mike stehr Posted December 17, 2003 Author Share Posted December 17, 2003 Well, the attenuator is really supposed to be for my tube pre-amp project. This is just kind of a quick fix for now. The attenuator is pretty bulky, it wouldn't fit in any of the vintage amplifier chassis's I have. Erik, Yes, the caps are the outputs. Is that a bad thing? Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted December 17, 2003 Share Posted December 17, 2003 Hi, Mike: I just surprised you have them there. Was this from a schematic you found some place? Try this just for fun! connect (just tack solder)a lead to the output of the pot that is long enough to reach to the output jack's center pins. Now, disconnect the wire that connects to the OUTPUT side of the caps (just heat with your iron and pull out!). Now connect the other end of the new lead you attached to the output on the pot directly to the center pins. In other words, you're using a wire to make the output connection rather than through the capacitor, first. This would take ten minutes to do! I could see if this was a very small value DC blocking capacitor, but it looks bigger than that to me. It also looks possibly like an electrolytic cap, but I can't quite tell. What value is the capacitor? Honestly, try going from the output of the pot to the pin with just a straight wire, you could very well hear things really brighten up, soundwise -- possibly significantly. Since you already have a high output impedance on the output of the control (say, if the control is 100k, the output impedance might be something 50k-60k. That's just one of the drawbacks of this kind of passive control. There are other types that are transformer coupled that have a very high input impedance (that's good) and an extremely low output impedance. The problem with high output impedance on a passive, is that it can have trouble driving the capacitance of the interconnect -- especially if the IC is more than a few feet. So, adding extra capacitance there might not be the best thing, but I'm just speaking in theory. Give it a go and see what happens! Passives can be great, and I was using one up until the point when we got the K-horns. The amps are too far away from sources to use very well with a passive, which just doesn't have the drive. Man....sorry for blabbing on like this! Take that cap out and see what happens (of course when you've got the time!). I'm really curious to see what happens. I love the old wood box, the logo, the intelligent resourcefulness! Quote Link to comment Share on other sites More sharing options...
mike stehr Posted December 17, 2003 Author Share Posted December 17, 2003 ---------------- On 12/17/2003 7:18:00 PM Erik Mandaville wrote: Hi, Mike: I just surprised you have them there. Was this from a schematic you found some place? >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> I hooked it up and had popping between detents on the left side without the coupling caps. That isn't good, it's a anomalie with the attenuator and may require to tear it apart and try to fix the problem. It might not even help, I dunno... I browsed around and seen the Goldpoint stepped attenuator site. They mention DC offset from switching and to combat it with a cap or resistor on the outputs. >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> Try this just for fun! connect (just tack solder)a lead to the output of the pot that is long enough to reach to the output jack's center pins. Now, disconnect the wire that connects to the OUTPUT side of the caps (just heat with your iron and pull out!). Now connect the other end of the new lead you attached to the output on the pot directly to the center pins. In other words, you're using a wire to make the output connection rather than through the capacitor, first. This would take ten minutes to do! >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> I'll try again, but I'm pretty sure I'll end up with cannon shots through the left side >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> I could see if this was a very small value DC blocking capacitor, but it looks bigger than that to me. It also looks possibly like an electrolytic cap, but I can't quite tell. What value is the capacitor? >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> I started off with a 2 mic cap on the outputs, and moved down in value. I'm using 0.1 mic 1000 volt Russian military caps, a little overkill, but the offset was pissing me off! I need to figure out a break point and still keep the noise to a minimum. >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> Honestly, try going from the output of the pot to the pin with just a straight wire, you could very well hear things really brighten up, soundwise -- possibly significantly. >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> I'm with you there, but it's switching noise..... You don't mind if I float you Email with a few questions? Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted December 17, 2003 Share Posted December 17, 2003 Yes, that's right -- I remember now. Those switching explosions can be bad. So they are snubbing capacitors, ok, I've got it. I want to go watch Siendfeld with Marie, and will look at this again later, Mike. Sure, email away! Quote Link to comment Share on other sites More sharing options...
mike stehr Posted December 17, 2003 Author Share Posted December 17, 2003 No rush. Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted December 17, 2003 Share Posted December 17, 2003 You might try a small value capacitor (say .01mf) between the wiper and ground, rather than wiper and output jack center pin. Or, another way to do it would be to take out the larger caps, and install the plain wire to the output the way you first had it. Then, install the capacitor (voltage rating doesn't need to be very high)between the output jack center pin and the ground tab of the jack. I think I've seen this done somewhere, and actually think I did it on my Moondogs, once! I've done so many different things on those I can't remember them all now! Quote Link to comment Share on other sites More sharing options...
