So here is my very first DIY electronic component - and it is still a project in progress, almost a year after I started it. If you're not familiar with this pre-amp, check out the Bottlehead web site . The base kit costs $150 and should be easy enough for anyone who can use a soldering iron and has decent eye sight to put together. For the money, it sounds amazing. But that's not where it ends - there are so many published tweaks for the little shoe box amp published on the web, that after some education, you will be able to rebuild the Foreplay and bring it up to a level of multi-thousand dollar pre-amps. It has its quirks, even after tweaking, but you'll grow to like that little box and you'll forgive some of the shortcomings, because when it plays music (and that's why we use it, right?) it really delivers.
The pictures below show where I have arrived in June 2003, with some updates done in December 2003. I am planning to start a second Foreplay from scratch some time in 2004, because the only way I feel I can improve the current pre-amp would be with a total tear-down and a transplant into a bigger case. However, then I'd be without music for a while and that's not acceptable... the things sounds too good to go back to my old pre-amp.
Below I'll give you a tour through the inside of my first pre-amp project.
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This image from summer 2003 shows the Foreplay on my (rather cheap but sturdy) rack, resting
on a pile of vibration isolation stuff. From the bottom up, the isolation materials are bubble wrap foil, 17" square 1/2" MDF,
under inflated 12" bicycle inner tube, 12" marble tile, 3 DIY "roller bearings" made of spoons and chrome ball bearings. On top
of that, another marble tile, with the polished face down towards the bearing balls. this configuration has changed
recently: the upper marble plate is gone and the Forplay itself now has a 1/4" 7075 polished aluminum base plate that
rests directly on the ball bearings.
The power cord is a VenHaus Type 2 DIY cord plugged into an isolation transformer not visible in the shot. The interconnects are also DIY silver VenHaus style, with Eichmann Bullet plugs. For once, my rack actually seemed to be of advantage, allowing me to lead the wires to the top mounted RCA jacks at the proper angle to keep the roller bearing action smooth and without tension in the wires. |
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This top view shows again how the rack allows the wires to be routed to the top RCA jacks. However, since I won't keep this rack much longer, I am planning rear mounted RCA jacks in my next Foreplay project. In the back of the image the second isolation transformer for digital source components and TV, etc. |
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Up close, you can see that I clear-coated the aluminum face plate, painted the transformer black, and tinted the wood black (with Dick Blick india ink) before applying a few coats of a polyurethane semi gloss finish. The tubes are Telefunken ECC802S (expensive, but once you try them you will never want to use any others), with some tube coolers that also help dampen some vibrations. th RCA jacks are the upgraded gold type, plus there is a custom mute switch right in front of the power switch. It allows me to power the Foreplay up and down without sending major voltage spikes to my power amps, which are never to be powered down. There are stainless steel screws in all four corners of the face plate, holding it down to wood blocks which I have glued into all four corners of the wooden frame. |
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Tube coolers and clear-coat finish of the face plate up close. If I did this again, I'd put some sort of protective tape on the entire clear-coat surface to be peeled off when all work on the unit is complete. I have a number of small scratches in the finish, which I may be able to polish out. if not, I'd have to repaint it, and that pretty much requires a complete tear-down of the amp... |
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The bottom of my Foreplay is closed, since there are small fingers in my house who may not always remember that there are some pretty dangerous voltages under that black wooden box with the two glowing glass thingies on top. This picture shows the very latest version of the base plate, made from 0.25" thick 7075 grade aluminum, polished to a mirror shine for best performance on the roller bearings. |
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the backside sports a custom Schurter IEC connector, which I put at the bottom edge to allow fast removal without having to de-solder the internal wires every time I need to take the top plate off the wood frame. Also note the foam and rubber grommet isolation of the transformer. it is still grounded due to a small piece of cat-5 wire that leads down to the chassis plate. |
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Opened up, the rope caulk on the base plate inside surface becomes visible. Also, the tin foil wrapping the interior of the wood. There is a small piece of wire on the bottom right of the frame, which connects the bottom plate to the chassis ground via the tin foil. Also clearly visible are the wood blocks in the corners, which serve to anchor the screws holding down the top plate. |
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Lets go inside: This image shows the front of the amp, with the volume controls and source selector switch to the left, C4s boards over the tubes and filament snubber parts in the middle, and the last caps of the pseudo dual mono power supply on the right. The black round caps are Panasonic 390uF 250V TS-HB, while the square blue bypass caps are 1uF 630V Vishays, if I remember correctly. These caps are again bypassed with 0.01uF 630V caps (the small blue rectangles right in front of the large blue caps). The yellow capacitors are the output caps: 3.0uF Auricaps, bypassed with 0.1uF Hovland Musicaps. Note the white clay-like mess on the surface of the mounting plate: more rope caulk for vibration control. Not pretty but it really works. It also holds the caps in place, without being hard to remove. |
