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Old 17th November 2005, 09:02 PM   #1
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Default Need a little help, TT and PC? Amp Kit?

I have been considering redoing my Rotel RX-203, however it seems like a lot of money and effort.

I then found this, http://www.madaboutsound.com/prod_det.asp?product_id=1 and considered that I could put an amplifier togather for under $100. I have some questions though if I went with it.

I however am wondeirng if there are any tube amplifiers around that area? I am actaully using the same Tangband speakers as sold on that website, the W3-871S, as an Elf kit from CSS. I have been thinking, and asking around about maybe making horn boxes for them.

Any ways my delima I have no idea about what I could plug into the amplifiers. Would a switch between sources work? Would I have to turn it off before switching? The only two sources I have are my computer and my mmf-5 turntable. I was wondering if I need a pre-amp in order to get my turntable to work with the Power Chip Amp, or what ever else I use... I figured on using that log pot on the website if I got the kit.

Any help would be appreciated, thanks!
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Old 17th November 2005, 11:01 PM   #2
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I find it hard to believe no one can comment.
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Old 17th November 2005, 11:10 PM   #3
dhaen is offline dhaen  Europe
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OK, I bite..

I don't think you'll be able to build a tube amp for $100, but I'd love to be proved wrong...
There are some single ended designs using EL84 or ECL82 that can sound quite good. They will probably cost a little more dpending on how frugal you can be.

An amp can use a simple source switch. In fact if you only have 2 sources it can be very simple. You shouldn't have to switch anything off. The volume control can connect between this and the amps input.

Turntables usually output a very low level signal from the cartridge. This needs amplifying to get it to a suitable level for a power amplifier. These are often called phono preamps or RIAA preamps.
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Old 17th November 2005, 11:13 PM   #4
Sherman is offline Sherman  United States
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You can find at least one tube amp kit, 8 watt per channel, push-pull for $139. Check the tubesandmore.com website. You'll need to add some type of chassis and if you want selectable sources at switch to do that.

Lighthouse Electric also has a nice looking kit (no idea how it sounds) for a couple hundred. (lhelectric.com IIRC)

To do source selection with only 2 sources all you need is a DPDT toggle switch. Mount 4 input jacks on your chassis for your 2 sources. Connect two of the jacks to two of the "outside" tabs on your DPDT switch. Connect the other two jacks to the other outside pair of connectors. Connect the middle two connections of the switch to the left and right inputs of your amp. Use shielded wire for all those connections. If you want more than 2 sources you have to get a rotary switch with 2 poles and the proper number of positions. You don't have to power off before switching but turn the volume control down before you switch.

The tube amp kits come with volume pots so no worries there.
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Old 18th November 2005, 12:36 AM   #5
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FWIW, there's a low cost project ($100 in "iron") here.
==> "El Cheapo" Project

I'd like to believe that an "El Cheapo" will sound better than the low cost 11MS8 PCB kits.
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Old 18th November 2005, 01:57 AM   #6
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Thanks for the suggestions, I may have to consider that tube amplifier kit. I can make a chassis and get the rest of the componets for not to much.

Do you think 8 watts would be enough for my Tangbands? They are in small ported boxes at the moment..... Now if I had some sort of a horn box it would be plenty I am sure. The Rotel puts out 20wRMS, SS, and will bottom out my speakers if I turn it up to high.

Any suggestions on how to very cheaply make the input for my turntable to work? I guess I am spoiled with a reciever that automatically does this.

I still have to figure out about the possibility of making horn boxes for my Tangbands, I am limited on space in a dorm room.
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Old 18th November 2005, 02:53 AM   #7
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A phono stage with 50 dB. of gain is needed to raise the level of a "typical" MM cart. to that of a CDP. The least expensive decent way to do that is with a Hagerman "Bugle". However, the "Bugle" is based on opamp ICs. A tubed phono stage has to cost a good deal more, even if you carefully scratch build.

Hagerman Site
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Old 18th November 2005, 06:40 AM   #8
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Ouch I may have to stick with my Rotel...... I honestly doupt it is that amazing of an amplifier, but what am I to do... It has input for phono and any thing else.
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Old 18th November 2005, 11:01 AM   #9
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Let's put things in perspective. Rotel stuff is decent and way ahead of the mass market guano. Tubes it aint, but it's not cr*p.

You say receiver, which implies both phono and FM. Both cost and space are obviously of concern to a student. For now, use the phono section and tuner of the receiver to drive the "integrated" tube amp. Connect the recording O/Ps of the receiver's tape monitor loop to the tube amp's I/Ps. Connect your CDP to the receiver. The receiver's selector switch controls which source you hear. The arrangement described bypasses the line and power amp sections of the receiver.

If the receiver has a preamp-out/amp-in feature, you have additional options. Please feedback about the presence or absence of the feature.
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Old 18th November 2005, 01:17 PM   #10
Sherman is offline Sherman  United States
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Quote:
Originally posted by Destroyer OS.
...

Do you think 8 watts would be enough for my Tangbands? They are in small ported boxes at the moment..... Now if I had some sort of a horn box it would be plenty I am sure. The Rotel puts out 20wRMS, SS, and will bottom out my speakers if I turn it up to high.

Any suggestions on how to very cheaply make the input for my turntable to work? I guess I am spoiled with a reciever that automatically does this.
...

Think about power this way. Each 3dB increase in loudness requires a doubling of the amplifier power. Therefore a 20W amp only plays (at max volume) 3dB louder than a 10W amp. The difference between 8W and 20W isn't as huge as it might seem at first.

The type of music and the size of the room has a lot to do with how much power you might want but I think 8W would be fine. (I'm playing Advent/1 speakers with amps that have about 7W and listen to all types of music and am happy with the volume.)

The cheapest way to make the TT work on an amp without a phono stage is to buy a separate phono preamp. Cheap ones are available all the time on eBay for $25. You plug your TT into one side and the other side has jacks that plug into your amp. Not exactly high-end but they do work and in any case the sound will be better than an MP3 from a computer source.
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