AndrewT said:
Hi Andrew,
I assume the bias polarity depends on which polarity of the electrolytic cap pair are face to face with each other? If so, does that mean a -Vbias for -Ve face to face and +Vbias for +Ve face to face?
I trust you had a good Christmas Holiday and will have a Safe and Happy New Year's Eve and Day.
Regards,
John L. Males
Willowdale, Ontario
Canada
29 December 2006 11:42
dc servo
ok, this dc servo is adapted from the APT-1 amp. the input goes to the amplifier output, and the output goes to the amplifier inverting input on the diff amp. you will need to remove the cap in the amplifier feedback circuit and jumper it (that's the 22uf/25v cap), and change vr1 to (2) 50 ohm resistors.
if you want an offset pot, you can make a voltage divider from the +12 to the -12 rails with (2) 1k resistors and a 200 ohm pot in the middle. the wiper goes to a 4k7 resistor, which then goes to the inverting input of the op amp.
this provides a completely independent DC feedback path which does not alter the balance of the amp's diff amp (i.e. you introduce no 2nd harmonic distortion in the diff amp).
i also have another DC servo that seems to work as well,and possibly better, and i will upload that one in my next post.
ok, this dc servo is adapted from the APT-1 amp. the input goes to the amplifier output, and the output goes to the amplifier inverting input on the diff amp. you will need to remove the cap in the amplifier feedback circuit and jumper it (that's the 22uf/25v cap), and change vr1 to (2) 50 ohm resistors.
if you want an offset pot, you can make a voltage divider from the +12 to the -12 rails with (2) 1k resistors and a 200 ohm pot in the middle. the wiper goes to a 4k7 resistor, which then goes to the inverting input of the op amp.
this provides a completely independent DC feedback path which does not alter the balance of the amp's diff amp (i.e. you introduce no 2nd harmonic distortion in the diff amp).
i also have another DC servo that seems to work as well,and possibly better, and i will upload that one in my next post.
Attachments
another servo
this is a servo i came up with for an amp design i'm working on. the rolloff frequency is about 5 Hz. the design discharges the caps when power is removed (the APT-1 used a fet switch which added a little more complexity).
this one is an inverting design, and adds the offset correction to the + input of the amp instead of the - input.
btw, my avatar image is an m1 tank...... spent some time in the army, and m1's are amazing vehicles...... i also like amps built like a tank.........
this is a servo i came up with for an amp design i'm working on. the rolloff frequency is about 5 Hz. the design discharges the caps when power is removed (the APT-1 used a fet switch which added a little more complexity).
this one is an inverting design, and adds the offset correction to the + input of the amp instead of the - input.
btw, my avatar image is an m1 tank...... spent some time in the army, and m1's are amazing vehicles...... i also like amps built like a tank.........
Attachments
Hi Uncle,
why the feedback resistor added to the integrator cap?
How about adding a T filter on the output to reduce the noise being injected back into the LTP input?
The first shows 1M0 and 100uF. How long does this take to trigger?
What effect will reverse polarity have on the 10u & 100u caps? add reverse DC protection.
why the feedback resistor added to the integrator cap?
How about adding a T filter on the output to reduce the noise being injected back into the LTP input?
The first shows 1M0 and 100uF. How long does this take to trigger?
What effect will reverse polarity have on the 10u & 100u caps? add reverse DC protection.
why the need to DC couple? I realise that the DC servo allows operation as a DC coupled amp, But why MUST the cap be removed?
the resistor actually sets the gain at DC, as well as discharging the cap after power is removed. reverse polarity shouldn't be much of a problem if you use A> a higher voltage cap (like a 50v or higher) since the actual voltage seen at the cap is quite low, and most electrolytics tolerate a small amount of reverse voltage. B> a bipolar cap or opposed pair... bipolars are expensive and oversized, so an opposed pair is probably the cheapest and takes up less "real estate".
rolloff frequency for both circuits is about 5hz.
removing the cap from the original feedback loop A> removes a reactance from the feedback loop which can cause phase shift in the feedback and instability in the amp. B> with the dc servo the purpose of the original cap in the feedback loop is redundant. you can actually do more with the servo, such as tailoring it's frequency response, adding an offset control (outside the signal path), that you can't do with the "cheater" cap.
any noise generated by the op amp is below 5hz, and about nonexistent with a good low noise op amp. noise is proportional to the square of the frequency, which is why noise is usually expressed as nano- or picovolts per square root hertz.
rolloff frequency for both circuits is about 5hz.
removing the cap from the original feedback loop A> removes a reactance from the feedback loop which can cause phase shift in the feedback and instability in the amp. B> with the dc servo the purpose of the original cap in the feedback loop is redundant. you can actually do more with the servo, such as tailoring it's frequency response, adding an offset control (outside the signal path), that you can't do with the "cheater" cap.
any noise generated by the op amp is below 5hz, and about nonexistent with a good low noise op amp. noise is proportional to the square of the frequency, which is why noise is usually expressed as nano- or picovolts per square root hertz.
