Thanks Eric!
Yes, I used a few TX2575's in a couple places.
Most of the resistors are Takman metal films with one stray Shinkoh at R9.
R9 was only really because the closest Takman I could get was 510R
JackinNJ made some posts about sources of noise and 6L6 also mentioned that R7, 8 and 10 might be a good place for better resistors as well.
I'm also thinking about the Cap in series with R14.
One thing to note regarding hum is that I have a high output MM (Ortofon 2M black) and I do start hearing some hum at about 6 dB higher level than I would ever listen. Switching to a low output MC might make the hum an audible issue. I plan to add MuMetal shielding of the transformer and AC cabling at some point and report the differences I hear / can measure.
For now I'm going to enjoy the Pearl as is for a while and then perhaps make some "adjustments". I have a couple of other projects in process which I promised my wife I would finish. Next up is finishing the soapstone plinth for the TD-124 and then there is a SP-10 MkII sitting there in need of some TLC and then ...
Yes, I used a few TX2575's in a couple places.
Most of the resistors are Takman metal films with one stray Shinkoh at R9.
R9 was only really because the closest Takman I could get was 510R
JackinNJ made some posts about sources of noise and 6L6 also mentioned that R7, 8 and 10 might be a good place for better resistors as well.
I'm also thinking about the Cap in series with R14.
One thing to note regarding hum is that I have a high output MM (Ortofon 2M black) and I do start hearing some hum at about 6 dB higher level than I would ever listen. Switching to a low output MC might make the hum an audible issue. I plan to add MuMetal shielding of the transformer and AC cabling at some point and report the differences I hear / can measure.
For now I'm going to enjoy the Pearl as is for a while and then perhaps make some "adjustments". I have a couple of other projects in process which I promised my wife I would finish. Next up is finishing the soapstone plinth for the TD-124 and then there is a SP-10 MkII sitting there in need of some TLC and then ...
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Berd: Here is an another method that might help block some hum from your power supply. I purchased my chassis from ParMetal with an alodine coating for EMI / RFI shielding. They sell an optional internal divider plate that fits the chassis from front to back. Scroll to the bottom of the page. I used one of these in my BA-3 to separate the power supply from the signal circuitry and will likely order another for my Pearl chassis.
Do the SP-10 first. You'll sell the Thorens, trust me.
+110%,....
the SP-10 is a vastly better TT. There is every incentive to get it up and running properly. There is a good thread on DIYaudio to help. This link gives a lot of extra information:
TECHNICS SP-10 : SP-10Mk2 : SP-10Mk3 Direct Drive DD Professional Studio Turntables Panasonic
My personal SP-10....which has effectively been stolen by Vantage Audio here in the UK.....was used with all boards moved to 'outboard' with a 1m umbilical cord.......this mod makes a vast improvement to performance. Also consider getting rid of the top-plate and mount the motor directly in a solid heavy plinth. IF you can find info on the Kinyata (spelling?) mods this will explain.
This mod was to be my next move and I have a slate plinth ready for such an installation. [
6L6...DO try this - even if only on a piece of heavy board!]Hum update
I tried a couple of things this morning to try to figure out the source of the small amount of hum I do hear. While the hum is not an issue for me at all, I thought the following qualitative results might be informative to others here.
1) Is it the transformer and diode bridge ? Test: turn off the power switch and see if there is any observable change while running from caps only, i.e. transformer and diode bridge is not on so cant be source of hum. Note: Before doing this turn the volume down and make sure you don't have any loud switching transients (I did not). Result: No observable change in level of hum when opening AC switch (with Preamp at level 65)
2) Is it the motor on the turntable ? The table is is about 10" to the right of the Pearl inputs. Test: Turn off the turntable and see if there is any change. Result: no observable change in level of hum
3) Is it the power supply of the XP-20 preamp ? The power supply is about 12" below the Pearl and below the XP-20 main unit. Test: Lift Pearl up by about 12" (limit of the cables I had) Result: no observable change in level of hum.
4) Is it the Phono cables / tonearm ? Test: Listen to hum with preamp at level 65 then mute preamp, unplug phono cables, un-mute preamp (level 65) and listen to hum. WARNING: THIS WILL PRODUCE A VERY LOUD POP if you do not mute the preamp or leave the volume up when you unplug phono cables.
Result: The hum disappeared completely. I then increased preamp volume to level 83 (max) and the only observable noise was a very slight white noise hiss.
The phono cables I am using are Grover Huffman Empress - which I love. When Grover and I were discussing them I was concerned about the high capacitance of the cable. At my request, he built them without some of the layers of shielding. BTW: This was successful in that the capacitance I measured was 80 pF versus 150pF (I think) he estimated for the normal cables. I also have the cables that came with the SME 312s (Vanden Hull 502's I think) and I can try an A/B comparison between the two later tonight.
