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Messages - gfr

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Guitar News / Re: Virtual concerts and live streams
« on: April 07, 2020, 09:07:44 AM »
For those who like classical guitar, these pages are doing live sterams with "home concerts" and interviews. The past ones are archived:

Tubes and Hybrids / Re: 12 v tube preamp
« on: December 17, 2019, 08:17:29 PM »

Some theory, and some ideas for improvements.

Amplifier Discussion / Re: Univox U65G DC on speaker
« on: November 26, 2015, 07:08:01 PM »
That's a headache for every song in the set list :)

Try one (or two :)) of these:

Amplifier Discussion / Re: Fender Sqiuer 10
« on: November 18, 2013, 05:39:43 AM »
0) Added an input with very high input impedance, for piezo pickups.

1) I'm not sure about pulling the diodes - some acoustic units (see behringer adi 21 / samsamp acousti di) have diode clipping to "warm up" piezo pickups. Also, limiting with diodes in the pre may sound cleaner than the power chip amp distorting.

2) problably.

3) AFAIK it's just a small full range speaker just as the "electric" version, perhaps with a different (fuller?) response.

Amplifier Discussion / Re: Fender Sqiuer 10
« on: November 13, 2013, 06:18:25 PM »
If it's similar to a Squier 15 or an Epiphone Studio 10 (and I've seen a bunch of schematics for these little practice amps that are **** exactly identical ****, from a variety of manufacturers), then it's a 4558 or a TL072. Even when it's not identical, the structure is basically the same: a pre with a dual opamp, diode cilpper and passive eq, and a TDA2030 power amp.

I'd like to see the schematic for a Squier SA-10 to see what they have tweaked to make it "acoustic".

Amplifier Discussion / Re: Univox Stage 65
« on: November 02, 2013, 10:25:39 AM »
Not my video, I just found it on YT.

Here's a recording of mine, unfortunately I don't have a photo with the amp:

Both the guitar and the bass through the same U65, everything recorded with the built-in mic on a portable radio/tape recorder. Hard times :). We used to plug a mic at the 3rd input of this same amp too... The guitar is a Giannini 1982 Les Paul copy (I hated it), DIY fuzz (741 + diodes on the feedback loop). My guitar, my amp, my fuzz, however I didn't play on this one - but it's the best sounding recording I have of this gear.

Some schematics:

From Univox:

From Giannini:

The reverbless version (that's the one I owned):

The bigger brother U75:

Amplifier Discussion / Re: Univox Stage 65
« on: November 01, 2013, 08:49:27 PM »
My first amp was the brazilian equivalent of this (Giannini U65G). Mine was the version without reverb, just tremolo.

Just like this one:

The power amp driver uses a transformer as a phase splitter, I think it's the "secret" of its bluesy clean sound.

I used the chassis and cabinet of mine to build another amp, but I still have all the guts (including the transformers). I plan to rebuild it someday :)

BTW there's a slightly higher wattage version, the U75, that doesn't have the interstage transformer (and that doesn't sound as good).

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