Path: csiph.com!eternal-september.org!feeder.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: Don Kuenz Newsgroups: sci.electronics.design Subject: Re: How to increase the volume of a metronome? Date: Mon, 13 Feb 2017 19:58:01 -0000 (UTC) Organization: A noiseless patient Spider Lines: 29 Distribution: world Message-ID: <20170213f@crcomp.net> References: <20170213a@crcomp.net> Injection-Date: Mon, 13 Feb 2017 19:58:01 -0000 (UTC) Injection-Info: mx02.eternal-september.org; posting-host="2eced9cbef81c239930a640cc3c023bf"; logging-data="3029"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1+1fRevYrC3re9oUK2Kl3k1" Cancel-Lock: sha1:bUmmQeF7ZvEf5RgzLhHpL8PspR0= Xref: csiph.com sci.electronics.design:447584 bitrex wrote: > On 02/13/2017 10:28 AM, Don Kuenz wrote: >> Greetings, >> >> Comments are sought on additional circuitry to increase the speaker >> volume of the circuit shown between the lines. Comments on circuit >> simplifications are also sought. (Maybe a 555 with a couple of pots is >> as simple as it gets sometimes?) > > You can't drive an 8 ohm speaker from the emitter of a 2N3904 like that > - it only has a low output impedance for small signals, and the drive > current available is not symmetric. > > Either use a small impedance matching transformer in the collector lead > (like 2k-8 ohms maybe) with a 0.1uF cap in parallel with the primary, or > use the 555 output to drive a proper complimentary BJT pair power > driver. Or just use a small audio output driver IC to drive the speaker, > like the LM386 - the output automatically biases to around half the > single supply and you can block it from the speaker with an > appropriately-sized cap. The LM386 looks like a winner to me, provided that Tim's "narrow pulse" makes the timbre sound warm enough. Thank you, -- Don Kuenz KB7RPU