Trace Elliot V-type Bass Combo

bostjancek · 26th May 2006, 05:34 AM

Hello

Recently I bought from secondhand an Trace Elliot V-type Bass Combo (model 5001, 300W, build 1996). The combo is sounding verry good but it has one problem. It has verry loud 50Hz hum. It is disapear if I set the gain or volume at minimum. I have opened it and I saw that the power modul (bipolarbear) has been repaired - the output transistors were changed (now are BD249C and BD250C). From the service manual they must be 2SA and 2SD typ for 300W. Then i measured the DC offset and it was 0,5V. I tried to set it down but the minimum I was able to set it was 150mV.

Strange thing is that the power amp itself don't hum and the preamp is also quiet when is connected thrue DI.

Can somebody give me any advice how to repair this annoying hum?

Cheers

sreten · 26th May 2006, 07:48 AM

Hi,

Your hum is a problem with the preamp or the preamp wiring.

Start off by checking the ground connections at the input.
Also check the input sockets, you may need new ones.
(If the plating has worn through and your getting bad contacts)

/sreten.

bostjancek · 26th May 2006, 09:07 AM

Quote:

Your hum is a problem with the preamp or the preamp wiring.

I agree but why when the amp is connected through the DI there is no hum. Also all the connections are made with snap in connectors and they look like they are all OK. The preamp is made around the two ecc83 tubes. The signal ground in the preamp is connected to the case (ground) through some 100nF decoupling caps. It is possible that this caps (if they are bad) cause the hum? Also in power amp the signal ground is decoupled from case ground with 100nF + 10k ohm resistor. I don't know but this 10k ohm resistor is not a bit high? I usualy use 10 to 100 ohm resistor for decoupling.

Quote:

Also check the input sockets, you may need new ones.

This will be done in no time!

Cheers

JensRasmussen · 07:13 PM

Sorry to restart this old thread,

I'm trying to fix a Trace Elliot V-type 5001 power amp (Bass head)... for a friend, but I need a schematic... can anyone help.

The problem is in the solid state output stage, as signal is present at its input.

When power is connected to the power stage, the mains fuse blows - I suspect that the output needs new transistors - but it looks like somone have tried to fix it before.

Does anyone know why there are 2 heatsinks with 3 power devises on one and 2 power devises on the other??

Input is much appreciated

\\\Jens

phase_accurate · 22nd June 2010, 05:54 AM

The following is just speculation but I mention it anyway:

The reason for having two heatsinks might be because they don't insulate the transistors from the heatsinks and insulate the whole heatsinks instead.

Just sepculation but you will be on the safe side if you care about that.

Regards

Charles

JensRasmussen · 22nd June 2010, 06:02 AM

Hi Charles,

I just got the thing working last night, and you are right...the two heatsinks are not isolated from the transistors collector, and thus each sits with either the positive or negative rail voltage.

Anyway I replaced the output transistors and the thing was alive.

The third transistor on the one heatsink seems to be part of the fan control circuit???

\\\Jens

sreten · 7th July 2010, 12:10 PM

Quote:

Originally Posted by JensRasmussen

Hi Charles,

The third transistor on the one heatsink seems to be part of the fan control circuit???

\\\Jens

Hi,

Typically it would be there for thermal feedback for the biasing circuit.
It may be as you say the that the bias circuit also controls the fan speed.

/Sreten.

26th May 2006, 05:34 AM	#1
bostjancek diyAudio Member Join Date: Aug 2003 Location: Koper	Trace Elliot V-type Bass Combo Hello Recently I bought from secondhand an Trace Elliot V-type Bass Combo (model 5001, 300W, build 1996). The combo is sounding verry good but it has one problem. It has verry loud 50Hz hum. It is disapear if I set the gain or volume at minimum. I have opened it and I saw that the power modul (bipolarbear) has been repaired - the output transistors were changed (now are BD249C and BD250C). From the service manual they must be 2SA and 2SD typ for 300W. Then i measured the DC offset and it was 0,5V. I tried to set it down but the minimum I was able to set it was 150mV. Strange thing is that the power amp itself don't hum and the preamp is also quiet when is connected thrue DI. Can somebody give me any advice how to repair this annoying hum? Cheers __________________ Some are born with more and some born with less so don't take for granted the life we've been blessed it's hard to understand thet we're only a guest and each one of us shall be put to life's test.

21st June 2010, 06:43 PM	#4
JensRasmussen diyAudio Member Join Date: Jul 2002 Location: Denmark - Jutland	Sorry to restart this old thread, I'm trying to fix a Trace Elliot V-type 5001 power amp (Bass head)... for a friend, but I need a schematic... can anyone help. The problem is in the solid state output stage, as signal is present at its input. When power is connected to the power stage, the mains fuse blows - I suspect that the output needs new transistors - but it looks like somone have tried to fix it before. Does anyone know why there are 2 heatsinks with 3 power devises on one and 2 power devises on the other?? Input is much appreciated \\\Jens Last edited by JensRasmussen; 21st June 2010 at 07:13 PM. Reason: Updated error info

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26th May 2006, 07:48 AM	#2
sreten diyAudio Member Join Date: Nov 2003 Location: Brighton UK	Hi, Your hum is a problem with the preamp or the preamp wiring. Start off by checking the ground connections at the input. Also check the input sockets, you may need new ones. (If the plating has worn through and your getting bad contacts) /sreten.

22nd June 2010, 05:54 AM	#5
phase_accurate diyAudio Member Join Date: May 2002 Location: Switzerland	The following is just speculation but I mention it anyway: The reason for having two heatsinks might be because they don't insulate the transistors from the heatsinks and insulate the whole heatsinks instead. Just sepculation but you will be on the safe side if you care about that. Regards Charles

22nd June 2010, 06:02 AM	#6
JensRasmussen diyAudio Member Join Date: Jul 2002 Location: Denmark - Jutland	Hi Charles, I just got the thing working last night, and you are right...the two heatsinks are not isolated from the transistors collector, and thus each sits with either the positive or negative rail voltage. Anyway I replaced the output transistors and the thing was alive. The third transistor on the one heatsink seems to be part of the fan control circuit??? \\\Jens