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SUPPORT FORUMS FOR ZKITS >> ZSP1 Support forum >> zsp1 completed but have a problem
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Message started by Hasafraker on 07/26/10 at 13:21:01

Title: zsp1 completed but have a problem
Post by Hasafraker on 07/26/10 at 13:21:01

I completed my zsp1 last night, however, when it's all connected I have no volume control. I was using my pc as a source, into the zsp1, into a no-name old EL84 console refugee that I use in the basement.

At 0 volume I could control the volume from my pc and that's it, if I turn the volume up the sound distorts, the more I turn it the worse it gets. If I return it back to 0, I can crank my pc all the way up and it sounds fine, but if I touch the volume control at all, the sound goes to crap. :(

The best I can do for pictures is a link to my flickr account, you can see 3 views, my power supply section, the preamp section and one of the whole thing. http://www.flickr.com/photos/28861421@N02/

Any help will be greatly appreciated

Paul

Title: Re: zsp1 completed but have a problem
Post by Hasafraker on 07/26/10 at 13:25:40

after reading through the posts in here, a wild guess tells me that chopchip might actually be suffering the same issue I am. If your source doesn't have a volume control I could see from what I have vs. what you have that you might just get low volume and then distortion the more you turn it up.

I'm going to trace out the circuit tonight if I have time and confirm all resistor values etc. I measured every single one of them before assembly so I'm pretty sure they're all correct but who knows. Something is definitely not right.

Title: Re: zsp1 completed but have a problem
Post by Hasafraker on 07/26/10 at 22:55:21

ok it was pointed out to me that the volume pot needs grounded, each side so a lead from the lug that connects to pins 3 and 8 for each channel to the input ground tab, viola, volume control works!

Now I have wicked 60hz hum... not a tune I like much >< It seems to be pretty consistent no matter what volume level I have it at, if I lift the needle on my turntable and turn the volume all the way up at the very top it gets a little more intense but not much. It's VERY noticeable at 8 feet at normal - low volume. I will have to track this down.

It does sound pretty good tho.

Title: Re: zsp1 completed but have a problem
Post by Steve Deckert on 07/27/10 at 04:08:40

Looking at your photo of the entire unit, I noticed that you have another problem besides the volume pot not being grounded.

At the bottom of the picture the 8 terminal strip with the ground wire threaded through the eyelets... The last one on the right must be soldered so that the ground is connected to aluminum plate. You have a wire touching it, but no solder.

Steve

Title: Re: zsp1 completed but have a problem
Post by Hasafraker on 07/27/10 at 10:54:46

Steve,

Yeah I noticed that too when I put the ground wires on the volume pot and soldered every tab to the wire so that is also corrected but the hum is still there.

Title: Re: zsp1 completed but have a problem
Post by dank on 07/27/10 at 14:37:27

Paul

The 60hz hum that you are describing now just might be a Zkit1 thing and not a ZSP1 problem. I'd take the ZSP1 out of the system for a quick check before spending hours looking for a problem in the wrong box (been there, done that).

Dan

Title: Re: zsp1 completed but have a problem
Post by Hasafraker on 07/27/10 at 15:12:37

the Zkit1/SE84DIY amp is upstairs in my listening room and not connected to the ZSP1, that is the system it will eventually find it's way into.

I connected an mp3 player directly to the zsp1, and output to an EL84 based amp in the basement which produced the hum. I took it upstairs to my vinyl system which is 100% silent and swapped out my 5687 preamp for the zsp1 and it produces the hum in this system too.

Title: Re: zsp1 completed but have a problem
Post by Hasafraker on 07/28/10 at 10:58:01

well I checked my solder joints, hit a few again just to be sure, I've traced the circuit out a dozen times and I just don't know what I'm looking for.

The hum is constant after the filter caps are fully charge the hum is in full effect, doesn't matter if the volume is changed the hum stays the same.

Just to see if there was a change I clipped the center tap for the 6.3v heaters and the hum tripled and got real raspy so I put it back.

My plate is only painted on one side, the underside is bare aluminum so it's not like something isn't making good contact to ground.

Title: Re: zsp1 completed but have a problem
Post by Hasafraker on 07/29/10 at 01:41:20

well not one to sit on my ass and let a solution come to me I did a ton of reading today on hum resolution, so when I got home I tried a few things, the last of which was to flip the leads on the IEC socket where the AC comes in, I must have had them reversed because that's fixed the hum completely. I need to take the preamp upstairs and connect it to my vinyl rig again and see how it does compared to my 5687 preamp.

I'm sitting here listening for the first time and it sounds fantastic. It would seem that the schematic just shows black wire and black wire for the AC into the trans. The black lead with the white stripe (for me) goes to the L post on the IEC socket.

Title: Re: zsp1 completed but have a problem
Post by Hasafraker on 07/29/10 at 02:06:50

bah spoke too soon...

Ok, now instead of really loud hum it's just mildly annoying hum :P

observations:

if I turn the volume on the amp nearly completely down and then use the volume on the zsp1 it's very quiet but in order to reach listenable levels I have to have the amp at about 1.5 on the dial so there is a tad bit of hum.

If I pull the Left output to the amp, hum is totally resolved, dead silent with just the Right channel. If I pull just the Right, hum actually gets minimally worse.

If I turn the zsp1 off, it sounds perfect as the caps drain which lasts almost 45 seconds, during this time, no hum at all.

If I have the amp volume at 3 the hum is very audible, adjusting the volume on the zsp1 has no affect on the volume of the hum.

I'm going to try building another set of interconnects, I'll try them between the amp and the zsp1 since disconnecting either input has no effect on the hum.

oh well... the battle continues!

Title: Re: zsp1 completed but have a problem
Post by Hasafraker on 07/31/10 at 02:08:38

got it.

Dead silent now.

I removed the original ground return to the IEC socket and installed a new ground wire.

I then removed both output jacks, using one of my step drill bits by hand I drilled out one more step and installed the back plate nylon washer for the output jacks isolating them from the plate. I reinstalled the jacks and checked, neither is grounded now. I then ran a wire from the left ground tab to the right ground tab and then to one of the unused ground tabs in the middle of the plate.

Even downstairs I could tell it was quieter now. I took it upstairs and connected it to my vinyl rig... dead silent. Turn the volume on the amp to full, no hum like before, nothing at all in fact... turned the volume on the zsp1 all the way up, with both at full volume I hear what sounds like slow air leaking out of a tire or something but ZERO hum! I put my ear up to the speaker and at this distance I can hear a slight 60hz hum but it's virtually inaudible any further away than that.

returned volume controls on both to normal levels, dropped the needle on some Miles Davis, Coltrane, Sinatra and now listening to Scheherazade... gawdamn this thing sounds great! Even my wife commented on how clear it sounds.

I will post a link to the finished preamp once I get a box built for it. 8-)

Title: Re: zsp1 completed but have a problem
Post by Hasafraker on 08/02/10 at 01:13:13

For anyone who cares to see, I added some finished shots to my Flickr account tonight. I built a case out of oak, it's not bad, but it's nothing to write home about. My woodworking skills are not as good I'd like but there ya go.

http://www.flickr.com/photos/28861421@N02/

Title: Re: zsp1 completed but have a problem
Post by Steve Deckert on 08/02/10 at 03:11:28

Congratulations! It looks great!