Rowe MM1 R3680A amplifier

Here again .......... :)

The channels are fine now but the amplifier's heat sink heats up really hot in the standby position, which is why?

Hello Vellu,


I don't know this amplifier exactly, but Powertransistors are real sensitve on correct setting of Bias-current. Usually you can find this setting-procedure inside the manual.

Greetings

Helmut

Hello Vellu,
heating in standby (without input signal) is caused by the bias current in the output transistors which is needed to achieve distortion free operation of the amplifier. There is no adjustment for the bias or symmetry in this circuit. You can measure the DC voltages shown in the schematic to check if the operating points of Q54 and Q53 are ok. The midpoint voltage at the collector of Q54 is a good indicator if something is wrong, it should be 0V on both channels.
Regards
Jürgen

Thanks for the answers, the problem is that how do I adjust the current because the amplifier does not have any control potentiometer (do I need to change components) and secondly I don't own the correct manual (Onlineshop is not open at the moment)

good news, i found the manual from the internet,i keep research if there are instructions for adjusting the current .
thanks Jürgen for tips.

Hello vellu

The bias current cannot be adjusted with this amplifier. There is a transformer between the driver and the output stage. The output stage is therefore independent of the driver stage.

In the output stage there are four diodes which sometimes cause an increased bias current, although they are measured as good.

Best regards - charly49

Hello and thanks for information

Is this the reason that Rowe rejected this amplifier model?
What do you suggest, what would I check?

r. vellu

Quote
Jürgen02
You can measure the DC voltages shown in the schematic to check if the operating points of Q54 and Q53 are ok. The midpoint voltage at the collector of Q54 is a good indicator if something is wrong, it should be 0V on both channels.

... see picture...

You can also measure D2 and D4, they only affect the bias current if they have a short. You need to desolder one side to measure it.
The bias current is defined by the forward voltage of D1/D3 and R61 to R66 . As Charlie49 wrote, the Diodes can measure ok with a diode tester, but still be faulty in the circuit. Any of the resistors R61 to R66 as well as the 3055 transistors can be the problem. All voltages depend on each other, so this is not easy to find.
R62 should be 4.7Ohm - I believe - another error in the plan ?
By the way, how hot is "hot" ? 30-40degC on the heat sink may be ok after some time. If the amp survives a longer session at high volume and does not sound distorted at low volume, it`s a good sign that the bias current is at least stable.

Regards
Jürgen

Thank you so much for the information and advice to you all. Now it is so that my wife forbade touching the Jukeboxes before Christmas, and i have to be nice before Christmas :) ... :( ,but I do research after Christmas and tell you what happened. Merry Christmas and a Happy New Year to all.

Good decision, Happy Wife - Happy Life !

Hello hello, the amplifier is fine, I replaced all 8 diodes and it helped. Now a new problem, Nsm city 2 and the screen is dark, the screen itself is okay. What is the next doubt in your mind in control box. And wife, she is.....:)