Velleman Volume and Tone Control Preamplifier Kit

Velleman Volume and Tone Control Preamplifier Kit

Brand:| Model: K8084
Overview
Amplifier kits and modules are great for an audio project but you often find that you need a volume control and preferably also tone control. This kit comes complete with all input and output connections and potentiometers.
Highlights
  • Stereo volume control
  • Stereo bass and treble control with center detent
  • Customizable attenuation or amplification
  • Complete with knobs
  • True hi-fi performance
Part # 
320-176
Weight: 0.561 lbs.  
IN STOCK
List Price$40.80
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Your Price
$34.60
Part # 320-176
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Product Details

Velleman Volume and Tone Control Preamplifier Kit

Amplifier kits and modules are great for an audio project but you often find that you need a volume control and preferably also tone control. This kit comes complete with all input and output connections and potentiometers. Furthermore it is possible to amplify or attenuate the input signal.

Specifications: • Power: 2 x 12VAC/100mA • Frequency response: 3~500,000 Hz (-3dB) • Signal to noise ratio: 98 dB • Harmonic distortion: < 0.005% (@1KHz) • Maximum output: 5V RMS • Tone control: + and -15dB @ 20Hz / + and -15dB @ 15kHz • Input impedance: 50k ohms • Dimensions: 4.1" W x 2.75" H



Product Specifications
  • Project Kit TypeAudio & Bluetooth
Velleman Volume and Tone Control Preamplifier Kit
  • BrandVelleman
  • ModelK8084
  • Part Number320-176
  • UPC5410329374440
  • Product CategoryElectronic Project Kits
  • Unit of MeasureEA
  • Product Rating
    (2 Reviews)
  • Weight0.561 lbs.
  • California Prop 65

    Warning: California residents only. Please note per Proposition 65 that this product may contain chemicals known to the State of California to cause cancer and birth defects or other reproductive harm.

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Reviews

Velleman Volume and Tone Control Preamplifier Kit
Velleman Volume and Tone Control Preamplifier Kit is rated 3.5 out of 5 by 2.
Rated 4 out of 5 by from Good little kit with manageable issuesI have built 2 of these and used them for over a year.Kit easy to assemble for anyone with soldering experience and a 30 W iron. Small alligator clip for heat sinking leads from transistors and Zener diode used for on-board regulated power supply also recommended.Important to be sure of op-amp (IC) polarity before applying power. Putting one or both in backwards will crater both op amps, Zener diode and PS transistors, speaks voice of experience (silly me!). Replacement parts cost about $8 so if you screw up, do not despair, just replace all of the above (don't forget solder wick for removing the blown parts) and the board will work.This is a high impedance circuit design and is therefore very hum susceptible. Preamp therefore must be mounted in metal case (readily now available from Parts Express--look under Hammond Industries) which will need drilling. 4 or 8 jack RCA jack arrays available from Radio Shack for input/output. Suggest borrowing use of drill press for this (tricky for hand drilling). Use wooden block for backing during drilling for best results. Mark position of pots using bare board before construction to get positions of holes correct. Also drill 4-40 holes for standoffs (long 4-40 screws with multiple nuts easiest) in bottom of case, and holes in back for cables or RCA jacks.Performance very good (audiophile quality) when properly constructed. Modification of feedback resistors recommended (substitute 100K or 220K high quality carbon film or metal film resistor for 1K provided--also available from Parts Express.DO NOT mount power transformer inside metal case unless maybe using a toroid. Better to mount in separate plastic or metal case, run 12-0-12V AC to preamp board using shielded 2 conductor cable.Additional audiophile mods possible:Balance control--use 50K linear single pot, wiper to ground, left contact to R channel (facing shaft of pot, right contact to L channel. Insert either after 1st stage (connect outer contacts to wiper contacts of volume pot) or add to output.Replace TL072 op amps with NE5532 (about $1.50 each), more important if using higher gain for 1st stage.Replace input caps with larger non-polar (tantalum) electrolytic or foil caps.Make external +/- 15 V regulated PS (easy, use 7815 and 7915 regulator ICS, in between 2200 uF electrolytic caps after bridge rectifiers attached to aforementioned 12-0-12V transformer--easy to cobble together using perf board or solder terminal strips. Connect power to appropriate holes in preamp boaard, without mounting on-board PS components. If using long cable from PS to preamp, decouple power with 10 Ohm resistor followed by 100 uF cap to ground between power cable and preamp board at preamp end. Bypass 2nd pair of 2200uF caps with 0.1uF ceramic caps.2 pole rotary input switch--will work fine as long as all cables between RCA jacks and switch, and between switch in preamp input shielded (2 conductor shielded also good for this). Use shorting switch to avoid crosstalk between inputs. Easier approach--outboard audio or audio-video swich box--also available from Parts Express.Results: Unmodified kit if properly shielded pretty much noiseless, no appreciable distortion even at high drive. Also quiet with 100K or 220K resistor substitution. I will take issue with 'you get what you pay for' here--this kit is a very good value, and I note that with 2 exceptions (Gemini and Pyramid so-called 'pro' preamps, comparable preamp/tone control amps are very expensive (and also, I am not surprised, often use similar op-amp designs). Yes, it is possible to substitute 1% metal film resistors, auricaps, and Burr-Brown op amps in this sort of circuit, or use discrete transistor designs, and get better results, but I leave such exercises to hyper-audiophiles who have many K$ to spend on gear.
Date published: 2013-11-02
Rated 3 out of 5 by from Not too BadI purchased this kit to learn and experiment with. However, the final goal was to replace a tube preamp section of an integrated amplifier because I didn't like the performance of the tube based preamp. Initially, I thought the kit didn't work but after poring over the schematic I discovered that I installed one of the voltage regulators incorrectly as well as the wrong value for the RA resistor. After correcting those mistakes the kit works better than the tube preamp.Does it work better or as well as a more expensive preamp? NO, but you get what you pay for.Here are the highs:Sensible PCB layoutDesign allows for flexible applicationDecent quality potentiometers. Although, one note on this is that the volume pot on my kit does not have a linear response across the range. It reaches a peak at 3/4 volume and then begins to fall again. I have not yet investigated if this is caused by a weak power supply. I can say I have supplied the power with a transformer that has ample headroom according to the kit specifications.Here are the lows:Absolutely junk line level inputs and outputs. If you will use the line level ins and outs do yourself a favor and purchase a set separately to install.
Date published: 2012-01-12

