^ Within context, you're saying that increasing the gain such that a 2Vrms input will drive an F4 to voltage clipping into an 8 ohm load will not increase distortion noticeably?
I increased to 10dB and noticed no difference. I did not measure the difference. I have no idea what an F4 would take to drive.
Who cares, as long as you are happy with your volume and the sound, there is no reason for further dialisys.
Most of the discussions I see about driving the F4, have the caveat of «driving it to full output». Well, you might not need full output. In which case one might consider it more important not to waste signal attenuating it at the pre.
Hugz,
Baby V
Most of the discussions I see about driving the F4, have the caveat of «driving it to full output». Well, you might not need full output. In which case one might consider it more important not to waste signal attenuating it at the pre.
Hugz,
Baby V
FWIW, if one wants to drive the F4 to its full rated power, the preamp will need to swing a bit over +/20V. So you likely will want to run it at a min +/-23V rails. For the gain, doubling from the current 3.7x to 7.4x should do it with a 2V RMS input. The distortion will increase with a 6dB decrease of feedback.
An interesting question to me is how high the distortion might be at +/-20V output. That probably calls for some measurements. 🙂
I've used a 2V RMS output DAC + the standard gain preamp into F4/Mofo. That's less than 7W RMS into 8 ohms max and I was pretty happy with the result.
An interesting question to me is how high the distortion might be at +/-20V output. That probably calls for some measurements. 🙂
I've used a 2V RMS output DAC + the standard gain preamp into F4/Mofo. That's less than 7W RMS into 8 ohms max and I was pretty happy with the result.
I care, that's why I asked. Seems Marconi118 may also, since they asked the origin question, but I'll let them speak for themselves.
Why post equipment specs at all? Some people like to understand potential specs / performance before building or buying; me being one. Others may just strictly rely on 6Moons reviews. The choice is ours.
Kidding a bit of course. Always enjoy your posts.
Hugz back,
Patrick
"The distortion will increase with a 6dB decrease of feedback."
"An interesting question to me is how high the distortion might be at +/-20V output. That probably calls for some measurements. "
Agreed. I was wondering how high RickRay had gone with the gain since it followed Marconi118's follow up. (At least) two elements would be in play; gain structure alterations and voltage output. Both will likely effect the outcome. I was / am curious to the extent.
Either way, fun stuff!
I can say it is VERY easy to change the gain, just one or two resistors are changed. If I get my measurement system sorted I could make some measurements.
For my fully balanced preamp, I want to add rcas next to both the balanced inputs and outputs just so the preamp is more versatile to allow an rca source or single ended amp.
I would create switches to tie pins 1 and 3 together.
No resistor changes required, correct?
Thanks!
I would create switches to tie pins 1 and 3 together.
No resistor changes required, correct?
Thanks!
Ok. So I wouldn’t need a switch for the output. I just add my rcas, then jumper wires.
Pin 1 on xlr goes to ground
Pin 2 on xlr goes to rca middle barrel output
Pin 1 on xlr goes to ground
Pin 2 on xlr goes to rca middle barrel output
Another quick question. If running dual mono with two power supplies but add a Muses control, is it better to add one more PSU or power it off one of the two PSU boards?
Would it affect the sound of the one channel powering the volume control board?
Would it affect the sound of the one channel powering the volume control board?
I see a reference to R30 as 47k but nothing on the schematic. The search function doesn't educate me and I've 'only' read the first third of this thread.... (I know I'm lazy and this question shows a lack of commitment etc...)
I'm guessing this might sit between the output and ground to protect the output in the event that it is shorted to ground?
Can someone please confirm?
many thanks
I'm guessing this might sit between the output and ground to protect the output in the event that it is shorted to ground?
Can someone please confirm?
many thanks
Lenny with Academy Audio answered my question and recommended going with just one PSU to drive the Muses control and that balanced IN and OUT could be achieved with only one Wayne's board with his BIB and BOB boards (balanced in and out) plus the VCX.
Has anyone tried building Waynes preamp balanced IN/OUT with the ability to drive headphones? This would be without the muses and two Waynes boards.
- Make the schematic changes and use the more powerful transistors?
- Run a headphone output off pins 1 and 2 while leaving pin 3 floating?
Like many of you, I'm using a Glassware Dual Bipolar power supply for this preamp.
I built and tested the supply earlier, which worked just perfectly. After a lot of work on a complex case, I installed the power supply in the preamp. When I tested prior to powering up the pre board, now there's a problem. Output voltage from the PS.basically bounces around 100mv, like when you grab the probes in your hands--basically zero on both the + and – legs.
