Voltage on 6dj8s
Hi Frank
I built the circuit you have shown in post #2 of this thread. When the outputs of the ccs are unloaded (ie not connected to the 6dj8's) I get a reading close to 24V dc but when the 6dj8's are connected the voltage is down to 12.1V.. Is this ok? The trannys are 1 amp devices so i figure its not that. All components are as specified in the circuit diagram... Sounds good either way though
Thanks for any help
Nick
Hi Frank
I built the circuit you have shown in post #2 of this thread. When the outputs of the ccs are unloaded (ie not connected to the 6dj8's) I get a reading close to 24V dc but when the 6dj8's are connected the voltage is down to 12.1V.. Is this ok? The trannys are 1 amp devices so i figure its not that. All components are as specified in the circuit diagram... Sounds good either way though
Thanks for any help
Nick
Hi,
I assume you measured this voltage between plate and ground?
It's nothing to worry about for as long as it's consistent between channels.
I suspect the BF244As you've used are what's causing it in conjunction with the load.
These diodes vary quite a bit from one manufacturer to another, some only causing a voltage drop of a few volts, some dropping about half the rail voltage.
Different tubes will also make this voltage vary which is to be expected.
IME, the ones you have now are doing a good job and I'm sure the sound is as it's supposed to be.
Enjoy,
I assume you measured this voltage between plate and ground?
It's nothing to worry about for as long as it's consistent between channels.
I suspect the BF244As you've used are what's causing it in conjunction with the load.
These diodes vary quite a bit from one manufacturer to another, some only causing a voltage drop of a few volts, some dropping about half the rail voltage.
Different tubes will also make this voltage vary which is to be expected.
IME, the ones you have now are doing a good job and I'm sure the sound is as it's supposed to be.
Enjoy,
Hi,
There's isn't a particular brand I favour but since the BF 244A is obsolete for quite some time now it's not uncommon to find rebranded other stuff that masquerades as a BF 244A.
They do tend to vary a little from one another as well however and if the difference is too great I'd suggest replacing it with one that's within range.
In general terms, the greater the voltage drop the better they work and the better the circuit will sound.
The BF244A is quite sensitive so don't go swapping out tubes with the headamp turned on, allow it to discharge properly first.
Cheers,
There's isn't a particular brand I favour but since the BF 244A is obsolete for quite some time now it's not uncommon to find rebranded other stuff that masquerades as a BF 244A.
They do tend to vary a little from one another as well however and if the difference is too great I'd suggest replacing it with one that's within range.
In general terms, the greater the voltage drop the better they work and the better the circuit will sound.
The BF244A is quite sensitive so don't go swapping out tubes with the headamp turned on, allow it to discharge properly first.
Cheers,
Should i use batteries?
Hi
I checked and its still 12V but thanks for the advice.
Whats your opinion on the amount of filtration on the circuit? I am tempted to run the 24v section off 2 12v batteries in series.. at least with the heaters run off mains power the drain shouldn't be too much.
Regards
Nick
Hi
I checked and its still 12V but thanks for the advice.
Whats your opinion on the amount of filtration on the circuit? I am tempted to run the 24v section off 2 12v batteries in series.. at least with the heaters run off mains power the drain shouldn't be too much.
Regards
Nick
WHat i have found
Hi Again Frank
I have the mc head amp described in post #2 feeding into Jim haggermans Comet octal phono stage and then the line stage is the srpp 6sn7 cicuit described here:
http://www.tubebuilder.com/images/schematics/preamps/6sn7_sig.gif
For reason of copy right i sha't include the circuits.
In order to get the match between the headamp and the comet octal phono, the resistor to ground out of the headamp is 47k as is the resistor to ground on the input of the phono stage of the haggerman. I tried 1M but rather than mains hum it was like a bassy hum, almost a vibration... likewise in the hagerman phono stage which has a 300k resistor to ground on its output, i found less of this noise on using 150k..The output from the phono preamp(haggerman) goes to a 4 way selector switch into the 6sn7 srpp line stage.
Being new to the tube scene i still dont get input and output impedances in the sense that lets say on the input of the comet octal phono stage we see a 47k resistor to ground.. so is that the input impedance? Likewise the 6sn7 has a volume pot directly connected to the grid so is the input impedance calculated by measuring the r values to ground of the pot OR is it all tube impedance?
What sets the output impedance or how do we match from one stage to another?
This to the experienced tubers of this forum will probably be a dumb question.
How does one match all of the stages?
Thanks in advance for your time
Regards
Nick
Hi Again Frank
I have the mc head amp described in post #2 feeding into Jim haggermans Comet octal phono stage and then the line stage is the srpp 6sn7 cicuit described here:
http://www.tubebuilder.com/images/schematics/preamps/6sn7_sig.gif
For reason of copy right i sha't include the circuits.
