hey.
I've built a 5e3x2 power amp section (4x6v6gt at 412v and about 20ma) sounds good (with the signal injector on either one side or the other side of the power amp)
but when i connect the phase inverter (ive copied this one nearly exactly) The Long-Tail Pair if i connect the signal injector to the input i get clear sound - good. if i connect to one side of the power amp directly it sounds fine also, obviously quieter.. but if i connect to the other side it sounds strange, off balance and just plain bad.
im not sure how i can explain this better, but if anyone has some suggestions for a better PI, do let me know.
I chose the PI from aiken amps page, simply because i was told it is better.
thanks for any help.
I've built a 5e3x2 power amp section (4x6v6gt at 412v and about 20ma) sounds good (with the signal injector on either one side or the other side of the power amp)
but when i connect the phase inverter (ive copied this one nearly exactly) The Long-Tail Pair if i connect the signal injector to the input i get clear sound - good. if i connect to one side of the power amp directly it sounds fine also, obviously quieter.. but if i connect to the other side it sounds strange, off balance and just plain bad.
im not sure how i can explain this better, but if anyone has some suggestions for a better PI, do let me know.
I chose the PI from aiken amps page, simply because i was told it is better.
thanks for any help.
The problem is not the PI, but probably a wiring issue. A LTP has been the industry standard for years and years with excellent sound. Most guitar sounds we all love went probably through one 
.
Can you post a schematic of the amp? And what exaclty do you meen with 'one side' of the power amp? I guess it's a push-pull amp. Connecting one side should not work good at all. First guess would be you paired up the wrong output tubes together.
.Can you post a schematic of the amp? And what exaclty do you meen with 'one side' of the power amp? I guess it's a push-pull amp. Connecting one side should not work good at all. First guess would be you paired up the wrong output tubes together.
Here is a schematic I've drawn of exactly what I have built so far. Any suggestions welcomed. I'm not even sure if there is a problem but when I inject a 2k tone into pin 5 of v2 it sounds drastically different then if the signal is injected into pin 5 of v4. I can make a recording if it would help.
http://db.tt/tuQPtUxh schematic.
http://db.tt/tuQPtUxh schematic.
Here is a schematic I've drawn of exactly what I have built so far. Any suggestions welcomed. I'm not even sure if there is a problem but when I inject a 2k tone into pin 5 of v2 it sounds drastically different then if the signal is injected into pin 5 of v4. I can make a recording if it would help.
http://db.tt/tuQPtUxh schematic.
http://db.tt/tuQPtUxh schematic.
it's like i thought you do have a feed back loop so applying your signal there it's going to be affected by the loop(the feedback is out of phase so cancellations will occur)it won't be noticeable on the other half because the phase relation is as intended
this doesn't rule out the possibility that you may have a leaky cap if the bias for the output isn't drifting it's not likely the cause
this doesn't rule out the possibility that you may have a leaky cap if the bias for the output isn't drifting it's not likely the cause
Last edited:
Thanks, I just confirmed by disconnecting the cap from the 10k resistor and it sounds normal on both sides, reconnected the cap now I know what was causing it.
Turk 182 - would you mind commenting on another circuit, I was recommended to modify it in this way but I'm not sure what the effect would be . link here. http://db.tt/FJNysDDd
Turk 182 - would you mind commenting on another circuit, I was recommended to modify it in this way but I'm not sure what the effect would be . link here. http://db.tt/FJNysDDd
Thanks, I just confirmed by disconnecting the cap from the 10k resistor and it sounds normal on both sides, reconnected the cap now I know what was causing it.
Turk 182 - would you mind commenting on another circuit, I was recommended to modify it in this way but I'm not sure what the effect would be . link here. http://db.tt/FJNysDDd
Turk 182 - would you mind commenting on another circuit, I was recommended to modify it in this way but I'm not sure what the effect would be . link here. http://db.tt/FJNysDDd
well that was tricky switching between the two pic's to see what's what.
near as i can tell it will extend the low frequency limit and add gain this may or may not be needed or can be done later in the build process.
keep in mind the hotter you run your output tubes it's shortening their lifespan
no idea why this mod was recommended ?
near as i can tell it will extend the low frequency limit and add gain this may or may not be needed or can be done later in the build process.
keep in mind the hotter you run your output tubes it's shortening their lifespan
no idea why this mod was recommended ?
Last edited:
Thank you very much. You have helped me a lot and now I'm going to go ahead with the rest of the build. (2x 6au6 one channel and 2x 12ax7 for other channel guitar amp both with pre and post gain on each so either can be used for overdrive or clean with a slight different character)
I'll post a final build thread with recordings and full schematics when it is done.
I'll post a final build thread with recordings and full schematics when it is done.
Thank you very much. You have helped me a lot and now I'm going to go ahead with the rest of the build. (2x 6au6 one channel and 2x 12ax7 for other channel guitar amp both with pre and post gain on each so either can be used for overdrive or clean with a slight different character)
I'll post a final build thread with recordings and full schematics when it is done.
I'll post a final build thread with recordings and full schematics when it is done.
The cap connected from the OPT's feedback to the 5k pot is in the wrong place. You're getting frequency dependent feedback. The second grid is getting the full spectrum, while the tail is getting 318Hz and above, with all the resulting issues. The cap connected to the pot adds another bump to the response btw.
