consumes about 100 ma. Any tranny with 0.150 A 150 V-180 V should be fine, the supply is regulate no need to worry much about voltage.
For heater, you need 2.5 A for 6AS7 and 0.3A for 6DJ8 so 0-9 V 5A should do the trick. To run this amp cool 7A or higher is better and you need bigger heatsink for 1083 regulator IC. Better separate high voltage and heater tranny.

 

[mateusfig]

For high voltage side, each channel draws about 50 ma, so total circuit consumes about 100 ma. Any tranny with 0.150 A 150 V-180 V should be fine, the supply is regulate no need to worry much about voltage.
For heater, you need 2.5 A for 6AS7 and 0.3A for 6DJ8 so 0-9 V 5A should do the trick. To run this amp cool 7A or higher is better and you need bigger heatsink for 1083 regulator IC. Better separate high voltage and heater tranny.

Thank you very much for the reply. I think I build wrong transformer (heater current lower dimensioned) and my amp is running too hot.

 

[AudioCats]

can anybody do a long-term impression report on this amp?

 

[AudioCats]

Parts kit (PCB and all electronics component, excluding volume pot and tubes) are now $30 on aliexpress.

might be worth considering, at this price.

the same kit is also available on ebay for a little more $.

update: I couldn't resist and ordered one. Mainly to see if the "regulated high voltage rail" rumor is real.

 

[AudioCats]

(I probably should have figured this out before placing the order..............) by looking at the picture of the PCBs, the "G40N1500" device looks to be part of a capacitance multiplier, it does not regulate HV rail voltage. No wonder it doesn't have a heatsink.

probably easy to convert to a series type regulator.

 

[AudioCats]

somewhat off topic..............aliexpress seems to have quite a few tube amp kits on sale lately, like this 12ax7/el34 kit (including basic tubes and output transformers), for less than $90 shipped.
Add an Antek power toroid (275v / 100va) and an enclosure and you can (potentially) get a EL34 amp, capable of driving most orthos.
All capacitors in that kit will likely need to be replaced/upgraded, though. At least the HV power caps will need to be at least 450v rated instead of the 400v stuff shown in the pictures.

 

[AudioCats]

If you have enough loose parts laying around, this 5670/6as7 headphone amp can make a good project as well. Probably an easier build since all component values is shown on the silk screen.

The PCB looks to be very similar to what is inside a littleBear p8.