Both legs of the transformer secondary show 19.8vac. There are no toasted parts. No burst caps. No short on output. It's screwed to the chassis bottom with nylon screws, with a sheet of insulation underneath.
I'm stumped, and not sure what to look at next. Any thoughts on how this PS might fail like this, or what to test? Really don't want to tear this out and start over, but I really need to get it working so I can use the pre and show it off to you.
If this is not the right thread to discuss this, point me in the right direction. All the research results on this PS were here.
I built and tested the supply earlier, which worked just perfectly. After a lot of work on a complex case, I installed the power supply in the preamp. When I tested prior to powering up the pre board, now there's a problem. Output voltage from the PS.basically bounces around 100mv, like when you grab the probes in your hands--basically zero on both the + and – legs.
Both legs of the transformer secondary show 19.8vac. There are no toasted parts. No burst caps. No short on output. It's screwed to the chassis bottom with nylon screws, with a sheet of insulation underneath.
I'm stumped, and not sure what to look at next. Any thoughts on how this PS might fail like this, or what to test? Really don't want to tear this out and start over, but I really need to get it working so I can use the pre and show it off to you.
If this is not the right thread to discuss this, point me in the right direction. All the research results on this PS were here.
Hello Buckapound,
your Glassware - psu is screwed directly on the bottom of the case with a sheet of insulation (plastic? perhaps very thin insulator?) underneath.
Does that mean you have no standoffs under the pcb?
It is a symmetrical psu (V+ / ground / V-) - ground of the PSU connected to earthground at IEC-inlet?
Cheers
Dirk
your Glassware - psu is screwed directly on the bottom of the case with a sheet of insulation (plastic? perhaps very thin insulator?) underneath.
Does that mean you have no standoffs under the pcb?
It is a symmetrical psu (V+ / ground / V-) - ground of the PSU connected to earthground at IEC-inlet?
Cheers
Dirk
Thanks, Dirk.
Yes, PS board sits on ~2mm thick sheet of polycarbonate, with no standoffs, w/ nylon screws. Very tough sheet and hard to imagine punching through it with the little solder/wire stubs on the board's underside. Last resort, I'll make room to lift up the board and verify, but everything is very tightly packed in this chassis so I'll have to unbolt the transformer, etc.
PS ground is not connected to the main ground, but it wasn't when I tested it either. As you know, grounding can be confusing, and with that unusual PS design I wasn't sure It should be connected. Easy enough to do. BTW, I have a robust star ground connected to the case just a few cm from the IEC inlet. Signal ground is connected through a diode bridge as NP and others suggested.
--Randy
Yes, PS board sits on ~2mm thick sheet of polycarbonate, with no standoffs, w/ nylon screws. Very tough sheet and hard to imagine punching through it with the little solder/wire stubs on the board's underside. Last resort, I'll make room to lift up the board and verify, but everything is very tightly packed in this chassis so I'll have to unbolt the transformer, etc.
PS ground is not connected to the main ground, but it wasn't when I tested it either. As you know, grounding can be confusing, and with that unusual PS design I wasn't sure It should be connected. Easy enough to do. BTW, I have a robust star ground connected to the case just a few cm from the IEC inlet. Signal ground is connected through a diode bridge as NP and others suggested.
--Randy
One way to look at is that if you increase gain 6 dB the distortion goes up by 6 dB due to less feedback. This is approximate on the curves because of thd + noise. The distortion starts off quite low on this so it is pretty easy to kick the gain up with out hurting things.
Hello Buckapound,
how you describe it - your groundig scheme with starground will be o.k.. Same with your 2mm thick polycarbonate insulation sheet.
I was afraid there could be a short...
If it is bouncing 0,1 V up and down (railvoltage of PSU) - perhaps it is your DMM or the PSU needs some load. I would test it.
I would hang the BA2018 board on the PSU and would test it. For the first run with a dimbulbtester - could be a 'life insurance'.
But I am pretty sure / hope, that all will be good...
Cheers
Dirk
how you describe it - your groundig scheme with starground will be o.k.. Same with your 2mm thick polycarbonate insulation sheet.
I was afraid there could be a short...
If it is bouncing 0,1 V up and down (railvoltage of PSU) - perhaps it is your DMM or the PSU needs some load. I would test it.
I would hang the BA2018 board on the PSU and would test it. For the first run with a dimbulbtester - could be a 'life insurance'.
But I am pretty sure / hope, that all will be good...
Cheers
Dirk
