You're right, I missed that. But that also indicates that the resistor values are probably fine, at least the plate and cathode resistors.
If you have an analog voltmeter and a sense of adventure, you can do some signal tracing (if you have a scope and a generator, this is easier and more precise). Hook the voltmeter between the junction of C3/R7 and ground. Now touch the "hot" terminal of the input jack- I'd do this using an interconnect cable to keep fingers away from live circuitry. See if the needle swings. This will tell you if your problem is in the first or second stage.
My bad on the voltages. I apologize for the unwarranted rant. I was the lazy one, and went off of SY's post, instead of carefully re-reading the first post.
Did you find the same results, or close, on both channels? The heater voltage difference will not cause the problems you are seeing. However, it will shorten tube life, so you want to sort that out.
Print out a schematic and measure resistance from point to point. Write them on the schematic. If something is out of place, it will be easier to spot this way. Believe me. Everyone here has had to track down a mistake at some point. I've done many. Welcome to the club. It's very inclusive.
Sheldon
Thanks fellas...I get very frustrated when I can not easily find the solution...plus I'm still learning...
The voltages I measured at the plate and cathode for both channels and stages were all on target.
87/86P 2.45/2.45C #1
84/85P 2.46/2.46C #2
I have to travel for work so I will yank out the board and do some complete measuring this weekend.
I appreciate the help.
Carl
The voltages I measured at the plate and cathode for both channels and stages were all on target.
87/86P 2.45/2.45C #1
84/85P 2.46/2.46C #2
I have to travel for work so I will yank out the board and do some complete measuring this weekend.
I appreciate the help.
Carl
Be careful of resistors that are off by a decimal point. It's easy to overlook, because it reads out the digits that you expect, you can miss the fact that it's off by factor of 10, for instance. One of those had me going for a while on a project.
Once you check everything out, look at the gain at 1kHz. Set up your soundcard to output say 1V at 1k (lots of freeware programs for frequency analysis). Use your voltmeter to set and measure the levels. Make a divider for the card output so that you can reduce the signal by a factor of 100 (40dB). At 10mV input to the phono stage, you should see about 1V output.
Sheldon
Once you check everything out, look at the gain at 1kHz. Set up your soundcard to output say 1V at 1k (lots of freeware programs for frequency analysis). Use your voltmeter to set and measure the levels. Make a divider for the card output so that you can reduce the signal by a factor of 100 (40dB). At 10mV input to the phono stage, you should see about 1V output.
Sheldon
Absolutely inclusive indeed - and there's always room for one more. And membership is a minimum requirement for achieving anything at all.
Now we all wonder what on this planet are we overlooking? Some value in the equalising network? (And if it turns out to be a 'stupid' mistake, welcome to another inclusive club!)
Well done. That certainly is consistent with your observations. R11 is not critical. Anything from around 300k to 1meg will do. R8 will influence the RIAA curve, but if you are within 10% of 470k, (a pair of 1meg resistors in parallel, for instance), the effect will be negligible. Variation in the preceding components, especially tubes and capacitors, will tend to be more significant. I'd measure your curve before I worried too much about getting the exact value. It's most important to get good channel to channel match.
Sheldon
OK,
Now that I have my resitor values straightened out I have another problem. There is a reallly bad humm - but only when the TT is plugged in. When I plug in the zone 2 source or my Ipod there is ALMOST no humm. Using a little proto board I rectified to DC and there was no change - humm still there. Makes no difference with the grounding lug coming out of the TT along the RCA cable either. Everything is star grounded to one point in the phono pre
Things I have left to try:
1. Use insulated IN and OUT rca plugs and ground to the board - just using the cheap ones now that are grounded to the top plate.
2. Utilize the center tap - I can use the same bias point from the Aikido.
3. Use a 6.3V xformer I have and rewire the heaters.
Since the AC/DC experiment had no effect I plan to get AC to work - running AC on the Aikido and it is very quiet.
So Close!
Now that I have my resitor values straightened out I have another problem. There is a reallly bad humm - but only when the TT is plugged in. When I plug in the zone 2 source or my Ipod there is ALMOST no humm. Using a little proto board I rectified to DC and there was no change - humm still there. Makes no difference with the grounding lug coming out of the TT along the RCA cable either. Everything is star grounded to one point in the phono pre
Things I have left to try:
1. Use insulated IN and OUT rca plugs and ground to the board - just using the cheap ones now that are grounded to the top plate.
2. Utilize the center tap - I can use the same bias point from the Aikido.
3. Use a 6.3V xformer I have and rewire the heaters.
Since the AC/DC experiment had no effect I plan to get AC to work - running AC on the Aikido and it is very quiet.
So Close!
1. Certainly.
2. What center tap?
3. OK, but how does that differ from you current arrangement?
Get rid of the major hum first. The fact that it is influenced by component connection, indicates that it is ground related. Once that is sorted, you can see if you need to work on filament power. One thing at a time.
Sheldon
Last edited:
Cjkpkj,
Mmmmm ... not sure whether I read you correctly, but perhaps to try more of a 'one-thing-at-a-time' procedure.
