OK I have only listened for a short time..
I can tell exactly what it is....when the ct was disconnected there was a frequency shift from bass to treble..ie bass was light by comparison
Now there has been another shift...treble is less..bass is grainy maybe more but possibly moved lower down the scale
Regards
M. Gregg
I can tell exactly what it is....when the ct was disconnected there was a frequency shift from bass to treble..ie bass was light by comparison
Now there has been another shift...treble is less..bass is grainy maybe more but possibly moved lower down the scale
Regards
M. Gregg
Here you go, Some simple PSU layouts with descriptions....
http://www.audiodesignguide.com/my/ocl.jpg
http://www.audiodesignguide.com/my/ocl.jpg
Alastair,
I have fitted 300 Ohm and it sounds great hum is very very low in the speakers..
I would go so far to say I cannot hear anything in the one speaker
(I do mean can't tell its on, thought the speaker cable was disconnected)I guess with a bit of juggling of the 6633C's I could get it lower on the other side...
So I think this is the value I will stick with plus the unequal resistors..
To me the difference is chaulk and cheese..
Thanks for the links..for me the 1K in the PSU is now 300 Ohms..
Regards
M. Gregg
I have fitted 300 Ohm and it sounds great hum is very very low in the speakers..
I would go so far to say I cannot hear anything in the one speaker
(I do mean can't tell its on, thought the speaker cable was disconnected)I guess with a bit of juggling of the 6633C's I could get it lower on the other side...
So I think this is the value I will stick with plus the unequal resistors..
To me the difference is chaulk and cheese..
Thanks for the links..for me the 1K in the PSU is now 300 Ohms..
Regards
M. Gregg
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It is better to connect the center tap of the trafo right to the capacitors without the 1K resistor , and use a protection circuit for the loudspeakers to prevent any DC voltage that can destroy them .Alastair..
Just thinking out loud here..
While after 4hrs listening to the OTL with Deadmau5 (for want of a better name)
deadmau5 "16th hour" - YouTube
Got to test the bass haven't you..
Shakes my laptop across the table.. and hammers the Alpairs into submission
Very deep bass....anyway..yes there are fuses and bypass caps just not on this pic...
Some discussion going on....
Sounds great!!
Regards
M. Gregg
Not yet work getting in the way...I will keep trying different things..and post what I find..
There is no question that with the resistors as they are the sound stage is way better...it closed in with the Ct direct connection..why I don't know at the moment...
There must be a reason for this I will try a few things..see what happens..
I have thought about a crowbar circuit that just plugs across the speaker..small module..
Also looking at the cheep choke idea...or electronic choke....so much to try..lol
Regards
M. Gregg
Dimitris,
What value are you thinking of reducing to and why?
I would like to hear what your thoughts are on this topic
Title: Avoiding unpleasant overdrive tones
Its at the bottom of This link:
http://www.freewebs.com/valvewizard/cathodyne.html
Regards
M. Gregg
If u haven't found the OTL amp on this thread that is to your liking and if youre hell bent on a 6AS7G OTL you'll find it on t he Bonavolta home page then click on Audio & Electronics page, click on amps go down a long list of all sorts of amps, click on 6AS7 PP & OTL then click on 6AS7GA OTL there u will find a scheme by Bruce Rosenblitt Glass Audio 1990 (yikes, its 21 years old! Don't led Leadbelly see this! Or were in for a Spanking!) Personally, I did not like what I saw. Too many tubes to get down to 8 Ohm. No less than 8 tubes per channel. Personally I would try Alistair-E's project.
No reason why you shouldnt use 6AS7G/6H13C or any of its varients in this circuit...
You'll prob have to play around with the cathode-resistors to get the bias you want but I see no reason why they wouldnt perform when set up...
I'm currently running some 6C41C which has a similar ratings of two sections of 6AS7G wired in parallel....
The 470K is there for a reason--As described in that article. At normal signal levels, it has no effect on sound, as the PI has a very high input impedance, Its only when the PI gets to the point of clip of the PI that it comes into effect....
Alastair,
Have you seen this?
GoodSoundClub - Romy the Cat's Audio Site - 6C41C ? the journey to nowhere.
Regards
M. Gregg
Yup--Read that some time ago.
His amps are SE designs so are probably much more sensitive to the valve type, particularly Anode-Impedance....
Its a common 'mistake' to think the 6C41C is equivalent of 'half' a 6C33C.--Even refered to it myself that way on occasions....
--How can it be though....?
The Cathode of the 6C41C is only about two-thirds the size of a single cathode of the 6C33C.
--Its Published Ratings may be close to half the full 6C33C valve,(Both heaters) but Not for the published ratings of Half (single-heater) of the 6C33C...
I personally think of 6C41C as approx One Third of a 6C33C.
I'm thinking of trying a variety of valves in this design. Ive used the 6C33C, single and both heaters--we know that works pretty well.
Now on the 6C41C and for 'normal' listening is pretty good, although NOT as good IMHO as 'Half' (single-heater) of the 6C33C, and when pushed shows its limits in power--I think I know what 'Romy-The-Cat' means about that compression effect he saw.
I would like to try the ever popular 6AS7G, both sections wired in parallel, and for a larf, will try the big ole Pentode line-output bottle, the PL509, triode-wired...
I'm pretty sure I have some PL509 round here, NOS bottles, marked up 'MAZDA' but I think originated from 'Ei' Have to dig around, not sure how many I have...
