Jeff, a couple more questions if I may:
1. The rails, according to the labels on the PCB, are 24V. However, the Toroidy transformer you used has 25V secondaries. I apologize if that is a stupid question, but I know Toroidy can supply 24V secondaries as well as 25V secondaries... Which should I order? Does it matter?
2. HPA-1 has no Gain or Impedance switches. How easy would it be to add Gain High/Low and Impedance High/Low switches? I intend to use the HPA-1 mostly for headphones, and I have in my collection both headphones that are harder to drive (require more gain) as well as ones that are very easy to drive and require less gain. Also, I have headphones with very low impedance (e.g. planars with sub-30 Ohms impedance) as well as high-impedance (300 Ohms) headphones.
3. Someone mentioned 2nd harmonic THD, measured in previous builds, which made me think... Has anyone considered or attempted to integrate H2 Harmonic Generator (https://www.firstwatt.com/pdf/art_h2_v1.pdf)? I think it would be really cool, with the addition of a switch to bypass H2 Harmonic Generator, so I can turn it on and off at will... Even more interesting would be to have the H2 circuit with a pot to control the amount of 2nd harmonic added to the HPA-1. Thoughts? Suggestions?
Thanks again for all the help!
Zachi.
1. The rails, according to the labels on the PCB, are 24V. However, the Toroidy transformer you used has 25V secondaries. I apologize if that is a stupid question, but I know Toroidy can supply 24V secondaries as well as 25V secondaries... Which should I order? Does it matter?
2. HPA-1 has no Gain or Impedance switches. How easy would it be to add Gain High/Low and Impedance High/Low switches? I intend to use the HPA-1 mostly for headphones, and I have in my collection both headphones that are harder to drive (require more gain) as well as ones that are very easy to drive and require less gain. Also, I have headphones with very low impedance (e.g. planars with sub-30 Ohms impedance) as well as high-impedance (300 Ohms) headphones.
3. Someone mentioned 2nd harmonic THD, measured in previous builds, which made me think... Has anyone considered or attempted to integrate H2 Harmonic Generator (https://www.firstwatt.com/pdf/art_h2_v1.pdf)? I think it would be really cool, with the addition of a switch to bypass H2 Harmonic Generator, so I can turn it on and off at will... Even more interesting would be to have the H2 circuit with a pot to control the amount of 2nd harmonic added to the HPA-1. Thoughts? Suggestions?
Thanks again for all the help!
Zachi.
I have Jeff's PCB on-hand, but I have not started soldering yet. Still easy (and inexpensive) to make a switch to a different (more suitable?) PCB.
I am very proficient with soldering iron, and following instructions, but I am not a EE and have no experience with PCB layout... ;-)
My options are using a design as-is, or make small modifications with re-wiring.
@mokaonli - the PCB layout that you show above, was it tested / verified by anyone? Or did you slap it together to show me how it can be done?
If verified / tested - I would love to order this variant and have a simpler and cleaner build for sure!!
Hello,
A V2 version with pads for cable soldering. The first version was equipped with a JST connector.
For verification and real testing, all that has been done is the removal of the 12V power elements and the addition of pads to connect your cables. You just need to check the wiring, which is very simple.
Pay attention to Jeff's comment regarding the delay of the output. Without it, you will need to unplug your headset before turning it on/off.
Have a great day!
Jérôme
A V2 version with pads for cable soldering. The first version was equipped with a JST connector.
For verification and real testing, all that has been done is the removal of the 12V power elements and the addition of pads to connect your cables. You just need to check the wiring, which is very simple.
Pay attention to Jeff's comment regarding the delay of the output. Without it, you will need to unplug your headset before turning it on/off.
Have a great day!
Jérôme
Attachments
THANK YOU!!!
Would it be possible to add the delay to your V2 design?
How is it implemented in the original design by Jeff? I am not a EE, but I was trying to skim through and figure out which component(s) implement the delay...
Also, I assume delay is only needed during power-up. Right? No need for a delay when turning PreAmp ON/OFF to avoid "pop" (if active speakers are driven by it)?
Anyone??
I am looking for ideas on how to implement a "pop protection" without using the entire front-panel-control-scheme that Jeff implemented (following the original design)...
Alternatively, would using an external (to the main PCB) soft start mechanism (https://diyaudiostore.com/collectio...speaker-turn-on-delay-and-dc-protector-boards) negate the need for "pop protection"?
