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Old 23rd July 2011, 05:46 PM   #161
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Quote:
Originally Posted by jcx View Post
the diff pair cascode resistive bias will compromise performance

1 . ---a simple improvement is to use resistive bootstrap - add a R from the output to R19 in the ratio of the feedback resistors

I would still add a follower between the diff pair degen R and the cascode bias - the diff pair shouldn't be subject to resistive load or positive power supply noise injection at this point - check the psrr performance/look for ps ripple frequency sidebands - the filter for the front end is not that great for ps ripple frequencies


#2 - why no current clamp on the VAS - you already have the emitter degen R?


3# - and I could (have) go on at some lenghth about TMC - a interesting criticism could be that the "single pole" "damped step response" of the global loop is in fact dangerous in a beginner's amp since the true stability margin is not reflected in the step response
I must respond separately to this post .

#1 - I simulated this (the simple resistor-R55). (below 1) is the extra R - is that right ? (Below 2) is PSRR without it. (Below 3) is with R55.

#2 - Ran the amp at 45-0-45Vdc massively clipping w/ 8R load in a water bucket overnight. Q9 was just warm , actually Q10-12 (to-126's) on the small VAS heatsink became warmer. I can't blow it.

#3 - Never had a problem with the current values for this amps TMC , but ... the option remains for conventional miller compensation.

Please comment on #1 , to add R55 would be a simple pad/trace addition.
(neat trick).

EDIT !!! - the resistive bootstrap raises 1k THD from .38ppm to .004% , not good tradeoff....
OS
Attached Images
File Type: gif bootstrap.gif (17.7 KB, 1772 views)
File Type: gif No R55.gif (20.0 KB, 1750 views)
File Type: gif with R55.gif (20.4 KB, 1455 views)
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Last edited by ostripper; 23rd July 2011 at 05:56 PM.
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Old 23rd July 2011, 05:49 PM   #162
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Quote:
Originally Posted by Sound_Buster View Post
Although have built few amplifiers (only two... ), I had noticed these mutual influence between drivers and outputs on simulations.

What is the schedule for the boards appearing at DiyAudio Store?
Mid- august (maybe sooner). Variac presented this to me right before I was going to move (to Albany NY) , 1000 mi. away. I might be "away" for a couple weeks ..
(No internet).

OS
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Old 23rd July 2011, 06:51 PM   #163
jcx is online now jcx  United States
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the correct value to make the bootstrap R(55), R19 equal the feedback ratio is [edit: I'll get this right eventually] ~2.7Meg : 68 K = 33K : 820 this boosts the common mode impedance biasing your cascodes

drop the impedance of the added output boostrap R(55) and R19 while keeping the ratio and another option is to just not stuff the parts connceting to the diff pair tail - the cascode still moves with the AC input signal


and if you intend to get differential amp rejection of error V across the ground breaker you have R3 connected wrong - of course the cancellation can only work with a near zero Z source

Last edited by jcx; 23rd July 2011 at 07:18 PM.
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Old 23rd July 2011, 10:07 PM   #164
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Quote:
Originally Posted by jcx View Post
the correct value to make the bootstrap R(55), R19 equal the feedback ratio is [edit: I'll get this right eventually] ~2.7Meg : 68 K = 33K : 820 this boosts the common mode impedance biasing your cascodes

drop the impedance of the added output boostrap R(55) and R19 while keeping the ratio and another option is to just not stuff the parts connceting to the diff pair tail - the cascode still moves with the AC input signal


and if you intend to get differential amp rejection of error V across the ground breaker you have R3 connected wrong - of course the cancellation can only work with a near zero Z source
First of all , I did not reconnect R3 to the "lifted" ground on the schema(fixed).
It IS correct on the PCB . So , I zero'ed my sources.

(Below 1-2) is with a 2.2meg bootstrap from OP (R55). I only gained 2db PSRR at low frequencies. But , THD went down to .1ppm. (.000012%).

(Below 3-4) is with the standard 15v zener referenced to ground. Here I gained 5-6db below 20hz - in the audio band , still at my standard -82db PSRR.
distortion stays at .32ppm , same as the original design.

Very small "return" using the bootstrap , the grounded zener actually does slightly better in the PSRR results.

PS -I . stepped between 500k - 3meg for R55.

OS
Attached Images
File Type: gif 2.2meg schema.gif (17.9 KB, 1437 views)
File Type: gif 2.2meg BS.gif (21.0 KB, 1405 views)
File Type: gif zener schema.gif (48.9 KB, 269 views)
File Type: gif ZenerPSRR.gif (18.6 KB, 265 views)
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Old 24th July 2011, 06:14 AM   #165
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Bonsai - I am about to " execute the bit" (Come on, Variac )

Quote:
Originally Posted by AndrewT View Post
post151.
Can you explain 0r01 for R57&58
I use them to monitor the uV's (currents) in the simulation. I will use these insignificant resistances to plot a stepped response or on the rails to either create simulated ripple or monitor Ic. I am to the point of quite faithfully predicting what the "real world" will do before the fact. (no surprises)

Below is the short "book" describing what functions the basic sections of this amp perform , as well as what modifications can be done to each section.
Verbose instructions for all 3 trimmers are explained , as well as stuffing the PCB right up to the drivers and using THEM as the experimental outputs BEFORE installing the expensive power devices. VERY comprehensive , my kids could build this !!

