Hi Dave,
Please provide more info on the transformers. I'm having difficulty visualizing your situation. A schematic would be good if you have one. For instance what's the AC voltage of the secondaries. Are they currently available commercial units and if so who is the maker and what is the model number?
I consider what I did to be sub-optimal. I just did it because I wanted to use transformers (ex A40) I had in my junk box.
BAT is not the only company that positions their main filter/reservoir caps in such a way. In my opinion this is an example of marketing hype attempting to use an existing situation create differentiation.
Cheers,
Graeme
Please provide more info on the transformers. I'm having difficulty visualizing your situation. A schematic would be good if you have one. For instance what's the AC voltage of the secondaries. Are they currently available commercial units and if so who is the maker and what is the model number?
I consider what I did to be sub-optimal. I just did it because I wanted to use transformers (ex A40) I had in my junk box.
BAT is not the only company that positions their main filter/reservoir caps in such a way. In my opinion this is an example of marketing hype attempting to use an existing situation create differentiation.
Cheers,
Graeme
aleph 1.2's to AX100
GL, I was consdering buying 4-625VA trannies at 25+25volt sec with a max current of 12.5amps. I would use two per mono block.
www.avellindberg.com model y236850.
On each transformer I would run the secondaries in parallel so I would have one 25 volt secondary at 12.5 amps ac.
For each mono block I would use two trannies, one trannie connected to the diode bridge that supplies positive dc to the cap bank. The negative to the diode bridge would go to the center tap between the PS caps.
The other trannie would be connected to a different diode bridge with the negative supply going to the negative connection on the PScap and the positive side of the diode bridge going to the center tap connection between the PS caps.
Will this work? This gives me 1.3KVA but also 12.5 amps per rail to play with.
Option B is to get the 1KVA avel lindberg trannie with 25+25 secondaries run as a center tap. This unit is rated at 20 amps ac.
Avel lindberg model y236950. I would hook this up in the standard way and it gives me 10 amps per rail.
The difference is of course the diameter as the 1kva is approximately 2" larger, just enough to keep me from adding some extra caps. The 625 va units I can stack vertically.
This is not a serious issue for me so if I get lazy Plan B will work.
The difference in cost between the 4 - 625's and the 2-1kva's was about $80.
GL, I was consdering buying 4-625VA trannies at 25+25volt sec with a max current of 12.5amps. I would use two per mono block.
www.avellindberg.com model y236850.
On each transformer I would run the secondaries in parallel so I would have one 25 volt secondary at 12.5 amps ac.
For each mono block I would use two trannies, one trannie connected to the diode bridge that supplies positive dc to the cap bank. The negative to the diode bridge would go to the center tap between the PS caps.
The other trannie would be connected to a different diode bridge with the negative supply going to the negative connection on the PScap and the positive side of the diode bridge going to the center tap connection between the PS caps.
Will this work? This gives me 1.3KVA but also 12.5 amps per rail to play with.
Option B is to get the 1KVA avel lindberg trannie with 25+25 secondaries run as a center tap. This unit is rated at 20 amps ac.
Avel lindberg model y236950. I would hook this up in the standard way and it gives me 10 amps per rail.
The difference is of course the diameter as the 1kva is approximately 2" larger, just enough to keep me from adding some extra caps. The 625 va units I can stack vertically.
This is not a serious issue for me so if I get lazy Plan B will work.
The difference in cost between the 4 - 625's and the 2-1kva's was about $80.
Hi Dave,
Aha.
My first choice would be the single big transformer. I would compensate for the loss of cap space by substituting Panasonic TS type caps for the CG's. They have most of the performance and you can usually find a package that's long and skinny and gives good use of space. I'd also use one full wave bridge for each secondary rather than one bridge + CT for the two voltages. Lots of examples at PASSDIY.
If it has to be the 625VA units I would rectify then parallel, not the other way around. I know they say you can do it but any mismatch in secondary voltage however small will create energy losses and potential heating problems.
Graeme
Aha.
My first choice would be the single big transformer. I would compensate for the loss of cap space by substituting Panasonic TS type caps for the CG's. They have most of the performance and you can usually find a package that's long and skinny and gives good use of space. I'd also use one full wave bridge for each secondary rather than one bridge + CT for the two voltages. Lots of examples at PASSDIY.
