3transistor spare parts Guitar headphone amplifier - Page 1
Forum section: electronics / projects

author: dave_j_fan
author_rank: Regular Contributor
timestamp: October 01, 2018, 09:29:23 pm
content: took a heapphone amp and added a preamp stageour basic guitar headphone amp is heresome restrictions : 4.5V operation as in Vox ampsthis is working but two issue1) a bit distorted2) weaker HP signalPlease help

author: NiHaoMike
author_rank: Super Contributor
timestamp: October 01, 2018, 11:21:51 pm
content: Read up about opamps and some simple headphone amplifiers based on them.

author: Audioguru
author_rank: Super Contributor
timestamp: October 02, 2018, 12:49:59 am
content: Of course it is distorted. The output transistor has no negative feedback.

author: Audioguru
author_rank: Super Contributor
timestamp: October 02, 2018, 01:16:35 am
content: Please translate "HP" into English.I looked at the schematic and the datasheets for the battery and BC547 transistor. Then I did a little arithmetic and discovered that many bC547 transistors will clip badly or be completely saturated in that poorly designed circuit:

author: dave_j_fan
author_rank: Regular Contributor
timestamp: October 02, 2018, 03:16:07 am
content: thank you,i am thinking of this with first pre stage of my amplifierhttps://circuitszone.com/portable-headphone-amplifier-circuit-based-3-transistors/what u think

author: dave_j_fan
author_rank: Regular Contributor
timestamp: October 02, 2018, 09:04:31 pm
content: Here is the circuit i modified- gain in stage one reduced- stage isolation with 680E-final power transistor usage : As per audioguru high gain transistor is removedvolume is vv loud .. working very wellwill upload recordings later

author: mikerj
author_rank: Super Contributor
timestamp: October 04, 2018, 04:40:50 pm
content: That circuit puts a constant DC current through your headphones which isn't the best idea.

author: Zero999
author_rank: Super Contributor
timestamp: October 05, 2018, 04:13:24 pm
content: Presumably you're talking about an inductive guitar pick-up?A guitar amplifier needs no voltage gain, as the output level is quite high. Indeed, some voltage attenuation may be necessary.What is required is an amplifier with a high input impedance >1M and a fairly low output impedance, perhaps even a unity gain buffer.What impedance are the headphones?Here's a design I've just done in LTSpice. It has a gain of under 1. No doubt it will need tweaking if build in real life. It uses bootstrapping to keep the input impedance high. The input impedance is over 1M for frequencies under 6kHz and over 300k up to 20kHz.No doubt a simpler design can be made with a J-FET pre-amp or just a pair of MOSFETs.

author: NiHaoMike
author_rank: Super Contributor
timestamp: October 06, 2018, 02:40:30 am
content: The right solution is an audio opamp like the 4580.

author: Zero999
author_rank: Super Contributor
timestamp: October 06, 2018, 12:46:44 pm
content: Quote from: NiHaoMike on October 06, 2018, 02:40:30 amExcept it's not specified to work below 4V, which wouldn't give much battery life out of three AA cells.The bootstrapping configuration I posted has an almost rail-to-rail output. It would be better to only use two transistors in the feedback loop of an op-amp with a rail-to-rail output.

author: NiHaoMike
author_rank: Super Contributor
timestamp: October 06, 2018, 04:26:02 pm
content: Then look for headphone amplifier chips that are rated to work from both 5V and 3.3V - there are truly a lot.

author: Zero999
author_rank: Super Contributor
timestamp: October 07, 2018, 08:46:40 am
content: Quote from: NiHaoMike on October 06, 2018, 04:26:02 pmI agree, the circuits posted above are more for educational purposes. Using a purpose designed IC is the right way to do it.

author: dave_j_fan
author_rank: Regular Contributor
timestamp: October 17, 2018, 07:44:58 pm
content: ic i dont prefer getting chips for many countries is real pain and expensivefor eg here in Asia digikey takes 40$ for 0.1$ part as shipppingi wanted a design that uses very low cost parts still sounds goodHero999, Thank u for the circuit but that bulky220ufs are and issue for small casesi hope 22u will work

author: Audioguru
author_rank: Super Contributor
timestamp: October 17, 2018, 11:45:56 pm
content: There are electronics chat websites in India that talk about parts that are available in India. On this website we talk about Western parts.If the 220uF capacitors replaced with 22uF capacitors then the circuit will produce no low frequency bass sounds in music and not produce voice sounds from many men.