BentMike

I just discovered that the Crown D75A is no more, news to me anyway. Crown is selling the CSA 2120 (under the JBL Commercial name). It is a half rack 1U form, and the transformer is a second like sized box. Has anyone looked at this amp? Is this new amp anything like the old?

I really want to thank you guys. The results are actually fantastic. I tried the shorting the jacks business and had to put the lifted ground back in place, still not right, but one jack was worse and it traveled when I switched speakers. You kept asking me about the cables, so I decided to pay really close attention to them (I was being casual). I found the best coax in my closet - I have bunch of odd stuff I pick up at university surplus, and redid them using this. I check resistance as went along to make sure the jacks weren't breaking down or something, no problems. I will never be so casual about cable making again. I am so glad - these things sound great. They are the best sounding small speakers I have ever heard. 50W high, 50W low, times two. No amps and pre's to mess with - so simple. I like a lot of music and so far they cover it all from bass heavy, weird electric sounds techno, to Russian men's choir in a cathedral, nasty shredding, and sweet Wailin' Jennys. It is all good, and very powerful. They are meant to be placed about a meter away, but they are wasted if that is all you do with them. I am amazed. There is something to this cabinetry, the baffle is 40mm thick, the rest 19mm. Very dense. I may have to try some Klipsch-ish stuff, or build some horns...seems like you smart guys know what you are talking about. 'nuf said, Thanks so much for the help. BentMike

So then this is how the AC gets coupled to the DC... I would worry about this in laying out conductors for data (also inductive coupling) acquisition, but I haven't got much understanding of audio. BM

To me that looks like good isolation - how do these become a problem? You are talking to an ME not an EE, so I may be quite dense and uninformed. I don't get why the Y1's are there though. The few PS I have put together don't have caps like that. BM

Oh OK, 1:1 transformer. I use them on power with Faraday shield when necessary. Edcor doesn't say what it does. Hypothesize with me, what about the PC makes this happen where the music player does not cause it? I'd still expect the common to be common to both channels. I have a problem where if my USB-USD-DAQ touches my laptop or my fingers or...it stops working until I disable it and enable it. I have the whole mess wrapped in a rubber sheet so I don't trip it out (I move it around a lot). I find the whole mess to be finicky as hell. I have an unfounded impression that PCs are not well suited for music this way. Probably it comes from my being uncontrollably cheap and insist on trying out the lower cost stuff. Someone has to do it. Thanks, BM

The Edcor buffer, why is this pertinent? Or, how do we know it is pertinent? No to be impertinent. I would want to have a better understanding before plunking down $60.

The speakers are at work, and I am not there this weekend. I'll get back later after I can try some of the suggestions. To reiterate - there is no noise at all, and no hum, no drop outs when I use a battery powered music player. The problem is when I connect to a PC. The PC requires a 3.5mm jack, and there is 2 signals and a common. The same common and one signal goes eacf the active speakers, and the connection is a 1/4" headphone jack, the signal is wired to the tip contact. I haven't been able to locate a schematic of the amps. The owners manual says very little that helps with troubleshooting, I know the output is by MOSFET, that is about all. The chips look like an LM3886 or similar. Spec sheet. Input 32 kW balanced on combined XLR/jack Sensitivity 0.775 Vrms (0 dBu) Crossover frequency 3000 Hz Amplifier output power LF 50 W rms (4 W) HF 50 W rms (4 W) Output noise - 80 dBV Power supply Fixed mains voltagev IEC inlet with detachable power cord Power consumption 10 to 160 VA Drive unit Tannoy shielded 6.5 bass driver Tannoy shielded 1 soft dome tweeter Low frequency design Optimised bass-reflex loaded, in 12 litres Cabinet construction 40 mm MDF front baffle, 16 mm high density particle board. Cabinet finish Azure blue satin finish front Grey suedette vinyl sides and back Cabinet dimensions (HxWxD) 340 mm x 210 mm x 260 mm Cabinet weight 8.5 kg Shipping dimensions (HxWxD) 440 mm x 620 mm x 290 mm Shipping weight 18.5 kg NOTES : (1) +/- 3 dB , measured at 1m in an anechoic chamber. (2) Peak SPL at mix position for 1 pair driven