Re: another servo
Hi unclejed,
I have some questions (sorry guys my New Years resolution did not include "no more quetions!" lol lol lol):
I have the APT PreAmp (agmonst a few others - CL-34, Aragon and yet To Do Aleph 1.7) and I do like the APT PreAmp. Sadly I never was able to buy the APT-1 amplifier.
Which version of the schematic for quasi's amplifier are you referring to? The most recent schematic does not appear to have a 22uF capacitor or am I blind?
Are you suggesting VR1 be replaced because you favour fixed (film) resistors instead for noise reasons? I know there were some during the open comment part of the refinement of the design wanted fixed resistor values instead of VR1 on basis of greater stability and much less noise on fixed resistors as opposed to using any sort of pot (aka VR1).
Quasi can correct me if I am in error, but the decision to leave VR1 was to ensure the least DC offset possible could be set. Can one still choose to use a pot for VR1 notwithstanding your below suggestion for an offset pot via the +- 12V opamp supply??
Pardon my lack of design knowledge, but is a DC servo that much better than the usual feedback circuit. No need for any involved explanation. If you wish to explain I suggested your keep it basic as I do not understand NFB design for am amplifier. I only have a basic understanding of how to tweek and a bit about validating the rolloff frequency, not the shelving element part of the BFB.).
Does a "traditional" NFB circuit produce 2nd order harmonic distoration?
Have you determined which of the servo designs you proposed you prefer?
Is that any preference from a design perspective if one uses a servo desigh that adds the offset correction to the + or - if the input LTP/diff pair?
Which capacitor are you referring to in both servo designs?
Ideally one would use a non-polar capacitor?
Ho does one calculate the rolloff frequency for each servo design you proposed?
In the "traditional" NFB design there is a RC time constant suggested be desinged for. The current quasi design NFB RC time constant for the RC leg to ground is at least 100ms minimum. Do either of the proposed servos meet this minimum requirement? What are the RC time constants for the two proposed servo circuits?
Which capacitor is being referred to?
My understanding from the above comment is the revelant capacitor needs to stay in the circuit as designed. Yes or no?
Sorry unceljed, I am now becoming very confused which capacitor is being refered to. Can you enlighten me?
Does this mean one could incorporate the same essence as the Leach NFB Feedforward de either of these servos?
What is the "cheater cap" in quasi's design?
Would a NE5332, TL071, ADxxx, OPA's or similar be acceptable for the opamp for your DC Servo's designs? I do not need to get into the pro's anc cons of which one is better. If you feel a need to exporess stongly in favour or against any AP amp for the DC Servo design I an willing and able to hear your thought regarding.
The DC servos you are proposing would change the current setup procedure quasi has documented for the current quasi design?
Are you aware of the LM317K related circuit in the Anthony Holton N-Channel amp design? Would you say the LM317K designed used in the Anthony Holton design is also a DC servo?
Regards,
John L. Males
Willowdale, Ontario
Canada
03 January 2007 02:51
Hi unclejed,
I have some questions (sorry guys my New Years resolution did not include "no more quetions!" lol lol lol):
unclejed613 said:
I have the APT PreAmp (agmonst a few others - CL-34, Aragon and yet To Do Aleph 1.7) and I do like the APT PreAmp. Sadly I never was able to buy the APT-1 amplifier.
Which version of the schematic for quasi's amplifier are you referring to? The most recent schematic does not appear to have a 22uF capacitor or am I blind?
Are you suggesting VR1 be replaced because you favour fixed (film) resistors instead for noise reasons? I know there were some during the open comment part of the refinement of the design wanted fixed resistor values instead of VR1 on basis of greater stability and much less noise on fixed resistors as opposed to using any sort of pot (aka VR1).
Quasi can correct me if I am in error, but the decision to leave VR1 was to ensure the least DC offset possible could be set. Can one still choose to use a pot for VR1 notwithstanding your below suggestion for an offset pot via the +- 12V opamp supply??
