meters and transformers

by **rick** » Thu Aug 24, 2006 12:54 am

i still have more sifam meters and line in / line out transformers then i will ever use come and get them whilei have got them ( ...cheap)

perhaps there is a report about some of the different transformers i have sent aeound the country
uses, successes failures..?
i know the specs of the sowters i have are excellent but some of the others must have found a warm home by now ...?

by **chris p** » Fri Aug 25, 2006 1:05 pm

I've liked the idea of adding a VU to some of my projects, but felt uncomfortable about my lack of knowledge. So can anyone help?

It is as simple as hanging the VU meter across the +/- outs, with a resistor of some value to get the VU into the right range? Does the load affect the sound? I've seen some schematics that are way more complicated to get around (what I assume) is this problem, but I don't have any feel for the ease (or lack therefore) by which metering can be accomplished.

by **rick** » Sat Aug 26, 2006 12:24 am

for most of audio history a vu meter simply just hangs of the output of the output transformer, neves did it like that for a very long time and most of the diy projects out there are from old designs that did it this way
technically this adds the tiniest bit of distortion , but i must admit i have never noticed that distortion ( i have measured it but not really heard it as distortion)
i just hung them across the + an - for the last twenty years with no problems

however a better way and now i have a willing tech to do it is to use buffer boards to isolate the vu meter from the circuit , rob at proharmonic has been busy over the last few months adding buffer boards to all kinds of new and old turtlerock mastering stuff.

i told him to make up a vu meter buffer circuit board and he said nah its easy to use vero board as i need them
with no end to the amount of vu buffer boards he still has to make for me i wonder if he will see the light and get them made up , ( and maybe sell them unpopulated to the hoards of diy geeks on the world wide waste of time ( hint hint... rob are you listening ? )

by **Andrew** » Sat Aug 26, 2006 1:52 am

Hi Rick, Can't report on the transformers just yet cause I have not finished the desk yet :oops: but...i'm only days away now (just finishing star grounding). Didn't know you had sifam meters? how much?

by **rick** » Sat Aug 26, 2006 3:20 am

[quote="Andrew"]Hi Rick, Can't report on the transformers just yet cause I have not finished the desk yet :oops: but...i'm only days away now (just finishing star grounding). Didn't know you had sifam meters? how much?[/quote]
meters with bezels $50 each less for more

by **chris p** » Sat Aug 26, 2006 9:03 am

Hey Rob

If not a board, can you post a nice simple schematic? I'm sure I'm not the only one interested.

Regards

by **Andrew** » Sat Aug 26, 2006 11:47 pm

actually after posting that I think you did tell me about the meters before. My memories like a siv lately.

by **rob** » Mon Aug 28, 2006 9:59 am

errrm yep..... it's on the "to do" list

Rob

by **mfdu** » Thu Aug 31, 2006 9:58 am

hi rob - consider this number two for you to do - i am interested in your buffer boards, also.

not to be hassling you or nuthin!

chris
:)

by **rob** » Sat Sep 09, 2006 11:41 am

I discovered something the other day that arose from one of my long chats with Joe Malone of JLM Audio.

The "VU" meter from Altronics, which in most respects seems a good cheap meter for DIY and the small but funky little blue one from Jaycar are not really VU meters as we know and love them.

The difference ? A fundmental aspect of what was traditionally a VU meter and what set it apart from a convential DC volt meter was that VU meter contains a bridge rectifing circuit within it. This is usually constructed from germanium diodes and converts your incoming audio into a DC voltage that can drive the meter coil and thus push the needle across the scale.

(as an aside, it is also this diode bridge that creates the low level distortion imposed on the audio when you just hang a VU meter across a line signal, typically about 0.1% THD gets generated )

These budget meters from Altronics and Jaycar contain no diode bridge! If you place them across an audio signal they'll do jack-shit.

The solution is either to make up a diode bridge from germanium or schottky diodes and apply your audio ( if the distortion doesn't bother you ) or....impliment a much more complex buffer driving circuit to drive the meter and interface to your audio.

I'm thinking of the easiest, cheapest and most universal way of doing this.....

back to the drawing board

Rob

by **astrovic** » Sat Sep 09, 2006 11:17 pm

Rob - having been reading up on this issue for the last 1/2 hour or so, I wish I had seen your post first!

