It seems I have been doomed to not do any of my DIY projects since my main computers hard drive crashed followed shortly after by my laptops (the laptop has had another crash after that, and the drive is now on the way out again!!)

After having to pull the cables out of my chipamp last week and plug the TV into it (because the MythTV box refused to play a DVD and I can't plug the DV18 DVD player direct to the chipamp because it has no volume control) I decided I had better get off my backside and finish my pre/active crossover. I had to do it again tonight as well (plug the tv into the chipamp), sigh...

This is all because my playmaster had something in the pre die again and is only working on one channel and I just haven't been bothered fixing it. I thought that being inconvenienced might make me more likely to finish the other projects but it has been broken for about 6 months

So on Monday I decided that I should re-install Holm-Impulse...

I think I must be afraid of failure. I still haven't built the YARPS power-supply I've mostly worked out the layout on verro-board, and I still have a number of components (not least of which is a transformer) to purchase. You would think that the three months I've been waiting for the silmics I could have got the rest organised... sigh...

The Synergy active crossover, I haven't even started on the layout for the YARPS is a prerequisite for powering it up, but once again, nothing stopping me from doing other stuff.

Today finally received the 14, 1000 uF elna silmic II's today that I ordered months ago. I need two for the PS output and the other 12 are destined for the Synergy (yeah I know WTF?) the current schematic doesn't show them but in a case of gross overkill they will be used for separating different sections of the circuit if I can fit them Basically they will be decoupling the various sections from the supply (and each other). 1 cap per...

Following on from YARPS I thought I would post the design I have been working on for my active crossover (which is in fact is what the YARPS power supply was designed to drive).

So here I present the Synergy "Active" Crossover. Please note I have only simmed it at this stage (and when I started I knew nothing about active filter design) so there is no guarantee it will work.

Why have I put "Active" in quotes? Because whilst this filter uses active components, for all intents and purposes it behaves like a passive filter. It basically emulates either an LC or a CL passive 2nd order filter.

Why the name Synergy? Well I though it was the best word to describe the differing technologies working together to give the end result

The design goal is to have an active crossover that for all intents and purposes is transparent. That is it does nothing other than split the frequencies at the desired crossover point....

edit: applogies to anyone viewing this at less than 1280 screen width... It formats properly with that (two images side by side) but I'm not going to go and redo all the images now!!! I already did twice....

OK Continuing on where Part 1 left off. The next step was to attach the Power Supply wiring. I will continue the numbering from the first blog entry for consistency.

18. 19.

images 18 and 19 show the completed amplifier with +ve -ve and zero volts wires connected. Note also that there is a separate zero volts return from the zobel capacitor to the star ground on the PS board. The red wire is the +ve the blue wire the -ve and the green wire is the zero volts. The return for the speakers is direct from the speaker output jack to the star point on the PS board. So in all there...

edit: 17th April 2011. Just to set the record straight, although I refer to this chipamp as a "gainclone" strictly speaking it is not. A gainclone is I believe actually a clone of the 47 labs gaincard, however many people refer to chipamps as gainclones incorrectly (myself included).

edit: apologies to anyone viewing this at less than 1280 screen width... It formats properly with that (two images side by side) but I'm not going to go and redo all the images now!!! I already did twice....

Well I said about 4 years ago that I would do a build writeup for my P2P gainclone. I took all of the pictures but never got around to it. I'm off sick and lacking energy so decided it was as good a time as any to have a crack at it

I started out with the BrianGT schematic. I wanted to build something that people were using and was likely to just work. Here is a copy of the schematic
...

I'm finding DIY'ing a very different ball game now that I have started again. The difference being I have a 21 month old daughter now. Gone are the days when I could sit down for 10 hours straight working on something. I have to take on tasks that I can complete in 2 hours (or work on into the night and suffer sleep deprevation!)

Yesterday I did some more sanding on my speaker boxes, I think I could just keep sanding until the 25mm MDF was only 20mm I better stop soon and get on with the veneering.

Tonight I attacked the problem of the switching thump in the amp. I found some 47uF Nichicon FG caps in the cupboard and soldered them into the negative feedback circuit in the preamp. That brought the DC coming out of the gain stage in the preamp down from -1.1V to about -210 mv. I'm not sure if I will try and tackle getting rid of the rest of the dc, but it is a substantial improvement. The cap basically put between the second resistor in the feedback...

Well I drilled some holes and wired up the new RCA's on the back of my amp, so now I can switch between direct input (bypassing the preamp) and the normal integrated path. Works nicely and I suspect that the slightly soft top end was actually due to the preamp as the sound seems a bit crisper now on the direct input.

However.... when I switch from direct to via the preamp, or vice versa I get a big thump from the speakers I can avoid if I switch the speakers off but it is not particularly family friendly, especially since I have a 21 month old who will love to switch the switch on and off

So I'm not sure if it is switch contact bounce or perhaps just switch on thump (the fact that there is no thump at all when switching to the off position leads me to belive it is more like a switch on thump), but it is rather anoying. Puts a bit of a damper on an otherwise successful mod. The switch is a center off type, I might have to get a three pole...

Sanded down the second box so it is now in a state that is close to ready for veneering. Filled the screw holes with filler and also the bottom of the front baffle which was for some reason a mm or so short. can't remember if that was a measurement stuff up or a problem with the saw accuracy, probably the former I'd guess! Actually now that I think about it, it was an assumption that the mdf was really 25mm thick and it was slightly more... Only problem is the filler takes 48 hours to dry, so next weekend before I can start trying to slap on any veneer.

Also attacked the amp again. Plan was to put in the bypass of the preamp. Got most of the way there but was getting too late so left the drilling of the back pannel (for the rca sockets) for tomorrow. All in all it was a worthwhile excercise. The way the input caps were installed was nothing short of shocking, I think I did it to check it was ok, but never got around to doing it properly, I decided to use cat5e twisted...

Last night I built an earth loop breaker for my trusty old Series 200 100W mosfet amp. It's been annoying me with Hum ever since I moved to the new place. Combination of having the mythtv HTPC and also cable like TV antena that is shared through multiple units. Well it cut it down but it didn't cure it.. The gainclone is dead quiet... the differece? I used an 12 Ohm resistor on the gainclone, and it is running without a pre, the series 200 one I used a 10 ohm as per Rod Elliot's article (and the connection is through the preamp built into the amp. Tomorrow I plan set up a switch and some new "direct" RCA jacks so I can run the HTPC direct bypassing the integrated pre.... hopefully that'll do the trick. If not I'll probably try bumping the resistor up to 12 ohms...

Today I was going to glue the back baffle on my second MTM but it got very gusty and I thought it would rain (my work space is on the balcony, so not good for gluing if looking like rain). So I only...