sds1 wrote: ↑Tue Nov 09, 2021 2:00 pm
This thread should be unpinned, that's great that everyone has come up with their own creative ways to trim the PI, their own opinions on the purpose of this calibration, but Dumble had a very specific outcome in mind for this trimpot and a very specific calibration procedure to go with it, and it's buried in this thread among other answers which are not challenged, the bad info is spreading more than the good and thus nobody knows about the Ampeg procedure, or understands how besides the point it is to calibrate the phase inverter to itself when there's a feedback loop, tubes, etc to consider.
Anyhow... Please. Unpin.
The Frenchie videos are wrong too.
Respectfully.
I would love for you to tell me how mine are wrong... I love learning.
I explained in mine how to balance them evenly. I don't know from memory if i ever said "this is how dumble did it" in fact I thought I said that he often intentionally imbalanced them a bit to improve 2nd order harmonics... but I made the videos a long time ago at this point. Just calling something 'wrong' doesn't make it wrong until you provide actual corrections, it will only help the community if you provide meaningful feedback.
Just telling people what's wrong, doesn't mean you're actually right. Maybe I'll just say you are wrong and move along.
I made those videos to share information and create discussion. I pinned this topic because it allows for an open discussion about something that comes up a TON. I was asked for a link to my video on this from a FB member because they were trying to find it and wanted to review the information.
I'll also add your thought that all the 'bad' info swallows up the 'good' in the thread, this is 100% how almost this entire forum works. (and ALL forums work for that matter) You'll see questions and discussion on the first page or two, and someone will come along with a definitive answer on page 3... nobody goes back and deletes all the content prior to page 3, we leave the history for people to read and research on their own.
I 'PERSONALLY' (and again my own opinion) think that Dumble philosophy with the overdrive special amps was to make sure the only distortion sound was generated in the overdrive circuit, and therefore keeping the PI as clean as possible for as long as possible with the advent of trim pot between the PI plates as an adjustment tool to match the sine wave of both sides of the LTPI, using the SVT method and an oscilloscope. Dumble always, purposely set the plates with a 10K difference (like 110K and 120K for example), and then added a 5K to 15K trim pot for the adjustment.
For the steelstringsinger family he took a different approach. He always had the plates with matched values (like 100k and 100k). His choice of adjustment trim pot value varied between 5K and 15K. Matched plates and a 5K adjustment present on SSS 001 and DL 014 would clearly not be enough range to match the LTPI sides.
I don't think a lot of people in the community share this view, but I personally think his ambition with the steelstringsinger was to purposely leave the PI unbalanced, but in a methodical way. The steel string singer is a very clean hi-fi style amp, and by adding some power amp distortion and extra overtones and harmonics in the PI, makes the amp less sterile and much more lively and rich. Otherwise, in my view, if he wanted the matched sides, he would have set these amps with the same 10K plates differential, present on the overdrive special
I would love for you to tell me how mine are wrong... I love learning.
Have a look at the Ampeg SVT schematic, the calibration procedure is there.
Just telling people what's wrong, doesn't mean you're actually right. Maybe I'll just say you are wrong and move along.
This thread is "wrong" simply for being ambiguous, and for burying the info the community would benefit from the most.
The Ampeg SVT procedure isn't even mentioned until post #12.
In post #16 additional information is provided to support the claim that the SVT calibration is indeed the procedure Dumble used.
This is the information that should be prominent in a sticky, and not buried in some other thread alongside a dozen other procedures that are technically dissimilar.
Measuring PI plate voltage at zero signal, versus injecting a test signal and scoping waveform at the speaker jack -- how are these possibly valid alternate methods for the same procedure? One of them is definitely "wrong".
IMO
P.S. the method you follow in your videos disregards the remainder of the power amp
Bombacaototal wrote: ↑Tue Nov 09, 2021 7:54 pm
Otherwise, in my view, if he wanted the matched sides, he would have set these amps with the same 10K plates differential, present on the overdrive special
But there's up to a 25k differential available via the trimpot...
The SSS trimpot has 15k more adjustment range compared to the ODS. I'm more inclined to believe the 100k plates were to simplify the BOM.
Bombacaototal wrote: ↑Tue Nov 09, 2021 7:54 pm
Otherwise, in my view, if he wanted the matched sides, he would have set these amps with the same 10K plates differential, present on the overdrive special
But there's up to a 25k differential available via the trimpot...
The SSS trimpot has 15k more adjustment range compared to the ODS. I'm more inclined to believe the 100k plates were to simplify the BOM.
I am afraid that is incorrect. Please refer to #001 for example, or #014 both of which use 5K
Bombacaototal wrote: ↑Tue Nov 09, 2021 7:54 pm
Otherwise, in my view, if he wanted the matched sides, he would have set these amps with the same 10K plates differential, present on the overdrive special
But there's up to a 25k differential available via the trimpot...
The SSS trimpot has 15k more adjustment range compared to the ODS. I'm more inclined to believe the 100k plates were to simplify the BOM.
I am afraid that is incorrect. Please refer to #001 for example, or #014 both of which use 5K
I would love for you to tell me how mine are wrong... I love learning.