Pardon my lack of design knowledge, but is a DC servo that much better than the usual feedback circuit. No need for any involved explanation. If you wish to explain I suggested your keep it basic as I do not understand NFB design for am amplifier. I only have a basic understanding of how to tweek and a bit about validating the rolloff frequency, not the shelving element part of the BFB.).
Does a "traditional" NFB circuit produce 2nd order harmonic distoration?
Have you determined which of the servo designs you proposed you prefer?
unclejed613 said:
Is that any preference from a design perspective if one uses a servo desigh that adds the offset correction to the + or - if the input LTP/diff pair?
unclejed613 said:
Which capacitor are you referring to in both servo designs?
Ideally one would use a non-polar capacitor?
Ho does one calculate the rolloff frequency for each servo design you proposed?
In the "traditional" NFB design there is a RC time constant suggested be desinged for. The current quasi design NFB RC time constant for the RC leg to ground is at least 100ms minimum. Do either of the proposed servos meet this minimum requirement? What are the RC time constants for the two proposed servo circuits?
Which capacitor is being referred to?
My understanding from the above comment is the revelant capacitor needs to stay in the circuit as designed. Yes or no?
Sorry unceljed, I am now becoming very confused which capacitor is being refered to. Can you enlighten me?
Does this mean one could incorporate the same essence as the Leach NFB Feedforward de either of these servos?
What is the "cheater cap" in quasi's design?
Would a NE5332, TL071, ADxxx, OPA's or similar be acceptable for the opamp for your DC Servo's designs? I do not need to get into the pro's anc cons of which one is better. If you feel a need to exporess stongly in favour or against any AP amp for the DC Servo design I an willing and able to hear your thought regarding.
The DC servos you are proposing would change the current setup procedure quasi has documented for the current quasi design?
Are you aware of the LM317K related circuit in the Anthony Holton N-Channel amp design? Would you say the LM317K designed used in the Anthony Holton design is also a DC servo?
Regards,
John L. Males
Willowdale, Ontario
Canada
03 January 2007 02:51
The output offset / DC servo World According to Quasi.
DC servo utilisation would be an interesting upgrade to this amplifier. In practice though once set the DC offset drifts very little through quite a wide temperature range. I would be surprised if most constructors found more than a 10mV drift.
The Quasi Mos Amp is intended to be a minimalist design. I.e; using the bare minimum components that are commonly available to achieve a high quality and powerful amplifier. A DC servo would add to the complexity, albeit a fairly easy one with a small daughter board.
So each to his own provided results (and piccies) are posted.
Ciao
Q
DC servo utilisation would be an interesting upgrade to this amplifier. In practice though once set the DC offset drifts very little through quite a wide temperature range. I would be surprised if most constructors found more than a 10mV drift.
The Quasi Mos Amp is intended to be a minimalist design. I.e; using the bare minimum components that are commonly available to achieve a high quality and powerful amplifier. A DC servo would add to the complexity, albeit a fairly easy one with a small daughter board.
So each to his own provided results (and piccies) are posted.
Ciao
Q
Re: The output offset / DC servo World According to Quasi.
For my two cents worth,
One amp I recently bought by chance about 6 months ago is a BiPolar HT design using a toroid and the 2SC5200/2SA1943 and 2SB649A/2SD669A for each amplifier. The "stable" DC offset for all but two channels is about 1.5mv, one is about 10.5mv and other is about 16.8mv. Oddly it is the main channels that are higher even though all 5 amps are of same design. I have to assume even these higher DC offsets are very respectable for a modest commerical amp? I know from curiousity checking that the drift is next to nil. I can tell you the initial DC offsets at outputs were 1.8/10.8/14.4mvDC about 30 seconds after turning on the amp. I assume that is not much of a drift to the stable. All of these are when no signal is applied to the input. When using average listening levels there really is not much difference to the noted stable DC offsets. I am sure this amp uses the traditional NFB circuit like quasi uses, as I cannot obtain a schematic for it and there is no need for me to open the amplifier.
It sounds to me the servo may in theory be better, but perhaps not worth the extra complexity it may add, let alone modify the PCB. I am not sure I would be a fan of using a daughterboard. For me I now know the current quasi design well enough to adjust to parts availability and a few personal biases I have on a few elements. such as more output capacitance for output rails to output devices, maybe add in the Leach Feedforward NFB now that I fully understand the calculations, perhaps regulated supply for the input/driver stages (at same PSU voltage as output stage) and add a balanced input. The latter is just addition in the case, not a change to the base quasi design.
