rafafredd
Well-known member
check those Freds polarity! One of them is miswired... :green:
Tube comp/limiter under development
- Thread starter NewYorkDave
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check those Freds polarity! One of them is miswired... :green:
NewYorkDave
Well-known member
The power xfmr I'm planning to use can spare another 400mA or so on the heater winding, so maybe I'll give 6AL5 a try. After all, they're cheap and it means mooorre tooobs, maan... :wink:
NewYorkDave
Well-known member
What's the advantage? less leakage?
[quote author="NewYorkDave"]I was considering doing a stereo link on my tube compressor by mixing the signals into the sidechain amplifiers. I discussed this with PRR and straight away, he pointed out the pitfalls. For me, it was one of those "slap your forehead" moments; it became apparent immediately that linking after the rectifiers was definitely the way to go. It works as a sort of "absolute value" circuit and ensures that the GR of both channels tracks the highest signal amplitude present in either channel, regardless of polarity or phase.
[/quote]
This is copied from another thread in another room. I brought it here for the benefit of us onlookers as the development continues.
Keep the ideas brewing in my head, Dave. I have a stew slow cooking in my simpulator
[quote author="analag"]do you have any Edcor trannie in the signal path, Dave.[/quote]
This is an irrelevant question.
analag
[/quote]
This is copied from another thread in another room. I brought it here for the benefit of us onlookers as the development continues.
Keep the ideas brewing in my head, Dave. I have a stew slow cooking in my simpulator
[quote author="analag"]do you have any Edcor trannie in the signal path, Dave.[/quote]
This is an irrelevant question.
analag
jdiamantis
Well-known member
re: leaky diodes.
The ol' CBS audimax used 1n456a's in a very high impedance circuit; around 2-5meg. I recently rebuilt one of these, which suffered from leaky diodes, and new ones did the trick. Still available from most vendors.
The ol' CBS audimax used 1n456a's in a very high impedance circuit; around 2-5meg. I recently rebuilt one of these, which suffered from leaky diodes, and new ones did the trick. Still available from most vendors.
NewYorkDave
Well-known member
Just to give a better idea of how the diodes are being used, here's a basic outline of my detector circuit (as it appears after the sidechain amp):
Image
It's set up this way to prevent the release time constant of either channel changing when two units are linked. I didn't want to indulge in the complexity of a full master/slave arrangement, which would be a PITA with the two channels in separate chassis. But on the other hand, I wanted something a little better than the usual "tie the control lines together" quick-n-dirty approach.
The DC load resistor shown at the junction of the three diodes is 10M at present; I realize that's excessive but I wanted to ensure minimum additional current draw and started with the highest value I had on hand. I can reduce this easily if needed. The release resistance in the main TC circuit goes as high as 1M.
The threshold control voltage can be varied from 0 to +25VDC, and the AC output of the sidechain amp (into the primary of the rectifier transformer) can go as high as 30VRMS or so. The DC threshold voltage supply has a low AC impedance to ground.
I think the first thing I'm going to try is to reduce the value of that resistor and pull a little more current through the diodes in the fullwave rectifier.
Image
It's set up this way to prevent the release time constant of either channel changing when two units are linked. I didn't want to indulge in the complexity of a full master/slave arrangement, which would be a PITA with the two channels in separate chassis. But on the other hand, I wanted something a little better than the usual "tie the control lines together" quick-n-dirty approach.
The DC load resistor shown at the junction of the three diodes is 10M at present; I realize that's excessive but I wanted to ensure minimum additional current draw and started with the highest value I had on hand. I can reduce this easily if needed. The release resistance in the main TC circuit goes as high as 1M.
The threshold control voltage can be varied from 0 to +25VDC, and the AC output of the sidechain amp (into the primary of the rectifier transformer) can go as high as 30VRMS or so. The DC threshold voltage supply has a low AC impedance to ground.
I think the first thing I'm going to try is to reduce the value of that resistor and pull a little more current through the diodes in the fullwave rectifier.
Winston OBoogie
Well-known member
[quote author="NewYorkDave"]The power xfmr I'm planning to use can spare another 400mA or so on the heater winding, so maybe I'll give 6AL5 a try. After all, they're cheap and it means mooorre tooobs, maan... :wink:[/quote]
Gotta love mo' tooobs man.
Artifartifacts: Don't know your T.C. arrangement but how about a little series R after your S-S diodes? Doesn't have to be much and, in power supplies, I usually end up chucking in about 10R after a "Fred & Barney' bridge. Seems to slow them down - meaning 'shut them up' - enough to be on a par with valve rectifiers. TV dampers excluded.
