HH audio output stage?

[Kevco]

I am building HH ver C, option 1.

On the audio output stage, it is driving the speaker with one connection to the Negative Rail (-VB). I am attaching a snippet of the schematic, in it's original option 1 layout.

I wish to use either a headphone jack, or a speaker. So that when a headphone is inserted, the speaker is disconnected - as many devices work. But the headphone jack I bought is expecting to be mounted with one side to ground. Since the output stage is a darlington pair, can't the speaker and "volume" pot be connected between Q11's collector and chassis ground? See the attached modified schematic (but not showing headphone jack added to circuit).

Is this a valid way to use the headphone jack I purchased, without needing to insulate the jack from chassis ground? I'm lazy, and don't wish to bother getting an insulating headphone jack, nor modify the mounting hole I already drilled for the headphones.

Opinions?

[Qiaozhi]

I am building HH ver C, option 1.

On the audio output stage, it is driving the speaker with one connection to the Negative Rail (-VB). I am attaching a snippet of the schematic, in it's original option 1 layout.

I wish to use either a headphone jack, or a speaker. So that when a headphone is inserted, the speaker is disconnected - as many devices work. But the headphone jack I bought is expecting to be mounted with one side to ground. Since the output stage is a darlington pair, can't the speaker and "volume" pot be connected between Q11's collector and chassis ground? See the attached modified schematic (but not showing headphone jack added to circuit).

Is this a valid way to use the headphone jack I purchased, without needing to insulate the jack from chassis ground? I'm lazy, and don't wish to bother getting an insulating headphone jack, nor modify the mounting hole I already drilled for the headphones.

Opinions?

Your modification will not work as you expect. But it would function if you replace Q11 with a 2N3906 (same orientation as Q7 - i.e. swap over collector and emitter). It's not an ideal mod, and may not have the same volume. Personally I would either change to the VCO option, or simply use a plastic headphone jack.

[Gwil]

I don't think a 2N3906 would work in this circuit. It's a PNP, so its base current needs to come from the negative supply but Q7 is connected to 0V.

Gwil

[Qiaozhi]

I don't think a 2N3906 would work in this circuit. It's a PNP, so its base current needs to come from the negative supply but Q7 is connected to 0V.

Gwil

That's why you need to flip over the transistor, and add some bias resistors. Basically I'm suggesting that modifying the circuit is not going to be the lazy approach.

[Kevco]

Thanks Qiaozhi,

It's been over 25 years since I did electronics full time at work (before SMT became so popular). So, my memory is not good anymore

I'll take your advice, and get another headphone jack, which is insulated.

[Qiaozhi]

Thanks Qiaozhi,

It's been over 25 years since I did electronics full time at work (before SMT became so popular). So, my memory is not good anymore

I'll take your advice, and get another headphone jack, which is insulated.

Good choice!
Please let us know how you get on with the Hammerhead (with photos).