I like the design for the simplicity and part flexibility. The only element is the MJE340/350 in that they are hard to match for their robustness. Not a negative comment, just amazing how such a popular part has few if any alternates considering other parts have range of choice of alternates based on either availability or one's perference.
I am not sure how I will be able to compare the NFB changes, added module capacitors, large non-polar NFB capacitor, or regulated supply to the base design if I do not have the time to build a few base boards as reference. The regulated PSU is easy to effect as it has very little impact to the PCB modifications to accomodate. The additional capacitance changes are partly a cost factor for most part and a very big cost factor if I go to 120uF non-polar for the NFB leg. Adding in the Leach NFB network will require a bit more effort via my graphics editing methods of the PCB, but I have already laid out a number of changes to the base PCB over the course of last months. The few days to make these changes will likely not be a reason to avoid the Leach NFB. I will then need to merge all the PCB changes into one PCB which would take a few days work.
In end it is the simplicity of design, parts flexibility and consistant stable results all have experienced building the quasi amp that make the quasi amp so compelling to build and enjoy. A bonus is the BiPolar/"transistor" Brother version that keeps the same design and is likely the only pair of designs one could use to truely compare MOSFET and BiPolars by having same input stage as close to similar driver stage as allowed using different output devices. The two close to same designs enables one to mix MOSFET and BiPolar amps in an active system for those that feel a need to suit a driver or frequency range of their system whilst keeping the amps close to the same design/character.
Regards,
John L. Males
Willowdale, Ontario
Canada
05 January 2007 18:24
For my two cents worth,
One amp I recently bought by chance about 6 months ago is a BiPolar HT design using a toroid and the 2SC5200/2SA1943 and 2SB649A/2SD669A for each amplifier. The "stable" DC offset for all but two channels is about 1.5mv, one is about 10.5mv and other is about 16.8mv. Oddly it is the main channels that are higher even though all 5 amps are of same design. I have to assume even these higher DC offsets are very respectable for a modest commerical amp? I know from curiousity checking that the drift is next to nil. I can tell you the initial DC offsets at outputs were 1.8/10.8/14.4mvDC about 30 seconds after turning on the amp. I assume that is not much of a drift to the stable. All of these are when no signal is applied to the input. When using average listening levels there really is not much difference to the noted stable DC offsets. I am sure this amp uses the traditional NFB circuit like quasi uses, as I cannot obtain a schematic for it and there is no need for me to open the amplifier.
It sounds to me the servo may in theory be better, but perhaps not worth the extra complexity it may add, let alone modify the PCB. I am not sure I would be a fan of using a daughterboard. For me I now know the current quasi design well enough to adjust to parts availability and a few personal biases I have on a few elements. such as more output capacitance for output rails to output devices, maybe add in the Leach Feedforward NFB now that I fully understand the calculations, perhaps regulated supply for the input/driver stages (at same PSU voltage as output stage) and add a balanced input. The latter is just addition in the case, not a change to the base quasi design.
I like the design for the simplicity and part flexibility. The only element is the MJE340/350 in that they are hard to match for their robustness. Not a negative comment, just amazing how such a popular part has few if any alternates considering other parts have range of choice of alternates based on either availability or one's perference.
I am not sure how I will be able to compare the NFB changes, added module capacitors, large non-polar NFB capacitor, or regulated supply to the base design if I do not have the time to build a few base boards as reference. The regulated PSU is easy to effect as it has very little impact to the PCB modifications to accomodate. The additional capacitance changes are partly a cost factor for most part and a very big cost factor if I go to 120uF non-polar for the NFB leg. Adding in the Leach NFB network will require a bit more effort via my graphics editing methods of the PCB, but I have already laid out a number of changes to the base PCB over the course of last months. The few days to make these changes will likely not be a reason to avoid the Leach NFB. I will then need to merge all the PCB changes into one PCB which would take a few days work.
In end it is the simplicity of design, parts flexibility and consistant stable results all have experienced building the quasi amp that make the quasi amp so compelling to build and enjoy. A bonus is the BiPolar/"transistor" Brother version that keeps the same design and is likely the only pair of designs one could use to truely compare MOSFET and BiPolars by having same input stage as close to similar driver stage as allowed using different output devices. The two close to same designs enables one to mix MOSFET and BiPolar amps in an active system for those that feel a need to suit a driver or frequency range of their system whilst keeping the amps close to the same design/character.