Thank for confirming what I had been suspecting - I have an Altronics and and Jaycar "Vu" meter sitting here that tend to do diddly squat - well, I get some wild readings of gain reduction on Altronics meter in my G1176, but that's about it.

I was also planning on building a passive Vu meter as a piece of test equipment with one of the Jaycar fellas - It's built, except for the lack of a rectifier on the Vu (as I now understand my problem to be). Sounds like I could do worse than putting in a diode bridge and seeing if that does the trick (if it doesn't, well I learn something new doing it, huh?).

I'm tempted to ask how to build a diode bridge, but hang that, I'll do my own research and see if I can figure it out. I think I know, but then I think I know lots of things :)

If I get it right, I'll post my findings here, so the learned ones around here can chuckle at the small things that amuse small minds.

Cheers guys

by **astrovic** » Sun Sep 10, 2006 12:00 am

I think this is what I'm looking for:

Hats of to Elliot Sound for such an amazing website :)

And if this doesn't do the trick, there's a better approach on the same page. Looks like I learned something!

by **rob** » Sun Sep 10, 2006 10:46 am

yep that's the idea.

note:
you need to use germanium diodes for this to work ( ensures sensitivity at low levels )
the exact value of R and C will come from some experimentation. I'd leave C out to begin with a get a picture of the ballistics of the meter you are using. This is where the opportunity to put it side by side with a known "good" meter would be of benefit.

I'll look at this aspect of these cheaper VUs sometime this week and post my thoughts of the accuracy of their ballistics.

you'll also need some means of accurately measuring level in order to calibrate your meter ( by adjusting R ) for a meaningful 0VU reading ( ie 0VU = +4dBu )

Rob

by **astrovic** » Sun Sep 10, 2006 8:01 pm

I've pinched Kev's schemo, which uses trimmers in parallel for 0dB, +4dB and +8dB: http://www.diyfactory.com/data/passive_vu_01.pdf I've skipped the +8 dB, as I don't really need it, but otherwise followed this approach. I'll pay a visit to Jaycar during the week and pick up some germaniums, to see if I can get this fella finished.

I'll be very interested in your comments, Rob

by **mfdu** » Mon Sep 11, 2006 9:36 am

you can always trust that cheeky kev, can't ya?

keep me posted - i'll mod my existing cheapass meters, and i do want to pop a meter into my opto compressor . . .

just placed an order for tubes for my LA2A's ,and just got my new 65mm road wheels for my skateboard. which will i attack first?

chris.

by **rob** » Mon Sep 11, 2006 10:37 am

i'd be putting the new wheels on the skateboard.

my priority this week is to get the tomatoes planted

:) R

by **mfdu** » Mon Sep 11, 2006 6:54 pm

the new wheels are fantastic.

apparently we put our tomatoes in too early. but we composted with pea straw, 'cause 'they' say it's good . . .
all the peas have sprouted and it's just a green sea of peas.

sigh. the sun is glinting. looks like the summer's going to be all pea and skittles.

the new wheels are fantastic.

chris.

by **astrovic** » Mon Sep 11, 2006 8:11 pm

sugar cane straw...been using this for a couple of years after a couple of years of peas before that :)

I skipped tomatoes this year, but have everyting else in. Yum yum!

by **astrovic** » Tue Sep 12, 2006 12:10 am

Just popped the germaniums into my build of Kev's passive Vu meter...worked a treat (and first time! that's the first time I've built something that worked straight off the bat).

I bought some extra germaniums so I can build a rectifer for my G1176 - I'll be interested to see how it goes in there, and to compare against the sifam's.

That was fun!

by **JLM Audio** » Sun Sep 17, 2006 8:25 pm

Yes most cheap meters need to have the rectifier and level matching resistor added externally to work at all. These meters are usually just 100uA or 500uA meters with a VU scale fitted.

To stop the audio output THD from going up a decimal point from the diodes you need a unity buffer between the audio output and the meter.

If you are building a compressor that uses the meter for gain reduction as well as output level you can get away without a unity buffer one as long as you are in Gain reduction mode while recording. This also applies to using 1176 and LA2A compressors as well.

Joe

by **chris p** » Sun Sep 17, 2006 11:36 pm

Hey Joe

Where you going with that gun in your hand?

