Digitech Stereo Valve Amplifier AA-0474

[crackle]

Hi
Would you all agree with me that the output of this amp is not likely to be 25 watts RMS. The output valves appear to be equivalent to an EL84.
https://www.radiomuseum.org/r/unknow...r_aa_0474.html

Mike

[Nuvistor]

What are the valves doing when there are a pair of LM1875 Integrated circuits designed to deliver 30watts inside that amp?
https://www.radiomuseum.org/tubes/tube_lm1875.html

[snowman_al]

Oh dear, that's been doing the rounds for quite a while. I comes with lots of different names, Nobsound, Mistral, Jaycar, etc., etc.
It is an LM1875 'chip' amp with embellishments... and there is nothing under the 'transformer cover'!
Here is one in pieces https://www.youtube.com/watch?v=xS-D...annel=Zone1242

[Herald1360]

That first listed name seems rather the most appropriate

Conversion to a stereo pair of 3-3 amps would be an interesting use for the chassis hardware.

[crackle]

Interesting. I have to admit to missing the fact that it was an solid state IC doing the OP.
So its not really what it is pretending to be at all..

Mike

[roffe]

The valves are cathode followers in cascade,supplied by +-12V.
Tone controls are 4558 op amps.
The output stage is sometimes LM1875 and sometimes transistors,so there are differences.

[Techman]

Overrun valve heaters too, presumably so that they light up brighter and look more attractive in your room for both you and your visitors!

[Edward Huggins]

All that Glows is not Gold!

[Radio Wrangler]

The valves are in the signal flow. They may be overrun on heater volts to light them up prettily, but they are starved of HT voltage, just getting the supplies the transistor stuff runs on. So we can expect them to add distortion.

Where I come from, adding distortion amounts to damaging the signal. I would expect different valves shoved in these sockets to do different amounts of damage.

Some people like distorted sound. It's a free world. Other than that, the valves are just window dressing. Upping the heater volts shows exactly what the highest priority was and the empty transformer box hammers that interpretation home.

This amplifier is designed to take people for a ta-ta.

It isn't alone. Much of hifi is designed to look hey! WOW! while inside things are either nothing special, or are specially bad in order to make them actually sound different.

File under A for avoid, or L for Laugh.

David

[crackle]

Just for interest I attach a couple of PDF documents which were sent to me from Australia.
One explains the marketing of these amps, and the other explains a project to turn the chassis into an actual valve amp.


Mike

[Radio Wrangler]

I'm very impressed with Jaycar's action subsequent to the real nature of that amplifier coming out.... it's towards the end of the .pdf that Mike's attached above.

It's good to see responsibility taken and positive action to see no-one loses out.

It's good business sense. They've lost the profit on one item out of a catalogue of thousands of items, but they've saved the reputation of their entire company. Bit of a shame other firms don't work this out for themselves and try to minimise their immediate losses at all costs. It could have so easily turned into a Ratner moment.

David

[Herald1360]

Not quite a pair of 3-3s but an interesting conversion nevertheless. I particularly liked the redesign and reuse of the original mains transformer!