[mike678]

I have the the BP 25 that came with the original small power supply, with the MP1 added to me, it is quiter and all, but...too damned much bass. Is there some regulation or resistance change somewere that compensates between the models that came with the small power supply and the MP1? The schematics I find on the website only show the post-MP1 schematics, so I can't find a difference.

[James Tanner]

I have the the BP 25 that came with the original small power supply, with the MP1 added to me, it is quiter and all, but...too damned much bass. Is there some regulation or resistance change somewere that compensates between the models that came with the small power supply and the MP1? The schematics I find on the website only show the post-MP1 schematics, so I can't find a difference.

Hi Mike - email Mike Pickett - mpickett@bryston.com

james

[mike678]

I wrote email to service via the website, and to Mike directly. No response so far.

[mike678]

Still no response. Anyone have anything?

[FullRangeMan]

Too much bass! This is a embarrassment of the rich.
A two-way pocket loudspeaker will have few bass and may match your preamp.

[mike678]

Yes, it can be an embarrassment of riches!

But too much bass causes loss of focus and, paradoxically, loss of the sensation and tone of the bass. For instance, you can lose the "growl" of a good electric bass if there is too much around 60 to 120Hz. I can manually compensate in the room DSP, but I would just like to find a preamp, or make this one be, actually transparent to the source. Every high end one I have tried has a rather gross flavor somewhere that does not sound like the source. Whatever glories they might have or add, they are NOT transparent.

The BP25 on the MP1 supply tends to thicken the sound, quite a bit more than on the tiny supply it came with. I HAVE used the trick of coming in on the tape in, which bypasses the buffer module, and that does help a bit.

I may change the output capacitors to film values that roll the bass off slightly, or sell the thing. Not sure which yet. The sacrifice would be losing the Bryston's great ability to drive long cable runs, but I don't have the need here.

[rob80b]

I doubt very much that the BP25 and its associated power supply is the culprit here….it's about as linear as any pre-amp can be….it’s proportionately amplifying the source’s reproduced signal of the recording…I would definitely look elsewhere…speaker, speaker placement and room interaction come first to mind. Do you have sub a involved as the 60-120hz region is the most problematic with regards to seamless integration of the crossover. Looks like you’ve tried a few things but unless something inheritably wrong happened to the BP25 it really does not make sense????

[mike678]

This is noticed in comparison to running the Prism Orpheus straight into the amplifier, vs into the BP25. Also into the BP25 with its native (small) power supply, and into the MPS1. Very noticeable difference in each case. Also quite noticeable when going around the first buffer via going in the tape input.

So, differences are heard when the preamp is inserted , and all else remains the same.   What I am trying to fix here, if Bryston will tell me what changes they made when they went to the larger supply, is that bottom end. And if they did not make changes, but accepted that sound because it sold well, then just tell me so. The same discrete op amps are in the 1.5 phono stage and that is nicely balanced (the MPS1 was the power supply it came with, so it was made around it). The 1.5 is one of my favorite phono stages.

The BP25 was not QUITE transparent, tonally, with original PS, but was pretty close. With the bigger supply, its prominent in a gentle bell curve with a Q of  about .6 centered at 60Hz out to about 200 or so compared to the original source, the Prism. The amplitude is a few tenths of a db, which sound like nothing, but it is much more than most cable changes do, and over which us audiophiles will fight major wars! (Many cable differences are in the hundredths of a db.) The difference is that between a bass blur, and a well defined growl on stringed bass.

There is no sub, the speakers are DSP tuned to the room  with the Prism Orpheus as the source (its what I do for side money, I am quite good at it). Any flavor changes noted are relative to that baseline condition.

[James Tanner]

Hi Mike

As far as I know there were no technical changes in the MPS-1 larger power supply other than allowing for more connections (4 rather than 1) so more units could be used with a single power supply. 

James

[TJ-Sully]

hi mike678 - do you still have 'too much' bass with the MPS-1 power supply?

[mike678]

Thank you James for the reply, but I meant the change in the preamp side of things to accomodate the different power supply impedance. Regulator, feedback, resistance, SOMETHING? Like how the BP26 sounds pretty darn flat on the bigger power supply and the BP25...not so much.

Yes, TJ I still have the same flavor difference on the BP25 with the bigger supply. It was built around 1998 or so, with the small ac transformer ouboard supply.

[James Tanner]

Thank you James for the reply, but I meant the change in the preamp side of things to accomodate the different power supply impedance. Regulator, feedback, resistance, SOMETHING? Like how the BP26 sounds pretty darn flat on the bigger power supply and the BP25...not so much.

Yes, TJ I still have the same flavor difference on the BP25 with the bigger supply. It was built around 1998 or so, with the small ac transformer ouboard supply.

I will ask Mike but as far as I know there were no significant chages.

james

[Mike Pickett]

Thank you James for the reply, but I meant the change in the preamp side of things to accomodate the different power supply impedance. Regulator, feedback, resistance, SOMETHING? Like how the BP26 sounds pretty darn flat on the bigger power supply and the BP25...not so much.

Yes, TJ I still have the same flavor difference on the BP25 with the bigger supply. It was built around 1998 or so, with the small ac transformer ouboard supply.

Hi Mike;

Sorry for the lack of reply on this; I've e-mailed you directly as well, this morning...

Lots of folks, including myself, have used this preamp with a different power supply than it shipped with, and while I expect differences in noise floor and sound stage, a frequency response anomaly is difficult to explain.  We'd like to get your unit on the bench here to reproduce and correct this.

Thanks,

Mike

[mike678]

Excellent Mike, thank you. I will get that info to you later today, the unit is packed away right now. It's pretty early in the morning here. On the one hand, its something that bothers me, on the other hand, it already gave me 17 years of service (it was a demo unit from the now-defunct Laserland). Very few things last that long.

[mike678]

Well folks, the Mystery is solved! I measured the regulator voltages as per Mike, and all was well.

But in looking at the output capacitors I see that I had bypassed them all together (jumpered with a wire)  somewhere about 2003. I had read somewhere that they weren't needed as there was normally no dc offset (there indeed was none). This was back in my audiophile "Electrolytics Be Evile" days.   This was some years before finding out that bipolar electrolytics used in this manner have distortions quite a bit below -110db and simple 2nd at that.  I seem to recall I made this change just before getting the new power supply, though I can't swear to it.

I returned to stock configuration, all works as it should now. If you are tempted to bypass the outputs, don't.

Thanks again to Mike Pickett for giving me what I needed to check things out. Spectral and IM tests of all sorts of multiple tones shows this baby is clean as can be. At least into adc/dac loads.

Re bipolar electrolytics in unbiased coupling duty  https://linearaudio.nl/sites/linearaudio.net/files/Bateman%20EW%2012%202002%20mar2003%201uF%20electrolytic%20or%20film.pdf Page 12

[Elizabeth]

WOW! wonderful you got it solved. 

[mike678]

Yeah, Mike got me thinking in the right direction, so I had to look for something else other than my pet theory. I am really happy now. *Jumps up and down repeatedly...*

[rob80b]

We were  on that one.
As I mentioned in another post, Bryston got my 10 year old BCD-1 fully functioning again..... it's reassuring to know they've got our backs.

[mike678]

As the caps are breaking back in the sound is getting nice and smooth. I left the preamp on very high into a turned off amp all night, woke up to a nice, lovely, smooth sound.