Product Q&A

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Velleman Volume and Tone Control Preamplifier Kit

Gain?

I would like to use this to act as a sort of preamp for use with a Sure T-amp. Will this unit provide any gain from the input source? I will primarily be using an iPod for the source, and am currently using the iPod to control the volume. I find that if I turn the iPod up to about 75% volume it is not as loud as I would like, and anything past that is fairly distorted and "noisy".
Asked by: Travis Rysdam
Yes, according to the specs, you can amplify or attenuate the signal with this unit.However, the source of the distortion could be one of many things (you didn't say exactly where the distortion occurs, so I'll cover some of the possibilities I can think of):1. Some older iPods distort on bassy songs when a bass-boosting EQ is enabled on the iPod, such as "Bass Boost", "Hip-Hop", or "Rock". This is an internal flaw of the iPod and will occur no matter which headphones, speakers, etc are connected to the affected iPod (although, it will be more obvious with some headphones than with others). Try disabling the EQ and see if the distortion goes away.2. Although these Sure amps list a range of voltages that they can be powered from, you will only get the full rated power output when using a supply with the maximum voltage in that range. Power supplies with voltages near the low end (such as a 12V supply) will put out significantly less power than the specs state, and thus there will be lots of clipping distortion at fairly low volumes.3. Even if you are using a power supply with the maximum-rated voltage for the Sure amp, you will still get a lot of distortion at the highest volumes. At maximum power output these Sure amps (like pretty much all class D or T amps) have 10% distortion, which will sound quite bad.Also, try using a few different audio sources, to see if the amp/speaker setup distorts with those other sources as well. If it does, then the distortion is most definitely a result of either the amp or the speakers, so using this Velleman volume controller to boost the signal won't do any good.
Answered by: eboyer
Date published: 2011-11-18

Would this pair well with these power amps for bookshelf speakers?

I'd like to replace a full-size integrated amp I use for my computer office; it is failing and I really want something more compact. My speakers are Paradigm Titan bookshelf.Will this work well with either of these:Velleman 30W Stereo Audio Amplifier Kit (http://www.parts-express.com/pe/showdetl.cfm?partnumber=320-212)2x15W Class-D Stereo Power Amp Kit TPA3122 (http://www.parts-express.com/pe/showdetl.cfm?partnumber=320-322)Also, how would I switch between 3 inputs?Thanks!
Asked by: csilvest
This would be a better match for the Velleman Amplifier kit. The Class D is not recommended for systems that use a preamp.
Answered by: Chrisf
Date published: 2012-12-03

Do you have an appropriate enclosure for this kit?

I would like to be able to just drill holes for volume and connectors and have a working preamp.
Asked by: Siggma
The enclosure depends on how you handle the power supply for this kit. If you assemble and power it as instructed by the kit documentation, you need an appropriate sized metal box(aluminum or steel) because it will need good shielding. If, on the other hand, you power it with bipolar DC (or 2 12VDC wall warts wired in series, grounding the central connection), you can use a plastic enclosure. In any case, keep the power transformer at least 6 ft. from the preamp (it can be closer if you use a toroid transformer). The enclosure size will need to be about 6 x 4 x 2 inches for ease in working inside.
Answered by: Doc Jones
Date published: 2013-01-28

How to bypass/remove the tone controls?

Asked by: MrsS

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