Yes, the model is called Reveal Active, there is a Reveal Passive using the same cabinet, but with no amplifiers. Yes, there is a receptacle package - exactly as on a Crown 75A that has both a 1/4" headphone jack OR a balanced jack - XLR? it is called? I am using 1/4" jacks, the PC com is on the shield, the signals are in the core. The passive model obviously doesn't have to go that far. FWIW, these are the older model that is charcoal gray and teal blue, dark turquoise, whatever it is. Each speaker has two amps one for each driver (or at least I can see two chips that look like SS amp chips clamped up against a heat sink. There is a nice little toroidal transformer makien ±28VCD. Some pretty small 4300mF caps and little inline bridge package. it is a nice clean package all around. I like them. Kind of handsome, not big. And seemingly great with a music player - though it may predate such things. Something like this would make a very nice DIY to copy. I tried grounding the chassis while running off of a music player - no signal drop out. SO it happens when running off of the PC or off of my Toshiba pre. This is diverging: I normally run a Crown 75A off the Toshiba - and with humming noise. I tried this setup getting power from an isolation transformer (Faraday shielded) with a dedicated ground 10 feet in wet soil with 00 wire brazed to it. (I have been having other noise trouble.) I have a rats nest of wires. Could be some coupling - hard to solve that. BM

120VAC--> power stripA-->PC integral sound card-3.5mm recept on back of PC-->3.5mm 2ch jack-->1 com & 2 sig --split --> split (cont'd)--> 2, each com and sig--> each, 1/4in jack --> each, Tannoy powered speaker input receptacle 120VAC--> power stripA--> power stripB-->L Tannoy powered speaker IEC Receptacle 120VAC--> power stripA--> power stripB-->R Tannoy powered speaker IEC Receptacle,w/gnd to chassis lifted In theory, they all have the same power and ground coming in.

Sorry, that is ruled out now. Truth is, I get hums out of all sorts of stuff that is plugged in (including my regular preamp to Crown 75A to passive speaks), but in this case the signal gets completely suppressed if I don't lift the ground. I am unfamiliar with bi amping, and powered speakers, so it is perplexing.

These are equivalent to what I soldered up. So I am not sure why they will help. Like I said, it works great with a not connected to AC music player. An edit: My wiring is equivalent to the little one piece 3.5mm stereo to 2 RCA adapter. I don't know what those big honking 3 pins and a shield jobbies are doing. But, I still have to bring the com and signal from the PC to each of the speaks. Is there some sort of magic in the extra stuff that buffers the com?

I have not, yet. This is a found project. Going cheap for now. I am pretty sure it a ground loop since I have to lift a ground to get any function, but I am willing to hear other opinions. I would like to actually understand whatever solves it...not always achievable with noise and hums. When I run it on a battery powered music player the speaks are quiet as can be. I should reattach the ground while running off the Stone. But gotta work right now. Thanks for your thoughts. BM

Please bear with this non-Klipsch query...I trust you all more than most. I happened upon some Tannoy Reveal Active nearfield monitors. Awesome little cabinets. They will be nice of at one end of the lab. They are pretty pleasant to me except... Just to try them out I soldered up a splitter to a PC audio output cord (that is the easiest and most ready source of tunes here) - the shield on each side goes to the ground of each 1/4" jack. (If I swap shield and signal - no sound.) I plug one in and it works, the second does not. So I start messing around and pull the power cord (instead of switching) I get a blurt of music. Tells me the amps CAN work, and that it is probably not the PC sound card -as it sounds like, when lifting the ground, it lets the caps run the amp for just a moment. After some messing around I realized I got music when I lifted the ground on the back of the IEC socket. But I get a hum now that is qui te'annoying. I moves to the other speaker if I switch the cord. These speakers each have their own small ±28V PS and I think they are bi amp'ed - looks like one SS amp for each driver - no crossover seen. I put a meter (set to Amps) between the speaker (with the lifted ground) back plate and a conduit (grounded)..sound drops right off, but there almost nothing flowing - 6microA I saw. Voltage as about .02 AC, and .02 DC. PC and both speakers are plugged into the ame power strip. About all else I can do is smell it and look around. Nothing seems burnt. Is it just not possible to use a PC with tow active speakers for some reason? I haven't ferreted out any schematics yet. I am not very productive with such things, though I have a nice scope I can bring into play. Help? BentMike