In order to get the match between the headamp and the comet octal phono, the resistor to ground out of the headamp is 47k as is the resistor to ground on the input of the phono stage of the haggerman. I tried 1M but rather than mains hum it was like a bassy hum, almost a vibration... likewise in the hagerman phono stage which has a 300k resistor to ground on its output, i found less of this noise on using 150k..The output from the phono preamp(haggerman) goes to a 4 way selector switch into the 6sn7 srpp line stage.
Being new to the tube scene i still dont get input and output impedances in the sense that lets say on the input of the comet octal phono stage we see a 47k resistor to ground.. so is that the input impedance? Likewise the 6sn7 has a volume pot directly connected to the grid so is the input impedance calculated by measuring the r values to ground of the pot OR is it all tube impedance?
What sets the output impedance or how do we match from one stage to another?
This to the experienced tubers of this forum will probably be a dumb question.
How does one match all of the stages?
Thanks in advance for your time
Regards
Nick
Hi,
The 1M ground resistor is there to discharge the circuit when switched off. It does not in any way determine the Zout.
If you replace it with too low a value it will influence the input impedance of the next stage. For example: 47K of your phono input + 47K Rout of the Headamp will make an effective input resistance of 47K/2 = 23K5. This low value may alter the behaviour of your phono stage.
IOW I'd leave the 1M output resistor as is.
I'm not familiar with the equipment you're using other than by name but if you want to check the headamp for hum related problems, short the MC inputs and see if there's noise on the outputs.
This is a very sensitive circuit after all so any hickups in the circuit layout may be a cause for hum or worse, RF pickup.
Putting a grounded metal shield between the xformers and the tubes may reduce things to inaudability.
Using shields on the tubes proper may help too.
Bottomline is, layout is very critical for best results.
As for battery PSU, I've tried this but it didn't make any difference at all. PSRR of the circuit is extremely good even though it may look simple at first glance.
Ciao,
The 1M ground resistor is there to discharge the circuit when switched off. It does not in any way determine the Zout.
If you replace it with too low a value it will influence the input impedance of the next stage. For example: 47K of your phono input + 47K Rout of the Headamp will make an effective input resistance of 47K/2 = 23K5. This low value may alter the behaviour of your phono stage.
IOW I'd leave the 1M output resistor as is.
I'm not familiar with the equipment you're using other than by name but if you want to check the headamp for hum related problems, short the MC inputs and see if there's noise on the outputs.
This is a very sensitive circuit after all so any hickups in the circuit layout may be a cause for hum or worse, RF pickup.
Putting a grounded metal shield between the xformers and the tubes may reduce things to inaudability.
Using shields on the tubes proper may help too.
Bottomline is, layout is very critical for best results.
As for battery PSU, I've tried this but it didn't make any difference at all. PSRR of the circuit is extremely good even though it may look simple at first glance.
Ciao,
Seperate psu
Hi Again frank
Ok will do re 1M.
I have a seperate outboard psu for the headamp. I have tube sheilds and am thinking of placing the head amp unit in a copper enclosure.. How does one discern between rf and other nasties?
Might I say its a dam fine sounding headamp.. really detailed and warm.. beat the daylights out of the transformer set up i had.
Thanks
Hi Again frank
Ok will do re 1M.
I have a seperate outboard psu for the headamp. I have tube sheilds and am thinking of placing the head amp unit in a copper enclosure.. How does one discern between rf and other nasties?
Might I say its a dam fine sounding headamp.. really detailed and warm.. beat the daylights out of the transformer set up i had.
Thanks
Need help on harshness
Hi Frank
I have ben trying to quell some upper mid harshness in my analogue (phono ) section with no success. I have messed with caps (types of0 and of course the rather voluminous jungle that is resistive loading.. so far i like the response tha 50 ohm loading has . The cartridge is ortofon mc20 Super mark11 (internal impedance of 5 ohms... ortofon recommend 20 to 150 ohms)
What i seem to be getting is a harshness on say violins, brass voices i reckon round 7k but could be having my self on re the frequency. It just isnt right.. if i play the cd of the same record the harshness is not there.. so heres the rub
What can i try?
i have tried the following
1.VTA
2.Cartridge alignment
3. Output caps on your head amp... i cant hear much difference on any value from .47uF to 3uF I have tried 4.7uf... The bass lost its definition at that value.
http://www.diyaudio.com/forums/attachment.php?s=&postid=1215189&stamp=1179753229
Thats the link to the phono stage I hope Im not breaking forum rules by posting it here but i did download it from here.
I have read a lengthy froum post where you contributed .. and again i have become a tad lost in what can be done with a mc cart...
Any suggestions would be greatly appreciated.
