jleaman said:
If we are talking about the resistors for the T X-BOSOZ according to the schematic R14-R15 are 10K and R18-R19 are 39K. I just finished put my boards together but haven't tested them yet.
Hope this helps
Dave
jleaman said:
Put it on the table, and do this:
Try to find another pre amp you like, whatever it is . . . 😀
Babowana said:
Put it on the table, and do this:
Try to find another pre amp you like, whatever it is . . . 😀
Nah, bad idea. Just
the table and send the pre to me🙂
Jason,
Actually those measurements look about right, considering they are being measured as part of a completed circuit.
Did you get a chance to measure the other resistor values?
Another thing I would suggest checking is the voltage across the cascode voltage references (the LM4040-10's) to be sure that the cascodes are properly set. Do this measurement with the preamp turned on.
Terry
Actually those measurements look about right, considering they are being measured as part of a completed circuit.
Did you get a chance to measure the other resistor values?
Another thing I would suggest checking is the voltage across the cascode voltage references (the LM4040-10's) to be sure that the cascodes are properly set. Do this measurement with the preamp turned on.
Terry
Member
Joined 2002
What other resistors do you need measured ? I can do this all tonight if you like. I only have one complaint for this pre-amp the hushing sound.. Other than that it is perfect sound and really clean Especially with these new SMD mini Aleph's that i got up and running.
As to the hushing, I believe we can quiet it down, its just going to take some detective work. If you can bear with me (as I can't always respond very quickly) I'll keep working with you until we get this sorted out.
Member
Joined 2002
metalman said:
email me ? I can send this unit to you if you like. Im only a ferry away 🙂
jase@jasesspace.com
Jase
Volume control and source selection on XBOSOZ
This was covered briefly in this thread but I hope to get some clarification. If one purchased 2 Joshua tree boards, it would be possible to have separate Left and Right volume controls in a balanced mode operation? Has any one done this? A second question has to do with source switching. I currently have no balanced sources but I am hopeful when Russ finishes his DAC I will have one. Is there a consensus on how to switch between balanced and unbalanced sources?
This was covered briefly in this thread but I hope to get some clarification. If one purchased 2 Joshua tree boards, it would be possible to have separate Left and Right volume controls in a balanced mode operation? Has any one done this? A second question has to do with source switching. I currently have no balanced sources but I am hopeful when Russ finishes his DAC I will have one. Is there a consensus on how to switch between balanced and unbalanced sources?
I think you would need two controller boards (one to control each channel's level). That would work though.
Metalman in a previous post you wrote:
"Jason,
A general practice I use with every project (one I suggest for everybody) is to always test projects in the smallest convenient portions before assembling a project as a whole. I learned this through the many experiences of building projects to completion before performing any testing, only to find it not working properly and needing to disassemble it down to smaller portions in order to find the source of the problem. In fact, I don't think I have ever had a project ever be perfect on the first attempt. Now when I buy parts for a project, I also buy parts to create dummy loads and circuits so I can test protions of circuits as I build. Saves me a lot of frustration.
In your specific case, here's what I suggest. Lets first find out if the problem exists in the power supply or the pre circuit. Disconnect the pre circuit from the power supply. Find a couple of 25k or larger resistors (1/4W rated). Connect one between the power supply positive rail output and ground. Connect the other between the negative supply rail and ground. Turn on the powersupply and measure the AC voltages before the bridge rectifier diodes. Next, measure the DC voltages of the unregulated rails immediately after the bridge rectifier diodes. Then measure the DC voltages of the regulated rails at the power supply output. Lastly measure the DC voltage across the Zener stacks of the positive and negative sides, and also measure the voltages across the resistors that bias the zener stacks (R3 and R5?). Report these back here, and we will have a pretty good idea if the power supply is working correctly, and where the problem might exist. This experiment will run the power supply at between 1 and 3 mA, which will be a very easy load for the power supply, and ensures that we don't overload it. If you have a variac, you can do more or less the same thing, but with even less risk as you can start with supplying only 20 or 30V AC instead of hitting with an instantaneous 120V."
Could you publish what these measurement should approximately be? Any other suggestions for checking the power supplies will be appreciated. Thank-you.
"Jason,
A general practice I use with every project (one I suggest for everybody) is to always test projects in the smallest convenient portions before assembling a project as a whole. I learned this through the many experiences of building projects to completion before performing any testing, only to find it not working properly and needing to disassemble it down to smaller portions in order to find the source of the problem. In fact, I don't think I have ever had a project ever be perfect on the first attempt. Now when I buy parts for a project, I also buy parts to create dummy loads and circuits so I can test protions of circuits as I build. Saves me a lot of frustration.