Tom Mobley Posted December 17, 2003 Share Posted December 17, 2003 Erik said "I love the old wood box, the logo, the intelligent resourcefulness!" me too. anybody can throw money around, but making something out of nothing or not very much is totally cool. I thought I was doing good buying a cheap Eico on ebay and fixing it up and here you're into the single digits. Tom Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted December 18, 2003 Share Posted December 18, 2003 Mike. Just quickly... I think you probably have the best arrangement for 'pop management right now. Just use as small a capacitor as possible to do the trick wo you don't compromise your high frquency response. If things sound good and not dulled or rolled off, just use it and enjoy! The best solution would of course been to build the control from a better make-befor-break sort of swtich, which probably would have really improved things. But you still have a great qaulity control with excellent resistors! Quote Link to comment Share on other sites More sharing options...
mike stehr Posted December 18, 2003 Author Share Posted December 18, 2003 ---------------- On 12/18/2003 8:13:33 AM mdeneen wrote: Mike - Nice job there! As for the series caps, what is the input impedance of the amp you are driving? (What's the resistor to ground on the input tube grid?) >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> I thought they were 470K. I just looked, and the resistors to ground for the input tube grid are 1 Meg. >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> The cap, as wired, will set the LF response with the input resistor. If the input is 470K (likely), your LF point is 3Hz with a .1uf cap. Just right. If it is lower than 470K, like 220K, you may want to try a .22uF cap. (f3=1/2pi*r*c) >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> Ah! It's the same Formula as figuring LF break points between tubes.(Cap coupling between plate and grid.) I had thought about the Formula, but wasn't too sure. Being that it only figures the LF minus 3 decibel point. With the one Meg input resistor and 0.1 mic series output cap with the attenuator, I can't figure out if the -3db LF roll-off is at around 160 hertz, or around 1600 hertz. I think I'm getting more bass than that, It sounds like I'm getting below 160 hertz. I could have the math wrong as well. I think the capacitance value (well, the number I come up with) to use with 1 meg would be around 53, or something like that. (Decimal Damage! Argh!) I'm wondering if trying to shunt a cap from the output jacks + pins to ground pins would kill the switching noise, like Erik brought up? It would eliminate the caps in series with the outputs. Dunno the Formula there, I'd guess it's just trial and error. >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> I am assuming the wiper is on the AMP side, not the input side. What's the value of this attenuator? 100k? >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> Yes and yes. The Eico PP mono's and the Magnavox PP use 470k for input ground resistors. I'm good there I geuss. I thought and wanted to just run the damn attenuator straight, oh well. It still beats a carbon pot, IMO. I'll figure something out. >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> I love the cigar box, not to mention that Ferris Wheel in there! >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> I trying to train some Fleas to run the thing, but they keep hopping away! Quote Link to comment Share on other sites More sharing options...
sheltie dave Posted December 18, 2003 Share Posted December 18, 2003 Mike, is this the Sodexho Ultimate with Sweet Screams modification and Careless Whisper, Sorry, My Tounge Slipped a Groove Tunisian pine box? I think you won't be needing the Up a Creek passive linestage How does it sound? I'm bummed you aren't here in the Lou - we could have some fun on the roadtrip down to New Orleans to pick up the shorthorn! What are you going to do with the Carver? Heck, throw it on EBay with full description of your mods and how the transport is roughing you up. Some electrical genius will be happy to give you $400, and that will give you a running start to wrap up the 300B project Man, you'll be busy with Edmond sending you the other Eicos. That sounds like something Cyndi Lauper is singing. Catch ya later.. Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted December 18, 2003 Share Posted December 18, 2003 Hi, again Mike: I'm going to take apart the front end of the Horus amps this weekend for a complete overhaul. The existing coupling capacitors (.1mf Jensen PIO)will not be needed, and if you'd like to try them with your passive, email me your address, and I'll get them in the mail to you to try. If you like, them, I will accept an installment of, say, $50/mo. until they are paid-off -- say sometime in 2007. ...but seriously, let me know and I'll just give 'em to you. I think I also might have some good .22 mf in my parts bin, but they are aren't PIOs -- Hovlands or Kimbercaps, I think. What's in there right now? they almost look like non-polarized electrolytics. I've heard of those being used for this application, but it might be worth it to try something else. Just let me know, ok? Erik Hey, Do you have the schematic to your amp? Mark had a good idea in checking the input impedance and sensitivity. Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted December 19, 2003 Share Posted December 19, 2003 A request, Mark: Would it be possible for us to do some sort of mind-meld? Sheesh, you zoom around the math of all this with amazing ease and proficiency. Leo is the same way -- and it is his profession. Is that what the input impedance is on that amp? 1 meg? I have only found those on some fairly vintage schematics. Another thing he might try (just temporarily) is a variable resistor -- just a linear taper pot -- from grid to ground on the input. Maybe try a 500K pot and fine tune the output cap value on the passive/input impedance by ear -- and then replace with a fixed resistor. He could install a trimmer pot in the amp, or just use the control outboard and not mounted at all until the best resistance is achieved. I'm wondering if the circuitry downstream might like seeing the higher impedance, though....possibly try both 470K and 220K? ...what am I doing in here!? I need to get some work done! Quote Link to comment Share on other sites More sharing options...