If it has to be the 625VA units I would rectify then parallel, not the other way around. I know they say you can do it but any mismatch in secondary voltage however small will create energy losses and potential heating problems.
Graeme
aleph 1.2's to AX100
GR, thanks, again you have convinced me to go the simpler route.
I will check on the Panasonic caps in digikeys catalog.
The caps I have are "honkers" they look like beer cans but taller.
I have had them laying around for the last 15 years. I will get back to you once I find the caps. Hey if the cost is less than $80 bucks I will come out ahead. dave
GR, thanks, again you have convinced me to go the simpler route.
I will check on the Panasonic caps in digikeys catalog.
The caps I have are "honkers" they look like beer cans but taller.
I have had them laying around for the last 15 years. I will get back to you once I find the caps. Hey if the cost is less than $80 bucks I will come out ahead. dave
Hi Magura,
You are probably right. I was simply saying that in my opinion I wouldn't risk a DIY project that I had put lots of time and money into on a set of electrolytics that hadn't had a charge on them for over 15 years. Even more so if if they were bought surplus. I've had a few bad experiences.
Graeme
You are probably right. I was simply saying that in my opinion I wouldn't risk a DIY project that I had put lots of time and money into on a set of electrolytics that hadn't had a charge on them for over 15 years. Even more so if if they were bought surplus. I've had a few bad experiences.
Graeme
aleph 1.2's to AX100
GL--Your right, I got these caps from a friend and who knows how old they are now? They were extra caps from a OTL tube amp project. I built a 220 watt Output Transformerless AMP.
I used to call it the Popcorn amp which had 6AS7's on the outputs
(20 tubes per mono amp with each tube having two sections that was 40 sections per amp) because if the needle dropped too hard on a record the tube sections would light up like the lights on a police car and the cathode wires would melt. It sounded nice and warm and heated the room up like you wouldn't believe.
Not much good detailed bass but it could drive 8 ohm speakers.
I used to get 6AS7's new for $6 and used for less, now they are over $20 to $30 and this kind of amp is no longer a feasable design option.
The Pass Aleph's were a big improvement and I am hoping for another improvement with this project. I will get new caps.
I am also thinking of installing a speaker saver time delay relay on the outputs if I have thumps on turn on. I don't with the aleph's, I just have a switch noise that I don't want my tweeters to see. dave
GL--Your right, I got these caps from a friend and who knows how old they are now? They were extra caps from a OTL tube amp project. I built a 220 watt Output Transformerless AMP.
I used to call it the Popcorn amp which had 6AS7's on the outputs
(20 tubes per mono amp with each tube having two sections that was 40 sections per amp) because if the needle dropped too hard on a record the tube sections would light up like the lights on a police car and the cathode wires would melt. It sounded nice and warm and heated the room up like you wouldn't believe.
Not much good detailed bass but it could drive 8 ohm speakers.
I used to get 6AS7's new for $6 and used for less, now they are over $20 to $30 and this kind of amp is no longer a feasable design option.
The Pass Aleph's were a big improvement and I am hoping for another improvement with this project. I will get new caps.
I am also thinking of installing a speaker saver time delay relay on the outputs if I have thumps on turn on. I don't with the aleph's, I just have a switch noise that I don't want my tweeters to see. dave
aleph 1.2 to XA160
GL, I ordered all the parts for the driver boards for the aleph conversion to XA from digikey. Not too bad at about $78.
I had a lot of the resistors and caps left over from other projects and since I am reusing the output stage and chasis I don't have those costs. I haven't bought the xformer yet but I will do that monday. I am still back and forth with 1kva vs 1.2 kva (only because I don't want any noise). I also am awaiting a dc blocking and noise reduction circuit board from diycable to try out and I will eliminate my old style EMI/RFI box I got from fair radio since it has a 6amp limit and I am already drawing 5 amps ac.
I looked into the top of my Pass 350.5 and saw that NP is using the standard metal film resistors so I am not going with any exotics like Vishay or Caddock on the inputs (I did not remove the top due to the unit being under warranty--just in case NP reads this). I do have them on my phono and line amps but there the signal is quite small and noise is a bigger factor.
Once I establish the final rail voltage (I will be using 6 devices per quad) I will need your advise on setting the CCS at 50%. I think looking at your schematic that it is just a resistor change. With beautiful summer weather and vacations and business travel coming up and having two amps to redo this could take a while.