I tried a couple of things this morning to try to figure out the source of the small amount of hum I do hear. While the hum is not an issue for me at all, I thought the following qualitative results might be informative to others here.
1) Is it the transformer and diode bridge ? Test: turn off the power switch and see if there is any observable change while running from caps only, i.e. transformer and diode bridge is not on so cant be source of hum. Note: Before doing this turn the volume down and make sure you don't have any loud switching transients (I did not). Result: No observable change in level of hum when opening AC switch (with Preamp at level 65)
2) Is it the motor on the turntable ? The table is is about 10" to the right of the Pearl inputs. Test: Turn off the turntable and see if there is any change. Result: no observable change in level of hum
3) Is it the power supply of the XP-20 preamp ? The power supply is about 12" below the Pearl and below the XP-20 main unit. Test: Lift Pearl up by about 12" (limit of the cables I had) Result: no observable change in level of hum.
4) Is it the Phono cables / tonearm ? Test: Listen to hum with preamp at level 65 then mute preamp, unplug phono cables, un-mute preamp (level 65) and listen to hum. WARNING: THIS WILL PRODUCE A VERY LOUD POP if you do not mute the preamp or leave the volume up when you unplug phono cables.
Result: The hum disappeared completely. I then increased preamp volume to level 83 (max) and the only observable noise was a very slight white noise hiss.
The phono cables I am using are Grover Huffman Empress - which I love. When Grover and I were discussing them I was concerned about the high capacitance of the cable. At my request, he built them without some of the layers of shielding. BTW: This was successful in that the capacitance I measured was 80 pF versus 150pF (I think) he estimated for the normal cables. I also have the cables that came with the SME 312s (Vanden Hull 502's I think) and I can try an A/B comparison between the two later tonight.
The distortion of the first gain stage is about 1/10th the total distortion of the Pearl, so most of the THD% would appear to occur in the second gain stage.
Input Signal THD% First Stage (Measured)
1mV 0.011%
5mV 0.026%
10mV 0.052%
20mV 0.11%
According to the PASSDIY article, THD% of the Pearl is ~0.26% with 5mV input. When you do your RMS-ing, the THD% of the first stage is almost irrelevant.
Before you do that, read the helpful hints from the folks at muShield. They've gone out of their way to help DIYr's from spending a lot of money and not getting the results they were looking for. Besides, when you bend muShield, muMetal any deformations impair its effectiveness.
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Berd: Glad to hear you found the source of your hum! Even better when solutions are straight forward. I replaced the captive RCA cable on my TT with BlueJeans LC-1 and rewired the tonearm for a total capacitance of 55pF. This allows me greater latitude of adjustment than the default state of 350pF.
Jack: Thanks for the details on THD - interesting to know! I don't think my issue was one of THD, but one of too much gain that was overloading my preamp and creating bad distortion at the speaker. I adjusted the feedback to lower the gain in the second stage to no avail. Degenerating the jFets in the first gain stage with 20R instead of 10R cured my problem. Odd, though, that Berd didn't experience the same thing - I'm also using a 5mV cartridge (Audio Technica 150MLX). Perhaps my pre is just more sensitive to overloading than others?
Jack: Thanks for the details on THD - interesting to know! I don't think my issue was one of THD, but one of too much gain that was overloading my preamp and creating bad distortion at the speaker. I adjusted the feedback to lower the gain in the second stage to no avail. Degenerating the jFets in the first gain stage with 20R instead of 10R cured my problem. Odd, though, that Berd didn't experience the same thing - I'm also using a 5mV cartridge (Audio Technica 150MLX). Perhaps my pre is just more sensitive to overloading than others?
Adjusting the Pearl gain for a 2M Black
A quick update on the gain game:
I reduced the second stage gain by going to 50k at R15.
I had a second pair of 100k TX2575's so I soldered them into the location for C15 which is not used in my build.
This puts which puts a second 100k resistor in in parallel with the 100k at R15 for 50k.
I just replayed Joni Michell's "Court and Spark" - a track which created some audible distortion in one passage this morning (at 100k) and tonight at 50k there was no issue at all.
Ok, while admittedly the following may just me wanting to hear a difference, overall I think it sounds more relaxed and natural with 50k at R15 than with 100k. I was not attached to the outcome either way (it's a resistor and 5 minutes to solder it in after all) so I think this is real.
For folks with high output (5 mV) MM cartridges like the the 2M black, IMHO, you might want to try building / trying 50k or perhaps even a bit lower at R15.