PS- my discussion with "JCX" resulted in another "option" documented + the addition of a new jumper on the board (universal cascode reference option).
It's explanation is in the "mirror-cascode" section of the text. (below)



OS
Attached Images
File Type: gif another option.gif (39.5 KB, 377 views)
Attached Files
File Type: txt DIYA amp -options.txt (7.1 KB, 187 views)
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Last edited by ostripper; 24th July 2011 at 06:32 AM.
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Old 24th July 2011, 08:22 AM   #166
dadod is online now dadod  Croatia
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Quote:
Originally Posted by ostripper View Post
Bonsai - I am about to " execute the bit" (Come on, Variac )



I use them to monitor the uV's (currents) in the simulation. I will use these insignificant resistances to plot a stepped response or on the rails to either create simulated ripple or monitor Ic. I am to the point of quite faithfully predicting what the "real world" will do before the fact. (no surprises)

Below is the short "book" describing what functions the basic sections of this amp perform , as well as what modifications can be done to each section.
Verbose instructions for all 3 trimmers are explained , as well as stuffing the PCB right up to the drivers and using THEM as the experimental outputs BEFORE installing the expensive power devices. VERY comprehensive , my kids could build this !!

PS- my discussion with "JCX" resulted in another "option" documented + the addition of a new jumper on the board (universal cascode reference option).
It's explanation is in the "mirror-cascode" section of the text. (below)



OS
This is going to be great amp and I have only one complain here. To much possibilities and a torture for an inexperiance DIYer. I suggest that you chose one or maximum two possible configuration(better one only and the one according your taste).
dado
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Old 24th July 2011, 08:42 AM   #167
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Exclamation Final (management) and DIY'er review.

Below is the "output"...

- no jumpers in the board store double sided version. (except "CRZ")

-NO errors ... checked out versus the working one (mongrel),
the "technicolor" rail trace ,and when I made the book.

- DIY'er advice and comments/changes included. Thanks Andrew !

-Good looks and durable assets (fat pads - test points - multi pitch components)

- adaptable to 3 mounting styles.

- Solder mask is not used on test points and all through holes are masked on top but not bottom , this can be altered as desired depending on manufacturer , material , cost. Not my call.

Can't think of any more features , If I wasn't making my "DBT" triple ... I would throw these in my Altec - Lansing amp case in a heartbeat.

Management , please look this over carefully. You have the $$$'s - your call.

Thanks, (OS)
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Old 24th July 2011, 08:49 AM   #168
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Quote:
Originally Posted by dadod View Post
This is going to be great amp and I have only one complain here. To much possibilities and a torture for an inexperiance DIYer. I suggest that you chose one or maximum two possible configuration(better one only and the one according your taste).
dado
Ahhh... thought of that , too. They can skip the learnin' and decidin' and just follow the BOM EXACTLY !!! This will get them the exact amp the main schematic depicts. No more, no less. If their parts are not EBAY , it will work.

PS- they might want to read "Vbe" and "general construction" , as this will keep the "magic smoke" away.
maybe "advanced options.txt" would be better...
Or( "construction - advanced options") They should read all of it before they "play" , it is generalized on purpose and it would serve them to at least know the 5 sections of the topology (troubleshooting or questions) ... very basic class AB "stuff".
OS
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Last edited by ostripper; 24th July 2011 at 08:55 AM.
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Old 24th July 2011, 03:20 PM   #169
farjon is offline farjon  Brazil
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Quote:
Originally Posted by ostripper View Post
Below is the short "book" describing what functions the basic sections of this amp perform , as well as what modifications can be done to each section.
Verbose instructions for all 3 trimmers are explained , as well as stuffing the PCB right up to the drivers and using THEM as the experimental outputs BEFORE installing the expensive power devices. VERY comprehensive , my kids could build this !!
Hi, OS.

1- Is there a revised BOM corresponding to the Rev. 2.1 board? Or is the last published in this thread ok? Schematics also...



2- How low the power supplies can go? Its about recycling used transformers.


Last edited by farjon; 24th July 2011 at 03:37 PM.
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Old 24th July 2011, 07:29 PM   #170
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Default The "package"

- 3 texts (instructions , BOM , and component "extended" list.)
- PCB JPG. (toner transfer)
- The LT files
- Component overview
- "Technocolor" voltage overview

Have fun , please inform of errors.

OS
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