I'm still having some problems, but I got the heaters to work with the Antek transformer! It seems to be extremely stable which is really good news! I ordered the Edcor transformer but in the meantime I still want to get this working with the Antek. Maybe somebody can help me.
I'm not completely sure how to hook up the secondaries to the main psu. The lines are 250-0-250. I've tried hooking each 250 line to each pin in that section, and then I've tried soldering the two 250 lines together and hooking that to one pin, and then the 0 center tap line to the other pin. When I do it the first way, my R1 gets super hot, starts glowing and smokes. When I hook it up the second way, my fuse (which is 2 amps) shorts. I might be able to help narrow the problem down to something. I've noticed that I get continuity between the ground pad that is by the 350 regulator, to many of the components (resistors, the vactorols, and the tube holders). This happens even when I have the pcb board taken out of the case not hooked up to anything else. I can't see any problems with the soldering. I tried ungrounding the TL783 using a insulator pad in between it and the heatsink and I also used a nylon screw and nut. Are there any tests that I can perform to try and narrow this down? Where would you guys start looking first?
I took some pictures that might be able to give somebody a clue. I'm pretty stumped. Let me know if you guys need any other pictures or any other angles.
All righty. I've almost got this figured out. Got the voltage working on the main psu! It's passing audio and it sounds amazing! One issue I'm having is that without the tubes, the voltage in the heaters is set at 6.3V, but once I put the tubes in, I can't get the voltage above 5.79V. Not sure why, maybe somebody can give me some advice.
Muwahahahahaha. It's all working and sounds great. I had the heaters hooked up wrong and then when I finally hooked them up correctly, they went into thermal shutdown. I mounted the 350 on a HUGE heatsink and made sure not to ground it and it's working like a thing of beauty. I've still got to replace my linear pots with log pots but after that, I cannot wait to start using this thing.
I worked on this with my friends who I would not have been able to do it without! We made the case out of an old 90s Mitsubishi 5 disc CD player that I found at Goodwill for $15. It was the perfect size. Bought a faceplate for a 3U rack at my local electronics store for about $9. Gutted the CD player and drilled holes in the faceplate with my friend's drill press. Used a belt sander on the faceplate to take off the black paint and give it that look. Used painters tape, spraypaint and a French curve to get the stripe as close to perfect as possible. Had my friend who has handwriting like a robot, write all of the labels. We let it sit for about a week but then it started rusting pretty badly so we had to sand it down again (tried getting the rust off with alcohol, vinegar, and clr but it just wouldn't come off). Then we sprayed it with Krylon Acrylic Lacquer. We did it outside so it didn't finish as flat as we would have liked since it was night time and there was condensation in the air but it still looks great. Named it Chris after my drummer because he is a badass and it will hopefully make everything sound as good as he makes everything sound when he plays drums.
Edor WSM input and output transformers. Antek power transformer. (f**k if I know that 250-0-250 actually means 500 total volts in between!) Made a custom slope switch pcb to allow switching between nothing, blue led, anti blue led, red led, 100k resistor and 1k resistor.
Still gotta make sure that the slope switch works properly (does it matter that there is a second vactoral installed on the pcb already?) and I need to change the threshold to a log pot, but it's passing audio. I might mount a fan to the big heatsink with the LM350. It just seems a little warm, but I want to make sure that it doesn't overheat if I push it hard. Oh yeah, and we need to cut out some air vents on the side of the case and put some mesh covering for more ventilation.
Thanks for all of the helps guys! I still need to try running it through my console to see how it sounds on my tape machine. I'll report back!
Lundahl LL1540 wired as 1:2 on the input
Lundahl LL1540 wired reversed as 2:1 on the output
Most of the kubicki mods. Second vactrol for soft setting, blue led for hard setting
I have a 500 ohm trimmer in series with each of the 4 vactrols. I really needed these to optimize the compression in stereo mode.
Replaced R1 (2 watt 470R) by 2 parallel 25 watt 1K resistors! Just to make sure it doesn't overheat
Front panel made by Frank from nrgrecordings.de
Meters are old AKAI meters I bought from a member (Sahib?) here a while ago. (painted black)
assembled stepped switches from eBay
A big thanks to all who contributed to this great compressor!
Just completed the initial build and test on my D-AOC
Used once again my fav combo of Carnhill 4:1 (10K:600) transformers and Jensen 1:4 (2.4K:38K4) input transformers as well as a 3RU with 4 VU meters for both output level and GR.
