the Poor Man 660 support thread

[cannikin]

[quote author="emrr"]
Cannikin; DIY Daven's. I have some 12 position units like that which have an extra lug per position you can strap for MBB, or leave open for BBM. You need massive real estate to use them. Those are mighty high in price, I must say. You sometimes find them on ebay for 1/10th that price. But if you must have the best, there they are.[/quote]

I hear ya bro, couldn't afford them anyway but you know I love obnoxiously HUGE chassis :grin:

Question for you: are you planning to put a Pot on the attenuator to "fine tune" the levels? like they do with the attenuators on UA175 units. what do they call the pot "VERNIER" or something?

might be a great feature for people using only a 12 step rotary.

 

[cannikin]

Guys - I have never built a step attenuator before usually just buy them from goldpoint -- in theory looks cheezy easy but expect some simple/dumb questions :grin: Of coarse any i-net docs you can point me to would be great.

you've been warned, excited to learn.
:razz:

 

[emrr]

The Shallco 45 position attenuators at MPAudio come in at $139; same family, more steps, relatively comparable price for new. Just as big, I think.

[quote author="cannikin"]
Question for you: are you planning to put a Pot on the attenuator to "fine tune" the levels? like they do with the attenuators on UA175 units. what do they call the pot "VERNIER" or something?

might be a great feature for people using only a 12 step rotary.[/quote]

I don't see a way to do that here (that makes any sense). That's an entirely different approach. You'd probably be better off building a NewYorkDave style dual knob attenuator to use on the primary sides.

The existing method on the secondary keeps the level in the input iron consistent regardless of setting, and reflects a higher 1800 ohm Z back to the source(s).

If you went with a primary side arrangement you'd probably want to stick with 600 ohm input attenuators, meaning lower 600 ohm load on input source(s), and the level in the input iron would vary with setting. You'd have to work out optimal secondary load resistances. Only real benefit is you could use existing Daven 600 ohm ladders, which (at this junction) aren't terribly expensive. BUT, ladders will automatically kill 6 dB of input level, unless you add ANOTHER switch to bypass them at the top of the throw. Unless you already have some magically expensive Daven 600 ohm Ts. Or wire up the NYDave dual knob H pads.

You could really build big by finding two Daven 600 ohm decade attenuator panels, and incorporate them. But they probably now cost a fortune too. 1/10th dB, 1 dB, and 10 dB steps on three knobs.

I will play with some dual pots at the threshold position for the purpose of finding normal operating levels, 'sweet spot', etc. May leave them in if satisfied with performance, may wire up stepped version. Won't know until.

I was thinking of pot for time constant, but since I'm building stereo, am considering linear 12 position switches for matching. I've used 12 step on Gates SA-39's for attack and release, and they give plenty of range.

 

[mitsos]

[quote author="nielsk"]Mitsos, This can work.... on the second tranny (of the 120/240 to 6 volt hooked up to the 6 to 120/240 volt ala g9) only hook up one 6 v lead set to the 1st tranny, and take the second 6 volt lead set to a voltage tripler to get the -17 volts....[/quote]Wow, hadn't thought of that. Only thought of primary to secondary currents. hmm. My only issue with this is that I'm gonna have to build a V multiplier which will give me -17DC and then I have to skip part of the PSU that is supposed to rectify/regulate the -17V.. If the extra winding would work, then I can just go into the PSU board with AC. Maybe this will be clearer when I see the PCB..

[quote author="nielsk"]the big question is how much current is needed at the 245/136 legs and the -17 leg (?) one can typically use a pretty small transformer for the second unit[/quote]
From Should I thread:
[quote author="analag"]requires 250V @ 80mA, 15V @20mA and 6.3V @3A[/quote] He is referring to 1 channel.

And here is a stupid question... Are there no relays that work with neg DC?

 

[cannikin]

mitsos - stop killing yourself buddy, as NYD always said "just get the right transformer for the job"

Doug - you are one super knowledgeable guy... great analysis - rock on

 

[[silent:arts]]

[quote author="emrr"]I will play with some dual pots at the threshold position for the purpose of finding normal operating levels, 'sweet spot', etc. May leave them in if satisfied with performance, may wire up stepped version. Won't know until.[/quote]
Doug, now, this is the correct approach in DIY :thumb:

 

[kazper]

Probably covered before, min wattage value for resistors 1/4W or 1/2W?

I'm sure that if you can match the 1N4148's that bridge in the side chain it would help the compressor, similar to the needs in the 2254 and 33609.

 

[flintan]

Says half watt in the parts list, and some 2W..

 

[[silent:arts]]

half watt is for security, 1/4 watt should work - except for the 2W and 50W resistors ...

 

[kazper]

Flintan Thanks,

working for 24.5 hours straight, getting 3 hours of sleep and driving 3 hours home don't help keep the mind straight.