Klipschfoot Posted December 19, 2003 Share Posted December 19, 2003 ---------------- I wish I could get rid of that logo, without having to sand the thing down to nothing. ---------------- Can't you just turn the lid over to hide the logo? You guys have too much time on your hands. I don't know how you do it. Great resourcefulness and ingenuity, Mike. Quote Link to comment Share on other sites More sharing options...
mobile homeless Posted December 19, 2003 Share Posted December 19, 2003 Klipschfoot, do you actually own some version of the Pass ALEPH series powering Klipsch Heritage? kh Quote Link to comment Share on other sites More sharing options...
Klipschfoot Posted December 19, 2003 Share Posted December 19, 2003 It's a PASsive search. I don't own one as yet. I have seen a few on eBay but I'm not ready to buy. I have read a lot of good things about these amps and, to be honest, I like the look. Quote Link to comment Share on other sites More sharing options...
mobile homeless Posted December 19, 2003 Share Posted December 19, 2003 The only real bargain ducat wise of that line is the used PASS ALEPH 3 which comes up on Audiogon in the $800 and change range occasionally. I still think lower power tubes would bring more reward at this price point (even vintage pentode options). I have heard that many that have tried the ALEPH 3 approach on horns missed some of the harmonic richness in the mids. btw, those amps are surprisingly large in person, quite the opposite of the little Wright Sound 3.5 Monos, which appear almost dainty when you see them; you can easily carry one in each hand! Mike, you should take up Steve's offer to try that Creek passive device with remote. IT would be a very interesting comparison for you to see how that version with normal pot compared to your passive home brew. I would give it a go if ole Steve is willing. kh Quote Link to comment Share on other sites More sharing options...
mike stehr Posted December 19, 2003 Author Share Posted December 19, 2003 Who in the wide world of sports is Steve? I think you mean Sheltie Dave. Dave seems to be happy with Creek Passive once he tried it. He said the Remote is nice option when he's got his hands full of Toddler. Yeah, when I rebuilt the little SE amp, I changed quite a bit of things in the circuit. Except the input resistors grid to ground. I didn't have much reason at the time. It worked well from the Carver CDP's volume control output, had good gain and sounds nice. Antique? Gee, make me feel old. The amp is the same age as me. 39 years doesn't constitute a antique. Or does it? Quote Link to comment Share on other sites More sharing options...
mobile homeless Posted December 19, 2003 Share Posted December 19, 2003 I meant Dave. Yep, ole DAve. I would try that Creek out to compare to see just now much different that Dale Stepped Attenuator makes. I have the Creek OBH-12 passive here as well. Dont use it much (on the EL-34 amp now). I dont like passives with SET amps but do ok with PP with good front ends. I was thinking of ole Alaska Steve. The loon with the Rega and the bike. I am trying to imagine Alaska right now. Send medicine. kh Quote Link to comment Share on other sites More sharing options...
mobile homeless Posted December 19, 2003 Share Posted December 19, 2003 Man, the streaming audio from these station is very good, Mike. When one gets weak, jump to the others. UNC and Duke stations excellent. Some DJs are better than others. Usually it's pretty esoteric stuff. Comuputer and tubes works! COMPELLING RADIO - STREAMING AUDIO kh ps- WGTB is down till Jan Quote Link to comment Share on other sites More sharing options...
Tom Mobley Posted December 19, 2003 Share Posted December 19, 2003 Kelly, that is cool. How do you think of this stuff? Tom Quote Link to comment Share on other sites More sharing options...
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