I just got a vintage Brunetti Mille from Italy, I believe this one is the original version which was modelled after the CAE 3+ SE. It is very well built and came with Ruby 12AX7’s. My initial impression of the unit is very positive, surely better than most of the amps that I have built myself… So the preamp stage do make a big difference, duh!
Before I bought the unit, I was think about building one myself, there are some kits on the market, but after factoring the cost and time, especially the front panel and chassis drilling involved – the price on the used Brunetti was simply too good to pass up. As much as I like DIY, there is no way to make it as professionally looking and robust (unless you have all the necessary machining tools and how to use them) as the factory built unit.
Below are some pictures that I got from net, I actually quite like the unusal blue color of the front panel, it reminds me of the old Orban equalizers that I used to work on – and perhaps will acquire one of these days if the price is right.
I was thinking about modifying the VK212 when I first got the amplifier a few months ago, and came up with some potential modifications. But at the end, I abandoned the idea and went with a near-scratch build – I took out all the PCB’s, and put in a Marshall 2446 Vintage Modern clone in their place instead. This worked out great, since the chasiss has quite large so I had ample room to work with. Of course, I re-used the PT and OPT which were perfectly fine. I also saved the PCB’s from the VK in case if I ever want to put them back (which I doubt seriously). The only tricky bit was to modify the heater supply, since the VM uses one extra 12AX7 tube than the Vk212.
I don’t really like the series heater arrangement in the VK, however the PT came that way, and I did not want add another filament transformer to the chassis, so it would have to do. Of course, the disavantage is if one of the tubes go bad, the whole amp will be out of commission. Since it is just for home use, it is not a really big deal, but I would not want to take it on the road.
Instead of the 6L6’s that came with the amplifier, the output tubes have been changed to the 5881’s that I have laying around, so the output power was lowered to about 75W. I also took the opportunity to add a bias adjustment board, which is the small board mounted above the power tubes that you see in the photo. It came from a scrap’d hi-fi amplifier. With the board, each of the output tubes could be biased individually, which was sorely missing from the original VK212.
With the existing VK speakers, the amp sounded a bit bright to me, then again, I haven’t spend much time with it…
Here are some photos from the build:
I completed the ODS build a few months ago, here are some photos. I got the chassis from RJ Guitars, and the purple head shell from Glassworks, thanks guys.
This is a follow-up to the Trainwreck Express post.
As mentioned earlier, the amp turned out to be pretty noisy… While working on it over the weekend, I got it much quieter by re-wiring the PS, but somehow it also sounded much worse with obvious blocking distortion which wasn’t there before… After fussing with it for awhile, I decided to restore the whole darn thing back to the original 18W design but with a cascade switch added for some flexibility. I will try some new EL84s soon, so I can compare them to the Chinese 6P14s that are currently in the amp.
This is a re-post of the thread I started on music-electronics forum back in 04-23-2013:
Since there have been some discussions on the usefulness of SPICE models and circuit simulation on several recent threads, I thought it might be of interest to some of us – the non-believers can skip this – to see a comparison of the different SPICEmodels in action… The accuracy of any simulation depends on the models used, so model verification is an important step in the design process, alas tube models are notoriously in-accurate particularly in their grid modeling. While it is not so bad for hi-fi designs, where the designers try to avoid non-linearity of the tube at all cost, in guitar amp designs, quite the opposite happens, where the grid is often pushed way beyond its normal operating range, that’s when the trouble starts… So we are talking about the extreme cases here, actually most tube models work fine in their linear region.
Anyway, in the following comparison charts, I used Loudthud’s great scope trace as the reference. And three 12AX7 models were used to generate the plate voltage/current vs. grid voltage curves, the only change was to flip Loudthud’s scope shot around, so the coordinates match up.
So it can be seen that not only do the models differ greatly from each other, none of them matches the real thing! Although Ayumi’s model does come pretty close. For a more in depth look at the various models, please refer to the following:
[Update – July 15, 2014] Well that did not last very long, after hearing clips of the JCM-145 (a special version of the JCM-1 made for Anderson Music’s 45th Anniversary), I just had to try it out. Using the schematic made by Matec here (thanks!) It was a short order to convert the 3Watter into a JCM-145 clone, it sounds pretty good considering I am using a surplus line-distribution transformer, with reflected impedance of 26k Ohms, which is quite a bit higher than the spec 20k Ohms.
[Update – October 30, 2014] The line-distribution transformer just did not cut it… When the amp is turned up, its core would saturate and cause severe distortion – not the right kind! So I finally replaced it with a rather large 10k:8 OPT (loaded with 16R speakers), which really is an overkill for this little amp. But the result is well worth it, now the amp sounds much fuller, and the LF is surprisingly loud coming off the little 12AU7.
After taking the Princeton clone apart, I decided to re-use the chassis for another build – and I settled on a mash-up of the Princeton and the AX84 4-4-0 Studio, it’s a very simple circuit – even though I re-use the TMB tonestack from the Princeton, the amp actually sounds much better with it bypassed, so there’s really not much between the input jack and the speaker – less is more!
Here is the schematic:
Most of the parts were mounted on a surplus terminal strip board.
The completed amp, note that another 6N8P/6SN7 was added after the shot was taken, that boosted the output power to a whoppin’ 3 Watts.
With the volume ~ 2 O’Clock (single 6N8P/6SN7), here is the scope shot of the output into a dummy load:
The soundclip was recorded with my mobilephone, the volume was around 1 O’Clock, I used DI tracks straight into the amp, each clip starts with the DI track played on my hi-fi speaker followed by the amp played through an Emience Ragin’ Cajun in the AX84 cabinet. Sorry about the poor recording quality – the amp sounds much fuller… anyhooo, here’s clip:
To me, this little amp sounds better than both the Princeton clone and the much larger AX84 SEL… It was a very quick and enjoyable build, since I had all the parts and the chassis ready to go, it’s definitely recommended for those looking for a small bedroom practice amp.