Still early days yet..reflective thoughts..
Some hum corrected from my change of input earthing..Still some work to do...
Bass seems tighter..
OK yes I can hear someones shirt button hitting the guitar body..thought I was hearing things..Mary Black opens her mouth before she sings and breaths in...Yep can hear that..
Walk into the other room TV sounds rubbish the usual whats happened to it.....Nothing..
Still to early to comment further..I have some work to do on the PSU Gnd.
Mr Murre's must be near testing stage....
Perhaps it's time to build some Electrostatics just for fun...
Regards
M. Gregg
Some hum corrected from my change of input earthing..Still some work to do...
Bass seems tighter..
OK yes I can hear someones shirt button hitting the guitar body..thought I was hearing things..Mary Black opens her mouth before she sings and breaths in...Yep can hear that..
Walk into the other room TV sounds rubbish the usual whats happened to it.....Nothing..
Still to early to comment further..I have some work to do on the PSU Gnd.
Mr Murre's must be near testing stage....
Perhaps it's time to build some Electrostatics just for fun...
Regards
M. Gregg
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Alastair,
Do you have any other ideas on the cards...
I Have noticed that the caps in the signal path i.e. coupling from first to second stage and output pre to 6c33c grids do impart colouration...I will have to think more about this..
Here is an idea ...how do we DC couple the 6c33c's to the driver stage without frying the speakers...LMAO
There may be a tail to tell about the Amtramz caps...I will wait to see if I hear any info from my enquiry...
Regards
M. Gregg
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Yp--OK, will do in the next couple of days....
As to any more mods, Only thing I did think of was an arrangement to limit the blocking-distortion in the O/P stage, by using a MOSFET across the cathode-resistors and a zener feeding it, to trigger when cathode-volts rises....
Dunno if it would work, Or realistically if there's much point. This was never intended to be a high power design, but one that is fairly robust and straightforward...
As to any more mods, Only thing I did think of was an arrangement to limit the blocking-distortion in the O/P stage, by using a MOSFET across the cathode-resistors and a zener feeding it, to trigger when cathode-volts rises....
Dunno if it would work, Or realistically if there's much point. This was never intended to be a high power design, but one that is fairly robust and straightforward...
Alastair,
The gain is lower..however I have it running into the Alpairs...You have to raise your voice to be understood..Only one heater running..
The bass is tighter...
I still have some work to do.. slight buzz from both channels only quiet up by the speakers with no music running. alters with volume control position ie gets very low at full and low setting mid pos is the loudest...
Just thought its pickup..input is screened..low its at gnd...up its at source..Ummmm perhaps screen should be at Gnd not earth,,LOL
Well next task..
Regards
M. Gregg
The gain is lower..however I have it running into the Alpairs...You have to raise your voice to be understood..Only one heater running..
The bass is tighter...
I still have some work to do.. slight buzz from both channels only quiet up by the speakers with no music running. alters with volume control position ie gets very low at full and low setting mid pos is the loudest...
Just thought its pickup..input is screened..low its at gnd...up its at source..Ummmm perhaps screen should be at Gnd not earth,,LOL
Well next task..
Regards
M. Gregg
Alastair,
The gain is lower..however I have it running into the Alpairs...You have to raise your voice to be understood..Only one heater running..
The bass is tighter...
I still have some work to do.. slight buzz from both channels only quiet up by the speakers with no music running. alters with volume control position ie gets very low at full and low setting mid pos is the loudest...
Just thought its pickup..input is screened..low its at gnd...up its at source..Ummmm perhaps screen should be at Gnd not earth,,LOL
Well next task..
Regards
M. Gregg
Hmm....
The hum pick-up....
Try moving the earthy end connection of your vol-pot to directly to earthy-end of first-stage cathode-resistor...Just a thought, but sounds like its not in the best position currently.
I also had a very slight hum only in one channel until I fitted that remote-controlled vol-pot. I also at the time coupled the earthy-ends of stage 1 cathode-resistors of both channels to the single earth of the new board. The hum in that channel disappeared...
I guess for gain--IF its a problem, a Norton level-shifter instead of the potential-divider between the second gain-stage and phase-splitter could be tried.
Ive not found the gain to be a problem myself though, so havent explored any other options.....
Maybe even try increasing the value of the global-feedback resistor would be a simple way to increase the gain, but there's not that much GNFB at the moment anyway!
Using your normal sources, are you able to drive the amp to full power/obvious clipping still, or have you lost out on too much gain...?
For a larf, you could try a 6SL7 in the first stage....
Hmm....
The hum pick-up....
Try moving the earthy end connection of your vol-pot to directly to earthy-end of first-stage cathode-resistor...Just a thought, but sounds like its not in the best position currently.
For a larf, you could try a 6SL7 in the first stage....
LMAO...The SL7 works in this circuit...just tried it for a laugh...
I still have the hum in mid position...I am going to try a few different things and see what happens. I already have the pot connected to pre-section Gnd..So I'll let you know how it goes..