Regards,
John L. Males
Willowdale, Ontario
Canada
05 January 2007 18:24
Re: Re: The output offset / DC servo World According to Quasi.
Indeed. These truly are amazing transistors. Really the only alternative would be TO220 devices but these are larger, cost more and have a different pinout. Even so, some of these whilst rated more powerful than the MJE340/350 are less capable at higher voltages. All hail the 340/350!
In my other amp, "Brother of Quasi" I have switched to MJE15030 / 15031. The additional drive current required by the Bi-Polar output stage easily exceeds the SOAR of the 340/350. So they got the flick for that stage (it hurt). They are still there in the second stage although they could be replaced with BF469/470 or similar but they are more expensive (in Aus anyway).
Finally my biggest problem was finding transistors that could handle higher voltage rails, particularly in the input stage. Beyond a Vce of 80 volts transistor choices rapidly decline.
Cheers
Q
keypunch said:
Indeed. These truly are amazing transistors. Really the only alternative would be TO220 devices but these are larger, cost more and have a different pinout. Even so, some of these whilst rated more powerful than the MJE340/350 are less capable at higher voltages. All hail the 340/350!
In my other amp, "Brother of Quasi" I have switched to MJE15030 / 15031. The additional drive current required by the Bi-Polar output stage easily exceeds the SOAR of the 340/350. So they got the flick for that stage (it hurt). They are still there in the second stage although they could be replaced with BF469/470 or similar but they are more expensive (in Aus anyway).
Finally my biggest problem was finding transistors that could handle higher voltage rails, particularly in the input stage. Beyond a Vce of 80 volts transistor choices rapidly decline.
Cheers
Q
Re[03]: The output offset / DC servo World According to Quasi.
Quasi,
<kneeling>Though I am not the design god that you are.</kneeling> I had looked at the MJE15030/31 devices as alternate to the MOSFET version when I had difficulty finding the MJE340/350. The MJE15030/31 were nowhere to be found locally. I was aware you used one pair of MJE15030/31 in the "Brother" instead of the MJE340/350. For all intents I have considered the use of the MJE15030/31 in the "Brother" as equivalent for the purposes of comparing a MOSFET and BiPolar amp of same design.
I know many of the so-called subsitutes listed or so-called higher rated devices suggested for the MJE340/350 are in fact not as robust or able to handle higher currents at the higher voltages compared to the MJE340/MJE350. In fact some of the so called alternates are far from able to and I am sure they just blow up in many designs that call for the MJE340/350. I hope the KSE340/KSE350's I have will measure up as well as the MJE340/350 do for your amp.
Regards,
John L. Males
Willowdale, Ontario
Canada
05 January 2007 19:45
Quasi,
<kneeling>Though I am not the design god that you are.</kneeling> I had looked at the MJE15030/31 devices as alternate to the MOSFET version when I had difficulty finding the MJE340/350. The MJE15030/31 were nowhere to be found locally. I was aware you used one pair of MJE15030/31 in the "Brother" instead of the MJE340/350. For all intents I have considered the use of the MJE15030/31 in the "Brother" as equivalent for the purposes of comparing a MOSFET and BiPolar amp of same design.
I know many of the so-called subsitutes listed or so-called higher rated devices suggested for the MJE340/350 are in fact not as robust or able to handle higher currents at the higher voltages compared to the MJE340/MJE350. In fact some of the so called alternates are far from able to and I am sure they just blow up in many designs that call for the MJE340/350. I hope the KSE340/KSE350's I have will measure up as well as the MJE340/350 do for your amp.
Regards,
John L. Males
Willowdale, Ontario
Canada
05 January 2007 19:45
On Semi
Hey Folks don't forget On Semi's awesome sample policy. If you have a credit card and are willing to pay freight, they will ship a 5 piece qty on multiple line items. I picked up about $120 worth of On Semi that cost $30 US in shipping. Their sample policy may even be enough to get one amp built? Sometimes.
Cheers,
Shawn.
Hey Folks don't forget On Semi's awesome sample policy. If you have a credit card and are willing to pay freight, they will ship a 5 piece qty on multiple line items. I picked up about $120 worth of On Semi that cost $30 US in shipping. Their sample policy may even be enough to get one amp built? Sometimes.
Cheers,
Shawn.
anatech said:
Chris,
They pump them out like nothing and the cost is covered in the shipping fee. The program may morph but it will never get canned.
On Semi uses the data to generate leads and cold call data for internal marketing use. BTW there are restrictions, try to abuse it like me, and you'll see them.
Go get some today!
Shawn.