Have you tried with the (TT) disconnected and the input shorted at the terminal (plug)? Have you then tried to short the second stage grid to ground (thus eliminate the first stage) - or disconnect the first stage anode resistor? How exactly is your 6VAC heater winding earthed? If possible, earth one side of the heater and then the other - does that make a difference in the hum?
What Sheldon said is important: One thing at a time.
Mmmmm ... not sure whether I read you correctly, but perhaps to try more of a 'one-thing-at-a-time' procedure.
Have you tried with the (TT) disconnected and the input shorted at the terminal (plug)? Have you then tried to short the second stage grid to ground (thus eliminate the first stage) - or disconnect the first stage anode resistor? How exactly is your 6VAC heater winding earthed? If possible, earth one side of the heater and then the other - does that make a difference in the hum?
What Sheldon said is important: One thing at a time.
OK guys...update tonight:
I unhooked the 12.6V xformer in the phono pre chassis and ran some jumper cables to the 12.6V xformer in the aikido - its a 3A unit...and the hum was reduced greatly. With this result, I ended up yanking out the 12.6V xformer altogether and rewired my 4 conductor "umbillical" from the aikido that used to carry ground, B+, 110V hot, and neutral. Now it carries H+, H-, B+, and ground - it is a 16/4 shielded cable.
It is MUCH more quiet now. However, with the TT plugged in and as I turn the volume up the hum gets louder - no hum at zero volume and gets louder as I turn the volume up. I also noticed that if I partially unplug the TT left or right input so the ground is not engaged the hum goes EXTREMELY loud irrespective of volume on the aikido.
I am now thinking that insulated RCAs with a direct earth ground instead of just grounding from the top plate might help. Also, the TT is a late '70s early '80s Technics SL1300. The RCAs appear to be original so I may poke around inside the TT to examine the cable hookup points. A re-cabling may be in order.
The gain is really good and the overall sound is very nice. We are getting close...
Thanks for the suggestions...keep em coming!
I unhooked the 12.6V xformer in the phono pre chassis and ran some jumper cables to the 12.6V xformer in the aikido - its a 3A unit...and the hum was reduced greatly. With this result, I ended up yanking out the 12.6V xformer altogether and rewired my 4 conductor "umbillical" from the aikido that used to carry ground, B+, 110V hot, and neutral. Now it carries H+, H-, B+, and ground - it is a 16/4 shielded cable.
It is MUCH more quiet now. However, with the TT plugged in and as I turn the volume up the hum gets louder - no hum at zero volume and gets louder as I turn the volume up. I also noticed that if I partially unplug the TT left or right input so the ground is not engaged the hum goes EXTREMELY loud irrespective of volume on the aikido.
I am now thinking that insulated RCAs with a direct earth ground instead of just grounding from the top plate might help. Also, the TT is a late '70s early '80s Technics SL1300. The RCAs appear to be original so I may poke around inside the TT to examine the cable hookup points. A re-cabling may be in order.
The gain is really good and the overall sound is very nice. We are getting close...
Thanks for the suggestions...keep em coming!
Allright...wife got home and the kids are all in bed...after some experimenting I am now in the living room listening to Genesis - Lamb Lies Down on Broadway on the TT.
I think I am at just low enough not to get yelled at but loud enough to hear the full range...it sounds awesome...
I had the system hooked up to some fostex 127e's in temporary boxes (gonna build some Fonkens) and put back my Polk M4.5s which are 1db less efficient rated and a larger 6.5" driver. While those little Fostex drivers sound great I think I will leave them out until I get some proper cabinets built.
Anyways...I rearranged where all the components were...the TT, SimpleSE amp, Aikido, and the RJM phono - the Aikido and the phono pre are connected with an umbillical. Now the TT and the power amp are on an upper shelf in a built in bookshelf with doors and I moved the Aikido and the phono pre to the lower shelf. At "reasonable" listening volume the hum is not "readily" present while a record is playing - and I especially listen between tracks. If you put your ear right up to the speaker you will hear it a little.
Right now I would say I am one happy camper...I still have some tweaks to do with the insulated RCAs and experimeting with the TT cables but I think I am 95% there.
Thank you for all your suggestions and guidance with this.
Carl
I think I am at just low enough not to get yelled at but loud enough to hear the full range...it sounds awesome...
I had the system hooked up to some fostex 127e's in temporary boxes (gonna build some Fonkens) and put back my Polk M4.5s which are 1db less efficient rated and a larger 6.5" driver. While those little Fostex drivers sound great I think I will leave them out until I get some proper cabinets built.
Anyways...I rearranged where all the components were...the TT, SimpleSE amp, Aikido, and the RJM phono - the Aikido and the phono pre are connected with an umbillical. Now the TT and the power amp are on an upper shelf in a built in bookshelf with doors and I moved the Aikido and the phono pre to the lower shelf. At "reasonable" listening volume the hum is not "readily" present while a record is playing - and I especially listen between tracks. If you put your ear right up to the speaker you will hear it a little.
Right now I would say I am one happy camper...I still have some tweaks to do with the insulated RCAs and experimeting with the TT cables but I think I am 95% there.
Thank you for all your suggestions and guidance with this.
Carl
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