Do you have any sources for a nice looking meter either Watts or
Voltage that can be backlighted? I don't want to use an amp meter becasue I don't want it series with the outputs? I will make a new front panel when I am finished. thanks, dave
GL, I ordered all the parts for the driver boards for the aleph conversion to XA from digikey. Not too bad at about $78.
I had a lot of the resistors and caps left over from other projects and since I am reusing the output stage and chasis I don't have those costs. I haven't bought the xformer yet but I will do that monday. I am still back and forth with 1kva vs 1.2 kva (only because I don't want any noise). I also am awaiting a dc blocking and noise reduction circuit board from diycable to try out and I will eliminate my old style EMI/RFI box I got from fair radio since it has a 6amp limit and I am already drawing 5 amps ac.
I looked into the top of my Pass 350.5 and saw that NP is using the standard metal film resistors so I am not going with any exotics like Vishay or Caddock on the inputs (I did not remove the top due to the unit being under warranty--just in case NP reads this). I do have them on my phono and line amps but there the signal is quite small and noise is a bigger factor.
Once I establish the final rail voltage (I will be using 6 devices per quad) I will need your advise on setting the CCS at 50%. I think looking at your schematic that it is just a resistor change. With beautiful summer weather and vacations and business travel coming up and having two amps to redo this could take a while.
Do you have any sources for a nice looking meter either Watts or
Voltage that can be backlighted? I don't want to use an amp meter becasue I don't want it series with the outputs? I will make a new front panel when I am finished. thanks, dave
aleph 1.2 to XA100
GL, another question? Did you finally settle on a Macmillan resistor? Re reading part of this thread, there was a lot of conversation about the value. I think you went from 4.76 to 10k?
Did you use a half watt resistor? I was thinking of starting out at your last value and going from there. Has anyone ever installed a pot say 25k and just made adjustments to see what happened?
When people talk about readjusting the amp are they talking about the ccs? I have a scope and signal generator and a 250 watt 5ohm resistor which I will use to set the ccs at 50% but this is down the road a piece. dave
GL, another question? Did you finally settle on a Macmillan resistor? Re reading part of this thread, there was a lot of conversation about the value. I think you went from 4.76 to 10k?
Did you use a half watt resistor? I was thinking of starting out at your last value and going from there. Has anyone ever installed a pot say 25k and just made adjustments to see what happened?
When people talk about readjusting the amp are they talking about the ccs? I have a scope and signal generator and a 250 watt 5ohm resistor which I will use to set the ccs at 50% but this is down the road a piece. dave
Hi,
for the McMillan resistors you should use the highest value you can get away with for a decent absolute offset behaviour.
I noticed big improvements up to about 10-12k with the standard input and up to 20-22k with the Jfet input.
I didn´t install a pot but tried different values, measured and listened. As for absolute DC Offset the startup value normally doubles when the Mcmillan resistors are doubled. So 4V dc offset with 5k will change to 8V dc offset with 10k resistors.
This is the cold startup value for a 0V value when warm.
When you readjust the amp you can fiddle with three pots:
1. dc bias left side
2. dc bias right side
3. dc bias input diff pair (sets the absolute dc-offset)
William
for the McMillan resistors you should use the highest value you can get away with for a decent absolute offset behaviour.
I noticed big improvements up to about 10-12k with the standard input and up to 20-22k with the Jfet input.
I didn´t install a pot but tried different values, measured and listened. As for absolute DC Offset the startup value normally doubles when the Mcmillan resistors are doubled. So 4V dc offset with 5k will change to 8V dc offset with 10k resistors.
This is the cold startup value for a 0V value when warm.
When you readjust the amp you can fiddle with three pots:
1. dc bias left side
2. dc bias right side
3. dc bias input diff pair (sets the absolute dc-offset)
William
aleph 1.2's to AX100
Gl-what is the purpose of the 100k resistors on the input to ground? I am not including the 4.7 input dc blocking cap because my DEQX 2.6P does not put out dc and my tube line stage already has output 10uf caps.
I noticed you omitted the back to back 9.1 zeners from gate to ground to protect the input gates of the fets-do the zeners you have in place between the gate and source give the same level of protection. On your schematic the + input looks backwards.
thanks, dave
Gl-what is the purpose of the 100k resistors on the input to ground? I am not including the 4.7 input dc blocking cap because my DEQX 2.6P does not put out dc and my tube line stage already has output 10uf caps.
