Hello Solder slingers
I have a 3 Watt single-ended power amplifier made by Packard/Bell. It was scavenged from a small console stereo. I no longer have the preamp section or the speakers. But as a stand-alone amp using EL84 tubes it can power a full range pair of speakers. I'd like to turn this into a HeadPhone amp with volume control and a single input! I know very little about amplifiers, but I thought some guidance could be found here in Tubes and Valves. I do have a schematic someplace from a long-ago curiosity search. Help, suggestions, directions?
Thanks, kingfisher
I have a 3 Watt single-ended power amplifier made by Packard/Bell. It was scavenged from a small console stereo. I no longer have the preamp section or the speakers. But as a stand-alone amp using EL84 tubes it can power a full range pair of speakers. I'd like to turn this into a HeadPhone amp with volume control and a single input! I know very little about amplifiers, but I thought some guidance could be found here in Tubes and Valves. I do have a schematic someplace from a long-ago curiosity search. Help, suggestions, directions?
Thanks, kingfisher
The Schematic is the fundamental beginning requirement, in order to make intelligent modifications to an amplifier.
There likely are 100 or more different designs of single ended EL84 amplifiers out there.
It also might be helpful to have the model number of the original console stereo.
Might be able to know the rated speaker impedance as an example.
Next, what are the impedance of your headphones.
Are they sensitive (only need low power)?
The same questions for the speakers you will use.
What will you use for the signal source (most CD players put out about 2.1Vrms (3V peak).
Some old FM tuners only put out 200 or 300MV.
Gain might be an issue, depending on the amplifier circuit.
etc.
There likely are 100 or more different designs of single ended EL84 amplifiers out there.
It also might be helpful to have the model number of the original console stereo.
Might be able to know the rated speaker impedance as an example.
Next, what are the impedance of your headphones.
Are they sensitive (only need low power)?
The same questions for the speakers you will use.
What will you use for the signal source (most CD players put out about 2.1Vrms (3V peak).
Some old FM tuners only put out 200 or 300MV.
Gain might be an issue, depending on the amplifier circuit.
etc.
I'm glad to interest someone! I'll dig out the schematic and post again by including most answers to your points!
kingfisher
kingfisher
If the headphones are high impedance you might have to shunt the output transformer with a lower impedance to stop the primary ringing.
nigelwright7557 was right.
Because the amplifier was made for speakers, and not for headphones, the amplifier might have lots of hum, when played on many headphone types.
What you may need is a load resistor across the output (perhaps 8 Ohms), and a series resistor to the headphones (perhaps 330 or 1k Ohms).
That will attenuate the hum and signal to the headphones, and then you can turn the volume control up, so that the music signal is much larger than the hum.
Because the amplifier was made for speakers, and not for headphones, the amplifier might have lots of hum, when played on many headphone types.
What you may need is a load resistor across the output (perhaps 8 Ohms), and a series resistor to the headphones (perhaps 330 or 1k Ohms).
That will attenuate the hum and signal to the headphones, and then you can turn the volume control up, so that the music signal is much larger than the hum.
Thank you nigelwright7557 and 6A3sUMMER. To be safe, I am going to abandon this idea and use the amp as intended. 2 channel stereo with speakers. My intention was to give the amp to my son as his S.S. receiver has failed. A shout out to you 2 and also diyaudio.com for making answers to many of my questions.
kingfisher
kingfisher
On the subject of hooking headphones to a speaker output... I've found this calculator handy because you may need to both attenuate and load so that the travel of your volume control is normal. I've had situations where turning the volume control just a little bit blasted the phones, then I learned about L pads. Its kind of a two-part calculator but has instructions.
Network Calc
Network Calc
Wow! Lots of useful information stuffed into this link! Thank you. I'm sure many other explorers will be grateful to have this calculator on-hand.