Just for interest the SL does not sound as good as the SN so I'll stick with the SN7..LOL
Regards
M. Gregg
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Silence is golden ..golden but my heart sill……..can’t remember who did that song..anyway
Well looks promising….I will have to wait until tonight when it’s quiet.
I have found that moving and increasing the cable size from Ground Pre board to the common point on the O/P power supply caps which have a large earth connection has made a big difference.
It’s interesting to note that the preamp driver return is via mid-point power amp and 150 ohm resistor to ground..this cable (at least for me) needs to be low resistance.
So a few more tweaks to try for improved sound to do..
Regards
M. Gregg
Well looks promising….I will have to wait until tonight when it’s quiet.
I have found that moving and increasing the cable size from Ground Pre board to the common point on the O/P power supply caps which have a large earth connection has made a big difference.
It’s interesting to note that the preamp driver return is via mid-point power amp and 150 ohm resistor to ground..this cable (at least for me) needs to be low resistance.
So a few more tweaks to try for improved sound to do..
Regards
M. Gregg
Alastair,
What is the resistance value of the vol pot on the remote board?
Interesting Norton level shifter:
http://books.google.co.uk/books?id=QdGJlyCb7UsC&pg=PA216&lpg=PA216&dq=norton+level+shifter&source=bl&ots=MpLnNPYXZo&sig=AL8W6e4btJULcAs5jacxXqfuS1c&hl=en&ei=Eu-_TovNFMWo8APdr8WHDA&sa=X&oi=book_result&ct=result&resnum=1&sqi=2&ved=0CCoQ6AEwAA#v=onepage&q=norton%20level%20shifter&f=false
Page 217...Never used it....I think the gain will be OK its just this stupid Ipod dock needs a fet 2X boost stage..me thinks!
Regards
M. Gregg
What is the resistance value of the vol pot on the remote board?
Interesting Norton level shifter:
http://books.google.co.uk/books?id=QdGJlyCb7UsC&pg=PA216&lpg=PA216&dq=norton+level+shifter&source=bl&ots=MpLnNPYXZo&sig=AL8W6e4btJULcAs5jacxXqfuS1c&hl=en&ei=Eu-_TovNFMWo8APdr8WHDA&sa=X&oi=book_result&ct=result&resnum=1&sqi=2&ved=0CCoQ6AEwAA#v=onepage&q=norton%20level%20shifter&f=false
Page 217...Never used it....I think the gain will be OK its just this stupid Ipod dock needs a fet 2X boost stage..me thinks!
Regards
M. Gregg
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The vol-pot on that remote-board is 100K....
They didnt offer any other values so just went with that. It appears to work OK, there's no hum caused by it, and volume tracking is perfect all the way down to zero...
The pot is an 'Alps' pot, prob not one of their most expensive (Couldnt believe you can pay up to 500 quid for a bloody Pot!) but works just fine...
They didnt offer any other values so just went with that. It appears to work OK, there's no hum caused by it, and volume tracking is perfect all the way down to zero...
The pot is an 'Alps' pot, prob not one of their most expensive (Couldnt believe you can pay up to 500 quid for a bloody Pot!) but works just fine...
I still have a small amount of hum (not volume related)...I am going to look at changing the P/S heater to DC...see what happens..It's a lot better than it was..
I am going to try running the Power section again on it's own and trace it..
What level of hum do you have in the speakers with Volume at zero? Just looking at comparison..Just wondering how low I can get it!
Regards
M. Gregg
With mine, if you listen at the speaker-cone from 6" there is discernable hum.
Thats not really surprising, as I have only around 4,500uF on each of the main O/P stage rails.
At normal listening distance in a quiet room, I cant hear it though...
Have you tried 'biassing up' the heaters to around 40V on the input/second-stage valves?
Thats not really surprising, as I have only around 4,500uF on each of the main O/P stage rails.
At normal listening distance in a quiet room, I cant hear it though...
Have you tried 'biassing up' the heaters to around 40V on the input/second-stage valves?
I will look at biasing up the input tubes ...I think there at about 20V at the moment..
I know it made a big difference when I made the Aikido pre..
What values did you use for the divider?
Regards
M. Gregg
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Alastair,
I think you've done it again...
I guess the 20V lift was not enough for the 6SN7's.
So to keep to standard values and keep the current down because it's a ref voltage, I just used 680k and 100k gives me a lift of 42.5V on the DC heaters.
I did think about just using the cap to Gnd trick to allow the leakage to charge it but..
So there you go!
Few more tweeks to try..
Mainly component changes..
Did you ever try the Electronic choke?
Regards
M. Gregg
I think you've done it again...
I guess the 20V lift was not enough for the 6SN7's.
So to keep to standard values and keep the current down because it's a ref voltage, I just used 680k and 100k gives me a lift of 42.5V on the DC heaters.
I did think about just using the cap to Gnd trick to allow the leakage to charge it but..
So there you go!
Few more tweeks to try..
Mainly component changes..
Did you ever try the Electronic choke?
Regards
M. Gregg
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