Forums - Uhhh Ohhh

Evo

Ex Member

Uhhh Ohhh
03/30/10 at 03:44:16

I have got my zkit1 all wired up now, swithced it on, everything OK, no explosions, all tubes lit up.........

......tried to test the voltage as recommended. I could not find voltages similar to those listed at points 'A' or 'B'. Points 'C' and 'D' seemed fine. My multimeter is an 'el cheapo' one which doesn't measure a broad range of resistances, so my plan is to borrow my friends and check that all the resistor values are correct.

I also wanted to check that I was measuring at the right points and then post the results to see if anyone has any ideas as to what I might ahve done wrong. For point 'C' I measured across the 150R resistor, for points 'D' across the small resistors at the bottom. What two points am I supposed to measure across for points 'A' and 'B? Across the capacitors or resistors? Which ones? I couldn't make it out from the diagram.

Any other help appreciated,

Waiting anxiously,

Matt

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dank Seasoned Member pair of dual 18 Imperials Posts: 420	Re: Uhhh Ohhh Reply #1 - 03/30/10 at 14:14:30 Matt What voltages are you reading at "A" and "B"? I'd measure either side of the 1k - 6 watt resistor and either side of the 6.8k - 2 watt resistor for 4 voltages total. That will tell if you have the right resistor in the right spot as well as what the power supply output is. Measure all voltages with respect to ground. Dan
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Evo

Ex Member

Re: Uhhh Ohhh
Reply #2 - 03/31/10 at 10:18:48

Thanks Dan. The 'A', 'B', 'C' and 'D' measuring points are given by Steve in the construction manual with the values of what they should be.

The thing I was missing was that I had to measure the voltage relative to ground. Feeling really stupid now - can you delete embarrassing threads? Wink

I have now done that and the voltages are as expected. The problem now is that when I try to use the amp there is no sound. The tubes are lit, I can hear some noise coming through the speakers which gets louder as the volume increases and the voltages are measured as expected. What do you think might be wrong? What are the options I need to explore?

Thanks,

Matt

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Alan H Ex Member	Re: Uhhh Ohhh Reply #3 - 03/31/10 at 23:16:21 Triple check everything. Check integrity of the circuits bit by bit using your multimeter. Check for shorts. Check orientation of all capacitors. The photos on my website may help. http://www.jet5.com/triode.php
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Evo

Ex Member

Re: Uhhh Ohhh
Reply #4 - 04/01/10 at 23:08:02

Thanks for the replies.

I found out the problem - I hadn't wired the RCA connectors on the board correctly to my remote RCA sockets. Music is now playing, the problem now is that one channel is quieter than the other.

I have swapped the speaker connectors around and the RCA connectors from the CD player to just exclude speaker/source issues first. I have also swapped the tubes over. It is definitely the amp.

My next plan was to work back from the speaker outputs using my multimeter. Sound like a good idea? Any ideas what the most likely cause would be?

Cheers

Matt

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dank

Seasoned Member

pair of dual 18
Imperials

Posts: 420

Re: Uhhh Ohhh
Reply #5 - 04/02/10 at 11:17:21

Matt

How much quieter? It could just be a consequence of the dual ganged volume control if it is only slightly quieter on one side than the other. I have gone to two, single ganged, volume controls on my Zkit1 so I can adjust each channel...what with some recordings favoring one side over the other, coupled with no balance control, I found that 2 volume controls work better for me.

Trying to find a difference in volume between the right and left channel is going to be difficult with a multimeter, difficult but not impossible. I think the best way to do it is to connect a sine wave generator (set to 1-2 volts, 1khz) to the amp input. Since I assume you don't have a sine wave generator lying around, you can do the same thing with a PC (with sound) and a tone generator software package. I looked around a bit and found this free one that looks like it should work:
http://www.world-voices.com/software/nchtone.html

You will still have to come up with a cable to connect the PC's sound card line out (usually the green jack) to the Zkit1's RCA input connectors, but they are available (I even found them a couple times at the dollar store for $1, but usually you are going to pay $5-$10 for this cable). Then, with a tone going into the amp and the amp turned up loud (unplug speakers once you have things going before it drives you nuts) you should be able to compare the signal levels of the R and L channels at various parts of the amp with your multimeter set to AC volts. Be aware that your ear is a logarithmic thing. This means that a "just barley perceptible" difference in volume (3 db) is a AC voltage difference of 50% (huge AC voltage difference)...so small AC voltage differences on your meter are going to be inaudible.