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The rear of the Foreplay is mostly power supply. The smaller blue capacitors to the far left are part of the "snubber" on the high voltage transformer output. The diodes that are to the right of the larger Vishay snubber capacitor will soon be replaced with "Schotty diodes" - probably the final upgrade to this amp. There are actually four of these big Panasonic caps in the box - one is totally hidden under one of the large bypass caps on the right. They are probably overkill, but they didn't cost much more than 220uF caps. The mute switch is that dark blue square in the center of the bottom of the image. I chose that location mostly because, well, there was still some room there. |
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A different view of the front. The C4S boards are now much more visible. Almost all of the components on these boards are replaced (LEDs, resistors, all transistors) while I was doing some trouble shooting. I think one of the transistors was overheated in my first build. This taught me to use alligator clips for heat sinks when soldering. |
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Here a view that finally shows all the 390uF Panasonic power supply caps, the blue bypass caps as well as the left channel out put cap pair. A lot of the wiring in this area is CAT5 and Doc's original magnet wire, which I found extremely hard to work with. I guess you need a solder pot for that stuff, but I only have a $6 soldering iron. For signal wires I used some 32awg teflon insulated pure silver, left over from my interconnect projects. A bit too fragile and possibly too thin for some of the voltages in the Foreplay. Much of the ground wires are still the magnet wire, but there's some CAT5 in there as well. |
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HV snubber caps and resistors up close. I goofed when putting these in and had the transformer
grounded on the center tab of the terminal strip. Almost cost me the transformer. Panasonic 390uF up close in front, as well as
one of the 1k ohm resistors between them, covered in cheap tubing to avoid shorts. Once you short out the first big
capacitor you'll learn to be extra careful around these things ;-)
By now this entire tweak has been removed again: I installed some Schootky diodes in the rectifier section instead of the stock diodes. At first I couldn't tell a difference, but when I read that one can remove the snubber after the schottkys go in, I tried that. And - voila! things got just a tad crisper and more dynamic. A $5 tweak that was worth doing. |
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This view shows the HV rectifier section after the Schottky diodes were installed and the entire HV snubber assembly was removed. There's actually room in the unit again. What to do with it? |
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These are the S5 attenuators - going from the already upgraded "Sweet whisper" attenuators to these was one of the biggest improvements of all upgrades installed so far. The resistors are all Holco except for the 100ohm on the lowest volume step, which wasn't available anymore. Not a big deal, since it's only in use at the lowest setting, so a Radio Shack resistor went in. The key resistor is the 97.6K series resistor from the selector switch to each volume attenuator. I may try a "designer resistor" in this position, but probably not in this Foreplay. Note the very fine signal wires from the input jacks and and the dark spots on the C4S board in the foreground. I think I took these off about 20 times, replaced LEDs at least 4 times and fought with the magnet wire leads from the day I first installed them. They really need to go somewhere out of the way in my next build. To learn more about these attenuators, go Voltesecond's S5 attenuator I used dual deck 12-position shorting switches, but there's still some switching sound. I'll probably spend more on the switches in my next Foreplay - Goldpoints maybe. |
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Well, there was one possible upgrade of the attenuators without starting from
scratch: I could replace the series resistor (96.5k in my case) that sits between signal selector and each attenuator.
This is the only resistor the signal travels through, making it the prime candidate to try out some fancy "designer resistors". In the past I avoided Vishay S102's since at the required value for this position, prices were above $20 per piece! Somebody pointed me at the "naked version" of that resistor, supposedly better suited for audio (it isn't encapsulated like the industrial version, but otherwise it's the same. It also costs about half as much. So for about $12/piece I tried these resistors. I am glad I did! |
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In the center of the image is where all the grounds come together. Two resistors connect each channel ground to chassis ground. There's still a tiny buzz in my speakers even when the Foreplay is powered down, and it may originate right there. I'll try it without resistors, or with additional 0.01uF caps between grounds. Really tight there, and I'll have to remove C4S boards to do any soldering in this area. |
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The Mute switch up close - I'll change the wiring of this switch as well to see if it has something to do with the buzzing, or at least to kill it when I flip the switch. there is no buzzing hen the amp has been playing for a minute or more. The rope caulk used to hold and dampen the caps can be seen really well in this image. The 470k ohm resistors on the output jacks have already been replaced with higher grade resistors. Not much of a change, but it was audible and worth the $0.50 it cost. |
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Closeup of one of the tube sockets (bottom of the image) with the filament snubber installed. There's a lot of wires and a tricky connection point where a lot of wires come together in mid air. In between more of the 32awg silver wires. Messy looking, but it works. The brown cap is still original Foreplay - I should probably try a higher grade unit in this place, but I haven't really found any sources that stated that replacing this capacitor does anything to the signal quality. The blue resistors are original as well, but will get replaced the next time I breakdown the C4S boards over this area (you can see one hanging right over this tube socket with its ohmite resistor and red LEDs. |
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And this is what it looks like today |