Pearl 3 Burning Amp 2023

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#3,502
laverda said:
It looks like a pre reg or tracking pre reg, a regulated supply before the on board regs. They work very well at lowering the noise floor further. Its on my next to do list ....
Click to expand...

Hello laverda and All,

You could be on to something here.

I think along the lines that there could be more than a couple of things going on here.

Keep in mind that there are several CR stages in the shared power supply. Each CR has its' own resulting voltage drop. Add 2 or 3 CR caused voltage drops and the LM7815's and LM7915's may well be dropping out of regulation.

https://www.diyaudio.com/community/threads/pearl-3-burning-amp-2023.404054/page-168#post-7690386

Thanks DT
 
#3,505
@rhthatcher et al
I imagine that you mentioned these flex boards to me when I asked about designing the PSU such that the on board regs saw just enough voltage and current to work perfectly... but no more to keep excessive heat to a minimum.
as Craig's running a pair of 18-18v transformers that might be a concern if pre-regulation was not included.
Are boards available still?
 
#3,507
Craigl59 said:
Have only listened for a day but note the improved soundstage clarity and positioning, a certain secure fullness to the timbral accuracy, and a deathly quiet to all -- so much so that it rivals CDs. New vinyl (such as the just released rsd of Ronstadt's Asylum years -- 4 albums) sound stunning.
Click to expand...
Those are exceptionally good pop music recordings. I have the original LPs.
Ed
 
#3,508
jackinnj said:
You get better performance out of LMxxx regulators by driving them harder -- this owing to the positive relationship between pass transistor beta and the current flowing through it. As the beta goes up, the output impedance goes down.
Click to expand...

Hello,

The OEM P-3's on my bench draw right at 42ma each, likely typical of many or most of the Pioneer P-3's that 6L6 shipped. At 20VDC input and 15VDC output the LM7815" and LM7915's are dissipating about 0.21 Watts each. (20-15) volts X 0.042 amps.

The regulators are barely warm to the touch.

A shunt resistor between the plus and minus regulator outputs might drive the regulators a little harder, if it would help?

Measurements at the P-3 regulator outputs might shed some light, FFT, voltage and or noise.

Thanks DT
 
#3,512
@EdGr: Yes, I also have multiple copies of the original Asylum albums, some of them bought NOS in the last 3 years. They are superb. These new German pressings are even better to my ears and would love to know if they got ahold of the original master tapes. Gave away one of the 4-album sets at a Music/Pizza/Cirbbage party last week and had to rush out and get another. The record sale deal production is superb and there were only 3500 copies made.
 
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#3,513
Need to amplify my thanks to the estimable Randall Thatcher for his significant help the last 5 years or so. He has listened to some of my boring music tales and has provided a great deal of knowledge, boards aplenty, matched components, and a friendly ear. You are the kind of professional that makes these boards work. Recently, a trail buddy was listening to my system here in Flagstaff and was so impressed he started to examine the names on each component. Finally he said "who's this Thatcher fellow? He must really know his stuff." I said, "Yep he's the best. Knows how to write manuals as well..."
Thanks, Randy. Your version of the Aleph 30 has significantly improved my listening world.
 
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#3,514
mhenschel said:
I should think you'd do a load resistor to ground for each regulator, no?
Click to expand...

If you put 2 identical resistors in series between the + and - regulator outputs, then measured the voltage between the junction between the resistors and ground the voltage would be zero.

If everything is matching it will make no difference if the resistors connect to ground or not.

jackinnj is right it is just for fun.

Thanks DT
 
#3,516
Hi to all,

I'm seeking for some help as I'm running out of troubleshooting ideas.

Completed the Perl 3 but the sound appears to have very muted highs. The bass seems enhanced but I can't tell with so low highs.
The sound character is the same with jumper on or off, or with any DIP setup. (except the output level)

Power appears to be normal at -14.9 and 15.00 Volts

Op Amps measurements (close to identical both boards):
U1: 128mV
U2: 0.2mV
U3: G
U4: -14.9V
U5: -0.6mV
U6: -0.5mV
U7: 930mV
U8: 15V

I run R27 with 680Ω (3.4mA)

Not sure if it is related but I see in the schematic Q8 as ZTX851, but in the web instructions and the BoM, this is a ZTX457.

Any advice would be highly appreciated. Many thanks!

Screenshot 2024-06-02 at 10.18.27.png
 
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#3,517
Have you tried one channel at a time?
E.g. starting with the left so have simple as possible setup to start with?
I noticed you use different types of regulators. On right channel the type with metal back which you in some cases want to electrical isolate from the heatsink in case heatsink has chassis / gnd connection. I can't remember the layout of the P3 board if heatsinks are grounded. As It seems you measure -+15VDC from both boards it is probably not an issue......so just an observation.
 
#3,520
Ok, but usually the 3-pin regulators that have metal-back the metal-back has in some cases connection to the output pin of the regulator. So if heatsink has gnd connection at PCB (which I can't remember if this is the case) then it could cause troubles.....if not now then maybe later. So just a small concern.

Then to be 100% sure this is not your problem my idea was to disconnect the power (via the screw terminal) to the board which uses the regulators with metal-back and check if it makes a difference.
 
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