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Old 31st March 2005, 03:33 AM   #51
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I test a transformer by ohming out the windings. I should get readings from a few ohms to fractions of an ohm for a good winding. There should be infinite or many megaohms of resistance between different windings. Then I test it by powering it up with my combination isolation transformer and dim-bulb tester and check for the correct voltages on the outputs. The transformer shouldn't hum/buzz excessively nor should it heat up significantly without a load on it. But for a transformer that I bought and expect to be good, I'll just put it in the chassis along with the power socket, fuse, power switch, rectifiers, and filter caps and see if the power supply puts out the correct voltage before connecting the main amplifier circuitry to it.
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Old 31st March 2005, 03:50 AM   #52
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I think I found out what my transformer actually is
4365-P1S2 is a number on the side, I searched that on google.
http://www.fairradio.com/lowvol.htm

Appears to be a dual 17V, not 21V like the ebay auction said.

so 17V X 1.414 is approx 25v. perfect for the 360 preamp. A little under the 28v for a lm3886. Hmmmm... Will have to power it up and test to make sure then.
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Old 5th May 2005, 03:28 PM   #53
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Looks like I can start back on this project. Got a permanent job, therefore I have some money


One thing I need to do is create a preamp. I've been looking at this. I've been researching bass amps and preamps. It seems the bassics of a bass preamp contain:
Obviously input and output, and usually a passive and active input. Many have DI/XLR output, I don't need that. Some have line out, while that's cool and I could hook it up to my coputer I don't think I need that.
Then they all have some type of EQ/tone boosting/filtering. Most have 2,3,or 4 knob boosting. My hartke 2000 head has a 10 band EQ that you can turn on and off. It also has what it calls contour. From the sound of it, the two contour knobs are just low and high filter/boost.

FIY, the hartke 2000 has a tube and solid state preamp (each with own volume control so you can blend them, a compressor, 10 band EQ that you can turn on or off, two know contour control. Without the manual in front of me I am not sure where the compressor is in that chain, not sure if it is before or after the EQ.

For a DIY preamp that's all I'd be happy with, active and passive input, 3 band EQ, output to amp (with an effects send and receive between preamp and amp). If I want to use headphones I could just plug my headphone amp I built into the effects send.

I was wondering if there is a kit out there. I like the jfet bass amp that's out there because it looks simple enough to build. I think I'd prefer the 360 I linked earlier (did I link it earlier, I should have), but that looks a little more complicated.

Otherwise if I have to maek one my biggest problem is I don't know anything about EQ. I tried searching the internet but came up short. Found some theories but didn't really find anything on making my own. Also how does one handle active and passive inputs ?

I might make the preamp and power amp seperate (that way I can mix and match with my hartke).

I might start with the power amp and use my hartke 2000 as the preamp. I have to read the manual, I believe the effects send is after the EQ and such.
I think I will just get a kit from www.41hz.com. Probably the AMP2. Looking at their chart I will probably go with the
+/-45V 750VA 8 ohm bridged 1x600W Standard solution. I have a bunch of questions on this, will have to read their forum and/or email them.
I think right now for the power amp I'd rather have a kit. It doesn't cost that much more than buying all the componants myself and etching a pcb myself. Plus then if I screw up I know there are people with the exact same thing that could help
However, like others, maybe I will wait until the PSU board is available and then do the preamp first.

Just downloaded the manual for my amp. Grrr, the EQ is AFTER the effects. So I will have to go with the all or nothing route.
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Old 5th May 2005, 04:06 PM   #54
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Errr, maybe my hartke effects send and receive is post-EQ. Will have to email hartke to make sure. The block diagram differs from what is siad in the guided tour.
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Old 5th May 2005, 08:05 PM   #55
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I have a friend with a Hartke 2000. it rocks. I'm not 100% sure, bu i think that the compressor is before the effects loop, and the EQ is after the effects loop. The tube/SS preamp stuff and the contour are before the efx loop. BTW, the tube in there does run with DC filaments and a real B+ voltage on it

The line out is essentially the same thing as the output of the preamp. In many amplifiers, the output of the preamp (line out) goes to the effects loop out, and the effects loop in goes straight to the power amp. A tuner output is just a signal taken somewhere early on (before alot of tone shaping things like EQ, tone controls or distorton), buffered, and sent to a jack.

For a active/passive input, the "passive" input is just the regular input into the preamp, the "active" input is just a -20 db pad on the input to prevent you from overdriving the first gain stage with a particularly hot active bass. The "passive" jack should have an input impedance of at least half a meg, 1 meg is common with some amplifiers going even higher. Go to schematicheaven.com and look at how an ordinary Fender amplifier has their two inputs jacks wired up with the You can simply omit the "active" input if you do not need it.
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Old 5th May 2005, 08:31 PM   #56
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I might need active. Haven't decided yet. I'm a DIYer with everything I find (see http://free.hostdepartment.com/S/SirPoonga/yabcab.html)

I'm thinking of making my own bass using a warmoth neck. I've decided I am going 5 string, but not sure about active/passive pickups, etc... I found the body I want (http://mimf.com/library/moll_bass_final.gif) made out of some chestnut that was infected with worms. Will look cool

I don't think I will have an on board preamp, would be cool but that's getting overboard for something that just may not be that good .

Will probably make active/passive switchable. However, I like the look of the latest trend of having passive bass (no knobs). But that is difficult with two pickups. I'm thinking a neck humbucker and a bridge J pickup. I will probably just have the humbucker wired as dual coil, won't split the single coil. So that would leave me with 2 volume knobs and a tone. Will probably get wood knobs for that too. Actually, was thinking one concentric pot for volume, then maybe a push pull pot for tone and to toggle active/passive.

Probably won't happen for a year though.
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Old 22nd July 2005, 02:01 PM   #57
tmuikku is offline tmuikku  Finland
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Hello everybody!

SirPoonga, have you finsihed power- or preamp yet?

I'm also about to build a light weight bassguitar power amp (and preamp little bit later). Do you fellas think that Tracopower TIS series industrial powersuplies are suitable for audio use(t-amp)? I don't know pretty much anything about those parameters like EMI suppression, Ripple and noise, Line & Load regulation...

I'm planning to purchase AMP2 kit from www.41hz.com because it seems to be the most suitable for my use. I'd like to use switchingmode ps because of its light weight. Desired output could be (RMS) 2x200W/8ohm or 1x400W/8ohm or more bridged. Any advice given will please me a lot

ps. sorry my language, I'm at work and in a hurry Underlined: suitable switchingmode ps for 41hz AMP2?
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Old 22nd July 2005, 02:17 PM   #58
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I haven't been able to. Got a new job, had to move, etc... I haven't even thought about this in awhile
Won't probably get to it until fall or winter now. I have some other projects that "fell into my lap". Like someone gave me an asteroids machine that's working with no video. Trying to fix that.

I still want to do this but it isn't high priority now. Actually, getting a new bass is a little bit higher of priority. I am starting to out grow this one. As I expected I'd have issues with my current bass. It's a Squier P-bass. It served its purpose. It's a cheap bass that I bought to see if I was interested in playing bass. I am and this bass has its shortcomings. Thinking of getting a kit like a Carvin or Warmoth, I am a DIYer
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