Warwick CL

[lowell]

Is it me or is the power amp missing from Warwick's schematics? Trying to find source of hum on speaker out. Hum is after master volume. Both high V rails are ~ +/-27.3Vdc. There is only 20mvDC on output and about 40mvAC.

http://www.warwick.de/media/manuals/CL_CCL/CL_ND4.pdf

[Jazz P Bass]

Yeah, sure is a nice preamp
Did you look at some of the other CL schematics.
Maybe one is close.
Link:Warwick Basses Amps & Rock'n Roll

[lowell]

ahhhh.... wasn't thorough enough. Is an older version.

http://www.warwick.de/media/manuals/.../CL_ND4_V2.pdf

[lowell]

Ok so the low V supply is LOW. At ~ +/- 12v. Should be 15v after the 7815/7915 regulators. Voltages before regulators seemed low too. So I completely disconnected the lowV taps from the board. I'm only getting 10vAC with unterminated lowV secondaries. Figuring this may be RMS, I calculated peak to only be 14vAC. So, seems to me like a bad winding on the PT. Any thoughts? FYI the high V secondaries are measuring good at ~41vAC.

[Enzo]

How about the amp is set for 240v mains and you have 120v mains in your shop? That would explain all the voltages being half what they should be.

Does this have the little pry out fuse holder block as part of the power cord socket? And does that fuse block have 240v and 120v on it top and bottom? And is it in upside down?

[lowell]

Nice thought. But no I don't see any primary voltage OPTION. The mute was disabled by another tech at some point so I guess it's possible that it is wired wrong. However, isn't 41vAC on the Highv secondary at the bridge rectifier AC terminals correct?

[Enzo]

Darn, oh well, I would have been a hero if that was it. I've seen that enough times.

Yes, 41v looks close enough.

Power off and read the resistance of the 18v winding then. If it were shorted windings dragging the thing down to 10v, I'd expect it to get hot, and at least draw current. Can you disconnect the transformer from the circuits and just applky mains and see if it draws any current by itself?

[lowell]

gettin' a 1ohm reading with the 18v secondaries unterminated. Not good.

[mozwell]

You are only reading winding resistance, 1 ohm is ok.

Do you have 120VAC in your shop ?

On the last page, you can see the transformer primary wired for series & parallel primaries for 230V / 115V operation.
If you are getting 10VAC (unloaded) from the 18VAC winding, my guess is that the unit is wired for 230V & you have 115V power, as 10VAC woudl be a suitable no load voltage for a 18VAC winding with only half the mains supply voltage.

Disconnect all the secondaries (taking note of which wire goes where) & power it up. Use a light bulb limiter at first.
Do you get 45VAC and 18VAC on the appropriate secondaries ?

Check the primary wiring, is there a yellow & white wire joined together & a yellow & white going to the switch, or do all four wires go to the switch ?
If all four wires go to the switch, then your unit is set for 115VAC, if only two go to the switch, your unit is set for 230VAC

[g1]

Not sure how you are reading the AC on the HV rails, but +-27V DC at the outputs sounds like about half of what should be there with 63volt caps. Agree with Enzo & Mozwell, amp must be set up for 230/240V use.

[lowell]

Well, you are ALL correct. Enzo, Mozwell, g-one. I love this forum. I rewired the PT primaries, yellow and yellow to one side of 120v, and white and white to the other side. Voila! No more hum out of the speaker and the thing is reacting far better. It's ALIVE. So question about bias. I don't see a "turn-on" voltage for these MJ11016 darlington power transistors on the datasheet. However, being that they are BJTs and are darlington my guess is two forward diode drops, or ~1.4v. Am I correct?

[mozwell]

lowell
Now with the speaker DISCONNECTED can you pease give us some voltages. the + & - DC rail voltages, which from 45VAC secondary winding should be about +/-63VDC
the case of the MJ15003 is the positive rail, the case of the MJ15004 is the negative rail. You can measure 0V at the negative speaker terminal.

Being a BJT there is no "turn on" voltage, like you get on a mosfet.
A few more simple checks & we are done.

All rail voltages ok ?, if so, Page 4 of the pdf gives you the setup adjustments for the power amp.
1. measure the DC volts on the speaker outputs, should be less than 0.5VDC, adjust the trimpot to get as close to 0VDC on the speaker terminals as you can
2. measure the voltage across each of the 0.22 ohm resistors, and adjust the trimpot for 1mV across the resistor as shown. this adjusts the idle current through each device to 4.5mA, a little low IMHO, but you may as well set it as the manufacturer suggests. Even if you set it at 2mV, i dont think it will damage anything. Generally, if i have "big heatsinks" i will set the bias (quiescent) current to 20mA to 50mA, to minimise crossover distortion, but for a bass amp, we can proably get away with much less bias current , so just set it up as the manufacturer suggests. 1mV across the 0.22 ohm resistor.

I dont think there is any need to adjust the limiter,

[lowell]

+/-55v at highV rails.

Limiter will only adjust down to 22vac on output, cannot get it to specified 17.5v

Output is fine at 2mvDC

Thanks! I think it's good!