Hi Chris,
I had actually checked Sayal a few times for the MJE340/350 and their pricing was generally 50% to 300% more than the electronics parts store downtown. Also Sayal only had one in Mororola and the complementary in another brand. I had a mindset the two had to be same brand for my own reasons, but their pricing made it simple for me to not have to re-think that aspect. Oddly in many cases Sayal has much higher pricing for surplus inventory than Electrosonic has it new. Scarey I know, but true for at least many of the parts for this amp project. Sayal certainly has excellent pricing on many things, but not items I would want most of time. The 2SC2240 for example was twice as much at Sayal as downtown, so I bought my 2SC2240's downtown.
Newark, Digikey both have minimum quanity orders which was not compatiable with my needs most of time, not to mention I do not use/have credit cards. Too many mistakes made for the 3-4 times I would use one a year. Newark has a Toronto office so thought great, can send them the payment for order. Nope, have to send payment to US and nobody in the company could figure out how it is really done or if can do, despite Toronto office. BMM was another great source but they would not reply to my inquiry how to send them payment. When I send payments I am never in hurry so these places have the time to process the order.
Chris, your reference to Active is for Active Surplus or Active Components. The latter of witch seems part of the Future Electronics family of companies? Latter has very high pricing for many items as well as parts, latter of which actually has started to charge more for used no name items more than it is new.
I liek Shawn, know of a few places about the city where one can obtain parts at good pricing. I suspect Shawn having bee in the industry for some years he said knows more than I do as hobbyist and has a few connections. I am not bothered by one having connection, I just do not and go about my sourcing based on what I can do do and where I can find.
I really think a few APT4025BNs I picked up are great and wish I coudl find more as example. I found a place in US, but they only wanted to seel me the 500 of them they had, not the qty 75 I was interested in. They priced the qty 75 so they cost almost as much as to buy the qty 500.
My reserve about Credit Cards does not just stem from what we hear about related problems at times in news, I have done IT QA for many years and I cannot tell you why things like one bank has had a couple of major problems with the debit system and online banking, as well as others. All Canadian Banks I am talking about here. I use a credit union for my banking and until a few years ago the ATM worked flawlesss. Now that the credit union was pressured to go to Interac the ATM frequently will not access my Account at the ATM in my branch due to "Institution not available". To allow people to still make a withdrawal the CU has loaded special info into the ATM so you can take out cash, but oddly enough when you want to deposit the machine will not let you when this condition exists. When I asked the CU about this problem they said they cannot address the matter as it is an Interac problem in their system. A problem that has been ongoing now for over 7 years!!! when the ATM's were just the CU system, it was 99.9% flawless, and by the way had a more secure PIN than Interac, so we were forced to use the less secure Interac PIN system and format. We had a 6 digit PIN code befoer Interac. Sure I know may people use these systems every day with "no issues", but the numver of security hacks and administration messups I spend correcting is just not worth the hassle. Of course the banks and such like people to use these systems so they can charge people fees to use money that costs less to actaully deal with than the paper/coin currency in fact does.
Shawn,
Long time no hear. Did you finish your second round of quasi's with those 30-0-30 toroids you purchased and the 2SK's you were looking forward to building some of the amps with?
I trust you had a good and enjoyable holiday season.
You are bang on with Onsemi samples when it is the more expensive devices. Samples for more common devices is actually much more expensive. Of course most people know this and just sample the expensive devices.
I decided to give the Onsemi (I had tried to do same a couple years ago with IRF and Fairchild) a go, but the Onsemi web site had a major flaw in the creating profile that prevented one checking out anything after talking all the time to select the devices.. I told Onsemi was a major flaw, not what flaw was.
I then found the Onsemi distributor in Mississauga and they were willing to get me some samples in lieu of the buggy site, but they just did not really have time or interest to do what the Onsemi site does via phone or eMail. They handle only consumer based electronics companies in terms of orders instead of the companies ordering from Onsemi due to the volumes involved from these companies.
I then tried the Onsemi site again and that is how I discovered Onsemi clearly knows what the bugs are on the site, but did not advise me they fixed the bug. The fix was by Onsemi by editing my profile and not fixing the site code. Sadly once to checkout the Onsemi site wanted a Credit Card. Opps, sorry guys no CC and no wish to even use one if had a CC.