The feedback resistor should be directly connected to the tail, while the 100nF cap should be connected between the feedback path and second grid. Check the article on Aiken amps (awesome resource!) again, you just copied it wrong.
If there are still issues when the PI is connected the way it should, it could be the outputs from the PI to the power tubes should be reversed, to get the feedback in the correct phase to the tail of the PI (positive vs. negative feedback). Positive feedback is nasty and a cause for oscilations, while negative feedback reduces the signal a bit and makes it more linear.
Last edited:
To comment on the power sections, they've both got issues IMO.
In the first schematic's poweramp section, the second set of powertubes get their signal after it has gone through the gridstoppers of the first. Gripstoppers should be connected as close and directly to the tubesockets as possible.
I'm missing ground symbols. The OPT's neutral should be grounded when using the feedback loop, this might also be part of the problems you're hearing.
It's better to use separate coupling caps to the power tubes (and their accompanying grid leaks). Although they are cathode biased, one runaway tube could damage the other with the way it is now.
I don't have a clue why you'd want to use the second schematic, but I'm always learning as well.
In the first schematic's poweramp section, the second set of powertubes get their signal after it has gone through the gridstoppers of the first. Gripstoppers should be connected as close and directly to the tubesockets as possible.
I'm missing ground symbols. The OPT's neutral should be grounded when using the feedback loop, this might also be part of the problems you're hearing.
It's better to use separate coupling caps to the power tubes (and their accompanying grid leaks). Although they are cathode biased, one runaway tube could damage the other with the way it is now.
I don't have a clue why you'd want to use the second schematic, but I'm always learning as well.
Last edited:
Yes you are right about the grid stoppers, they are connected I'm the way you describe, the schematic is not correct I meant to draw a line all the way past the grid leak resistors and join to the coupling caps.
As for the opt being grounded, it is not, should I ground 0v? Is it perfectly safe? Do not want to blow an a transformer.
The second schematic was drawn by my grandfather, he has built some amazing amps that I've heard, but he is in his late 80s and I just wanted to check there were no huge errors in the schematic, but just a different way of getting the job done.
Yes, the 0V connection of the OPT should be connected to the audio path's ground, specially when used with global feedback! (and preferably to the tail of the PI). Check out a thread I started what happened when the ground came loose on a breadboard. It screwed up my PSU: http://www.diyaudio.com/forums/power-supplies/237144-series-mosfet-regulator-400v-what-hell.html
Did you also get my post before that concerning the cap in the PI's tail? Together with the loose ground, there seem to be number of issues, all concerning global NFB... You might want to do some reading up on the subject. Aiken amps is a great place, but I strongly suggest the books by Merlin Blencowe in your case. Excellent material and the learning curve is not overly steep.
Did you also get my post before that concerning the cap in the PI's tail? Together with the loose ground, there seem to be number of issues, all concerning global NFB... You might want to do some reading up on the subject. Aiken amps is a great place, but I strongly suggest the books by Merlin Blencowe in your case. Excellent material and the learning curve is not overly steep.
Last edited:
@ funk 1980 yeah I got your post, I'll be sitting down later today with the amp to make the modifications. I don't think I have any bad oscillation, I the 2, 4 and 9k tones (tone generator on my multimeter) looked pretty clean on my oscilloscope.
I'll do some more reading on Aiken amps, I've also been reading a lot of articles by mesa boogie, I I think randall smith.
I'll do some more reading on Aiken amps, I've also been reading a lot of articles by mesa boogie, I I think randall smith.
Finished the modifications to the pi, it seems to work fine now, keeping the coupling caps shared between each pair for now, not sure what was meant by the cap connected to the pot adds another bump in the frequency response.. Is that the cap from the wiper to ground or the one that was incorrect on the schematic?
I meant the cap from the wiper to ground. It's known as the 'presence control' and makes the local feedback of the long tailed pair frequency depended. It's a classic control found on many many guitar amps. The higher frequencies are shunt to ground through the cap, while the lower still 'see' the resistance of the pot. With the current values of the feedback resistor, pot and cap, the control will bump all frequencies above 352Hz.
Although this is the classic setup, there is a better way to implement a presence control though. In your current schematic, there's DC going through the pot. Maybe fine now, but it will make scratchy sounds in the future. If you make the current pot a fixed resistor and parallel connect a pot and cap (pot to ground, cap on top to block DC), with a higher value pot, you'll get the same performance, but no scratchiness.
Although this is the classic setup, there is a better way to implement a presence control though. In your current schematic, there's DC going through the pot. Maybe fine now, but it will make scratchy sounds in the future. If you make the current pot a fixed resistor and parallel connect a pot and cap (pot to ground, cap on top to block DC), with a higher value pot, you'll get the same performance, but no scratchiness.
Last edited:
Thanks, the presence pot does make sense, still shunts the high frequency to ground but no dc going through it. I will do that now too,
Preamp section is proving to be a pain in terms of layout so I'll give that another work over tomorrow (or later in the week, then hopefully start getting this thing into an amp I can use and gig with =D
Preamp section is proving to be a pain in terms of layout so I'll give that another work over tomorrow (or later in the week, then hopefully start getting this thing into an amp I can use and gig with =D
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.