Regards
Nick
Hi Frank
I have ben trying to quell some upper mid harshness in my analogue (phono ) section with no success. I have messed with caps (types of0 and of course the rather voluminous jungle that is resistive loading.. so far i like the response tha 50 ohm loading has . The cartridge is ortofon mc20 Super mark11 (internal impedance of 5 ohms... ortofon recommend 20 to 150 ohms)
What i seem to be getting is a harshness on say violins, brass voices i reckon round 7k but could be having my self on re the frequency. It just isnt right.. if i play the cd of the same record the harshness is not there.. so heres the rub
What can i try?
i have tried the following
1.VTA
2.Cartridge alignment
3. Output caps on your head amp... i cant hear much difference on any value from .47uF to 3uF I have tried 4.7uf... The bass lost its definition at that value.
http://www.diyaudio.com/forums/attachment.php?s=&postid=1215189&stamp=1179753229
Thats the link to the phono stage I hope Im not breaking forum rules by posting it here but i did download it from here.
I have read a lengthy froum post where you contributed .. and again i have become a tad lost in what can be done with a mc cart...
Any suggestions would be greatly appreciated.
Regards
Nick
Hi,
I'm sure it's not the headamp.
From what you're describing it may be cartridge mistracking though.
As for the output cap, since this is prior to RIAA correction, the smaller value is usually the better but again, I don't think the problem lies with the electronics.
Moving about different TTs is often not possible but maybe you can move the electronics to someone else's place (assuming there's a well set up TT present) just to make sure?
Sorry if I can't be of more help,
I'm sure it's not the headamp.
From what you're describing it may be cartridge mistracking though.
As for the output cap, since this is prior to RIAA correction, the smaller value is usually the better but again, I don't think the problem lies with the electronics.
Moving about different TTs is often not possible but maybe you can move the electronics to someone else's place (assuming there's a well set up TT present) just to make sure?
Sorry if I can't be of more help,
Im sure itsn ot the headmap either
Hi Frank
I know its not the headamp.. i am just out of ideas.. i reckon its the mc cart.... I might see if i can borrow one.
I wonder if its what Jim Hagermans' site refers to (the peak in the graphs).. You probably know of the page i speak of. The reason i have tried differing cap values is to see if that helped.
thanks for your help
Nick
Hi Frank
I know its not the headamp.. i am just out of ideas.. i reckon its the mc cart.... I might see if i can borrow one.
I wonder if its what Jim Hagermans' site refers to (the peak in the graphs).. You probably know of the page i speak of. The reason i have tried differing cap values is to see if that helped.
thanks for your help
Nick
I think i got it
Hi Frank.
I got to thinking re your suggestion of cartridge mistracking..
I have been using a particular alignment guide all this time but i thought to get out the trusty ole ortofon guide i have... i was able to determine that the overhang I had been using was a tad on the short side (the ortofon guide has a 2 point stylus reference point and depending on wether the back of the cartridge is to the left or right of the marked parallel lines tells you wether to move the cartridge further out or in wrt to overhang)
So i was able to rid myself of the dreaded harshness.. tommorow i will tweak a bit more.. I mean whats is a day in my life when im not wearing my head mounted led light? (my lady calls it the geek light).
Thanks for the suggestion Frank.
You have legend status in my book
Regards
Nick
Hi Frank.
I got to thinking re your suggestion of cartridge mistracking..
I have been using a particular alignment guide all this time but i thought to get out the trusty ole ortofon guide i have... i was able to determine that the overhang I had been using was a tad on the short side (the ortofon guide has a 2 point stylus reference point and depending on wether the back of the cartridge is to the left or right of the marked parallel lines tells you wether to move the cartridge further out or in wrt to overhang)
So i was able to rid myself of the dreaded harshness.. tommorow i will tweak a bit more.. I mean whats is a day in my life when im not wearing my head mounted led light? (my lady calls it the geek light).
Thanks for the suggestion Frank.
You have legend status in my book
Regards
Nick
I built a MC pre-preamplifier with E88CC some time ago. My recommendations:
Use a 12V battery (or two in series) for powering the tubes. The heaters can be connected in series and powered from the same batteries. Drop charge the batteries during power-off, disconnect the charging circuit during power-on.
Don't place any mains transformer close to the tubes, only DC voltage should enter in the box.
Connect two halves of a tube in parallel for one channel.
Select the tubes for lowest noise. Russian 6N23P-EV is also good.
I never tried a current source in the anode. A resistor was sufficient. Select the resistor for 1/2 to 2/3 of the supply voltage on the anode.
Use a good quality output coupling capacitor.
Use a 12V battery (or two in series) for powering the tubes. The heaters can be connected in series and powered from the same batteries. Drop charge the batteries during power-off, disconnect the charging circuit during power-on.
Don't place any mains transformer close to the tubes, only DC voltage should enter in the box.
Connect two halves of a tube in parallel for one channel.
Select the tubes for lowest noise. Russian 6N23P-EV is also good.
I never tried a current source in the anode. A resistor was sufficient. Select the resistor for 1/2 to 2/3 of the supply voltage on the anode.
Use a good quality output coupling capacitor.
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