gary o

Lots of questions Im afraid Im hungry to learn I have done lots of vari mu projects & experiments ....Ive made many projects without a lot of basic electronics Im trying to fill in the gaps so please bare with me, thanks

Ok here some questions some may sound silly but here goes

Firstly the Altec 436 (not got one so dont no how it sounds) i read lots of people saying they are junk no use not worth building or buying......do u have one, do you like it if so why ?? if not why ??

I see theres not a lot in them does that make them bad ?? if they so bad why are they bad.. transformers, tubes ... mention Abbey road & the Beatles suddenly that are great !! Is that just mojo bollocks, personally I dont like the Beatles or the sound they had really....there i said it....tho I love the song & the vocal sound they got on Hey Jude...Wow I love that..anyway so Abbey road thought the 436 was worth tampering with then, I wont bother asking if anyone has the abbey mod.....tho id love to see it...did Emi have the money or resources to get other compressors but thought a moddified 436 was better ?? I wonder if the mods are only the obvious ones like balance pots attack release threashold that youv all done and thats it the rest maybe hype !! If as i keep reading 436 is so crap why would EMI polish a turd.....maybe the crap sounding 436es are just not working correct after all these years......I wanna DIY one just have a listen..

The chiswic thingy seem is very similar to the 436 & I read people raving about them....are they that good ?? any better than 436 ?? circuit doesnt that that much different to me....

I noticed a daul pot for theashold on that one & never seen this on any other vari mu .....Is there any advantage ??

the 6AL5 daul diode seems to be popular in vari mu Ive seen it with a wide range of resistor values on its cathodes......18K to 510K pairs ? Is this bias point ? as I say Im lacking in basic electronics, I just read some info about bias points to help me understand.

And the resistors or lack of in some vari mu circuits on the cathodes of vari gain stage tubes.....they set a bias point right ?
And designing a vari mu we would want to choose a point that sounds good through out the gain reduction range ?

Ive noticed a couple of vari mu circuits have a little amp before the diode singnal into grids & bigger out the plates I suppose the give the diode more umfff ! does it ? does it speed up the attack ?

I thought we had to use remote cut off tubes for the vari gain stage of vari mu ?? I see some units use semi remote cut off tubes ? or other....I know PRR showed us the a ECC82 could be used but not for huge gain reduction.....so wouldnt remote cut off tubes be best everytime ?

Im currently fiddling with 4 DIY vari mu limiters on my bench comparing sounds recording vocals & listening then moddifing & redesigning any suggestions would be most welcome...

thankyou for your patience & happy new year to you all
« Last Edit: January 03, 2010, 08:45:32 PM by gary o »


syn

I played a lot with 436/vk 1 clone, well it is neither actually, P2Ping all day long. For the compressor action they are quiet the same for the sound side it depends what tubes/transformers u use, the sound would change. Nobody really seems to understand why a dual pot for the threshold (ratio), I talked to a couple of techs on that matter  and everyone went, like hmm, I don't get it, and the dc bias to the pot is missing (vk clone) so, might be an error on the schematic. Generally speaking both of this topologies are on the slow side of the vari mu land, but I like a lot the "mojo" of it. Like, you can "hear" the compressor kickin' in letting the transients pass, and than squashing. It is more of a creative tool than surgical one (if one likes what it does). It's like dynamic fx box, probably due to the errors in the schematic (vk). I'm far from being knowledgeable on the topic, just sharing my opinion. I think Vk side chain is f%8ked up big time, but than you can just plug in 436 SC with ~cool results (some things do need adjustment it is not plug the SC and play). LOTS OF CHARACTER- some will like it, others will hate it (I don't think the real VK is revolutionary different from 436, haven't heard it tho- just MHO) probably the biggest difference being from the tubes/transformers used.
« Last Edit: January 03, 2010, 11:40:07 AM by syn »

gary o

Cool thanks for responses Iv been messing around with a VK like circuit all day trying to get my head around the side chain & side chains in general...how they work & whats best

Am I right in saying that if no bias voltage is added as per VK schematics then the threashhold is at its lowest and so adding bias voltage would start to stop the compressing ????? so the more bias = higher threashold...

My VK is working great as per schematic but with a little popping on fastest attack & lowest threashold .... I built a seperate side chain copied from another vari mu comp ....it too worked best without the extra bias voltage as in its original circuit, and now popping is gone ( circuit balanced nicely with pot by the way) but this other external side chain had resistance on its 6AL5 cathodes, so is that raising threashold a little just enough to stop pops maybe.......or slowing attack....no...either way no point changing to this as in VK side chain I could just back off threashold or attack.....

Syn what makes you say the side chain is F%8k up ?? So it works better with 436 side chain then ??......maybe il have to breadboard then

Yeah I spose its slow Im just using mine for vocals and so far Im loving what I hear its a crooners machine I Had BIG Expensive Sowter BA6A O/P tran on it that sounded good but had to pad it, maybe as Im using a 1:4 Sowter input tran Iv now got the Sowter 8650 on the output and so dont need the pad.....I think its sounds as good but need to record both trans to compare.....

kambo

i had thumping, and i used 175 idea on 6bz7, and thumping disappeared....
used 2x22r (pin 3-8)
mine was fast enough for drums...
i made an accidental  short yesterday ( big booom ), and now my attack time slowed  ???
my DCV is all over the place... still working tho  ;)

gary o

Sorry to hear about yr short kambo hope you get that sorted....I been messing some more with the VK1 type circuit... doesnt the 6AL5 diode get its bias voltage from VR103 I couldnt get the threashold high enough so as I can have gentle or no compression, bare in mind I have a 1:4 input tran instead of 1:1 tho...  of the 2 schematics that are here one has 100K resistors feeding the daul threashold pots ...as does mine , the other has 18K, I tried 18K, yes gave me more range on my threahold pot, not enough stop it compressing so I tried 1K resistors and that gives me from no compression to full, its much better for me.....I dont no if Iv done something naughty nothing has fried yet, we'l see.......

syn

bare in mind I have a 1:4 input tran instead of 1:1 tho...  of the 2 schematics that are here one has 100K resistors feeding the daul threashold pots ...as does mine , the other has 18K, I tried 18K, yes gave me more range on my threahold pot, not enough stop it compressing so I tried 1K resistors and that gives me from no compression to full, its much better for me.....I dont no if Iv done something naughty nothing has fried yet, we'l see.......
I think 1:1 is better option, I'm not sure about 1k resistors but I had anything from wire to ~1meg in there just to see what will happen and apart from changing compressors ratio nothing bad happened.
I think VK clone SC is not perfect cause you can just use single 25kpot (instead of dual 47k) and adjust 18k value (don't remember what it was, but think it was not that critical in value) and still have the same results compression/sound wise. Again whilst I was playing with this, I had an impression that 436(NYD mod. thank you NYDave) is nothing short of in regard to VKclone. I don't know about real VK, never played with one.
But i like a lot the way 6bq7a(rca-nos) sounds, it has that special something, however someone else could dislike it.


 

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