So I just fumble locally as best I can. I have most of the semi's I need. My next challenge is finding electrolytics for the PSU. I have some fo rlower rail voltages, but I need quite a few for the 60V rails. My sense is for 100V types, ideally about 4700u, but I am flexible so I will hunt more as time permits. The last 6 months have been a real challenge personally and the next few months will be as well. That is ok, I still have some PCB changes to make which takes time when I have some. I also need to work out what balanced inout approach/circuit I will use and may need to make a seperate board for that. There are a few other auxilary add on circuity I want as well so there is still some time before I get to the bulding phase. I know I am very patient and rather sort out the details and what I want in the final result so I am not tinkering or reworking along way. As much as my be difficult to believe, it has been great that I have taken things slow and learn as I go along before I dive in.
Chris and Shawn, again thanks for your suggestions. I wish I could follow through on them and a few otehr places I found in my hunting, but seems most demand one use crredit cards and I had my fill of them and their administrative mistakes, online security concerns aside.
Regards,
John L. Males
Willowdale, Ontario
Canada
05 January 2007 22:49
I had actually checked Sayal a few times for the MJE340/350 and their pricing was generally 50% to 300% more than the electronics parts store downtown. Also Sayal only had one in Mororola and the complementary in another brand. I had a mindset the two had to be same brand for my own reasons, but their pricing made it simple for me to not have to re-think that aspect. Oddly in many cases Sayal has much higher pricing for surplus inventory than Electrosonic has it new. Scarey I know, but true for at least many of the parts for this amp project. Sayal certainly has excellent pricing on many things, but not items I would want most of time. The 2SC2240 for example was twice as much at Sayal as downtown, so I bought my 2SC2240's downtown.
Newark, Digikey both have minimum quanity orders which was not compatiable with my needs most of time, not to mention I do not use/have credit cards. Too many mistakes made for the 3-4 times I would use one a year. Newark has a Toronto office so thought great, can send them the payment for order. Nope, have to send payment to US and nobody in the company could figure out how it is really done or if can do, despite Toronto office. BMM was another great source but they would not reply to my inquiry how to send them payment. When I send payments I am never in hurry so these places have the time to process the order.
Chris, your reference to Active is for Active Surplus or Active Components. The latter of witch seems part of the Future Electronics family of companies? Latter has very high pricing for many items as well as parts, latter of which actually has started to charge more for used no name items more than it is new.
I liek Shawn, know of a few places about the city where one can obtain parts at good pricing. I suspect Shawn having bee in the industry for some years he said knows more than I do as hobbyist and has a few connections. I am not bothered by one having connection, I just do not and go about my sourcing based on what I can do do and where I can find.
I really think a few APT4025BNs I picked up are great and wish I coudl find more as example. I found a place in US, but they only wanted to seel me the 500 of them they had, not the qty 75 I was interested in. They priced the qty 75 so they cost almost as much as to buy the qty 500.
My reserve about Credit Cards does not just stem from what we hear about related problems at times in news, I have done IT QA for many years and I cannot tell you why things like one bank has had a couple of major problems with the debit system and online banking, as well as others. All Canadian Banks I am talking about here. I use a credit union for my banking and until a few years ago the ATM worked flawlesss. Now that the credit union was pressured to go to Interac the ATM frequently will not access my Account at the ATM in my branch due to "Institution not available". To allow people to still make a withdrawal the CU has loaded special info into the ATM so you can take out cash, but oddly enough when you want to deposit the machine will not let you when this condition exists. When I asked the CU about this problem they said they cannot address the matter as it is an Interac problem in their system. A problem that has been ongoing now for over 7 years!!! when the ATM's were just the CU system, it was 99.9% flawless, and by the way had a more secure PIN than Interac, so we were forced to use the less secure Interac PIN system and format. We had a 6 digit PIN code befoer Interac. Sure I know may people use these systems every day with "no issues", but the numver of security hacks and administration messups I spend correcting is just not worth the hassle. Of course the banks and such like people to use these systems so they can charge people fees to use money that costs less to actaully deal with than the paper/coin currency in fact does.
Shawn,
Long time no hear. Did you finish your second round of quasi's with those 30-0-30 toroids you purchased and the 2SK's you were looking forward to building some of the amps with?
I trust you had a good and enjoyable holiday season.
You are bang on with Onsemi samples when it is the more expensive devices. Samples for more common devices is actually much more expensive. Of course most people know this and just sample the expensive devices.
I decided to give the Onsemi (I had tried to do same a couple years ago with IRF and Fairchild) a go, but the Onsemi web site had a major flaw in the creating profile that prevented one checking out anything after talking all the time to select the devices.. I told Onsemi was a major flaw, not what flaw was.