(Sorry, Hendrix tragic joke)

Seriously, welcome to the wonderful forum, Mr Malone sir. You have many fans here.

by **mfdu** » Mon Sep 18, 2006 10:22 am

yes yes - you can count me as a fan!

chris.

by **astrovic** » Mon Sep 18, 2006 4:27 pm

Thanks for the input, Joe - good stuff!

FWIW, I've put a diode bridge behind the cheapo meter of my G1176 and it works nicely. I'm going to run with it for a while until I get used to observing its sensitivity, then swap in your 2-diode version as posted to compare the difference.

On another note - my daughter gave my wife and I some wonderful head colds, which meant I couldn't spent the weekend shovelling mulch in the garden as planned, but rather had to settle for second best and work on my GSSL which is now 85% build. Oh, the humanity!!! :D :D

by **mfdu** » Tue Sep 19, 2006 9:51 am

hey astro,

(i do like your name - i grew up with astroboy, and have an astroboy tattoo up my right forearm)

you'll have to let me know how your gssl is going - my build has been plagued with faults and i'm just over it - i need to get a couple more boards and do a fresh build.

are you doing the thrust circuit?

chris.

by **astrovic** » Tue Sep 19, 2006 1:24 pm

Hey Chris

My VCA's arrived yesterday, so I got everything together and fired it up. No luck yet. I want to post some questions on this over at the Lab, but my registration isn't happening (I changed my registered e-mail address and now things aren't working for me). It's passing audio just fine, my DC measurements all look good except for 0 VDC at pins 7 & 8 of the TL074, but the meter doesn't react and its not compressing. So the problem must be in the sidechain somewhere - could be a faulty TL074, but more likely some poor craftsmanship.

I haven't put in the thrust filter, but I do have Greg's HPF/external sidechain board in there. I don't intend to connect it up until I get the unit working in the ordinary way.

Cheers mate

Chris

PS I have no idea where I got astrovic from - forgotten in the mists of time! Maybe a combination of astroboy and victoria, but I'm not really sure...

by **Barney Loveland** » Tue Sep 19, 2006 11:30 pm

Hi lads,
I too have an gssl on the bench!! Is built and passing audio but there is some weird distortion that changes with the threshold from memory. Time permitting i'll get to it. But i have accidently ordered a few extra gssl highpass filter boards if anyone is interested. Don't have them yet though.

MFDU chris, maybe we could have a gssl workshop, i've just moved to Newport.

barney

by **astrovic** » Wed Sep 20, 2006 8:22 am

Well, I've located my fault with my GSSL - using the 2180's, you remove pin 4 from the left and right VCA's, but not from the sidechain VCA. Der. Good thing I only bent the legs rather than removing them altogether. So it looks like it works - I'm in the middle of re-doing the cabling to the Xlr's, as my first effort was pretty evil. I was nearly there when my better half intervened last night :) Looking forward to hearing the final result!

by **chris p** » Wed Sep 20, 2006 8:44 am

My GSSL unit #1 works fine, once I got my cabling to the XLR's correct. Its quite a lovely unit, my problem is that its makes the sound nicer at many different settings, so you need to play with the thing a bit to get a feel for which sort of niceness works best with different program material. I'll be using this one for stereo tracking (eg room, drum OH or whatever).

I'm building a second GSSL now for mixdown, but it has problems with its power supply (my power trannie may be at fault here). My attention is on building my JLM preamps, but I'll get back to it sometime soon.

by **mfdu** » Wed Sep 20, 2006 10:18 am

re. my output levels, i have tried different values for the (10k?) output resistors, trying to achieve unity gain. . .

so remove pin four on the l/r vca's???
what fault did that fix? low output signal?

i thought that pin 4 bend wasn't actually necessary, but given nothing else seems to work for me, i'll give it a go.
(i have already removed the trimmer network, which should then mean pin 4 is not connected to anything. but i'll bend it out tonight, and see)

chris.

by **astrovic** » Wed Sep 20, 2006 11:19 am

Chris, the pin 4 bend on the l/r vca's probably does nothing - given my state of noobness, I tend to follow accepted wisdom first before experimenting. No harm in trying, I suppose, but I doubt that's it.

meters and transformers

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