In your specific case, here's what I suggest. Lets first find out if the problem exists in the power supply or the pre circuit. Disconnect the pre circuit from the power supply. Find a couple of 25k or larger resistors (1/4W rated). Connect one between the power supply positive rail output and ground. Connect the other between the negative supply rail and ground. Turn on the powersupply and measure the AC voltages before the bridge rectifier diodes. Next, measure the DC voltages of the unregulated rails immediately after the bridge rectifier diodes. Then measure the DC voltages of the regulated rails at the power supply output. Lastly measure the DC voltage across the Zener stacks of the positive and negative sides, and also measure the voltages across the resistors that bias the zener stacks (R3 and R5?). Report these back here, and we will have a pretty good idea if the power supply is working correctly, and where the problem might exist. This experiment will run the power supply at between 1 and 3 mA, which will be a very easy load for the power supply, and ensures that we don't overload it. If you have a variac, you can do more or less the same thing, but with even less risk as you can start with supplying only 20 or 30V AC instead of hitting with an instantaneous 120V."
Could you publish what these measurement should approximately be? Any other suggestions for checking the power supplies will be appreciated. Thank-you.
Member
Joined 2002
BUT!
but i'm using dual mono power-supplies. ONe supply per channel.
Still want me to test this ?
Jase
but i'm using dual mono power-supplies. ONe supply per channel.
Still want me to test this ?
Jase
Jase,
I've been following this thread only intermittently, so I apologize if this has been raised before. I have seen no mention of checking for oscillation/RFI as the source of the shushing sound. Do you have or can you borrow a scope?
My breadboard BOSOZ (pre-X) was VERY sensitive to power lead dress - motorboating or HF oscillation depending on how the leads were placed. Are your power supply wires tightly twisted together, as short as possible and kept close to the chassis? Do you live near a source of RFI? (radio transmitter, cell tower, open case computer, etc.) A (few) hundred pF or so across the inputs may help.
Metalman's testing is also a good idea - although I'd add testing under load (could be your BOSOZ boards) If under load there isn't 5V or more available for the pass transistors to work, you may be getting some hash out of your power supplies that would result in noise out of your preamp.
This circuit doesn't have the best power supply rejection. That it works and sounds OK except for the noise makes me think it is likely a PSU issue.
I've been following this thread only intermittently, so I apologize if this has been raised before. I have seen no mention of checking for oscillation/RFI as the source of the shushing sound. Do you have or can you borrow a scope?
My breadboard BOSOZ (pre-X) was VERY sensitive to power lead dress - motorboating or HF oscillation depending on how the leads were placed. Are your power supply wires tightly twisted together, as short as possible and kept close to the chassis? Do you live near a source of RFI? (radio transmitter, cell tower, open case computer, etc.) A (few) hundred pF or so across the inputs may help.
Metalman's testing is also a good idea - although I'd add testing under load (could be your BOSOZ boards) If under load there isn't 5V or more available for the pass transistors to work, you may be getting some hash out of your power supplies that would result in noise out of your preamp.
This circuit doesn't have the best power supply rejection. That it works and sounds OK except for the noise makes me think it is likely a PSU issue.
Testing power supplies
I am just looking for a systematic way of checking the power supplies. I suppose I could sit down and do the math but I am hoping some of the guys with circuit simulators or those who have completed their units might already know the numbers. Can anybody supply results to the measurements that Metalman suggests?
I am just looking for a systematic way of checking the power supplies. I suppose I could sit down and do the math but I am hoping some of the guys with circuit simulators or those who have completed their units might already know the numbers. Can anybody supply results to the measurements that Metalman suggests?
The DC voltage after the rectifiers should be ~1.4 x VAC - 1
This should be at least 5V higher than regulated out.
Zener stack voltage should be ~Vout + 4V
Zener bias resistor voltage should be appropriate to give ~5 mA through the stack (I=V/R). Anywhere from 1-15 mA will work, I just shoot for 5 in general.
This should be at least 5V higher than regulated out.
Zener stack voltage should be ~Vout + 4V
Zener bias resistor voltage should be appropriate to give ~5 mA through the stack (I=V/R). Anywhere from 1-15 mA will work, I just shoot for 5 in general.
You're welcome.
Slight error in my last post - DC after rectifiers is correct at 1.4 x VAC-1, but it is the DC after the CRC that should be at least 5V above Vout. Not much difference in the low load test, but it could be an issue in the loaded tests.
Slight error in my last post - DC after rectifiers is correct at 1.4 x VAC-1, but it is the DC after the CRC that should be at least 5V above Vout. Not much difference in the low load test, but it could be an issue in the loaded tests.
Jason,
I did send a private e-mail to you a few weeks ago to initiate some help outside of the forum. Did you get it? Haven't heard back from you.
Terry
I did send a private e-mail to you a few weeks ago to initiate some help outside of the forum. Did you get it? Haven't heard back from you.
Terry
Member
Joined 2002
metalman said:
Yes i have your email i believe i wrote you back .. I have done lots of testing i guess i could borrow a scope again. I could send it to you to if you want.. i have some more ideas
maybe take the transformers right out of the chassis they could be causing some hush sound and maybe some other ideas but ill play with it. should i contact you via email to discus if you want me to ship it or not ?