=========================================================================== Digest of preamp construction articles. =========================================================================== --------------------------------------------------------------------------- Newsgroups: alt.guitar From: rstern@col.hp.com (Richard Stern) Subject: Re: Building your own (ONBOARD PREAMP!) Date: Tue, 29 Sep 1992 14:38:56 GMT Organization: HP Colorado Springs Division till@acid-rain.lucid.com (Don Tillman) writes: > > I personally don't like the sound of opamp-based preamp circuits. The > noises and distortions they produce are annoying and umusical and when > overdriven their clipping sounds very buzzy and recovery is ungraceful. > For me a discrete FET circuit is the best way to go and, as a side effect, > is only half the space (4 resistors, 1 fet, 1 cap, less wiring, add a cap > and a pot if you need the gain adjustment). Try this op-amp based pre-amp using the following circuit. This is a design from Mike McTigue who has posted this a few times already. Mike has this pre-amp in both of his electrics, I have it in 2 of my electrics, and we've built them for friends who are very happy with them. This circuit has no noticable noise or distortion, and a 9 volt battery seems to last forever (none of us have had to replace one yet in 2+ years). Please note that the purpose of this pre-amp is to act as a buffer between the R of the volume pot and the C of the cable. I did modify one of mine for gain, but I use it set to a gain of 1 almost all the time. 1M ohm 1M ohm +9v---\/\/\/--------O-----\/\/\/---gnd | from | pickup / switch 500k \ | ohm / +9v | \ |\ | 250k \ | 3 | \ | vol / <------||----O-----|+ \|7 pot \ .1 uF | \ / | u1 \_____o------\/\/\/----||-----> | 2 | / 6 | 50 1uF to | o------|- / | ohms cable gnd | | /|4 | | |/ | | | gnd | | | o-----------------o u1 LT 1012 uPower op amp or other low noise low power op amp (use a stereo jack to turn on/off the power) Richard Stern rstern@col.hp.com --------------------------------------------------------------------------- Newsgroups: alt.guitar From: till@acid-rain.lucid.com (Don Tillman) Subject: Re: Building your own (ONBOARD PREAMP!) Organization: Lucid, Inc. Date: 30 Sep 92 09:20:08 Date: Tue, 29 Sep 1992 14:38:56 GMT From: rstern@col.hp.com (Richard Stern) Organization: HP Colorado Springs Division Try this op-amp based pre-amp using the following circuit. (Umm, proper engineering practice requires you to decouple the 9v supply and to bypass the lower 1Mohm resistor with a .1 uF (or so) cap, especially if you're driving a load.) The design you present is nearly identical to the "Guitar Handbook" circuit that started this conversation, and suffers from the same problems -- high feedback, bad feedback topology, ungraceful overload and recovery, noise, and the signal has to go through a dozen non-linear devices inside the chip before it gets out. Exactly the sort of thing that gives solid-state amps a bad reputation! Date: Mon, 28 Sep 1992 13:15:11 -0500 From: Kurt Taylor Please post a schematic of your fet pre-amp. (I have tried many op-amp based circuits with little success, unless you like BAD pre-amps :')) Date: Tue, 29 Sep 92 10:34:54 -0400 From: tjs@godzilla.eecs.umich.edu (tim stanley) You mention your preference for FET based pre-amps. Can you give me any pointers to where I can lift a schematic of such a critter? Date: Tue, 29 Sep 1992 07:55:32 GMT From: chuck@spectrum.cs.unsw.oz.au (Mark Andrew Hawling) Can you post one of your FET designs that you think is good. Well okay. Here's a nice design from the "op-amps are for weenies" school. Low distortion, low noise, low feedback, graceful overload, simple, elegant, inexpensive, etc. This baby sings. It has a transfer characteristic somewhat similiar to the first 12AX7 tube in a Fender amp. +------------------------+--- +9v | | < | < 6.8k | < | | 5uF | +----||----+--- out | | | | |-+ | | in ---+----->| | | | |-+ | | | | | | < 10M < 2.2k < 51k --- < < < --- 10uF < < < | | | | | +--------+----------+-------------+--- gnd The FET is a 2N5457. The voltage gain is subtle, 3dB or so. You can substitute another low-Vdss FET if you know what you're doing. Power drain is about 0.5 mA, so a 9v batter will last a good long time. It does start to sound a little grubby when the battery sinks below 7v. It's also trivial to add a high-boost switch if you'd like; have it shunt the 2.2k resistor with a 0.05 uF (adjust to taste) cap. Or shunt the 2.2k resistor with a 10uF cap for more gain. Obviously you want to wire it so it's powered off when the instrument isn't plugged in -- it's far superior to use a switched jack instead of the weenie approach of using the second connection of a stereo jack. Also note that this design is easily phantom-powered, so you can even get by without installing a battery. -- Don --------------------------------------------------------------------------- Newsgroups: alt.guitar From: till@acid-rain.lucid.com (Don Tillman) Subject: Re: Building your own (ONBOARD PREAMP!) Organization: Lucid, Inc. Date: 7 Oct 92 16:06:03 From: db@seachg.uucp (David Bell) Date: 5 Oct 92 12:38:06 GMT Organization: Sea Change Corporation, Mississauga, Ontario, Canada In article till@lucid.com writes: > >Also note that this design is easily phantom-powered, so you can even >get by without installing a battery. > Excuse my ignorance, but what exactly does this meen ? "Phantom power", from the latin "phantasma potere" (powerful, but from no apparent source), means that the output signal of a preamp and the supply voltage to power it both run on the same wire. This is possible without compromise due to a fluke in the circuit: you can cut the circuit at drain of the FET, place the left half in the instrument, place the right half in a powered box a cable away, and it'll work just fine with just a hot lead and a ground lead. This technique is used alot with condenser microphones, and many professional mixing consoles offer phantom powered mic inputs -- inputs with a resistor pull to a supply voltage. Those Radio Shaft PZM mics are phantom powered f'rinstance. -- Don --------------------------------------------------------------------------- Newsgroups: alt.guitar From: mikem@col.hp.com (Mike McTigue) Subject: Re: Building your own (ONBOARD PREAMP!) Date: Mon, 5 Oct 1992 17:02:21 GMT Organization: HP Colorado Springs Division I'm the one who "designed" the LT1012 opamp circuit for a guitar preamp. I refuse to get into a disscussion (flame war) on this subject. Below I will state the reasons why I believe it is pefectly fine for THIS application. o High feedback is exactly what I want. I do not want this preamp to color the signal AT ALL. I have a tube amp to do that and it does that job very well. High feedback means it reproduces the input *exactly*. If I want something to color the sound, it goes in my effects. o Yes you probably should bypass the 9v battery. Use a 10uf tantalum or so. o Overdrive recovery is not an issue for this preamp. The signal is small and will never drive the output of the opamp anywhere near the rails. o What gives transistor amps a bad reputation is that they a) do not color the sound the way people have come to like and b) they do not saturate the same way as amps people have come to like. In summary, if you want a preamp that colors your sound then definately look into various fet preamps. The extent to which they color your sound will depend on how linear they are and what their transient response looks like. If however, you are already very happy with your sound but would like a preamp that simply buffers your signal so it can drive a capacitive cable without attenuating the high end, use a high feedback opamp circuit with enough slew rate. Mike M --------------------------------------------------------------------------- From: nm1@ukc.ac.uk (N.McBride) Newsgroups: alt.guitar Subject: Guitar-to-hifi box Date: 30 Nov 92 10:55:13 GMT Organization: Computing Lab, University of Kent at Canterbury, UK. Someone asked for a circuit that will enable guitars or microphones to be plugged into and aux input on a hifi, tape deck, ghetto blaster etc. Here is one based on the 741 op amp (this can be replaced with a better quality op amp) The noce thing about this circuit is that it can be powered from a 9v battery, is very cheap, and power consumption is very low so the batery last for ages. (Connections are at o): o--------------------o--------------------o 9v | | - |<--power rail(+) | |R1 | C1 - \ | || | | \ C2 o---||-----o------------------|+ \ +||- || | |op >------o---||----o ^ - |amp / | || | | |R2 o----|- / | ^ | - | |/| ___ | | | | o -------|___|----o | | | | | R3 | Vin | - | Vout | | R4| | | | | | - |<--power rail(-) | | | | + | | v | C3===== | v | | - | o----------o-------------o------o--------------------o 0v R1 = R2 = 220K C1 = 1uF (capacitor values R3 = 100K C2 = 15uF aren't critical) R4 = 100K C3 = 22uF Gain of the circuit is set by R4. Gains of 2, 5, 10, 30 are given by R4 = 100K, 24K, 11K or 3.3K respectively. Use the smallest gain that you can get away with (2 is adequate for most things) as a high gain will cause it to distort. The op amp connections with pin numbers (viewed from above) are: Out 9v | | | --o--o--o--o-- | 8 7 6 5 | | | 741 op amp | 1 2 3 4 | --o--o--o--o-- | | | -In | 0v +In I would recommend puting a switch an LED in between the power rails so you know when it's on (and can turn it off!): \ ----- | |Switch |_____| o o o | | | | ------------- | | | 9v +|o---------o | | cell | | | -|o------o o--------o-----------o 9v ------------- | | | - | | | 510 ohms | - | | | v LED | | o-------------o-----------o 0v Cheers. --------------------------------------------------------------------------- From: whc2993@ritvax.isc.rit.edu Newsgroups: rec.music.makers.guitar Subject: Build a Tube Preamp etc. Date: 15 Jan 93 20:49:50 GMT Organization: Rochester Institute of Technology The newest issue of Guitar Player has an article on how to build a tube preamp for under $100. I wish I was good at electronics. Part of the preamp contains a speaker simulator. I think some people asked about schematics for them and you could probably extract the speaker simulator part from the schematic provided. Question: Can a tube preamp be used in front of a solid state combo amp or would it mess up the sound because of the preamp in the combo? How about if the tube preamp was plugged into the effect return of the combo, because I think the effects sends are after the preamp. Bill C. --------------------------------------------------------------------------- From: larryh@fawlty.lmc.com (Larry Huntley) Newsgroups: rec.music.makers.guitar,alt.guitar Subject: Re: Guitar Player's Stack in a box Summary: Error in pre-amp schematic Date: 27 Jan 93 03:10:41 GMT Organization: Logic Modeling Corporation Beaverton, OR In article borst@cs.utexas.edu (Christoph W. Borst) writes: > >If anyone has built Guitar Player's stack-in-a-box or something >similar, I would like to know how good it sounded . . . > Sorry; I haven't built one, but I've looked at the schematic enough to warn you that there is one (at least) error in the schematic as pub- lished in the magazine (pg 94.) At the right side of the schematic where the wiring is shown for the polarity switch, S5, there is a mis-wire. This is the way it's shown: | +------o | | +---+--o This produces a dead short between the two complementary | | outputs. | | | +--o | | | | +------o | | | | This is the way it should be: | +------o | | | +--o | | | | | +--o | | | | +------o | | | | I'm assuming that this is a typographic error; if you buy the parts from PAIA they probably include a correct schematic. Since this was off-board wiring, it was more likely to cause someone trouble than an error in