Figured it out. I am red-faced to be sure. It isn't the amp, it is the speaker. You guys wisely challenged me early on. I should have paid closer attention. When I first checked out whether the distortion moved around when I changed speaker wires L to R, I wasn't careful. The problem only happens after the speaker is on for a few minutes - it has to heat up. I switched the "good L channel" to the bad R speaker and I heard no distortion. Then I swapped them back, "bad R channel" to bad R speaker and after some time elapsed there it was "back" on the R side. I was assuming the R speaker was OK and the amp messed up, rather than thinking about how to validly check it. What is wrong is an axial misalignment of the voice coil and the pole pieces or magnet. I can see a little kink in the surround, and I can feel it rub if I push just so on it. I should have been more wary of this, but I was too proud of a repair I did to the driver. When I bought the speaker the driver cam apart during shipping. I built a fixture to get it back together and it seemed good for a while. I was pretty puffed up about figuring how to get the driver back together and working after finding the magnet and pole piece loose in the cabinet. No way the distortion could have been from that speaker. I can probably fix it right, but it aint't easy so I bought a couple on eBay for not much. Thanks for working with me, I learned a lot. BentMike

The service manual shows a feedback loop going to an error amp. Balanced Input to Error Amp to Signal Translator to Last Voltage Amp to Output Stage. Feedback is from the Output Stage to the Error Amp. Error implies correcting for the undesired signal. But how successful is it? Anything it doesn't scrub is degraded signal out. (I am really BSing now).

. djk, Thanks for confirming my worries. I will stay away from the trim pots. I didn't yet know what they were for, and hands off seemed prudent. Don RIchard, Thanks for the plan. Hopefully, it won't come to all that. BM

djk, SN 028479 I have a service manual with the schematic # J0650-2 rev B 1996. I don't know how to tell what serial number it applies to. I will have to make a cord to try the jack output. IOC light is not on, but I should double check when I can play it out loud. I am paranoid about messing with the trim pots. I should be able to get them close to where they are now if I mark them, but exact is unlikely. Is my fear smart or just fearful? I will have to get back later. BM

Speakerfritz, Looking at the schematic, it is probably a single power supply - maybe the two windings are to get ±31VDC. It isn't perfectly clear because there are many different power supplies (for overseas and domestic use) are shown on a second page - and I haven't learned my way around it yet.. =============== I think this has been modded. The power caps in the schematic are shown as 5000µF 35V, mine are 10000µF 40V, but they have the Crown logo on them and a sticker about a work order. A factory mod? Or a revision difference between my schematic and the amp.

"you can't do a logic model that will lead to a 100% accurate 1st attempt problem detection and validation. meaning......list a dozen or so assumtions then open the amp and go to a particular device and establish that that devices is faulty. You need to abandon the logic model mapping and determine what approach you want to use to do a physical analysis. your problem sounds like inconsistency in the noise floor." Not trying for the perfect solution, just collecting ideas. But I like have pseudo plan before resorting to pure trial and error. I have a pdf of the service manual. Also the schematic, but Crown asked me not make these public as in on a web page for downloading or sale (still in production) . Clearly they are willing to share if you ask nice. Not quite sure how to honor their request. I guess I can email directly. The block diagram implies two power supplies.

