An all triode Class A amp Review: GPinto GP-H2A

[zodiac1234]

Quote:

THey were inverted I sent a mail to gpinto and they aiutorised me to invert channel  (i  inverted them at the imput selector) and now it's good but all the other problems were  there also before of this

 
Are you still having the same problems?

 

[palchiu]

Quote:

THey were inverted I sent a mail to gpinto and they aiutorised me to invert channel  (i  inverted them at the imput selector) and now it's good but all the other problems were  there also before of this

 
Same invert channel problem with mine.

Please be patient. It's like in hell during first 100hour.
 
This amp needs more time to burn-in, 200 hours at least then starting sound good from mine.
 
And my advice is get better tubes.

 
I using modern tubes, JJ ECC802S and Gold Lion. They sound nice, and not expansive like some good NOS tubes. (One TFK ECC802S can buy 12+ JJ ECC802S here. lol)
 

 
 
Quote:

If you have other 12au7 tubes you can replace them. Tubes 1-4 and 2-3 are paired.
Consider 1 channel:
tube 1 is preamplifier and phase inverter
tube 2 is power tube configured in push and pull
 
So if you want replace pre stage you need to change tubes 1 and 4. Otherwise tubes 2 and 3 for power stage.

 
You may get tubes in pair, I also try E80CC @pre-stage. It's working properly.
 
Another thing, make sure your source has enough power. I'm not sure how much Vrms that X-Fi HD has, don't forget turn the volume to max in computer.
 
Cheers
 
Pal

 

[zodiac1234]

Quote:

Please be patient. It's like in hell during first 100hour.

 
Exactly. This amp needs a loooong burn-in. + 200 hours I would say.
 
Be patient.
 
cheers.

 

[palchiu]

Quote:

 
Exactly. This amp needs a loooong burn-in. + 200 hours I would say.
 
Be patient.
 
cheers.

 
I think because the output transformers, let it needs more time to burn-in.

 

[zodiac1234]

Quote:

 
I think because the output transformers, let it needs more time to burn-in.

 
No, it is NOT the transformers.
 
It is the active devices; that is; the tubes.
 
If you change the tubes, you need to re burn-in the amplifier.
 
cheers

 

[vale25]

what's the right grid negative voltage?

 

[zodiac1234]

Quote:

what's the right grid negative voltage?

 
 
It is not a good idea to change the internal pot setting.
 
It profoundly effects the sound quality and the distortion characteristics.
 
The best way is to measure the THD for different pot setting, then set the correct bias for the lowest figures . It is not a trivial procedure at all.
 
I touched the pot on my amp, and it was very difficult to fix it. Remember, it effects the sound.
 
Wrong bias = doll sound, flat soundstage, and no extension.
 
Right bias = DEEP, wide soundstage, sweet tops, and remarkable transparency.
 
 
 
That is why I mentioned not to touch it.
 
My advice would be to contact the manufacturer. I am sure they could help you.

 

[vale25]

thank you for your answer... can you jast check cathode DC voltage and grid DC voltage in your amp? I'd like to know if the are the same

 

[vale25]

the same of mine of course... I read 193 V DC on cathode and 4,53 on grid for every section of the power tubes

 

[zodiac1234]

I have 220 Vdc on cathode, and 11.63 V on grids (by thd measurement & listening).
 
The tubes are Siemens ECC802's.
 

 

[vale25]

don't you think there is something strange on mine? tubes are sylvania jan 5814a

 

[zodiac1234]

How do you mean?
Sylvania 5841a are excellent tubes.
 
cheers

 

[vale25]

grid voltage is too low on mine or not?

 

[zodiac1234]

Quote:

grid voltage is too low on mine or not?

 
I see what you mean now.
 


It all depends on the valves you are using. The manufacturer measures & sets the correct bias for each set of output valves.
 
They vary from unit to unit because the valve-pairs are different.
 
The bias on your amp unit might be just the right value for the particular set of valves used, which might be quite different
 
than for the values on other amps.
 
 
 
A while ago I decided to change the original tubes to the much more expensive ones.
 
Contrary to my expectation, the sound quality dropped like a bag of potatoes.
 
I contacted a local electronics shop that charged me 200 dollars to tell me what I told you in post #37.
 
They used distortion measurements to find the optimal pot setting for the new valves that I put in the amp.
 
I have no idea what the old values were.
 
 
 
So my answer is:
 
- If you haven't touched anything and if all the tubes are quite warm (nr 2 & 3 should be warmer) to the touch after 30 min, then don't worry about it.
 
- If you have altered the internal pot, then:
       1. contact a local electronics shop
       2. ask them to find the optimum bias value for the new valves using THD analyzer.
       3. Once you get the unit home, then:
               a. Mark the position of the new pot setting (nail laquer)
               b. Listen carefully
               c. Make VERY VERY VERY minor adjustments to find the optimal sonic setting of the pot.
               d. Mark the new position & the tubes it is associated with.
 
It sounds shockingly unbelievable now!
 
cheers

 

[vale25]

thank you very much you were absolutely exhaustive!