the area that is actually on the PCB. - Larry Huntley -- (larryh@lmc.com) | ".... and if that, that don't kill you Logic Modeling Corporation | soon, the women will, down at the Beaverton, OR | Spanish Moon." - Little Feat From mcjimi@aol.com Sat Jan 14 13:52:47 1995 Path: zip.eecs.umich.edu!caen!hookup!news.umbc.edu!europa.eng.gtefsd.com!gatech!swiss.ans.net!newstf01.news.aol.com!not-for-mail From: mcjimi@aol.com (McJimi) Newsgroups: rec.music.makers.guitar Subject: amp kit catalog Date: 11 Jan 1995 14:41:29 -0500 Organization: America Online, Inc. (1-800-827-6364) Lines: 24 Sender: root@newsbf02.news.aol.com Message-ID: <3f1c99$dku@newsbf02.news.aol.com> Reply-To: mcjimi@aol.com (McJimi) Copeland Electronics ( PO Box 931, West Sacremento, CA 95691 ) makes a 50 watt, all tube, Marshall style amp kit for about $250. ( including transformers ) They also make a really cool "tube mod board" that lets you experiment with a 12AX7 in all kinds of circuits-gain stages, cathode followers ( these don't add gain, but they do lower impedance. Cathode follwers are often used just before the EQ circuits in many high gain, "British" sounding amps), phase splitters, etc. All you have to do is simply plug in various resistors and capacitors. Copeland also makes a cap mod board that can filter out the ripple of up to 800 volts. Great for quick design power supplies. They don't yet make a tube preamp kit ( low weight, high voltage (350-450 volts, 10-20 milliamps) transformer, 4 or 5 tube mod boards, cap mod board, chassis, etc ), but they might if enough people write and ask them to. Another good thing about Copeland is that they don't seem to hype their products like some other amp kit suppliers. They seem very straightforward. If you know of any other amp part/kit suppliers, please post the addresses here and/or e-mail them to me. I'm having a hard time finding transformers designed expressly for tube preamp use ( high voltage, low current for B+, and DC voltage for tube hear ) I do NOT want to use big, heavy, expansive amp transformers. Thanks. McJimi From mcjimi@aol.com Sat Jan 14 13:52:58 1995 Path: zip.eecs.umich.edu!caen!hookup!uwm.edu!spool.mu.edu!howland.reston.ans.net!gatech!swiss.ans.net!newstf01.news.aol.com!not-for-mail From: mcjimi@aol.com (McJimi) Newsgroups: rec.music.makers.guitar Subject: Re: amp kit catalog Date: 12 Jan 1995 17:18:33 -0500 Organization: America Online, Inc. (1-800-827-6364) Lines: 10 Sender: root@newsbf02.news.aol.com Message-ID: <3f49rp$ppi@newsbf02.news.aol.com> References: <3f1jb8$q0p@panix2.panix.com> Reply-To: mcjimi@aol.com (McJimi) Mr. Len Moskowitz wrote: Telephone information doesn't have a listing for [Copeland Electronics]. Might you have a phone number? -- Sure do. 916-372-0275 McJimi Len Moskowitz From UKRR38A@prodigy.com Tue Jan 24 11:44:20 1995 Path: zip.eecs.umich.edu!panix!tinman.dev.prodigy.com!prodigy.com!usenet From: UKRR38A@prodigy.com (Joseph Pennisi) Newsgroups: rec.music.makers.guitar Subject: Re: speaker->line level out for Fender BandMaster? Date: 24 Jan 1995 04:06:41 GMT Organization: Prodigy Services Company 1-800-PRODIGY Lines: 22 Distribution: world Message-ID: <3g1uch$4ufc@usenetp1.news.prodigy.com> NNTP-Posting-Host: inugap3.news.prodigy.com X-Newsreader: Version 1.2 Is there any product to convert speaker level signal to >line-level? I'd be willing to do the master volume mod if it didn't add >too much noise or devalue my equipment to much. Any hints? Nick: Go to your nearest authorized Fender dealer and grab a copy of the Fall '94 issue of Fender Frontline (Steve Winwood on the cover), the promo magazine that Fender puts out. On page 35 you will find an article called "Master Your Amps" in which they show you a simple circuit: I quote": "If your master amp has no Line Out but does have an External Speaker Jack, you can use the simple circuit shown here to attenuate your output to a workable line level." Hope this helps. Joe