Little Bear P7 mods based off a P8 thread
Dec 3, 2017 at 3:07 PM Thread Starter Post #1 of 15

ihavet0es

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Happy holidays all! My first post was a thank you on an old thread regarding mods to the Little Bear P8 that I've applied to my P7. I figured it would be good to start a new thread with pictures for anyone interested in the P7 and would gladly appreciate any comments, suggestions or fixes to any mistakes I've made.

I haphazardly purchased a Little Bear P7 off the Bay that arrived with a broken pot. After a partial refund and awaiting a replacement pot from China I decided to learn more about this amp and possible mods. Unfortunately, with the exception of sales descriptions and a few posts/reviews there is little to no information anywhere. So, I stalked many threads and sites on general mods and more specifically the Little Bear P8 from which the P7 is based. I've used the amp now for a couple of months while progressively changing parts and experiencing the sonic difference at each stage. Please, excuse my use of terminology, modification mistakes, and soldering skills. I have very little to no experience with electronics and audio equipment. The only test equipment I have are my ears, familiar songs I've listened to over the years, and online test tone generators. My setup is a newish Windows 10 PC using Foobar/asio/sacd-asio, streamed content and HK FL8550 HDCD player into a hacked Topping D30 with a shunted Burson V6 Classic, Senn HD558 (don't really use it anymore) and AKG K712 Pro headphones.

First thing's first, fix the broken pot. The original was an A100k logarithmic pot but the seller shipped a linear B100k pot. Does it impact sound quality? I have no idea but at least I can now use my amplifier! I'll say the amp sounded okay. The bass was lacking but things sounded clear with a little distortion in the highs like cymbals and I could hear the individual instruments separately. The only comparison I have is an E10K on DAC and amp duty powering the AKGs. Not as good separation and clarity, the bass sometimes sounded farty and I had to turn the volume up for it to sound "fuller" but listening was very fatiguing.

My first actual mod was the replacement of the 4 greenish blue MKP output coupling capacitors (I think they're Vishay) with Audyn True Coppers as suggested by Geetarman49. I stuck with the original 0.10uf capacitance value but upped the voltage to 630v. Whoa, talk about huge difference. The sound warmed up a lot, things sounded bigger, bass was a bit lessened but I could hear lower frequencies, the separation was still there and I could hear more details/new sounds never heard before on familiar tracks. One thing is odd though and the only way I could describe it that things sounded a bit slower (maybe I'm crazy). Bellial's 80's Love streamed on Soundcloud and Death's "Painkiller" are some tracks where I had issues with speed. Any ideas?

The next mod performed was adding Audyn .1uf 400v Q4 MKP caps to bypass the four output electrolytics and four PSU filtering caps. I should have done the bypassing of the power and signal stage separately but my soldering iron was already hot. I really couldn't tell much difference with this mod but I think things might have sounded faster but not as warm.

The big difference between the P7 and the P8 is the use of a switching mode power supply in the P7 where the P8 uses a toroidal transformer. The P7 has two separate internal switching power supplies one providing 180v (as labelled on the power input on the main PCB) and a single 6.3v for the 6n3 and 6n5 tubes whereas the P8 uses a single toroidal transformer with one 170v and two separate 6.3v outputs to the tubes. Also, the filtering stage capacitance is different with the P7 using four 82uf 400v caps and the P8 using four 220uf 300v with an additional 240k ohm 2w resistor at the end. My P7 has a spot for the same resistor but didn't ship with it installed. At this point, I had no idea how increasing the capacitance would impact the 180w PSU and amp overall but hell it's a learning experience so let the soldering begin! Jebus Chris removing large caps are a pain! I changed the four caps to 220uf 450v Nichicon KX (no bypassing yet). At first, I thought I screwed myself because after changing the caps my volume pot didn't work! Sound came out the amp sounding crappy and a bit warbly; rotating the pot resulted in no change in volume. Sound just kept coming out the amp. Seriously, I though ***, S*@t, and S*#t again did I just destroy my amp and headphones?!? NO! After a rain dance, prayers to spiritual beings and the Annunaki, turning on the amp letting it sit with no input signal a couple of times and rotating the pot many times with different headphones things turned out great! Now there's a lot more bass. Let's just say I can honestly hear the +3db bass that the AKG K712 Pro is supposed to have. The sound stage changed though, things sounded closer and a bit veiled. Also, the volume adjusts properly; however the sound doesn't go away when the pot is turned all the way down. Is this a leaky cap due to the increase of capacitance? Maybe, I should add that 240k resistor at the end of the filtering stage.