If you feel comfortable tweaking and modifying circuits designed by Nelson Pass, you might consider his "PSU Filter Relay" PCB which is in the Store and which is a bit cheaper: {{LINK}} . You only want that PCB's output muting relay function, and you don't want its filter-for-single-ended-power-supply function. So if you feel comfortable studying Nelson's schematics and deciding which components you can omit, you can probably (i) use that board; and (ii) save some money; and (iii) brag that your gear has an output muting circuit designed by Nelson Pass himself. But it will take some figuring out and circuit knowledge.
My original design has the delay built in to the front-panel logic. The flip/flop for the output relays has a small RC net on the CLR line, so until the cap fills neither output relay will engage.
The output of the transformer is AC. When rectified it will be a bit less than 1.4X larger in DC. But it will also fluctuate a lot. The power supply then regulates that down to the rail voltage.
The output of the transformer is AC. When rectified it will be a bit less than 1.4X larger in DC. But it will also fluctuate a lot. The power supply then regulates that down to the rail voltage.
I got a PM on relay choice. I remember that it turns out I used sub-optimal relays. Something about wanting the right amount of current through them for the contacts to be self-cleaning or something? (And I think I used one with too high a current rating?)
I looked back through the thread, but couldn't find the discussion.
Anyone remember it?
I looked back through the thread, but couldn't find the discussion.
Anyone remember it?
Here? https://www.diyaudio.com/community/threads/audio-switching-relay-recommendations.348883/
Got one of your PCBs on the way, so very interested if you have any long-term experiences to share
FWIW, I normally use RY-series (or Nais DS2 or Omron equivalents) for signal switching - and I have never noticed any difference between the types at least.
Got one of your PCBs on the way, so very interested if you have any long-term experiences to share
FWIW, I normally use RY-series (or Nais DS2 or Omron equivalents) for signal switching - and I have never noticed any difference between the types at least.
Bullseye. I had forgotten it was in a different thread....
I'm not sure my long-term experience is very germane. I use my HPA-1 as my main pre-amp, so it's on 24-7. The power goes out here 5 or 10 times a year, but that's still a lot less switching than someone might experience if they turn it on/off daily.
In any case, my relays are still fine. But I would go with the recommendations in that thread if I were doing it again.
I'm not sure my long-term experience is very germane. I use my HPA-1 as my main pre-amp, so it's on 24-7. The power goes out here 5 or 10 times a year, but that's still a lot less switching than someone might experience if they turn it on/off daily.
In any case, my relays are still fine. But I would go with the recommendations in that thread if I were doing it again.
FWIW, I used one with an EMI filter. https://www.mouser.ie/ProductDetail...GAEpiMZZMv1TUPJeFpwblT2m0XddNJBxi%2BgRStwSPw=
Question. I am considering either KG GS-X mini, KG CFA3 or this, the HPA-1. I have heard neither but I trust what comes out of PASS laboratories but a SuSy architecture would be interesting as well. Maybe one can have both worlds. Anyway, to my question.
Would it be worth while to build a dual PSU balanced version of the HPA-1 or is the SE plenty good enough ?
Would it be worth while to build a dual PSU balanced version of the HPA-1 or is the SE plenty good enough ?
Hello all,
Here is the progress of the work:
I haven't received my Toroidy 2x25V yet, so I powered it with a 2x23V transformer I had in stock. I have a stable 24V output with a small load to simulate the amplifier.
I have modified the design, integrated the 5V transformer into the circuit, and now I only need the 1uF capacitors to test the whole system and program the ARDUINO for the inputs/outputs.
Have a great day!
Jérôme
Here is the progress of the work:
I haven't received my Toroidy 2x25V yet, so I powered it with a 2x23V transformer I had in stock. I have a stable 24V output with a small load to simulate the amplifier.
I have modified the design, integrated the 5V transformer into the circuit, and now I only need the 1uF capacitors to test the whole system and program the ARDUINO for the inputs/outputs.
Have a great day!
Jérôme
Attachments
Which types (hfe) would you recommend?
Mouser and Digikey only have "F" from the KSC1845.
Mine are around hfe 400
Unfortunately, I only have "FA" from the KSA992, which are a little lower at around 350
Do you think that fits, or should they be better matched (P - N)?
Then I might have to get some KSA992 F
KSA992
KSC1845
Mouser and Digikey only have "F" from the KSC1845.
Mine are around hfe 400
Unfortunately, I only have "FA" from the KSA992, which are a little lower at around 350
Do you think that fits, or should they be better matched (P - N)?
Then I might have to get some KSA992 F
KSA992
KSC1845