Using R+C instead of LED.
- Thread starter garfo
- Start date
HD600s are 300 ohms, so the loading won't be that much different. I do however much prefer the HD600 to the Beyers myself. I would suggest not changing anything in the amp until you have listened enough to both to decide which headphone you want to use. Then you can start to fine tune the setup.
Paul Joppa
Moderator
I'll just mention a couple further technical issues.
Using a cathode resistor to set bias is sometimes called automatic bias because it provides negative feedback at DC to stabilize the plate voltage. Normally that would be the reason to avoid fixed bias such as an LED. But with a current source plate load e.g. Speedball in Crack the cathode current is constant so a resistor cathode bias will not supply the bias stability that it does in a normal resistor-loaded triode amplifier stage, so there is no reason to avoid it.
If the resistor is unbypassed, it can sound comparable to an LED. If the plate load is a current source, and the following load is high impedance as well, this won't affect the gain. But the negative feedback it provides in the audio range causes the plate or source impedance to increase. As long as that higher impedance is not a problem, there is no reason to avoid the resistor. In the new Stereomour II, I have increased the plate current in order to reduce the resistor value to where it does not make the 12AT7 plate resistance too high. I did this to get a bias voltage between the HLMP's 1.55v and the TL431's 2.50v. Engineering is always a matter of tradeoffs; the meaning of the word "best" varies with the context.
Using a cathode resistor to set bias is sometimes called automatic bias because it provides negative feedback at DC to stabilize the plate voltage. Normally that would be the reason to avoid fixed bias such as an LED. But with a current source plate load e.g. Speedball in Crack the cathode current is constant so a resistor cathode bias will not supply the bias stability that it does in a normal resistor-loaded triode amplifier stage, so there is no reason to avoid it.
If the resistor is unbypassed, it can sound comparable to an LED. If the plate load is a current source, and the following load is high impedance as well, this won't affect the gain. But the negative feedback it provides in the audio range causes the plate or source impedance to increase. As long as that higher impedance is not a problem, there is no reason to avoid the resistor. In the new Stereomour II, I have increased the plate current in order to reduce the resistor value to where it does not make the 12AT7 plate resistance too high. I did this to get a bias voltage between the HLMP's 1.55v and the TL431's 2.50v. Engineering is always a matter of tradeoffs; the meaning of the word "best" varies with the context.
Give the amp 100 hours to break in the capacitors. Then at hour 101, put the LED's back.garfo said:
-PB
Will certainly do that. Was referring to a better PSU because irrespectively from using an LED or an RC, the amplifier sits a bit when reproducing large orchestras and generally when reproducing complex musics. As long as u go with a jazz trio all fine of course, very nice textures and feel.
I'm not quite sure what is meant by that.garfo said:
Knowing about your source components and headphones would be helpful. This may be distortion on transient peaks that would happen at much higher power levels with the Speedball. (Sorry, the Speedball removes four resistors and adds even more LEDs!)
Nothing serious really. I meant to say the ability of the amplifier to resolve large and complex orchestral music into each single elements. At moment I'm on iMac USB into MF V-Dac tru Spotify Premium (of course it is not HD but overall very enjoyable). Of course Im used to the performance of my main system (MacMini firewire into Weiss Int202 into dCS Elgar, then Spectral DMC30/DMA100s into Magnepan MG12QR) which is quite revealing and exciting.
I'd try better source material. Spotify's ability to resolve complex orchestral music over an internet stream may well be the issue. (You also still haven't mentioned the headphones you're using)
I can remember working on a very early Crack prototype a long, long time ago for a musician who wanted a high end headphone amp. I remember sitting down and listening to at least 15 different tube operating points, then I finally found one that just sounded really good. I took voltage measurements, scratched my head a little bit, then realized the operating point was one that I had run into building Bottlehead kits with the same tube.
The biggest improvement to be had in the Crack, beyond the Speedball, is shunt regulation. Unfortunately, you really need a bigger power transformer and chassis to accomplish that.
-PB
The biggest improvement to be had in the Crack, beyond the Speedball, is shunt regulation. Unfortunately, you really need a bigger power transformer and chassis to accomplish that.
-PB
So what IS the accepted load resistor here to use with a capacitor?
I have seen everything from 390 to 470 to up to 1.5k or even 2.2k. A friend wants me to mod his Crack by removing the cathode LED's for 2.2K resistor and 2000µf bypass cap. Just running the values, it seems 2000µf is way overboard where a 470µf will do given 2.2k. Thoughts?
I have seen everything from 390 to 470 to up to 1.5k or even 2.2k. A friend wants me to mod his Crack by removing the cathode LED's for 2.2K resistor and 2000µf bypass cap. Just running the values, it seems 2000µf is way overboard where a 470µf will do given 2.2k. Thoughts?
I have done a lot of repairs on audio equipment with umbilical cords over the years, and only once was the umbilical not at least part of the issue. There really is nothing to be gained by doing this.garfo said:
Azimuth48 said:
I would let your friend know that the designer of the amp said this is a pretty substantial downgrade in performance.
Paul Birkeland said:
Yes, and a couple of other friends did the RC mod on their Crack and raves about it. I’m sure it IS different, and I highly doubt “betterâ€. I did the reverse mod for a similar design, the Darkvoice 336 SE and I loved the LED’s. So much better transients and speed. It dropped the hazy slow blunted sound.
But if this person INSISTS on the changes, I just want to say on the same operating point as close as possible.
Similar threads