PSU traffo was Musikding and tubes are EH au7 and at7. The output caps are ebay 'audiophilers', which are pretty cheap and like solen knockoffs. They work as well as anything else I've tried.
(never been able to pick the sound of caps very much)
Added hard relay bypass, JLM vu buffer amps and did a switched ratio/threshhold mod on a rotary+dpdt switch to provide 'soft', 'hard1', 'hard2', 'hard3' and 'out' settings.
They consist of the common mods of 100K, blue led anti parallel, 100R, red led parallel and no mod in circuit as the 'out' position.
The settings all seem to work as expected, so far. I figured I didn't need the second vactrol in parallel as the blue anti parallel effectively provides the fw rectification setting as described by Kubi. I wasn't sure if you could do the mods as well as Kubi's antiparallel vactrol mod.
I'll be doing some more experimental mods on the network, but for now it works well.
Noise performance is very good with unity gain noise at GR of 15dBu of around -75dBu on the RTA aggregated from 20Hz-48KHz. The RTA channel loopback is -83dBu and is calibrated using my CRO and true RMS meters to the best that I can for absolute voltage on the dBU scale.
Frequency response is ruler flat from 10Hz and -3dB down at 25KHz. At 20KHz it is -1.9dB down.
About as good as I can get
Problem was a fake LM350T - it craps out at 1.5A at 6.35V for an input of 10.5Vdc.
At the required 1.8A, it drops to 5.44V and who knows what current?
The unit does still work but noise goes to hell and a bunch of operating points are all over the place.
Checked the reg case temp to be 65C which is well below what I would expect for current limiting at the onset of thermal shutdown. Also tried reducing the voltage differential to reduce the dissipated power and no cigar.
The reg is a fake! Taking one sidechain tube out sorts the unit performance completely to expected. So, I need to get me some genuine LM350Ts to complete the box.
Other thing is I need to drop the B+ quite a bit - my HV are around 40V too high.
Looks like HV current is around 26.5mA per channel, so I need to up my HV feeding resistances accordingy.
The rest was all good off the bat.
Thanks to Volker and Analag for the cool designs and manufacturing.
GR tests show it is pretty easy to attain max of 29dBu in the hardest limiting mode.
I may tweak a little because I think even with 1:4 step up, it takes the Input knob to be more or less full up to achieve major GR. I also think it could use more makeup gain, so I may mess about some there too.
In use - quiet, extended bandwidth all the way up and down.
I would characterise the GR as ... SMOOTH ...... VERY SMOOTH ...
Virtually transparent. Very little 'tube-ness' I can discern. The amp characteristic is CLEAN AS
Compared to the D-LA2A, I can't hear the release virtually at all - seems fairly slow to let go, whereas the D-LA2A is quite fast in comparison.
Compared to the Poorman 670, it is virtually inaudible GR and super clean, with a reasonably fast attack and reasonably slow release. The 670 is like a crunchy granola suite with super noticable attack and release, they way I have it setup. That one remains my fav. tracking limiter.
I think this is a great candidate for a mastering limiter (with some careful attention to channel matching and so on. The hardest part of all !)
I think I can improve the noise performance a little and may tailor the threshold/ratio some more.
So far, quite happy and this fills in a spot in my system for a super clean and transparent but brutishly squashing limiter.
Apart from exploring further the thresh/ratio curves with the various mods people have discussed, I will also be experimenting with the input atten, bias and feedback on the input tube first stage .
I think I prefer less clean and more hair/gain .
In addition, reducing the input tube second stage feedback from output traffo primary for less linearity, more gain.
I'll be trying a 2:1 turns ratio on output (2K4:600) for increased gain. I think the line amp should handle the lower Z fine, being an AU7 CF (with active, ac noise cancelling load - dc coupled wcf? sort of thing).
I can always return to the stock arrangements if I want. I'll do one channel and compare with the other as I go.
Also, just finishing up a 'What Compressor', which is a discrete op amp based vactrol limiter with transformers all round.
Be very interesting to compare them - I'm thinking they will sound quite similar, with the What comp having the added flexibility of time constant control. I expect it will be very clean, like the stock doac, so the What comp will complement my system if I succeed in making the doac hairier and somewhat more stinky
[My other mastering limiter is a Finalizer Plus ;D]
It uses the vtl5c9 vactrol, as opposed to the doac's vtl5c4/2 vactrols - what diff will it make? Who knows