Hughes & Kettner

[52 Bill]

I'm still thinking that the problem is around the input ic. When the amp is put into bridge mode the left channel is driven by the right side chip. When the left side lights stopped working, it leads me to believe that there is no signal coming from the right side chip.

All of the voltage seem to be ok. Have you changed the ic?

Drive the right input with a signal and trace it through the amp starting at the input jack and see where it stops.

[Valvehead]

Found it !!

first i tried pulling T6 --that didnt work (can i leave that out ? )


then traced and i had no ac out of the right pot.
i wired in a 50k i had and --there it is--- amp seems good now !

THANKS GUYS --- definately learned a few things on this project !


im driving it with another amp / fx send. in stereo it sure seems like 25 watts instead of 100...... in bridge mode it gets nice and loud ! Ill try another amp or preamp--maybe the input signal is a bit low ?

[mozwell]

This amp has rails of +/- 38.5V, that should give you a bit less than 100W rms into a 4 ohm load, a bit less than 50W rms into an 8 ohm load.
bridge mode will give you double the voltage swing on the speaker, or 4 times the power. Dont run bridge into a 4 ohm load, unless the rating plate says you can. The amp is a CF200, thats 100W per channel into 4 ohm stereo mode, or 200W into 8 ohm bridge mode (i would guess)
If you are only running one speaker for a test, then you may only be getting 50W in stereo mode & 200W in bridge mode, no wonder it sounds louder in bridge mode.

if you feel there is not enough power, it may be that your input signal is not enough to get full power out of the amp. This looks to require a 500mV rms input signal for full output power.

have you measured the AC output volts, 100W rms into 4 ohm or 50W rms into 8 ohm is 20VAC rms.... use a sine wave test signal, you can get mp3 test tones off the net.
If you are not getting suitable output to the speaker, we can easily increase the gain, R24 & R18 are 10k, if you change both of these to 22k, you will be able to get full power from the amp with a smaller input signal....

[52 Bill]

Found it !!

first i tried pulling T6 --that didnt work (can i leave that out ? )


then traced and i had no ac out of the right pot.
i wired in a 50k i had and --there it is--- amp seems good now !

THANKS GUYS --- definately learned a few things on this project !


im driving it with another amp / fx send. in stereo it sure seems like 25 watts instead of 100...... in bridge mode it gets nice and loud ! Ill try another amp or preamp--maybe the input signal is a bit low ?

I'm glad you found the problem, but I thought that you had replaced the volume pot a few posts ago?

[Lockel]

Hi! I found here a shematic for the CF200, but I can not download, or see it. Can you help me, why?

[dmeek]

Here it is.

https://music-electronics-forum.com/...1&d=1588082703

[Lockel]

Thanks a lot! The power amp section is ok, but but the preamp seems to be damaged. This will help!