I was working on my new push pull amp with 6SN7 || -> LL1660S -> EL34 x 2 The 1660S is configured as ALT-B (SE to PP out). When I looked at the scope this is what I saw. There is considerable ringing on the 1kHz square wave. This output is taken from the plate of the 6SN7. The 6SN7 is running off 200V B+ and 750R cathode resistor, bypassed. Substituting two green LEDs did not improve the output. Any thoughts or suggestions as why this is happening?
Attachments
I haven't used the LL1660, but that looks fairly typical of unloaded interstage secondaries to me.
You can try adding resistors on the outputs (grid to ground), it will probably help. You can also use a series RC network. You should be able to damp the ringing, at the expense of frequency response.
Pete
You can try adding resistors on the outputs (grid to ground), it will probably help. You can also use a series RC network. You should be able to damp the ringing, at the expense of frequency response.
Pete
secondary loading
You could try to de-tune the LCR network by adding some resistors across the secondary winding... Maybe 47K ? Why dont you measure the period of those oscillations? You'll find they are up around 60kHz anyways... Set your trigger to leading edge and zoom in on the damped series of peaks, count horizontal divisions to get the period, and thus the frequency of the oscillation mode... If you want to be smart, count the number of periods as well to figure out what the damping envelope coefficients are.
-- Jim
You could try to de-tune the LCR network by adding some resistors across the secondary winding... Maybe 47K ? Why dont you measure the period of those oscillations? You'll find they are up around 60kHz anyways... Set your trigger to leading edge and zoom in on the damped series of peaks, count horizontal divisions to get the period, and thus the frequency of the oscillation mode... If you want to be smart, count the number of periods as well to figure out what the damping envelope coefficients are.
-- Jim
Got a very similar result with my LL1660PP time ago. I loaded the secondary windings with different combos R+C looking for the best 1KhZ. NOPE. There have been only slight improvements. At the end of the day I left 47kR+47kR. I didn't notice any difference in the sound.
Yes those rings are very typical with interstage trannies as Pete and Jim said ... but there is really nothing to worry with them as they are "local" instabilities. My experience with the ITs is that the output tranny usually cut these rings off flattening the square wave.
What about 10kHz square wave? Any issue with hi-freqs (say 50kHz)? You should notice a +3/+6dB boost there with the LL1660
Enjoy.
Gianluca
Yes those rings are very typical with interstage trannies as Pete and Jim said ... but there is really nothing to worry with them as they are "local" instabilities. My experience with the ITs is that the output tranny usually cut these rings off flattening the square wave.
What about 10kHz square wave? Any issue with hi-freqs (say 50kHz)? You should notice a +3/+6dB boost there with the LL1660
Enjoy.
Gianluca
Welcome to the world of high impedance interstage transformers!
Gluca is correct that you need a 47k on each secondary just to tame it slightly, and also that you probably won't hear the difference even then.
The problem is not square waves that cause oscillations all of the same family which cannot "fold back" into the audio band as IM, but rather that high order distortion components from previous stages are given a 6dB or more boost. You may or may not be worried about that, depending on the circuit.
Joel
My push-pull circuit using the LL1660S is on my website:
http://www.joeltunnah.com
Heya Joel ... I was looking at your very site yesterday (congrats!!). I saw your trans coupled EL84 project. You are using 47kR too. Great to see someone else found the same solutions as I did.
These interstages really like low Ra tubes. I used ECC99, 6H30 and 6N6. Probably you can get something better at 10kHz with these drivers.
Ciao
Gianluca
These interstages really like low Ra tubes. I used ECC99, 6H30 and 6N6. Probably you can get something better at 10kHz with these drivers.
Ciao
Gianluca
Hi Tony, John, Pete, Jim, Gianluca, thanks for your thoughts. I loaded it with 100K before but did not notice major "improvement" maybe 47K will do but I'll take the suggestions about not being able to get more improvemnt.
Hi Joel, I actually went to your site to have my waveform compared with yours
Hi Joel, I actually went to your site to have my waveform compared with yours
OOOPSIE!!
Well ... that's true!!! Thanks.
Actually I never used that LL tranny with higher Ra tubes ... but clearly I was wrong. And, yes I did see the same effect with an other IT (I mean high Ra -> damped rings).
On the other hand, higher Ra tubes need higher primary inductance (to have a large bandwidth) and this would suggest to use a different coupling method.
There is no free lunch here too.
But I would pick up a low Ra tube to have a large freq response and I would not care that much about these rings. And I did this way.
Ciao
Gianluca
Well ... that's true!!! Thanks.
Actually I never used that LL tranny with higher Ra tubes ... but clearly I was wrong. And, yes I did see the same effect with an other IT (I mean high Ra -> damped rings).
On the other hand, higher Ra tubes need higher primary inductance (to have a large bandwidth) and this would suggest to use a different coupling method.
There is no free lunch here too.
But I would pick up a low Ra tube to have a large freq response and I would not care that much about these rings. And I did this way.
Ciao
Gianluca
hi andrei, joel, kevin carter replied to me about his thoughts on this matter. he said adding the resistive load on the secondary will "swamp" the resonance at the expense of "killing" the sound.
http://www.audioasylum.com/forums/KandK/messages/4898.html
joel, thanks for the tip. i'll search for that in the kandk forum.
cheers!
http://www.audioasylum.com/forums/KandK/messages/4898.html
joel, thanks for the tip. i'll search for that in the kandk forum.
cheers!
I have testing the LL1660S
1- primary wave generator 1k in series o secondary to the scope with a load 47k
2- Primary parafeed from 6sn7 with 8uf ( Mundorf supreme ) coupled and secondary to scope with 47k load.
My surprise have been anomalies peak, not too different from test 1 to 2 Test 2 values 10hz +4.8db 41.7V 20hz to 15khz 0db 24V 20kh +1.7 db 28V 30khz +5db 42V 40khz +8.7db 63V With this values the 1khz square wave is horrible, The LL1660 will be as splitter parafeed from 2a3 (CCS load ) to 300PP, About low frequency peak I have reduce the parafeed coupled cap 8uf to 1,5uf the 10hz is cancelled but born another peak at 50hz. must I be worry about this LF and HF peak ? zobel filter affect to the sound ?,
I am a fanatic of transparency sound. I find in 4P1L driver – LL7903+LL1671 tests – Bartola(R) Valves with similar curves on LL7903
10hz +4.8db 41.7V
20hz to 15khz 0db 24V
20kh +1.7 db 28V
30khz +5db 42V
40khz +8.7db 63V
1- primary wave generator 1k in series o secondary to the scope with a load 47k
2- Primary parafeed from 6sn7 with 8uf ( Mundorf supreme ) coupled and secondary to scope with 47k load.
My surprise have been anomalies peak, not too different from test 1 to 2 Test 2 values 10hz +4.8db 41.7V 20hz to 15khz 0db 24V 20kh +1.7 db 28V 30khz +5db 42V 40khz +8.7db 63V With this values the 1khz square wave is horrible, The LL1660 will be as splitter parafeed from 2a3 (CCS load ) to 300PP, About low frequency peak I have reduce the parafeed coupled cap 8uf to 1,5uf the 10hz is cancelled but born another peak at 50hz. must I be worry about this LF and HF peak ? zobel filter affect to the sound ?,
I am a fanatic of transparency sound. I find in 4P1L driver – LL7903+LL1671 tests – Bartola(R) Valves with similar curves on LL7903
10hz +4.8db 41.7V
20hz to 15khz 0db 24V
20kh +1.7 db 28V
30khz +5db 42V
40khz +8.7db 63V
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.