Hi Rayma i am at work today but will get some pics when i finish. I just have basic equipment soldering and desoldering station digital multimeter and laptop with Real time analyser. I have gone over circuit and for the life of me cannot see anything obvious. I am using a rothwell mc1 stepup transformer but am losing gain somewhere in the phono stage. Hope this makes sense.
Thanks for reply
Jerry.
Thanks for reply
Jerry.
Ok, so you have signal in both channels, just too low in level.
First measure the power supply voltages, and then if that's ok,
measure the tube pin voltages.
Does it sound good though not loud, or is the tonal balance (RIAA eq)
also not right? Do you have a mm cartridge to try directly in without stepup?
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The main problem is that i have quite alot of hum and very little volume the power supply is putting in 6.5v and 203v. Yet when I measure output it is only 1 or 2mv my moving coil is rated at 5mv so with stepup 1to12 I should be seeing more than 2mv is this correct. I will check pin voltages tonoght and let you know.
Jerry
Jerry
Hi Ray,
Things have gone from bad to worse here... I now have no output at all, I was taking the MC stepup out of the circuit and placed it on the chassis forgetting it was still turned on and may have caused a short on the bottom of the step up transformer..I need to be a lot more diligent. The Mc transformer is still working fine. Schematics are at post#249.
I took valve pin voltages.
Pin V1 V2 V3 V4
1 .56V .58V .55V .66V
2 .16V 0V .20V 0V
3 .56V .58V .55V .57V
4 .10V .11v .10V .10V
5 6.3V 6.3V 6.3V 6.3V
6 2.5Mv 2.5Mv 2.5Mv 2.5Mv
7 72V 65V 74V 66V
8 .56V .58V .55V .57V
9 72V 65V 74V 66V
I have attached pics of my setup, and thankyou soo much for your help.
Regards Jerry
Things have gone from bad to worse here... I now have no output at all, I was taking the MC stepup out of the circuit and placed it on the chassis forgetting it was still turned on and may have caused a short on the bottom of the step up transformer..I need to be a lot more diligent. The Mc transformer is still working fine. Schematics are at post#249.
I took valve pin voltages.
Pin V1 V2 V3 V4
1 .56V .58V .55V .66V
2 .16V 0V .20V 0V
3 .56V .58V .55V .57V
4 .10V .11v .10V .10V
5 6.3V 6.3V 6.3V 6.3V
6 2.5Mv 2.5Mv 2.5Mv 2.5Mv
7 72V 65V 74V 66V
8 .56V .58V .55V .57V
9 72V 65V 74V 66V
I have attached pics of my setup, and thankyou soo much for your help.
Regards Jerry
Attachments
It's not likely that the audio circuit was damaged, especially in both channels.
I would say it's the power supply, but the supply output voltage is normal.
Are you measuring the supply voltage at the audio board, or on the supply board?
The tubes light up, right?
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Hi Ray, V measurements are at the audio board and yes the valves do still light up. I have some new electrolytic caps and also new silva micas for the riaa stage coming from hifi collective but they will not arrive till next week. Could it be that the second stage coupling cap needs a different value as the circuit suggests 0.22uf to 2uf i have 0.22uf. I am thinking about getting an oscilloscope hopefully this will help once I grasp the basics I am thinking maybe trace the signal path to see where it is falling down. My father was an avid electronics hobbyist I wish I had taken a greater interest when he was alive....but when your a teenager other things occupy our minds.....lol
You have some simple, basic problem, Don't start replacing parts
until the problem is localized.
First, check the DC voltage wrt to ground at each end of R53 and R54.
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Also it is possible that several resistors are the wrong value from reading the color code wrong.
With all power removed, measure all of the resistors and see if they are correct.
It almost has to be something like that, if the power supply is working.
Also, do you have another phono stage to substitute for this,
to verify that the rest of the system is ok? If so, do that first.
Hi Ray,
Great news I have got sound...lol... although it isn't very loud but I hope there may be something we can do to increase output..... it turns out that the input + and - labels are wrong on the board so I was basically shorting out the board to ground through the input rca. Is there anything I can do to increase the output.
Regards
Jerry.
Great news I have got sound...lol... although it isn't very loud but I hope there may be something we can do to increase output..... it turns out that the input + and - labels are wrong on the board so I was basically shorting out the board to ground through the input rca. Is there anything I can do to increase the output.
Regards
Jerry.
Attachments
There isn't any way to significantly increase the gain of the tube circuit.
Is your step-up transformer x10 gain? What is your cartridge's nominal output?
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Hi Ray, my MC output is 0.5 mv and transformer is 10 times si
O I will have to get larger step up.
O I will have to get larger step up.
That really should be enough gain. How about the gain in your line stage and power amp?
I will try the phono on my Denon tonight as the yamaha amp is from the early 90s and let you know. I will double check the stepup output as i did buy it second hand and the original owner was not pleased with its performance.
The step-up should have enough gain to allow normal volume with any associated equipment.
Hi Ray, I purchased an oscilloscope today and although I don't understand a lot about them yet it did allow me to observe voltages a bit better. I don't have a test record so just used normal lps and it seems I am not getting any more than 2 to 3Mv out of the step up transformer. I have a project Phono box from which I set to MM and plugged output into my phono stage then into an amplifier and it works fine although there are 2 RIAA circuits in play instead of one as the project box has its own RIAA circuit also. To achieve normal volume the phono stage needs 4.5Mvs so I am thinking I will need a pair of Lundahl LL1941 although I still don't know why the MC1 does not provide enough gain as it specs suggest it to be 1:12.9. The MC1 spec states 47Kohms for input impedance where the phono is 50Kohms does this have any bearing on gain.
You are measuring about right. There should be enough gain with the step-up and one phono stage.
All the specs are fine. Please don't start buying things, because you need to determine the problem.
Do you have a mm cartridge to try, or a different step-up?
Hi Ray I have added a moving magnet to my record player with .7 Mv output. There was a little improvement however still donot have enough gain to drive a normal amplifier input. I think now the only option is to build a line stage to get the signal gain after the phono stage. I spoke to Mark at Blueglow and he suggested that it may be the overall design and Bias I am still trying to learn as much as possible so hopefully I will grasp how to maybe adjust this when I learn more. Do you know what the actual gain of this design has been achieved by other builders or is it just a no brainer about incorporating a line stage preamp.
Jezza
Jezza
I read an article somewhere on the internet, with a phonoamp project with the D3a tube. Thought that the schematic was a little "messy", with three resistors on the schematic and only two of the mentioned on the drawing. Also found, probably, an old schematic of the same phonoamp, with fewer resistors and capacitors. Anybody outthere who built thisphonoamp?