In my system there is still PLENTY of gain to listen at ridiculously loud levels so it seems to be a reasonable trade off to reduce the second stage gain and along with it a little bit of the distortion.
It's very good and just keeps gettin better
A quick update on the gain game:
I reduced the second stage gain by going to 50k at R15.
I had a second pair of 100k TX2575's so I soldered them into the location for C15 which is not used in my build.
This puts which puts a second 100k resistor in in parallel with the 100k at R15 for 50k.
I just replayed Joni Michell's "Court and Spark" - a track which created some audible distortion in one passage this morning (at 100k) and tonight at 50k there was no issue at all.
Ok, while admittedly the following may just me wanting to hear a difference, overall I think it sounds more relaxed and natural with 50k at R15 than with 100k. I was not attached to the outcome either way (it's a resistor and 5 minutes to solder it in after all) so I think this is real.
For folks with high output (5 mV) MM cartridges like the the 2M black, IMHO, you might want to try building / trying 50k or perhaps even a bit lower at R15.
In my system there is still PLENTY of gain to listen at ridiculously loud levels so it seems to be a reasonable trade off to reduce the second stage gain and along with it a little bit of the distortion.
It's very good and just keeps gettin better
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Jack: I think we may be talking past one another here. The issue with my Pearl is that the output level into my pre was too high, causing the "Peak" indicator to remain constantly illuminated and resulting in terrible sound quality. I don't have capability to measure THD. Whatever distortion level is or isn't present was clearly being overwhelmed by an output level that was just too high. Changing the feedback in the second gain stage to lower gain didn't solve the problem. Reducing the bias of the first gain stage did solve the problem. Now everything sounds great.
Hi Eric,
If I'm reading things correctly, I think Jack is saying his sim shows increasing
the source resistance (as you've done to avoid the front end overload) only
increases the noise minimally but at the same time lowers distortion a bit
(increase in source degeneration).
So it seems increasing the source resistance is a reasonable thing to try, if
overload from the first stage is a concern.
Cheers,
Dennis
If I'm reading things correctly, I think Jack is saying his sim shows increasing
the source resistance (as you've done to avoid the front end overload) only
increases the noise minimally but at the same time lowers distortion a bit
(increase in source degeneration).
So it seems increasing the source resistance is a reasonable thing to try, if
overload from the first stage is a concern.
Cheers,
Dennis
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Hi Everyone,
I hope everyone is having a Great Easter Weekend.
Now that I have the power supply finished, I'm putting together an order for all the parts for the boards mostly from Mouser. I've been going through stuff I have left over from previous builds (most from 4-7 years ago) to keep the costs down. I have quite a few Relcaps and Clarity Caps from when I redid all my speaker crossovers around 6-7 years ago and will probably use them for many of the smaller value film caps. I should be able to fit them without any problem if I mount them vertically. I have some 20uF Clarity ESA caps that I might try as the output caps instead of the Silmic II. I'll order a couple of Silmics from Mouser as they're not that expensive. I'll put in some sockets and try them both. Once I decide which I like better, I'll remove the sockets and solder the caps direct.
I had a question on the resistor and cap for the cartridge loading. I thought the cartridge that was given to me was the AT-OC9II but it's actually the version 3. I did some research, and reading the reviews, many seem to think that 250R is the best resistive loading so I figured I would leave R15 empty and change R19 from 47.5K to 250R. They don't give any spec in the directions for capacitive loading, so I was wondering if it's OK to just leave both C9 & C15 empty for now maybe with some sockets?
I also had a question about adding photos to a post. In an earlier post, I clicked on the add a photo link when creating the post and put in the Photobucket URL's for the images. I ended up with large photos in the listing. How do you get the smaller thunbnails that can be clicked on for larger images into the listing?
Thanks, Bob
I hope everyone is having a Great Easter Weekend.
Now that I have the power supply finished, I'm putting together an order for all the parts for the boards mostly from Mouser. I've been going through stuff I have left over from previous builds (most from 4-7 years ago) to keep the costs down. I have quite a few Relcaps and Clarity Caps from when I redid all my speaker crossovers around 6-7 years ago and will probably use them for many of the smaller value film caps. I should be able to fit them without any problem if I mount them vertically. I have some 20uF Clarity ESA caps that I might try as the output caps instead of the Silmic II. I'll order a couple of Silmics from Mouser as they're not that expensive. I'll put in some sockets and try them both. Once I decide which I like better, I'll remove the sockets and solder the caps direct.
