Yes, any amp clips at full power !
The question is, wich was the power ? 1, 2, 10 Watts or more ?
When you change feed back or anything else, be sure to restore the output power at the level it was before changes or comparisons are meaningless
Yves.
Unfortunately I couldnt figure out how to show the output power on the Dscope. Which is a shame, because I wont be able to get back in the lab for a while.
Thanks for your tips, ill have to go back and have a look. It concerned me because I couldnt hear any sonical difference with and without feeback either. Is this something that is very minute, or is my circutiry wrong and the feedback should make a big difference...?
thanks
Thanks for your tips, ill have to go back and have a look. It concerned me because I couldnt hear any sonical difference with and without feeback either. Is this something that is very minute, or is my circutiry wrong and the feedback should make a big difference...?
thanks
I don't know how to use the Dscope, in fact I don't know what is a Dscope !
Just measure the rms voltage (U) accross the load (R) and compute the power (P) as P = U * U / R.
Should or shouldn't ?
This is very dependent of your loudspeakers (the weakest link) and your ears . . .
Yeah that's what I did. I made sure I wasnt taking it from the wrong tap too...
I have no reference with regard to feedback, so maybe I am missing something. I did the best A-B testing I could of with and without feedback, and couldnt tell the difference, but like I said, maybe this is because im not experienced with it enough...?
The fact that the noise floor rose so much with the feedback suggests to me that ive doen something wrong... but I am also just using a lead with a crocodile clip to test, and not screened cable..
The amp sounds really great, but it would be a shame to not get it really singing before it leaves me (its a present to someone for christmas)
Charlie
I have no reference with regard to feedback, so maybe I am missing something. I did the best A-B testing I could of with and without feedback, and couldnt tell the difference, but like I said, maybe this is because im not experienced with it enough...?
The fact that the noise floor rose so much with the feedback suggests to me that ive doen something wrong... but I am also just using a lead with a crocodile clip to test, and not screened cable..
The amp sounds really great, but it would be a shame to not get it really singing before it leaves me (its a present to someone for christmas)
Charlie
Low red moon talked to Ian about global feedback in post 312, 316
www.diyaudio.com/forums/tubes-valves/72536-el84-amp-baby-huey-32.html#post1342973
HTH
www.diyaudio.com/forums/tubes-valves/72536-el84-amp-baby-huey-32.html#post1342973
HTH
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I have Music!!
Sounds is beautiful. cleaner, airier and much fuller than my old Rogers Cadet.
I too thought I had a problem with my input signal until I discovered the CCS wasnt grounded. It only took hours of work to find it and in the end I'd photographed both sides of my circuit board and overlayed the connections with the intention of posting the pic on here to see if anyone else could see what was wrong and there it was staring me in the face - 1 little missing wire...
Ok next thing, I have only 14.8 volts on pins 1&6 of the diffamp. This should be around 170v. As I had 270v before I grounded the CCS I can only assume the problem is on the Cathode side of the tube. My CCS kicks out -2.9v what should the correct Voltage be?
Sounds is beautiful. cleaner, airier and much fuller than my old Rogers Cadet.
I too thought I had a problem with my input signal until I discovered the CCS wasnt grounded. It only took hours of work to find it and in the end I'd photographed both sides of my circuit board and overlayed the connections with the intention of posting the pic on here to see if anyone else could see what was wrong and there it was staring me in the face - 1 little missing wire...
Ok next thing, I have only 14.8 volts on pins 1&6 of the diffamp. This should be around 170v. As I had 270v before I grounded the CCS I can only assume the problem is on the Cathode side of the tube. My CCS kicks out -2.9v what should the correct Voltage be?
Charlie: You can wire in a pot (or a fixed R and a pot in series) to vary the feedback as the amp is playing, then when you find the sweet spot just measure the total R and replace with a fixed resistor. Alternatively, you can leave the pot in, but I think you'll find that you won't adjust it much once you find it's happy place...
Lots of feedback typically starts sounding a bit dull and lifeless.....even though the amp will typically measure better with feedback. You will hopefully notice subtle differences by adjusting while the amp is playing.
I use a stereo pot for the feedback resistor in my Baby Huey as Boywonder suggested. It demonstrates very well the effect - very good to impress listeners who wonder why one would go through the effort of dealing with tubes for audio.
With a lot of feedback the sound is quite similar to a good SS amp and many listeners initially like this setting if you start with it.
But if you then decrease the feedback to the "happy place" as Boywonder calls it, people will hear the difference (mostly accompanied by an open mouth).
The sound does not change as different EQ settings would (people are used to that) but actually changes in the way the music is distributed in the room (I guess people call that soundstage)
The amp got a very high WAF just because of this demonstration and is our main living room system (I built it as an integrated amp).
Cheers,
Martin
With a lot of feedback the sound is quite similar to a good SS amp and many listeners initially like this setting if you start with it.
But if you then decrease the feedback to the "happy place" as Boywonder calls it, people will hear the difference (mostly accompanied by an open mouth).
The sound does not change as different EQ settings would (people are used to that) but actually changes in the way the music is distributed in the room (I guess people call that soundstage)
The amp got a very high WAF just because of this demonstration and is our main living room system (I built it as an integrated amp).
Cheers,
Martin
I just got my amp back, and did a quick test out of curiosity...
Taking the wrong secondary tap for the feedback, I thought I would get oscillation but there was no difference. Shouldnt that be positive feeback?
So is this the reason I cannot tell the difference with and without feeback, my circuit wrong?......Or am I barking up the wrong tree here...?
Thanks
Charlie
Taking the wrong secondary tap for the feedback, I thought I would get oscillation but there was no difference. Shouldnt that be positive feeback?
So is this the reason I cannot tell the difference with and without feeback, my circuit wrong?......Or am I barking up the wrong tree here...?
Thanks
Charlie
In the past I have wrongly wired up the phase of an output transformer. Instead of getting negative feedback from the 4ohm tap I got positive feedback from the ground tap instead. The wailing sound from my speakers was very disconcerting.
As the Baby Huey is stable without global negative feedback, and you are not hearing any difference whichever tap used, ( I presume no ground tap used ) maybe you have NO global negative feedback at all.
Maybe time to check your connections.
As the Baby Huey is stable without global negative feedback, and you are not hearing any difference whichever tap used, ( I presume no ground tap used ) maybe you have NO global negative feedback at all.
Maybe time to check your connections.
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Some people think it's good practice to ground the output transformers' negative tap along with the frame of the output transformer to the chassis instead of leaving it just "floating". I think IIRC Gingertube thinks this also. However although I agree , it should still work fine if you havn't done that, mine does ( only a temporary measure )
You MUST ground one side of the secondary if you use a tap for feed back purpose.
I suggest to use a twisted pair to bring back the two connections together from the secondary to near of the input stage where you'll ground "the good one" only at this location.
This voids creating a ground loop that could introduce hum.
Yves.
I suggest to use a twisted pair to bring back the two connections together from the secondary to near of the input stage where you'll ground "the good one" only at this location.
This voids creating a ground loop that could introduce hum.
Yves.