Schottkys are pretty decent performers too but most are limited to 35V max I believe.
Gotta love mo' tooobs man.
Artifartifacts: Don't know your T.C. arrangement but how about a little series R after your S-S diodes? Doesn't have to be much and, in power supplies, I usually end up chucking in about 10R after a "Fred & Barney' bridge. Seems to slow them down - meaning 'shut them up' - enough to be on a par with valve rectifiers. TV dampers excluded.
Schottkys are pretty decent performers too but most are limited to 35V max I believe.
[quote author="NewYorkDave"]Don't worry about peace or politics, man. If you've got the goods, bring 'em. That's what the Drawing Board is all about.[/quote]
Ok....
The basic outline of a speeded up 436 type.
I left the pots and the TC network out of the schemo for the sake of simplicity.
analag
Ok....
The basic outline of a speeded up 436 type.
I left the pots and the TC network out of the schemo for the sake of simplicity.
analag
Larrchild
Well-known member
Change the 6DJ8's into remote cutoff tubes and feed some control voltage to their grids thru a pot. Like a "turbo" setting.
Vary both grid v and plate load with sidechain voltage as an added feature.
Also, I'd raise the B+ .. the top tube's not gonna saturate like a FET.
Mr. Narma examines Rowan's Work
Vary both grid v and plate load with sidechain voltage as an added feature.
Also, I'd raise the B+ .. the top tube's not gonna saturate like a FET.
Mr. Narma examines Rowan's Work
[quote author="Larrchild"]Also, I'd raise the B+ .. the top tube's not gonna saturate like a FET.
"Mr. Narma examines Rowan's Work"[/quote]
This is a 6BC8 and a 6DJ8 in series, If I remember it correctly they work safely at a maximum of 130V. So 250V across them should be good enough.
Have you tried this "Turbo Charged" GR setup, how does it sound.
If I followed your idea....it would be on fire
analag
"Mr. Narma examines Rowan's Work"[/quote]
This is a 6BC8 and a 6DJ8 in series, If I remember it correctly they work safely at a maximum of 130V. So 250V across them should be good enough.
Have you tried this "Turbo Charged" GR setup, how does it sound.
If I followed your idea....it would be on fire
analag
tommypiper
Well-known member
EDITED: Larr, thanks.
Larrchild
Well-known member
Yeah you're right.
Done!
Done!
Well, Larr you never answered my question. Show me a schemo as I understand that better than the words that go around it. And remember to put some frills around the edges with that Photoshop skills you seem to be honing
ha ha ha...just messing with ya, but a schemomatic demonstration would be nice though.
analag
analag
Larrchild
Well-known member
No, i have never tried that. But as I looked at the schematic, I thought the top tubes could be made variable in their conduction. I can imagine it augmenting the gain reduction sound a lot. Just not sure how good.
NewYorkDave
Well-known member
((Ahem)).. ANYWAY, I found that adjusting the value of that resistor (to as low as 100K) did little outside of dropping the DC output very slightly. Even removing it altogether had no discernible effect. A sweep of the sidechain reveals that the conductance vs. frequency characteristic of the rectifiers becomes very nonlinear with a large (30V) reverse-bias applied. I'm familiar with the "varactor effect" but didn't expect it to become a factor at these low frequencies. Or maybe that has nothing to do with it and I'm seeing the result of some other parasitic that I've overlooked. Anyway, reducing the back bias to 15V essentially flattens out the curve over the audio range. I think this will still give me adequate range of threshold adjustment, but we'll see.
Dave, sweeping the compressor at a set level of gain reduction, shows varying attenuation across the frequency band, which I think is a function of the whole, but your research may shed more light into this.
Lar, I beefed up the design and your prediction almost came true "Drag Time" ha ha ha....no I'll be nice. For a while at least.
analag
Lar, I beefed up the design and your prediction almost came true "Drag Time" ha ha ha....no I'll be nice. For a while at least.
analag
NewYorkDave
Well-known member
Well, do what I did. Disconnect the feed coming from the compressor section and inject a signal directly into the sidechain amp. Disengage any filters and set the release time to, say, 250ms or so. Sweep slowly across the audio range using a generator with stable output amplitude and observe the control voltage output. It should be fairly flat across the range, otherwise there's a problem in the sidechain.
The 6ES8/7ES8 supply seems to be almost exhausted everywhere. I think I'll be directing my neck of the research into using non remote cutoff tubes in these type of compressors, since soon we won't be able to find anymore of the famous stuff.
analag
analag
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