 

[no-fi]

I have a question I haven't seen mentioned in here (though it IS a big thread.... but I doubt it would have been brought up before any schematics arrived on anyone's doorstep)

the 10uF wimas - do they really need to be 250V?

I'm no expert on this design (or tube circuits in general) but spent a few hours going through the schematic and trying to understand what's going on yesterday, and my first thought is lower voltage part would be fine (if any Wimas in there need it, the 220nF will have the highest voltage across it, won't it?) I don't see anywhere those 10uF caps could get a significantly higher voltage across them than the 220nF part, and it'd be nice to trade voltage for precision... and, you know...... to save a bunch of $$ on the build and avoid having to order any more things via international post... (I've run up AU$100-odd already, in just international shipping of transformers & tubes & PCBs)

Of course if it really is 250V they see, or the large parts give some other characteristic that we need, I'm happy to go and get them! just want to be sure I need them, is all.



also - while i'm here - if I wanted to go and play with making the sidechain circuit more like the 670, would I be just bridging R18 & C4 and hooking the switch & RC combinations from the 670 circuit to the conector for RV7? or will I need to tweak these R&C values and the other parts on the PCB to work more like the original does?



also also - if I wanted to just leave out input level control for now (most stuff I would drive into the PoorMan has level control already!) then it just becomes two 1/4 watt 15k resistors under the "gain" connector on the PCB, and wire the input secondary straight to the board, right?


thanks!

PS, please let me know if this kind of discussion isn't appropriate (or isn't appropriate in this thread) and I can delete it out of here...

 

[[silent:arts]]

[quote author="no-fi"]the 10uF wimas - do they really need to be 250V?[/quote]
http://www.groupdiy.com/index.php?topic=28274&postdays=0&postorder=asc&start=327

 

[[silent:arts]]

[quote author="no-fi"]also - while i'm here - if I wanted to go and play with making the sidechain circuit more like the 670, would I be just bridging R18 & C4 and hooking the switch & RC combinations from the 670 circuit to the conector for RV7? or will I need to tweak these R&C values and the other parts on the PCB to work more like the original does?[/quote]
I don't understand why you people always want to do modifications before trying the "stock" circuit.
[quote author="no-fi"]also also - if I wanted to just leave out input level control for now (most stuff I would drive into the PoorMan has level control already!) then it just becomes two 1/4 watt 15k resistors under the "gain" connector on the PCB, and wire the input secondary straight to the board, right?[/quote]
a 2 x 6 rotary switch with 3dB steps isn't expensive and would give you more control.

 

[khstudio]

I'm sorry if I missed it but how should they be connected for "Stereo Link"?
... or is it even possible?

there's no wiring guide yet, so I'm not sure about adding this to my faceplate.

 

[[silent:arts]]

[quote author="khstudio"]I'm sorry if I missed it but how should they be connected for "Stereo Link"?[/quote]
for stereo you connect the control signal together, which is pin2 of PL1 in the schematic (the middle of the input gain control)

 

[no-fi]

Oh dear... I thought I'd checked that page already. sorry!


Anyway - in that case, I'll see what I can find around here in the range of 10uF parts... otherwise off to TAW, and more international postage.


As for the reason I'm asking about switched sidechain circuit components already.... well, I've already done $100 in shipping, so if I knew I might want a bunch of 4 & 8 uF caps in the future, and they had to be high voltage (ie, I also had to order the 10uF Wimas) well, I could order them all at once...



Oh, and that's a cool idea on the 6 position input gain switch. I was thinking way too much in an "all or nothing" mode - that will be really cheap and fast to do, and definitely better than nothing!

thanks!
:guinness: :guinness: :guinness: :guinness: :guinness: :guinness: :guinness: :guinness: :guinness: :guinness:

 

[emrr]

[quote author="[silent:arts]"][quote author="khstudio"]I'm sorry if I missed it but how should they be connected for "Stereo Link"?[/quote]
for stereo you connect the control signal together, which is pin2 of PL1 in the schematic (the middle of the input gain control)[/quote]


Probably needs diode isolation to keep time constants from shifting with parallel connection.

 

[[silent:arts]]

[quote author="emrr"]Probably needs diode isolation to keep time constants from shifting with parallel connection.[/quote]
does an original 670 have one ? :wink:

 

[Gachet]

hello

Treshold question:

I was planning to build the same attenuator for both treshold and input(12 steps log).But after reading this topic I think i will go for a 3K fixed resistor (lowest treshold I suppose), combined with a 12 steps 1K per steps.


Is that a good idea ?

Thanks

 

[emrr]

[quote author="[silent:arts]"][quote author="emrr"]Probably needs diode isolation to keep time constants from shifting with parallel connection.[/quote]
does an original 670 have one ? :wink:[/quote]

No, but every other stereo linked vari-mu does, or it ignores the shift. There is a good amount of commentary about this in other vari-mu threads.