Have a look at the Ampeg SVT schematic, the calibration procedure is there.
Just telling people what's wrong, doesn't mean you're actually right. Maybe I'll just say you are wrong and move along.
This thread is "wrong" simply for being ambiguous, and for burying the info the community would benefit from the most.
The Ampeg SVT procedure isn't even mentioned until post #12.
In post #16 additional information is provided to support the claim that the SVT calibration is indeed the procedure Dumble used.
This is the information that should be prominent in a sticky, and not buried in some other thread alongside a dozen other procedures that are technically dissimilar.
Measuring PI plate voltage at zero signal, versus injecting a test signal and scoping waveform at the speaker jack -- how are these possibly valid alternate methods for the same procedure? One of them is definitely "wrong".
IMO
P.S. the method you follow in your videos disregards the remainder of the power amp
Your high conflict approach is not going to work here. It doesn't matter what your opinion is, because your tone sucks and is confrontational. You have 11 posts to your name. If you want to contribute in a civil and calm and respectful manner, great. If you have knowledge and experience to share, it's welcome and so are you. But if this is going to be how it is with you, just say so.
I would love for you to tell me how mine are wrong... I love learning.
Have a look at the Ampeg SVT schematic, the calibration procedure is there.
Just telling people what's wrong, doesn't mean you're actually right. Maybe I'll just say you are wrong and move along.
This thread is "wrong" simply for being ambiguous, and for burying the info the community would benefit from the most.
The Ampeg SVT procedure isn't even mentioned until post #12.
In post #16 additional information is provided to support the claim that the SVT calibration is indeed the procedure Dumble used.
This is the information that should be prominent in a sticky, and not buried in some other thread alongside a dozen other procedures that are technically dissimilar.
Measuring PI plate voltage at zero signal, versus injecting a test signal and scoping waveform at the speaker jack -- how are these possibly valid alternate methods for the same procedure? One of them is definitely "wrong".
IMO
P.S. the method you follow in your videos disregards the remainder of the power amp
Your high conflict approach is not going to work here. It doesn't matter what your opinion is, because your tone sucks and is confrontational. You have 11 posts to your name. If you want to contribute in a civil and calm and respectful manner, great. If you have knowledge and experience to share, it's welcome and so are you. But if this is going to be how it is with you, just say so.
I don't see where I was disrespectful to anyone. No personal attacks. No assigning merit based on post count or anything lame like that. If there's something I should apologize for please be specific.
I've said my piece, if you high post count bros are comfortable with the clarity of this thread then let it be. It's a 9 year old thread god forbid it should be revisited.
Post #4 in this thread :
I think making this one method a sticky may be misleading to many.
Based on the information I am seeing posted elsewhere I would say this was correctly predicted.
Well, I do see where you were disrespectful to Phil and your tone is confrontational. Yeah, I get that the site is less than organized in places. But anyone who is a regular here figures it out and we all help each other find information. One of the mandates of the site's owner is that the history of the site will be preserved, so that's why the Sticky stands as it is, any warts and all. But being new here, I'm sure you didn't know that. Why don't you write up your particular procedure with references and a little treatise on the matter and your rationale and post a PDF? There is some serious resident expertise here that will welcome your input. Always good to hear new perspective and experiences. And, if you have specific Dumble knowledge that helped shape your view, please feel free to share that too.
One of the mandates of the site's owner is that the history of the site will be preserved, so that's why the Sticky stands as it is, any warts and all. But being new here, I'm sure you didn't know that.
Correct, I didn't know that. I joined in 2017 btw, same year as Phil. I was read-only before I joined. If that even matters.
There are already more accurate discussions on this matter in these forums, contributed by more knowledgeable folk than me, they are just not the sticky thread that gets the majority of traffic. So I'd love to help but I have no new info to add. Seems like this fix will take an admin to reprioritize information already available in the forums.
If you find a reference elsewhere on the forum that pertains to the PI Trim setting, you can always copy the link and post it here in this thread, as you have. That will help others that come to the Sticky as the master reference on the topic.
Bombacaototal wrote: ↑Tue Nov 09, 2021 7:54 pm ... For the steelstringsinger family he took a different approach. ...
As far as I know, A. Dumble's advice to adjust the “Dynamic Balance” control in accordance with the corresponding instructions for the Ampeg SVT/V9 power amplifier (method "A" or - without a THD meter - method "B") referred in particular to his SSS and ODS amplifiers with a 150W power amp:
SSS 150W SRV.png
external dynamic balance pot.jpg
121.jpeg
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Bombacaototal wrote: ↑Tue Nov 09, 2021 7:54 pm ... For the steelstringsinger family he took a different approach. ...
As far as I know, A. Dumble's advice to adjust the “Dynamic Balance” control in accordance with the corresponding instructions for the Ampeg SVT/V9 power amplifier (method "A" or - without a THD meter - method "B") referred in particular to his SSS and ODS amplifiers with a 150W power amp:
SSS 150W SRV.png
external dynamic balance pot.jpg
121.jpeg
Hi Max, do you know what was the value of the trim pot for balancing the PI on 121?
Again, this method would not have worked on 001 and 014, due to the low value of respective pots