I then found the Onsemi distributor in Mississauga and they were willing to get me some samples in lieu of the buggy site, but they just did not really have time or interest to do what the Onsemi site does via phone or eMail. They handle only consumer based electronics companies in terms of orders instead of the companies ordering from Onsemi due to the volumes involved from these companies.
I then tried the Onsemi site again and that is how I discovered Onsemi clearly knows what the bugs are on the site, but did not advise me they fixed the bug. The fix was by Onsemi by editing my profile and not fixing the site code. Sadly once to checkout the Onsemi site wanted a Credit Card. Opps, sorry guys no CC and no wish to even use one if had a CC.
So I just fumble locally as best I can. I have most of the semi's I need. My next challenge is finding electrolytics for the PSU. I have some fo rlower rail voltages, but I need quite a few for the 60V rails. My sense is for 100V types, ideally about 4700u, but I am flexible so I will hunt more as time permits. The last 6 months have been a real challenge personally and the next few months will be as well. That is ok, I still have some PCB changes to make which takes time when I have some. I also need to work out what balanced inout approach/circuit I will use and may need to make a seperate board for that. There are a few other auxilary add on circuity I want as well so there is still some time before I get to the bulding phase. I know I am very patient and rather sort out the details and what I want in the final result so I am not tinkering or reworking along way. As much as my be difficult to believe, it has been great that I have taken things slow and learn as I go along before I dive in.
Chris and Shawn, again thanks for your suggestions. I wish I could follow through on them and a few otehr places I found in my hunting, but seems most demand one use crredit cards and I had my fill of them and their administrative mistakes, online security concerns aside.
Regards,
John L. Males
Willowdale, Ontario
Canada
05 January 2007 22:49
rolandong said:
Go ahead key, I support your objective in comparing mosfet vs. bipolar sounds in quasi amp. Tell us how you find which device wins.
wonder how long that post would be
cheers!
Hi Rolandog,
My interest in comparing the two quasi brothers is a curiousty if I have the time and interest. When I am able to progress to a Bi/Tri amp configuration I have a strong preference to have them all be MOSFET quasi's.
I would like to build at least one pair of the BiPolar versions if I can. I am trying to decide on which TO-3 output device I will try with from a few choices available locally. I am not sure if I will choose to go to a plastic output device instead.
I also have a very good, not to mention steal of price HT receiver, I lucked out a few months ago finding that is based on the 2SC5200/2SA1943 which will be great to compare to both or just the MOSFET of the quasi's. I only need a stereo version of each to do the compare, not a HT set of 6. For sure not an active crossover based system. My hope is I will have a MOSFET version in about 8-9 months time. After I compare the MOSFET quasi to the 2SC5200/2SA1943 HT amp I would then consider trying to build a BiPolar version after that to compare. I have some 25-0-25 toroids that would enable me to build about a 50W stereo pair of each.
There was another gent here who I thought was well ahead of me and was going to build both the MOSFET and BiPolar and comment on the two.
I trust the length of my reply does not put you to sleep
Regards,
John L. Males
Willowdale, Ontario
Canada
05 January 2007 23:25
keypunch said:
Nope, the second round of Q has not yet happened. I have the set of 30-0-30 400VA ready to go into a Krell KSA50 Clone but I have requoted the same toroid through Plitron just recently. So the next quasi will happen but...I was promised a large sample quantitiy of Toshiba Fet's and sadly they have not arrived. I don't want to build my deluxe Quasi's with the IR mosfets as I would much like to try something else. Your post prompts me to tickle the nerve that supplies those samples one more time to see what happened. But I think I'm committed to trying some very nice On Semi if the Toshiba's don't come through. It is a shame because the soft start and power supply boards have been sitting here for a few months but why rush, it will happen when it happens.
Ask Chris how I was? I felt green like his avatar on New Years day over at his home. I hope to "bridge" that experience with another.
Nope, I sampled mostly small signal devices but I did manage to mix in some TO3's.
If you're having a hard time finding MJE340/350's go to Hoson at college and Spadina but beware the validity of the manufacturer is sketchy on small transistors with these folks. They always have tonnes in stock.
John, lately realizing the time spent on each project, I find it hard to purchase semi's from the non-franchised locals, good for passives and such but I think for now on, I will purchase(sample) all of my transistors through authorized distributors. Unfortunatley that is credit card only unless you phone them and set up an order payable by check. They'll ship the parts when the money clears.
Cheers,
Shawn. Happy New Year!