I'll order 4 of 6AS7G soon as I have a bit of spare cash, prob end of the week, Then the Proper 'Tube-Rolling' can begin...
His amps are SE designs so are probably much more sensitive to the valve type, particularly Anode-Impedance....
Its a common 'mistake' to think the 6C41C is equivalent of 'half' a 6C33C.--Even refered to it myself that way on occasions....
--How can it be though....?
The Cathode of the 6C41C is only about two-thirds the size of a single cathode of the 6C33C.
--Its Published Ratings may be close to half the full 6C33C valve,(Both heaters) but Not for the published ratings of Half (single-heater) of the 6C33C...
I personally think of 6C41C as approx One Third of a 6C33C.
I'm thinking of trying a variety of valves in this design. Ive used the 6C33C, single and both heaters--we know that works pretty well.
Now on the 6C41C and for 'normal' listening is pretty good, although NOT as good IMHO as 'Half' (single-heater) of the 6C33C, and when pushed shows its limits in power--I think I know what 'Romy-The-Cat' means about that compression effect he saw.
I would like to try the ever popular 6AS7G, both sections wired in parallel, and for a larf, will try the big ole Pentode line-output bottle, the PL509, triode-wired...
I'm pretty sure I have some PL509 round here, NOS bottles, marked up 'MAZDA' but I think originated from 'Ei' Have to dig around, not sure how many I have...
I'll order 4 of 6AS7G soon as I have a bit of spare cash, prob end of the week, Then the Proper 'Tube-Rolling' can begin...
This large value of resistor can make big reduction in high frequency response , and also a lot of phase shift due to the input capacitance of the next stage . For this it affect the sound not only in clipping but in normal conditions too . The use of large amount resistor like this has influence from this article ( Avoiding unpleasant ..... ) , why we don't make with another way , reduce the grid stopper say to 10KΩ or even smaller , and redesign the Cathodyne phase spliter with another more powerful tube to reduce the anode output impedance and stop thinking about overdrive too much .
LOL...yes I see your idea is to overcome the phase splitter problem and not to have to drive it hard in the first instance...
What phase splitter topology do you use..ie prefered type?
Regards
M. Gregg
For this topology - circuit , cathodyne is better .LOL...yes I see your idea is to overcome the phase splitter problem and not to have to drive it hard in the first instance...
What phase splitter topology do you use..ie prefered type?
Regards
M. Gregg
Nah, I disagree....
There's No Grid-Cathode-resistor,--so this can be considered infinite-- (Gets its bias DC coupled from previous stage) therefore the Input Impedance is well over 100M ohms....
Rin = ((Ri+(mu+2)*RL) / (Ri+(2*RL))) * Rgc, where Rgc is the Grid-cathode resistor (infinate in this case)
470K aint gonna make ANY difference at all for performance, as 'grid-stopper' but will prevent clip-distortion, frequency multiplication etc!
6SN7 is quite capable in this circuit, No need to make or change to 'more powerful' tube.
We are Not driving the 6C33 grids Positive, therefore, we Dont need a sledge-hammer to crack the Miller nut present on the grids, and dont need to source large current into them.
The scheme would need Another CF stage between the PI and O/P stage to achieve this properly, and for a simple, straight forward low-power OTL this is beyond its scope ...
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OK here is a question..
I have not tried this and someone may already know the answer..
If I replace the resistor known as R33 in the tim Mellow design.
This is 300 Ohms (my amp) at pressent in the Ct of the power Tx with a choke say 300 Ohms Dc resistance 10 or 20H for a laugh...What will be the result?
This is in the Ct of the +/- power supply.... In post 412# this thread its the 1k resistor I am refering to..
Regards
M. Gregg
I have not tried this and someone may already know the answer..
If I replace the resistor known as R33 in the tim Mellow design.
This is 300 Ohms (my amp) at pressent in the Ct of the power Tx with a choke say 300 Ohms Dc resistance 10 or 20H for a laugh...What will be the result?
This is in the Ct of the +/- power supply.... In post 412# this thread its the 1k resistor I am refering to..
Regards
M. Gregg
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Guess it would act as though the CT wasn't connected, as far as signal is concerned....
No benefit as far as I can see....
The omission of the CT connection just means that the PSU caps are both fully in series with the O/P signal....
--At least with the CT connected, the caps are religated to smoothing duty rather than de-coupling the signal as well!
No benefit as far as I can see....
The omission of the CT connection just means that the PSU caps are both fully in series with the O/P signal....
--At least with the CT connected, the caps are religated to smoothing duty rather than de-coupling the signal as well!
Well , I talk about input capacitance of the 6SN7 and not about input impedance , in this circuit the 470KΩ resistor with the input capacitance of the 6SN7 Cgk wich is 3pF plus the capacitance of the tube socket plus the capacitance of the circuitry , makes an RC filter wich its cutoff frequency is from 42,5Khz to 56Khz ( Fc = 1/ 2 * pi* R * C ), remember that the output impedance of the previus stage will added to this resistance and then the cutoff frequency will be smaller , so there is no need to lower the frequency of the amp ( in open loop ) that much .With a more powerfull tube , I didn't mean output power tube , maby the use of low output power tube , and I say it only to reduce more the upper output ( anode ) impedance ( with smaller Ra and Rk ) of the phase spliter to reduce the Miller effect of the output tubes , and have a better frequency response , and there is no need to drive the output tubes in classAB2 .
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