I noticed you omitted the back to back 9.1 zeners from gate to ground to protect the input gates of the fets-do the zeners you have in place between the gate and source give the same level of protection. On your schematic the + input looks backwards.
thanks, dave
Hi Dave,
Those resistors aren't really necessary. You would put them in if there was DC on the other side of the input cap in order to bleed off any charge that would cause pops when connecting, disconnecting or power cycling. But there is no DC here so the resistors aren't required. It's just me being an@l. I am planning to remove both the R's and C's soon. I just wanted to play it safe back when I powered things up for the first time.
Regarding the zeners I just copied what NP did on one of his earlier amps - look here:
http://www.passlabs.com/np/ALEPH-0-14 .pdf
The MOSFET polarity is reversed so the zeners are too.
Regards,
Graeme
Those resistors aren't really necessary. You would put them in if there was DC on the other side of the input cap in order to bleed off any charge that would cause pops when connecting, disconnecting or power cycling. But there is no DC here so the resistors aren't required. It's just me being an@l. I am planning to remove both the R's and C's soon. I just wanted to play it safe back when I powered things up for the first time.
Regarding the zeners I just copied what NP did on one of his earlier amps - look here:
http://www.passlabs.com/np/ALEPH-0-14 .pdf
The MOSFET polarity is reversed so the zeners are too.
Regards,
Graeme
aleph 1.2's to Ax100
GL-thanks, I am ordering the 1kva avel lindberg xformers. The secondaries are 25+25 and 20 amps. I will use the traditional hexfreds and the same caps as my Aleph but I will try to get some additional filtering. I also will have .75ohm resistors on the output device sources. I have 1.5's already connected and will parallel another 1.5 per device. This is based on your comment regarding the ability of the CCS. I will start out at 540ma/device with 6 devices this is 3.2 amps per quad just to get things checked out and then work with you to get to 50%. If I move up to 600ma x.75 ohms per device, I will get .45 volts across the source resistors. I hope the 20amps is enough when you figure in the speaker loads. dave
GL-thanks, I am ordering the 1kva avel lindberg xformers. The secondaries are 25+25 and 20 amps. I will use the traditional hexfreds and the same caps as my Aleph but I will try to get some additional filtering. I also will have .75ohm resistors on the output device sources. I have 1.5's already connected and will parallel another 1.5 per device. This is based on your comment regarding the ability of the CCS. I will start out at 540ma/device with 6 devices this is 3.2 amps per quad just to get things checked out and then work with you to get to 50%. If I move up to 600ma x.75 ohms per device, I will get .45 volts across the source resistors. I hope the 20amps is enough when you figure in the speaker loads. dave
Aleph 1.2 to XA100
GL or Grey, I have started stuffing the boards for my XA100+ or conversion of my Aleph 1.2's. One question is how important is resistor matching on for all resistors connected to the input differential pair? I have been going crazy measuring resistors to get them exact. I have got most to within 10.0ohms on the 10k input resistors and the 392 resistors are exact. The 10k macmillians are within 10.0 ohms. I am using the run of the mill metal films, mostly holco that I had left over from other projects.
I haven't condisered vishay or caddock since with the signal so large coming into the amp, Ididn't see the need. I have used caddocks on my phono preamps and lineamps where the signal is smaller and noise becomes a bigger issue. I have a pile of 9610's to sort and test--what variance did you use to keep dc offset low (.01gsv)? thanks in advance for the feedback! Got to take a break and spray my trees the Jap beatles are back. dave
GL or Grey, I have started stuffing the boards for my XA100+ or conversion of my Aleph 1.2's. One question is how important is resistor matching on for all resistors connected to the input differential pair? I have been going crazy measuring resistors to get them exact. I have got most to within 10.0ohms on the 10k input resistors and the 392 resistors are exact. The 10k macmillians are within 10.0 ohms. I am using the run of the mill metal films, mostly holco that I had left over from other projects.
I haven't condisered vishay or caddock since with the signal so large coming into the amp, Ididn't see the need. I have used caddocks on my phono preamps and lineamps where the signal is smaller and noise becomes a bigger issue. I have a pile of 9610's to sort and test--what variance did you use to keep dc offset low (.01gsv)? thanks in advance for the feedback! Got to take a break and spray my trees the Jap beatles are back. dave
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