I’ve just picked up some efficient horns so I’m thinking of replacing my ss power amp with something w tubes but I don't really have experience in that area. Is anyone running their BA2018 into a tube power amp? Any reason it wouldn’t work well or any things to look out for? Thanks
I've been using my BA2018 with a EL34 Baby Huey. Works very well and no issues.
There is no technical reason it sould not work great. This linestage works with everything. Just beware of gain structure. It is gainy with specced values. You can change this, at the cost of more feedback.
Well, it has taken me a while, but I have finally started on the BA2018 boards + parts kit I bought from the store quite a few years ago. The SMD parts are soldered and seem to pass the continuity test, so I have started on the resistors.
I have just finished reading through the entire thread (79 pages; it took a few evenings 😎) but I think I have all the info I need, except a few things that need clarification.
Questions:
1. Balanced and single ended input.
I expect to use it mainly with balanced input and understand:
But what happens when I want to use single ended inputs? Is grounding IN- enough or is it better to change the values of R20 and R18?
Another option is to install R18 and R20 directly to the XLR and cinch connectors, leaving them off the board. That way different values can be used for balanced and single ended.
Thoughts?
2. Benefit to add a 10pf cap across R18 (similar to R16 but for +IN), similar to BA1 front end.
Would this be audible?
Balanced and single ended use different values for R18, so probably need different value for extra cap as well. Which value to use for R18=100k (single ended input). I assume it is RC needs to remain constant?
If solution in Q1 above is valid, it would be easy to install different caps across R18 at the XLR and cinch connectors.
3. Switchable gain
Standard gain is about 3.7x (11dB), but I would also like higher gain, say 10x (20dB), to drive an F4 (I am aware not to clipping).
I understand gain is set by ratio of R16 and R17 (gain = [R16+R17]/R17).
I read through all the posts and found the following:
This confirms it. Leave R17 (10k) alone and only adjust R16 up for more gain.
But, #2668 goes on to say:
Which would make my solution at Q2 impossible!
So, an easier solution for me may be to leave R16 and C1 alone, and just change R17 (from 10k to 3k).
Q3a. Would this work (and sound good) or is this too simplistic?
Q3b. I assume R20 would also need to be changed from 10k to 3k (balanced input)?
Q3c.Would I have the correct gain single ended (i.e. leaving R20=100R and R18=100k)?
Thanks
I have just finished reading through the entire thread (79 pages; it took a few evenings 😎) but I think I have all the info I need, except a few things that need clarification.
Questions:
1. Balanced and single ended input.
I expect to use it mainly with balanced input and understand:
But what happens when I want to use single ended inputs? Is grounding IN- enough or is it better to change the values of R20 and R18?
Another option is to install R18 and R20 directly to the XLR and cinch connectors, leaving them off the board. That way different values can be used for balanced and single ended.
Thoughts?
2. Benefit to add a 10pf cap across R18 (similar to R16 but for +IN), similar to BA1 front end.
Would this be audible?
Balanced and single ended use different values for R18, so probably need different value for extra cap as well. Which value to use for R18=100k (single ended input). I assume it is RC needs to remain constant?
If solution in Q1 above is valid, it would be easy to install different caps across R18 at the XLR and cinch connectors.
3. Switchable gain
Standard gain is about 3.7x (11dB), but I would also like higher gain, say 10x (20dB), to drive an F4 (I am aware not to clipping).
I understand gain is set by ratio of R16 and R17 (gain = [R16+R17]/R17).
I read through all the posts and found the following:
This confirms it. Leave R17 (10k) alone and only adjust R16 up for more gain.
But, #2668 goes on to say:
Which would make my solution at Q2 impossible!
So, an easier solution for me may be to leave R16 and C1 alone, and just change R17 (from 10k to 3k).
Q3a. Would this work (and sound good) or is this too simplistic?
Q3b. I assume R20 would also need to be changed from 10k to 3k (balanced input)?
Q3c.Would I have the correct gain single ended (i.e. leaving R20=100R and R18=100k)?
Thanks
@albertNL
I've been (casually) pondering the balanced plus single-ended problem as well.
What were you thinking in terms of attenuator? I assumed that it should go between the input jacks and the board input. You'd need a four section unit for the balanced input but only require two for the single-ended, no?
I've been (casually) pondering the balanced plus single-ended problem as well.
What were you thinking in terms of attenuator? I assumed that it should go between the input jacks and the board input. You'd need a four section unit for the balanced input but only require two for the single-ended, no?
Yes, you would need a quad (or 2 x stereo) for balanced. A standard stereo pot would suffice for unbalanced. I plan to use a quad (the standard way for balanced).
I assume the quad pot will function without a hitch for unbalanced. In a traditional setup you connect IN- to GND using a jumper on the XLR jack or a switch when you have an unbalanced source.
The pot that sits between the input jacks and the amp is a voltage divider. In balanced use it directs a portion of the IN- signal to the amp at R17, and the rest to GND. Since IN- is already grounded when using unbalanced inputs, the net result is the pot does nothing. It may add noise (just like any part can add noise) but I assume this is negligible because everything is at GND potential. I have never measured it and don't have equipment sensitive enough, but assume the GND potential at different points are within uV of each other.