Dan

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Evo

Ex Member

Re: Uhhh Ohhh
Reply #6 - 04/02/10 at 12:59:21

Thanks Dan.

It is a bit difficult to tell how large the difference in volume is as my two speakers are different. Both use Hammer Dynamic Super12 drivers, but one is the original cabinet and the other is the Pro12 cabinet. That's why I swapped the speakers over. When you are sitting in the near field the difference in volume is not so obvious, but when sitting further away it becomes more pronounced as the soundstage has the vocals are coming from the side middle instead of from plum middle.

I thought that I might have to use a sine wave. Normally wouldn't be a problem connecting my PC to the amp as I use my computer as my source via an external DAC, but my DAC is currently being repaired, so I am using an old DVD player (again why I swapped the RCA cables over - I just didn't know what the DVD player's audio out was like). I have a programme that plays short tones for testing frequency response, but nothing that plays a sustained sine wave so thanks for the link.

I will probably have a look at it when my DAC comes back.

Swapping to two single ganged volume controls would take a bit of work as I have drilled a hole at the exact location where the controller comes from the board, so might take some work to make it look good again. Also I would also need to do a bit of soldering/desoldering to get at the board to change the connections.

I could always use the balance control on the computer as I use that as my source, but am not sure whether using a software based balance control would lead to a degradation in sound quality. Any ideas?

Will let you know how I get on if I find the issue once my DAC is back.

Happy Easter

Matt

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Alan H Ex Member	Re: Uhhh Ohhh Reply #7 - 04/02/10 at 15:04:00 Turn the volume control up full, and check that the resistance is zero for each channel. Then control the volume using preamp / source. That should tell you whether it is the pot or not.
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Evo

Ex Member

Re: Uhhh Ohhh
Reply #8 - 04/03/10 at 01:02:43

Good idea re: measuring the pot, Alan. Thanks.

As you probably guessed I couldn't wait until my DAC returned, so I managed to find a suitable RCA adapter for computer playback and guess what? No difference in volume across channels when playback is via the computer!

My guess is that the DVD player level out was the problem. When playing through the DVD player the volume on the zkit had to be turned all the way down for pain less listening volumes. A few degrees and it went from no sound to listening levels. From the computer playable volumes were found around 1/3 way around. My guess is that with the DVD slight differences in the pot across channels were noticeable, but with a lower input volume from the PC became neglible. I'm not great with electical know how, so that theory could be trite. Does that sound reasonable?

Only problem now is that at louder volumes there appears to be a bit of hum. I plan to check the grounding and see if that helps.

Can't say too much about the sound yet as the PC source isn't going to great without an external DAC. Will post photo and comments on sound when rest of the systme is up and running.

Thanks again for the rapid responses much appreciated.

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dank Seasoned Member pair of dual 18 Imperials Posts: 420	Re: Uhhh Ohhh Reply #9 - 04/03/10 at 12:31:14 Evo Be sure to read through the "hum problem" thread in the Zkit1 support forum if you are noticing hum problems. The 2 solid wires added from the RCA jack shields to ground really helped reduce the hum in my Zkit1, see picture in the 13th post. Also be sure that you have added a wire to ground the case of the volume pot. Dan
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Alan H Ex Member	Re: Uhhh Ohhh Reply #10 - 04/05/10 at 00:57:19 I'll second Dank's comment. Evo - your theory is very reasonable! Pots commonly lose balance at low volume levels.
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Evo

Ex Member

Re: Uhhh Ohhh
Reply #11 - 04/16/10 at 03:11:19

Problem solved. Took me a while to find suitable cable. In the end I used 6 stranded, solid core wire and connected it as Dan suggested.
Significant reduction in hum. Now only audible when volume is 80%+ and pretty quiet at that, so I can now listen to those pieces with still moments without irritation.

I have also managed to knock up a matching speaker, so now have two Pro12 cabs with Hammer Dynamic drivers inside. Much nicer. Just waiting to get my good DAC......

Thanks for the advice,

Matt

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