At the power input to the main PCB of the P7 there's a location for a 1000uf 35v cap that isn't installed. I figured since the there's a single 6.3v input for both tubes on the P7 the capacitor should help smooth out/buffer the current draw. I soldered on a Panasonic FM 1000uf 35v cap and bypassed it with an Audyn .1uf Q4 cap. Another huge sonic difference. The sound stage is now huge! Everything sounds larger, cleaner, more echoey, no distortion in the highs, excellent bass extension and attack, everything just sounds better and dynamic. I used on online test tone generator to hear the roll off of the bass and it sounds/feels like it extends down to 20hz without attenuation. Actually, this last mod is what prompted me to write this post. I'm extremely happy with this amp, extremely happy!

Yes, I know I've spent more money on the modifications than on the amp itself but I don't mind at all. I've learned so much and experienced sonic changes first hand rather than just reading about them. Now I think I can truly appreciate a higher end product.

Here's some songs you all might know played through the D30, modded P7, and K712 :

Sara Bareilles' - "Love on the Rocks" (320 bit mp3) sounds amazing. The piano and drums have excellent attack. There's dynamics/inflection and emotion of her voice that's non-existant on the E10k.

Tchaikovsky's "Francesca da Ramini's" (64 DSD) clarinet solo almost brought me tears at how good it sounded. I can tell where musicians are located. I can tell that the percussionists are at the rear of the orchestra, timpani sound like timpani, I can also hear the hand muting of a triangle and the turning of sheet music pages! (I was a classical percussionist in high school).

Barber's "Adagio for Strings" (128 DSD) evokes an emotional response that I've never experienced before. Maybe it's the increased dynamics.

Crisis'- "Prisoner Scavenger" (256bit mp3) no longer sounds like an apocalyptic mess of stop and go screams and raging instruments. Well it still does, but I can now discern the screams from the bass guitar and drums!

Mazzy Star's -"Fade Into You" (through HK8550 and FLAC) envelops you with her ethereal voice, crisp tambourine, strategic piano fortes, and wierd yet magical sliding guitar sound.

Veorra's - "Not Yet" (Youtube HD streamed) bass hits low-oh so low, drives hard and fast without hesitation while the synthesized trappy hithats and fem vocals remain well defined. I think this song draws a lot of power.

What's next? I'll change my pot to and ALPS logarithmic type, maybe increase the capacitance of coupling output stage (I need help here. All I know it's a high pass filter but don't really understand the impedance load as well as if it pertains to my situation with a switching power supply) to approx. 1283uf to optimize for the 62 ohm impedance of the K712s, try to fix the volume issue by adding a 240k 2w resistor, and then maybe finally change out the original Chinese tubes. Seriously though this has been a super fun and satisfying project!

BTW, how do I post images of what I've done? I'm trying to create an album and upload images but I keep getting an invalid image type.
 
Jan 8, 2018 at 11:12 AM Post #2 of 15

Mickxal

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Happy holidays all! My first post was a thank you on an old thread regarding mods to the Little Bear P8 that I've applied to my P7. I figured it would be good to start a new thread with pictures for anyone interested in the P7 and would gladly appreciate any comments, suggestions or fixes to any mistakes I've made.

I haphazardly purchased a Little Bear P7 off the Bay that arrived with a broken pot. After a partial refund and awaiting a replacement pot from China I decided to learn more about this amp and possible mods. Unfortunately, with the exception of sales descriptions and a few posts/reviews there is little to no information anywhere. So, I stalked many threads and sites on general mods and more specifically the Little Bear P8 from which the P7 is based. I've used the amp now for a couple of months while progressively changing parts and experiencing the sonic difference at each stage. Please, excuse my use of terminology, modification mistakes, and soldering skills. I have very little to no experience with electronics and audio equipment. The only test equipment I have are my ears, familiar songs I've listened to over the years, and online test tone generators. My setup is a newish Windows 10 PC using Foobar/asio/sacd-asio, streamed content and HK FL8550 HDCD player into a hacked Topping D30 with a shunted Burson V6 Classic, Senn HD558 (don't really use it anymore) and AKG K712 Pro headphones.