I had a question on the resistor and cap for the cartridge loading. I thought the cartridge that was given to me was the AT-OC9II but it's actually the version 3. I did some research, and reading the reviews, many seem to think that 250R is the best resistive loading so I figured I would leave R15 empty and change R19 from 47.5K to 250R. They don't give any spec in the directions for capacitive loading, so I was wondering if it's OK to just leave both C9 & C15 empty for now maybe with some sockets?
I also had a question about adding photos to a post. In an earlier post, I clicked on the add a photo link when creating the post and put in the Photobucket URL's for the images. I ended up with large photos in the listing. How do you get the smaller thunbnails that can be clicked on for larger images into the listing?
Thanks, Bob
When confronted with an issue like this -- I solder a SIP female socket so that I can listen and swap out parts. Get a recording of piano or male singing and compare.
I've used WIMA polyester caps in the RIAA network. Mouser carries. The most important issue with the RIAA caps is that the two (right and left) channels should match each other. Compliance to the RIAA curve, while important, is less critical than seeing that each channel matches up!
Will PM you wrt the NJ Audio Society!
Thanks. I have a strip of the Sip sockets in the order I'm putting together for Mouser. I looked up the NJ Audio Society online. I wasn't aware that NJ had an audio society until you mentioned it in your post. I'd be interested in more info.
Having some issues with subsonic frequencies on my system, I decided to insert Rod Elliot subsonic filter on the output of Pearl II. When I cranked the volume on my pre-amp I've notice large cone excursion from my mid-bass. After implementation of subsonic filter, the cone excursion is gone (no more pumping).
First Stage Gain Update
As I mentioned in an earlier post I have been hearing issues due to the high gain of the Pearl II when coupled with my Orotofon 2M Black (5 mV output)
I already reduced the second stage gain by reducing R16 from 100K to 50K by adding a second 50K in parallel.
This improved things significantly but I was still hearing signs of overload.
Last night I replaced the 10R resistors in the first stage (R21-R24) with 20R.
This change made another clearly audible improvement.
Some of the things I heard:
Reduction in distortion - Heard mainly in male and female voices.
Improvement in dynamics - Heard mainly in drums, bass and some piano chords
More cohesiveness in complex passages, i.e. Instruments stay localized instead of becoming homogenized.
Wider and deeper imaging across the board.
Rhythmic drive was also better which increased the toe waggling factor.
This was a very significant improvement, to the point that my wife commented on it after hearing it from the other room.
She later came in and listened to a couple of tracks and said it sounded much better.
While she does not have an "audiophile approved" vocabulary, she does have good ears.
Clearer and more lifelike are general purpose high praise terms from her but more importantly she started singing along and danced her way out of the room.
Previous descriptions during loud passages were "hurts my ears", "gritty", "electronicy" and "jumbly"
So, with all the YMMV disclaimers...
I think the Pearl II is a great phono stage but, as in all other things, it needs to be tailored to match the other components in order to to sound it's best.
A per-plan-build seems ideal for low to medium output cartridges but for high output MM's some alterations may be in order.
If you have a high output MM cartridge I would consider 20R in the first stage and 50k (or perhaps even lower) in the second stage.
As I mentioned in an earlier post I have been hearing issues due to the high gain of the Pearl II when coupled with my Orotofon 2M Black (5 mV output)
I already reduced the second stage gain by reducing R16 from 100K to 50K by adding a second 50K in parallel.
This improved things significantly but I was still hearing signs of overload.
Last night I replaced the 10R resistors in the first stage (R21-R24) with 20R.
This change made another clearly audible improvement.
Some of the things I heard:
Reduction in distortion - Heard mainly in male and female voices.
Improvement in dynamics - Heard mainly in drums, bass and some piano chords
More cohesiveness in complex passages, i.e. Instruments stay localized instead of becoming homogenized.
Wider and deeper imaging across the board.
Rhythmic drive was also better which increased the toe waggling factor.
This was a very significant improvement, to the point that my wife commented on it after hearing it from the other room.
She later came in and listened to a couple of tracks and said it sounded much better.
While she does not have an "audiophile approved" vocabulary, she does have good ears.
Clearer and more lifelike are general purpose high praise terms from her but more importantly she started singing along and danced her way out of the room.
Previous descriptions during loud passages were "hurts my ears", "gritty", "electronicy" and "jumbly"
So, with all the YMMV disclaimers...
I think the Pearl II is a great phono stage but, as in all other things, it needs to be tailored to match the other components in order to to sound it's best.
A per-plan-build seems ideal for low to medium output cartridges but for high output MM's some alterations may be in order.
If you have a high output MM cartridge I would consider 20R in the first stage and 50k (or perhaps even lower) in the second stage.