Crown D-150A II input sensitivity 1.4v ? Soundcraft MH3 can't drive it to full output. I think some bad luck on my part . I repaired the amp and set DC and Bias. All good but on my version of the PCB there is no way to set the input to .774v, Only the later version's have that. Maybe someone has some ideas? ?
My pcb has only one dual opamp and the layout is totally not the same.
My pcb has only one dual opamp and the layout is totally not the same.
Attachments
The MH3 can provide 21 dB more than its zero level of .775 volts. So it can drive your amplifier 15 dB past clipping. If you can’t do that your wiring between them is wrong.
Change R104 + R204 the feedback resistors? On U220 U102 input op amps? More resistance gives more gain. There is a pot after that, look like a DC bias pot.
R104 and R204 are part of offset adjustment, not what you need for adjustment of gain.
If I understand, the attached schematic is not correct for you amp? Can you identify your exact model? There's a good chance of finding the appropriate schematic.
If I understand, the attached schematic is not correct for you amp? Can you identify your exact model? There's a good chance of finding the appropriate schematic.
If memory serves me correctly, the MH3 provides balanced output and the D150 has unbalanced in.
Try driving the D150 from cannon pins 2 & 3, ignoring pin 1. That can give you 6dB more drive.
Try driving the D150 from cannon pins 2 & 3, ignoring pin 1. That can give you 6dB more drive.
Mister Audio might have something? ill check it out in the morning.
BSST- I have searched high and low for the schematic of my model and no luck Figuring out how to change the input sensitivity is beyond me, this is why I decided to post here. I will attach two pics. one of my PCB and the one with the jumpers found in the service manual. I think you will see a big difference.
What I can tell you is I hooked the Crown amp to my console and it sounds great but i could not drive it very hard towards full output.
mine above
service manual below
opamp below
BSST- I have searched high and low for the schematic of my model and no luck Figuring out how to change the input sensitivity is beyond me, this is why I decided to post here. I will attach two pics. one of my PCB and the one with the jumpers found in the service manual. I think you will see a big difference.
What I can tell you is I hooked the Crown amp to my console and it sounds great but i could not drive it very hard towards full output.
mine above
service manual below
opamp below
Last edited:
The amp is fixed at 1.4V. and you are correct the MH3 can output 21dbu and also the output is balanced.
No idea what to suggest without a schematic. Would you post pictures of front and rear panels?
Thanks.
Thanks.
Well, look up the datasheet of the 739 and see which op amps connect to the two inputs. Then increase the feedback resistor on those. I don't agree with BSST post 4, yes the feedback resistors do connect to DC adjust pot, but I don't see any later local feedback. There is global feedback from output, but messing with that messes with phase compensation. Pinouts of pin 8 and 13 as op amp inputs point to a 14 pin op amp, not an 8 pin one. Hint, the feedback resistor the third band will be yellow.
Agree for 1981 op amp production date, this is not a DC-150a. See schematic pdf on D150A, note says schematic is for serial # 140001 and above only.
Agree for 1981 op amp production date, this is not a DC-150a. See schematic pdf on D150A, note says schematic is for serial # 140001 and above only.
Last edited:
Thanks, Chrisng! Your provided link is certainly a much better match to Soundtec's photos.
@Soundtec
Assuming that the D-150A schematic is a reasonable match to your amp, I agree with your original assessment that it has no easy provision for modifying gain. Its gain is established as (1+R115/R109) or 20.6, or 26.3dB. There are two feedback loops in this design, so trying to modify their gains would be perilous.
Since you have repaired the amp, I suggest that that you confirm that it is generating the expected gain of 26dB. Do you have instruments to do that?
@Soundtec
Assuming that the D-150A schematic is a reasonable match to your amp, I agree with your original assessment that it has no easy provision for modifying gain. Its gain is established as (1+R115/R109) or 20.6, or 26.3dB. There are two feedback loops in this design, so trying to modify their gains would be perilous.
Since you have repaired the amp, I suggest that that you confirm that it is generating the expected gain of 26dB. Do you have instruments to do that?
I have no idea what Crown was up to but the Chassis clearly says D-150A Series II. As far as the PCB the foil version is M43197-8 and that is not the Crown D150 with the M1261A foil.
From what I can find out the D-150A series II had three board revisions and only the last one that the service manual was based on can be modified to .775v.
Today ill make a new cable balanced to unbalanced and see what I get. I will then put it back on the bench and do some more tests (26db gain)
From what I can find out the D-150A series II had three board revisions and only the last one that the service manual was based on can be modified to .775v.
Today ill make a new cable balanced to unbalanced and see what I get. I will then put it back on the bench and do some more tests (26db gain)
P.S. Double check of input sensitivity: I compute 80W RMS into 8 Ohms as 25.3VRMS. If gain is 20.6V/V, full power should be reached at 1.23VRMS, referred to input. Sound right?
This is the most useful link I've discovered. https://www.manualslib.com/download/1190440/Crown-D-150a-Series-Ii.html
I tried to upload, but file was too big for the forum; I hope the link works, but you may have this data already.
It's interesting that Crown seems to have been be very consistent in maintaining the same Ref Des for the gain setting resistors, R115 and R109. You could mimic the increased gain mod option by paralleling R109 with 825 Ohm 1%. Be cautious and test carefully before connecting valued speakers. In later versions, it's apparent that the amp was stable with this feedback revision, but I can't speak your variation. Most conservative course would stick with the lower gain, but the change may be perfectly OK.
Good luck!
I tried to upload, but file was too big for the forum; I hope the link works, but you may have this data already.
It's interesting that Crown seems to have been be very consistent in maintaining the same Ref Des for the gain setting resistors, R115 and R109. You could mimic the increased gain mod option by paralleling R109 with 825 Ohm 1%. Be cautious and test carefully before connecting valued speakers. In later versions, it's apparent that the amp was stable with this feedback revision, but I can't speak your variation. Most conservative course would stick with the lower gain, but the change may be perfectly OK.
Good luck!
You certainly nailed with that comment and I agree. Thanks for the unequivocal evidence.
Please keep us posted.
???
Well, what I trying to tell you is your board is looks like a Crown D-150A (not II) board, so maybe the D-150A service manual might give you some help or hints of possibility to increase gain of your board.😎
The first service manual you published seems to be a DC150A II rev-c, the latest evolution of the DC150A II which is far from your DC150AII, there must be a service manual specific to the DC150A II "a" or "b"
@huggygood, Please download link provided by @BSST in post #14, scroll down to page 7-9 you will find all the information.
I tested the Crown on my bench I measured the output wattage. At 24.439Vrms into 8 ohms I reach clipping 74.6 watts per channel. So no problem with the amp. i was using 1k at 1.4v output from my generator.
Problem is the Soundcraft MH3. Originally i was using a Hafler T1100 with an input of .774v I guess this is why i did not see the problem with the MH3 output.
Again thanks everyone.. As for myself a lot of good lessons learned.
Problem is the Soundcraft MH3. Originally i was using a Hafler T1100 with an input of .774v I guess this is why i did not see the problem with the MH3 output.
Again thanks everyone.. As for myself a lot of good lessons learned.