I assume the quad pot will function without a hitch for unbalanced. In a traditional setup you connect IN- to GND using a jumper on the XLR jack or a switch when you have an unbalanced source.
The pot that sits between the input jacks and the amp is a voltage divider. In balanced use it directs a portion of the IN- signal to the amp at R17, and the rest to GND. Since IN- is already grounded when using unbalanced inputs, the net result is the pot does nothing. It may add noise (just like any part can add noise) but I assume this is negligible because everything is at GND potential. I have never measured it and don't have equipment sensitive enough, but assume the GND potential at different points are within uV of each other.
Your are right! I had not thought about the attenuator yet when your post came in and completely forgot the pot is supposed to be between the inputs and the resistors.
Just a thought:
XLR -> resistors -> quad pot -> switch -> pcb for balanced
cinch -> resistors -> stereo pot -> switch -> pcb for unbalanced
changing the switch position so it sits between the output of the 2 pots and the pcb, it can also function as the "r17 to GND" switch.
Disadvantage is 2 pots and I don't know if the added length between the resistors and pcb will affect sound quality. Ideally, you would integrate the resistors and switch (using relays perhaps) on the pcb.
As I plan on probably using balanced inputs all the time, I think I will just build mine optimised for balanced inputs (so, correct balanced resistors on the pcb) and a quad pot. If it sounds so good I want to use it to replace my main preamp, I can always come back to it and perhaps design a new pcb.
Just a thought:
XLR -> resistors -> quad pot -> switch -> pcb for balanced
cinch -> resistors -> stereo pot -> switch -> pcb for unbalanced
changing the switch position so it sits between the output of the 2 pots and the pcb, it can also function as the "r17 to GND" switch.
Disadvantage is 2 pots and I don't know if the added length between the resistors and pcb will affect sound quality. Ideally, you would integrate the resistors and switch (using relays perhaps) on the pcb.
As I plan on probably using balanced inputs all the time, I think I will just build mine optimised for balanced inputs (so, correct balanced resistors on the pcb) and a quad pot. If it sounds so good I want to use it to replace my main preamp, I can always come back to it and perhaps design a new pcb.
Building WLS2018 and using Pete Millett's 15/25VA Dual Power supply to power it. I built the high output version with output voltage 18-22VDC of the power supply. Sort of new at this (Aleph J and DIYaudio store universal power supply). To test and set up the power supply I should:
1. Set RV1 /RV2 to 250 ohms.
2. Hook the board up to AC and hope for the best?
3. If no obvious issues set the output voltage to about 18 volts by adjusting RV1/RV2.
All of the above, none of the above or something different altogether??? I'd like to catch issues before powering it up so if there are some tests I could do with a multi meter that would be great. I've already double checked my board stuffing and soldering. Checked resistor values with VOM and double checked polarity of caps and transformer orientation.
1. Set RV1 /RV2 to 250 ohms.
2. Hook the board up to AC and hope for the best?
3. If no obvious issues set the output voltage to about 18 volts by adjusting RV1/RV2.
All of the above, none of the above or something different altogether??? I'd like to catch issues before powering it up so if there are some tests I could do with a multi meter that would be great. I've already double checked my board stuffing and soldering. Checked resistor values with VOM and double checked polarity of caps and transformer orientation.
getgoin it sounds like you've done what you can up to this point. Hate to slow you down, but myleftear is right: build a Poor Man's Variac. This is always step 1 in my testing and it doesn't take much to build. If you hook the board up and things go wrong when using this device you'll at least get some time to act (if anything starts to overheat and smoke) before things actually blow. There are many designs online.
Variac comes in handy when powering first time project and connect 100R (1/4 or 1/8W) resistor in series with positive supply, this way you can increase the voltage gradually let's say 3/6/12/18Vac. Turn Variac slowly to increase AC voltage and make sure the series resistor don't heat, then measure output DC offset should be close to zero.
Great advice and I've already built a dim bulb tester-- just forgot that it's waiting for me out in the shed!
I bought this and used it on a rather large amp. It worked well:
https://www.ebay.com/itm/124185768222
https://www.ebay.com/itm/124185768222
I'm building WLS. The boards are stuffed. I hooked up Pete Millett's 15/25VA Dual Power supply (Mine is the 18-24 volt version) via a dim bulb tester. (Preamp board is not connected.) The dim bulb tester did not light up at all. Both LEDs on the board were on. Nothing was hot or even warm. I checked the output voltage. V1 was zero and V2 was 19.5 volts. I didn't try to adjust the variable resisters. Ideas on what the problem might be? Happy to move this to the power supply thread if this is grossly misplaced.
Thanks for all the help. Here's the update. I measure the resistance across L12 and L2: .5 ohm. I measured the voltages for c5, c5 c7 and c8. All 19.4. Hmmm... Rechecked the output voltages at euroblock and discovered one of the tightening screws wasn't making contact. Problem solved. Below is photo of boards with what I think the connections are between various components drawn in. Are these correct?
Fantastic that you found the issue!! Wonderful news. 🙂 🙂 🙂
Can you post an in-focus photo (or at least higher resolution) of the current iteration showing the actual wiring?
Can you post an in-focus photo (or at least higher resolution) of the current iteration showing the actual wiring?