First thing's first, fix the broken pot. The original was an A100k logarithmic pot but the seller shipped a linear B100k pot. Does it impact sound quality? I have no idea but at least I can now use my amplifier! I'll say the amp sounded okay. The bass was lacking but things sounded clear with a little distortion in the highs like cymbals and I could hear the individual instruments separately. The only comparison I have is an E10K on DAC and amp duty powering the AKGs. Not as good separation and clarity, the bass sometimes sounded farty and I had to turn the volume up for it to sound "fuller" but listening was very fatiguing.

My first actual mod was the replacement of the 4 greenish blue MKP output coupling capacitors (I think they're Vishay) with Audyn True Coppers as suggested by Geetarman49. I stuck with the original 0.10uf capacitance value but upped the voltage to 630v. Whoa, talk about huge difference. The sound warmed up a lot, things sounded bigger, bass was a bit lessened but I could hear lower frequencies, the separation was still there and I could hear more details/new sounds never heard before on familiar tracks. One thing is odd though and the only way I could describe it that things sounded a bit slower (maybe I'm crazy). Bellial's 80's Love streamed on Soundcloud and Death's "Painkiller" are some tracks where I had issues with speed. Any ideas?

The next mod performed was adding Audyn .1uf 400v Q4 MKP caps to bypass the four output electrolytics and four PSU filtering caps. I should have done the bypassing of the power and signal stage separately but my soldering iron was already hot. I really couldn't tell much difference with this mod but I think things might have sounded faster but not as warm.

The big difference between the P7 and the P8 is the use of a switching mode power supply in the P7 where the P8 uses a toroidal transformer. The P7 has two separate internal switching power supplies one providing 180v (as labelled on the power input on the main PCB) and a single 6.3v for the 6n3 and 6n5 tubes whereas the P8 uses a single toroidal transformer with one 170v and two separate 6.3v outputs to the tubes. Also, the filtering stage capacitance is different with the P7 using four 82uf 400v caps and the P8 using four 220uf 300v with an additional 240k ohm 2w resistor at the end. My P7 has a spot for the same resistor but didn't ship with it installed. At this point, I had no idea how increasing the capacitance would impact the 180w PSU and amp overall but hell it's a learning experience so let the soldering begin! Jebus Chris removing large caps are a pain! I changed the four caps to 220uf 450v Nichicon KX (no bypassing yet). At first, I thought I screwed myself because after changing the caps my volume pot didn't work! Sound came out the amp sounding crappy and a bit warbly; rotating the pot resulted in no change in volume. Sound just kept coming out the amp. Seriously, I though ***, S*@t, and S*#t again did I just destroy my amp and headphones?!? NO! After a rain dance, prayers to spiritual beings and the Annunaki, turning on the amp letting it sit with no input signal a couple of times and rotating the pot many times with different headphones things turned out great! Now there's a lot more bass. Let's just say I can honestly hear the +3db bass that the AKG K712 Pro is supposed to have. The sound stage changed though, things sounded closer and a bit veiled. Also, the volume adjusts properly; however the sound doesn't go away when the pot is turned all the way down. Is this a leaky cap due to the increase of capacitance? Maybe, I should add that 240k resistor at the end of the filtering stage.

At the power input to the main PCB of the P7 there's a location for a 1000uf 35v cap that isn't installed. I figured since the there's a single 6.3v input for both tubes on the P7 the capacitor should help smooth out/buffer the current draw. I soldered on a Panasonic FM 1000uf 35v cap and bypassed it with an Audyn .1uf Q4 cap. Another huge sonic difference. The sound stage is now huge! Everything sounds larger, cleaner, more echoey, no distortion in the highs, excellent bass extension and attack, everything just sounds better and dynamic. I used on online test tone generator to hear the roll off of the bass and it sounds/feels like it extends down to 20hz without attenuation. Actually, this last mod is what prompted me to write this post. I'm extremely happy with this amp, extremely happy!

Yes, I know I've spent more money on the modifications than on the amp itself but I don't mind at all. I've learned so much and experienced sonic changes first hand rather than just reading about them. Now I think I can truly appreciate a higher end product.