Russ, All I have is a lubricated cleaner. Is that a bad idea for the time pots? Also, How do I get the pots back right after exercising them? That is why I hesitated to screw with them. Mike

Speakerfritz, The Crown D series are two separate amps that can be placed in series or used as two channels. That is about all I know about it. Looking at the transformer it is interesting - the laminations make a figure 8 and there are two completely separate windings. That is new to me, but it looks like they made two separate power supplies; also there are two big honking power caps. You are saying the power supply(s) is(are) before the amplification so maybe it is making noise that never gets amplified? But it is related to a certain frequency of content, that is in the amplifier section isn't it?

I cant help it. If I use headphones there is no distortion. If I switch the speaker wires - move the channel 2 wires to the other speaker - the distortion goes with it, and the channel 1 goodness switches to the previously ugly speaker. Therefore it isn't the speakers, it has to be the channel 2 amp. I assumed there was a separate amp for the headphones like in my preamp. But maybe this is a clue. Clearly the whole 45 Watts isn't going to the headphones. Either the headphones take off before the full power goes to the speakers or the full output is attenuated to save the head phones. The former seem more sensible. Or there IS actually a separate headphone section like my original assumption. The other odd thing is the distortion is not related to the volume control. It is just there and if I crank it up the distortion doesn't go up with it, I only hear it when the content drops in volume and the distortion is no longer obscured.

Just in case I wasn't explaining well at first... This is NOT a buzz or hum like a ground loop. I am going to stop using those words so there is no confusion even though it has a buzzy quality. This distortion is only present in response to a particular bit of frequency content on the channel 2 and only channel 2. There is no distortion coming from the headphone section. Just an ignorant theoretical question: if the distortion is only on one channel, and it is clearly related to the audio signal (there is no, or very little distortion if the content is very low or in the upper registers) - isn't it safe to assume it is not a problem in the power supply section? Thanks for helping. BM

Problem: A low volume distorted sound in the right channel (not nearly low enough). Eliminated speakers as source of distortion. Eliminated PreAmp as source of distortion. Headphone output sounds great.. Jacks not source of distortion. Wires OK. Amp is quiet with no signal (previous 60Hz hum is better with attention to grounding). Buzz is associated with tones in the mid range - a clean tone from a woman high in the octave above middle C really sets it off. Makes an almost bell-like buzz under the right excitation. Turning up the volume drowns it out - it does not appear to increase with increasing volume. Of course most songs are low volume at least somewhere, often somewhere that is normally very beautiful sounding.[] What I have tried: Contact cleaner everywhere sensible. Which is to say almost nowhere on a D75A. What an amazingly clean an well put together amp! I don't see anything on the boards that looks bad, no bad smells, Two wires off the transformer look like they got quite hot at some time, no shorts and ruined insulation. No plump caps Cleaned the two 3 pin connectors (signal out to power amps? Got a nice buzzy tone going and tapped things just to see. No changes to report. Plan A: See if the buzz is there when amp is cold started. Probably not any better cold, but seems like something worth knowing. Because I was going to anyway - recap the amp except the power supply caps are as big a cap as you can get in there. Get out the schematic and pretend I know enough to get an idea from, it and see if anything dawns on me. Maybe clean the header connectors between the big board and the small one with the power transistors on it. Contact cleaner on the trim pots, maybe articulate them - I am afraid to mess with them on GP. Thanks if you got this far, my present to you is listen to Sarah Jarosz. A wonderful young singer, songwriter, and instrumentalist (mandolin, clawhammer banjo, guitar). She has a beautiful voice, spot on, clear as a bell, and clever with chord changes. Write a nice song, not naive. Can't wait to see how she matures. At 21 she has a lot of room to grow. BentMike

We've Made Improvements to Cloud Player When you sign into the updated Cloud Player, we'll upgrade your music to high-quality 256 Kbps audio at no additional charge. It worked. Of course they don't upgrade tracks that aren't available in 256kbps. So I only got a few. I have a FiiO DAQ and Musiland Monitor USD 01 (experimenting with the price leaders). I could definitely hear the difference. BentMike