Sugden P28

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DennyG

Member
Joined 2010
Sugden A28 - bias and other voltage adjustment

I have a question about my Sugden A28 (original model, black front panel, white lettering, grey case and with the heatsink on the back). It sounds pretty good at lower levels but during louder complex music at more normal sound levels it tends to get a bit harsh. I'll eventually replace most electrolytics but I would first like to check and adjust the bias and the other critical voltage levels. Could someone explain how I should go about doing this? I have Michel's schematic.
 
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AndrewT

R.I.P.
Joined 2004
The P28 is a low power amplifier.
Louder music is quite likely to be clipping the amp output. That is the cause of the harshness as you turn up the volume.
Changing the bias will not help reduce the output clipping at higher volumes.
More efficient speakers will allow higher volume at lower power output and thus avoid clipping.
 
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ashok

ashok

Member
Joined 2002
You must have missed it.
It specifies it in the spec sheet for Line, Aux tape Input.
100mV into 180 K ohms for 35 watts output.
So there you go , it's 180 K ohm and I guess it's via a preamp. No idea if the volume control is at the input or mid stage.

Phono input impedance is as usual at 47 K ohm.

newbeenew: No. All that you need is a low output impedance from the DAC and high input impedance at the amplifier input. In a majority of situations ( 99% ? ) you needn't even look for these ratings as they will all be useable.
 
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DennyG

Member
Joined 2010
Update on my Sugden A28 restoration

I recently replaced the RCA sockets and all the electrolytics in my A28 with great results. Thank you Michel for all your advice and the circuit & pcb layout diagrams. I set the bias to 300mA.

The upgrade discussion took place in another thread as part of a complementary speaker upgrade:
http://www.diyaudio.com/forums/multi-way/93055-celestion-66-needs-mid-range-18.html#post3059049

A couple of posts down from the above linked post has a link to a replacement cap list I prepared.
 
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AntG

Member
Joined 2011
Hi Michel,
If possible could you send me the circuit diagram of the A28II.
<agxaudio(at)hotmail.com>
Last year I asked for some advice about a cracking volume potentiometer the advice to clean it solved the problem, unfortunately the unit has suddenly stopped powering on and all the internal fuses seem fine so maybe with the circuit diagram I can find the fault.
Many thanks
Ant G
 
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lany

Member
Joined 2012
HI fellow Sugden listeners

I would be very pleased if someone could send me scematics for Sugden P28 and A28II?
please send to "lasse at nylanders.dk"
I've bought a secondhand P28 in order to have a bridge setup with my A28II, but the P28 sounds terrible, and the PCB shows signs of burned resistors. All power Transistors have been changed an non of the are the same.

Is it even possible to have the amp restore so i can use it with mu A28?

If not I will try to use it in bi-amp instead any one has experience with this combo?

Hope someone can help me out here!

Thanks
 
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AntG

Member
Joined 2011
Hi Phil
I saw your post to Lany and I was hopping you could help me out a with schematic diagram for the A28II if you have it.
A while ago it stopped working and I have put off investigating further apart for a quick visual inspection until I have more information.
It would be most appreciated if you could assist.
<agxaudio(at)hotmail.com>

Thanks
 
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