A bit on the sharp side
The amps have now over 50 hours play time on them and my impression is that it has great dynamics and sparkling clarity. However, the overall tonality is very much on the sharp side. Violins, piano and even the cello sound unrealistically sharp.
First I tried biamping using the Sony Vfets for the mid/tweeter and the F5TV3 for the bass. This helped with the overall balance which was previously a bit bass shy. I then bypassed C5, C6 and C1, C2 with .01uf Vishay MKP1837. This seemed to smooth things a bit. Still too sharp for my classical music tastes.
What should I do?
Thanks. nash
The amps have now over 50 hours play time on them and my impression is that it has great dynamics and sparkling clarity. However, the overall tonality is very much on the sharp side. Violins, piano and even the cello sound unrealistically sharp.
First I tried biamping using the Sony Vfets for the mid/tweeter and the F5TV3 for the bass. This helped with the overall balance which was previously a bit bass shy. I then bypassed C5, C6 and C1, C2 with .01uf Vishay MKP1837. This seemed to smooth things a bit. Still too sharp for my classical music tastes.
What should I do?
Thanks. nash
I find that amps changed for about 200 hours or more. What do you have it biased at? If the bias is low I find it makes things brighter, increasing the bias smooths things out a bit. I also find that this amp is very revealing of problems elsewhere. Play with different sources and see if you can hear a difference.
My two cents,
Can you clarify, 1.58v across .1 ohms is a lot. Or are you saying 1.58 amps?
I run about 1.8amps. But I have large heatsinks.
For the front end 1.89v across the 47.5 ohms is fine.
Sorry I meant 0.158V or 1.58amps. I get 22.5C difference hottest point of heatsink to ambient. I think it should handle 1.75amps being monos. Maybe I will try that too.
Have you or anybody looked at the harmonic spectrum at different output bias voltages and are your two channels fairly close H2/H3? I will be hooking it up to my Focusrite for that purpose shortly. Just wondering what others have found since I dont see any pics posted.
BDP have you had any success changing the harmonics; you had posted about it on March 31.
nash
Hooked up to Arta/Focusrite, input 1khz sine, output was 2.82V across 8r resistor.
Note difference in H2/H3 between L and R at 1.51amps output bias (first two pics). I then set Lch first by reducing bias and listening till the complained sharpness was gone and that was at 1.23 bias (third pic) Set Rch with similar H2/H3 profile and that came out at 1.08bias (last pic).
Why does Lch H2 not change that much as the bias is changed while the Rch H2 really drops down?
Appreciate feedback.
Thanks. nash
Note difference in H2/H3 between L and R at 1.51amps output bias (first two pics). I then set Lch first by reducing bias and listening till the complained sharpness was gone and that was at 1.23 bias (third pic) Set Rch with similar H2/H3 profile and that came out at 1.08bias (last pic).
Why does Lch H2 not change that much as the bias is changed while the Rch H2 really drops down?
Appreciate feedback.
Thanks. nash
Attachments
Can do sometime. All four Jfets are curve trace matched, Mosfets are also matched, Irf's too, all from forum member NicMac.
With the now reduced bias settings of Lch 1.23a and Rch 1.08a amps sound very good. Just a bit of glare at the very top which sounds like cap induced glare. What are you using for C5, C6? I am using 47uf Elna Silmic/1837 and am wondering whether squeezing in a 220uf Elna there instead might be better? Dont have enough experience, is a larger value cap of same brand sound better? Very sensitive to glare.
Thanks for your help.
nash
With the now reduced bias settings of Lch 1.23a and Rch 1.08a amps sound very good. Just a bit of glare at the very top which sounds like cap induced glare. What are you using for C5, C6? I am using 47uf Elna Silmic/1837 and am wondering whether squeezing in a 220uf Elna there instead might be better? Dont have enough experience, is a larger value cap of same brand sound better? Very sensitive to glare.
Thanks for your help.
nash
Here are my right and left channels.
My VFETs were not the best matches.
The front end outputs were at about .01% distortion with no global feedback at 2.8 Vrms. No third harmonic. Offset minimum.
I haven't had a chance to adjust the cascode feedback resistors, but I will.
I have been trying 2.3K and 4.75K and no feedback
What was your Gain measurements?
BDP
My VFETs were not the best matches.
The front end outputs were at about .01% distortion with no global feedback at 2.8 Vrms. No third harmonic. Offset minimum.
I haven't had a chance to adjust the cascode feedback resistors, but I will.
I have been trying 2.3K and 4.75K and no feedback
What was your Gain measurements?
BDP