Here's some songs you all might know played through the D30, modded P7, and K712 :

Sara Bareilles' - "Love on the Rocks" (320 bit mp3) sounds amazing. The piano and drums have excellent attack. There's dynamics/inflection and emotion of her voice that's non-existant on the E10k.

Tchaikovsky's "Francesca da Ramini's" (64 DSD) clarinet solo almost brought me tears at how good it sounded. I can tell where musicians are located. I can tell that the percussionists are at the rear of the orchestra, timpani sound like timpani, I can also hear the hand muting of a triangle and the turning of sheet music pages! (I was a classical percussionist in high school).

Barber's "Adagio for Strings" (128 DSD) evokes an emotional response that I've never experienced before. Maybe it's the increased dynamics.

Crisis'- "Prisoner Scavenger" (256bit mp3) no longer sounds like an apocalyptic mess of stop and go screams and raging instruments. Well it still does, but I can now discern the screams from the bass guitar and drums!

Mazzy Star's -"Fade Into You" (through HK8550 and FLAC) envelops you with her ethereal voice, crisp tambourine, strategic piano fortes, and wierd yet magical sliding guitar sound.

Veorra's - "Not Yet" (Youtube HD streamed) bass hits low-oh so low, drives hard and fast without hesitation while the synthesized trappy hithats and fem vocals remain well defined. I think this song draws a lot of power.

What's next? I'll change my pot to and ALPS logarithmic type, maybe increase the capacitance of coupling output stage (I need help here. All I know it's a high pass filter but don't really understand the impedance load as well as if it pertains to my situation with a switching power supply) to approx. 1283uf to optimize for the 62 ohm impedance of the K712s, try to fix the volume issue by adding a 240k 2w resistor, and then maybe finally change out the original Chinese tubes. Seriously though this has been a super fun and satisfying project!

BTW, how do I post images of what I've done? I'm trying to create an album and upload images but I keep getting an invalid image type.
I want sosome pictures ASAP I bought a P7 throught aliexpress with GE 5670 Tubes aswell as a GE 6AS7G tube. I have a soldering kit and I would like to know how to improve this amp. I'm a noob at soldering and electronics though.
 
Apr 2, 2018 at 1:16 PM Post #3 of 15

William Song

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I'm very curious about all of this, it seems like the mod has really helped with it
If you could post some pictures of where everything goes, that'd be an absolute help. I'd like to do these mods, seeing as you had such enjoyment with the sound
Not terribly good with a soldering iron, and components and electronics, but I think with a good enough guide it should be fine

What would you rate the current compared to the stock?
Bass, Mids, Highs, Soundstage, Imagine?
 
Jul 7, 2018 at 11:34 PM Post #4 of 15

Reddart67

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I just got a LB P7. I like what I hear from it so far, but I’m interested in seeing what can be done with it.

I’m going to tube roll with it in stock form, then I might fiddle around with bypassing the output electrolytic capacitors with different film caps, and possibly the changing the filter caps.

BTW, does anyone know or have a recommendation for the output electrolytic caps...a pair of parallel 100uf /200V caps on each channel (bypassed with 0.1uf film caps). Most of the supposedly good “audio” electrolytic caps are low voltage, like <100v.
 
Jul 8, 2018 at 2:12 AM Post #5 of 15

Mickxal

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I just got a LB P7. I like what I hear from it so far, but I’m interested in seeing what can be done with it.

I’m going to tube roll with it in stock form, then I might fiddle around with bypassing the output electrolytic capacitors with different film caps, and possibly the changing the filter caps.

BTW, does anyone know or have a recommendation for the output electrolytic caps...a pair of parallel 100uf /200V caps on each channel (bypassed with 0.1uf film caps). Most of the supposedly good “audio” electrolytic caps are low voltage, like <100v.


It's written on the psu board that theirs a place for a 1000uf 35V capacitor. By doing that the audio got amazingly clearer especially with higher gain. The 35v 1000uf mod on the tube pcb is a must. What I also did is that I changed the 4 0.1uf film caps for 0.15uf caps because the amp lacks bass. I chose all my caps to be panasonic. Changing caps for better brands will no affect somic performance. Theres a 2w 240k resistor that is not installed on the tube pcb... Do not install it. It worsens and dulls up the sound. The other mod I did that improved my AMP to godliness is too buy two adapter of of ebay to adapt 6sn7. They are not electrically compatible it works and is safe for the long run. 6sn7 tubes sound so much better on this amp than the little tubes.
 
Jul 8, 2018 at 4:51 PM Post #6 of 15

Reddart67

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Thanks for the suggestions.

You wouldn’t happen to know the interior space dimensions, like from the board to both sides of the case? My P7 is at work, so I won’t be able to measure it until tomorrow. I’m curious how much space here is to add larger caps.
 
Jul 8, 2018 at 5:09 PM Post #7 of 15

Mickxal

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Thanks for the suggestions.

You wouldn’t happen to know the interior space dimensions, like from the board to both sides of the case? My P7 is at work, so I won’t be able to measure it until tomorrow. I’m curious how much space here is to add larger caps.


No I don't but you do have a lot of space. Just not over the tube pcb.
 
Feb 20, 2020 at 12:59 AM Post #9 of 15

daniloreyes

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Updates? I need the source for the tubes, mine arrives tomorrow...
 
May 9, 2020 at 1:11 PM Post #10 of 15

CADCAM

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I love the look of this unit, I purchased the "updated" version with the recessed inputs and internal ps. I've also ordered an RCA 6080 tube and a pair of matched Russian 6n3p drivers as I read the stock 6n5p runs hot.
I will be feeding it using RCA outputs from either one of my external DAC's or directly from a CD players outputs.
I used a $100 gift card to purchase it so I've got no money into it and my Loxjie P20 can use the 6n3p driver tubes I bought so if it needs to be returned no great loss but I'm praying this turns out well because I really like the look of it. Fingers crossed!
P7.jpg
 
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May 9, 2020 at 1:12 PM Post #11 of 15

CADCAM

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Can we get some pic of the mods so if some want to try them we have a reference??
 
Dec 9, 2020 at 4:11 AM Post #12 of 15

evonimos

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Hello,

I am pretty sure this Douk unit (especially Little Bear P8) is basically a reiteration of a common DIY PCB floating out there (or vice-versa).
It has an SRPP pre-stage(with 2C51 tubes) + a cathode follower at the output (6080 tube).
DC in the signal is then blocked by output capacitors.

I got this PCB some time ago and since completion it's serving as my 'main' unit.
I've populated the board with original parts of my liking plus a few modifications and in my opinion this amp sounds spectacular and is dead silent (powering my HD599).
It has replaced a hot-rodded DIY Lehmann BCL (a very nice solid stage design).

Here are a few pics of the completed unit. Notice the similarities with Douk's unit:
20201209_104420.jpg


20201209_104129.jpg


20201209_103954.jpg


20201209_104232_002.jpg


The main differences, should be in the power supply section.
All the heaters are fed by AC current and the B+ is unregulated. As I said, it is dead quiet, even with low impedance cans like my HD599.
I have used separate transformers, one fedding B+ and the 2C51 heaters while the other one is dedicated for the high-current drawing heaters of the 6080.

I've also added an EMI filter for the AC mains, just for the heck of it. I had the space plus it looks nice.

In general, I went with good quality resistors all around (a mix of carbon composition with some carbon/metal films) and larger values for the capacitors. Went a bit overboard with capacitors in series with the signal path (output caps), paralleling several Soviet-era PIO military surplus, Teflon and NOS film along with larger value electrolytics. It took me some time to figure out how they'll all fit inside that enclosure, but in the end i think it was worth it.
 
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Jan 18, 2021 at 12:23 PM Post #13 of 15

CADCAM

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Looks great!
 
Feb 25, 2021 at 11:57 AM Post #15 of 15

Reddart67

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Was really liking the amp, I had added some capacitance to the power caps and paralleled a film cap with the last stage power cap. Tube rolled with a ton of different 6080 types (my favorite was the graphite plate tungsol/red bank types), also added parallel resistors to the volume control to give a more useful adjustment range, but it finally failed, presumably in the power supply section. I haven’t had time to investigate it to try and fix it yet, but will hopefully get around to that at some point.
It is an interesting design, using a dc switching power supply (as opposed to the normal transformers like the homemade amp in the earlier post). I like the compact nature of this design, but obviously there is some week spot in it. I hope I can diagnose and fix whatever the problem is, with a more rugged solution.
 

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