Hi,
I'm new in the land of tube amplifiers. Now I have a "Little Bear" P5-1 preamp bought for my record player . I only have problems with it. The amplifier is very soft . I checked the PCB and saw that it was not good soldering . And so I have resoldered the PCB. But this did not help. I have also re-measured the voltages. These are somewhat on the low side. 11,6v instead of 12,0v and -27v instead of -28v . Now it is just that the + 28v indicated nothing . So I think this is a problem. Unfortunately I do not have any circuit diagram of this rpreamp . Also, I do not know where they are made . I see that Amazon and eBay sell this preamp 's . But who designed this preamp ?
Can anyone help me ?
Sincerely, Edwin Noorlander
I'm new in the land of tube amplifiers. Now I have a "Little Bear" P5-1 preamp bought for my record player . I only have problems with it. The amplifier is very soft . I checked the PCB and saw that it was not good soldering . And so I have resoldered the PCB. But this did not help. I have also re-measured the voltages. These are somewhat on the low side. 11,6v instead of 12,0v and -27v instead of -28v . Now it is just that the + 28v indicated nothing . So I think this is a problem. Unfortunately I do not have any circuit diagram of this rpreamp . Also, I do not know where they are made . I see that Amazon and eBay sell this preamp 's . But who designed this preamp ?
Can anyone help me ?
Sincerely, Edwin Noorlander
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Nobsound® 6J1 tube Pre-AMP based on X-10, info from seller websites.
The power supply maybe similar, there are transistor regulator for +-28V but transistors are different 2SD667/2SD647, you have to check if they burnt out.
The power supply maybe similar, there are transistor regulator for +-28V but transistors are different 2SD667/2SD647, you have to check if they burnt out.
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Hi Koonw,
physically I can not see if there is something wrong with the transistors. I'll still be able check with my DSO. Thanks for the scheme and hint. greeting Edwin Noorlander
A lot of the reviews suggest swapping tubes over to a set of GE JAN 5654Ws. They're pretty cheap, and GEs are known to be reliable. The bottom of the board just looks like it needs a bit of >91% rubbing alcohol.
What is the Little Bear preamp supposed to do, apart from look pretty? With that circuit you can't have low gain, low distortion and low output impedance: you have to choose two but you need all three for most sources.
Most headphone impedances range anywhere from 50 ohm-600ohms, save for the very low-impedance Fostex drivers floating around out there. Line-out impedance is around the same, between 100 and 600ohms.
Is it a preamp or a headphone amp? In either case, my comment still stands.
Cathode degeneration lowers gain and distortion, but raises output impedance.
Low value anode load resistors lower gain and output impedance, but raise distortion.
So, as I said, you need low gain, low distortion and low output impedance but you can only have up to two of these with the circuit shown in post 4.
Cathode degeneration lowers gain and distortion, but raises output impedance.
Low value anode load resistors lower gain and output impedance, but raise distortion.
So, as I said, you need low gain, low distortion and low output impedance but you can only have up to two of these with the circuit shown in post 4.
I just got one of these a few weeks ago and when i put it between my preamp and power amp combo (kenwood basic C2 into a km-107) i saw a huge drop in output. I assumed it was some sort of impedance-matching issue so I spent a night reverse-engineering and testing.
I traced one of the channels in order to locate the input and output resistors and after doubling up the 4.7k input resistors in parallel to halve the value (just piggybacked the new resistors on top) and swapping out the old 100k output resistors for 150k (and swapping them around to the other side of the pcb for easy access if I change my mind).
It now seems to have a proper level, and I have my preamp volume control where I used to have it.
My impressions of it:
I really like how it cuts the harshness of digital sources.
It seems to have extended the soundstage, perhaps due to unique phasing and EQ effects caused by the tube characteristics. (and these 6j1's might just be "bottom of the barrel" quality.
It appears to be slightly microphonic. I plan to remove the rattle-y side panels and try to add some damping solutions to the case: rubber feet, o-rings or some other soft washers on top and bottom of the pcb at the 4 mount points.
I've got some GE jan5654w's on the way to compare.
I traced one of the channels in order to locate the input and output resistors and after doubling up the 4.7k input resistors in parallel to halve the value (just piggybacked the new resistors on top) and swapping out the old 100k output resistors for 150k (and swapping them around to the other side of the pcb for easy access if I change my mind).
It now seems to have a proper level, and I have my preamp volume control where I used to have it.
My impressions of it:
I really like how it cuts the harshness of digital sources.
It seems to have extended the soundstage, perhaps due to unique phasing and EQ effects caused by the tube characteristics. (and these 6j1's might just be "bottom of the barrel" quality.
It appears to be slightly microphonic. I plan to remove the rattle-y side panels and try to add some damping solutions to the case: rubber feet, o-rings or some other soft washers on top and bottom of the pcb at the 4 mount points.
I've got some GE jan5654w's on the way to compare.
The GE jan5654's are definitely WAY better. Highly recommended. The microphonic issues have gone away.
I bought 10 so that I could match a pair. If anybody is experiencing balance problems it is likely because your tubes are not matched. I matched mine by ear with a recording that I am very familiar with.
I bought 10 so that I could match a pair. If anybody is experiencing balance problems it is likely because your tubes are not matched. I matched mine by ear with a recording that I am very familiar with.
Hi there,
I will quickly share my experience - since my DAC has a very low output I decided to put up some gain of the LB and add caps on top of the cathode resistors - for me the result is good with 2200 uf. Plus replacing the output caps with good qlty film foil - I have tried several values and at the moment listen to 8.2 uf - good bass section in my case.
Cheers,
Ignat
I will quickly share my experience - since my DAC has a very low output I decided to put up some gain of the LB and add caps on top of the cathode resistors - for me the result is good with 2200 uf. Plus replacing the output caps with good qlty film foil - I have tried several values and at the moment listen to 8.2 uf - good bass section in my case.
Cheers,
Ignat
Sorry to resurrect this thread, but I just got one of these units and it suffers from the same low output issues. I do have good GE tubes that work well and are matched.
I just ordered new rubycon caps to replace all the chong caps in the unit. I would love to up the output, but I need help locating which components to replace or add to. One of the other posters here said to replace some of the resistors. Another said to add a capacitor.
I do have another issue wit this unit, that I suspect is in the volume potentiometer. Regardless, I want to replace the volume pot anyway. Anyone have a suggestion for a high quality replacement?
I just ordered new rubycon caps to replace all the chong caps in the unit. I would love to up the output, but I need help locating which components to replace or add to. One of the other posters here said to replace some of the resistors. Another said to add a capacitor.
I do have another issue wit this unit, that I suspect is in the volume potentiometer. Regardless, I want to replace the volume pot anyway. Anyone have a suggestion for a high quality replacement?
I forgot to add, I already re-flowed all solder joints. My problem is that I get a non stop buzz noise coming from the right channel only. The left channel is silent. It's not my amp, it's definitely the P5-1. Any ideas?
Hi, sorry, it was years ago and lot of changes from then. Will try to find something about it and reply.
Regards
Regards
Thanks, much appreciated. I know I shouldn't be wasting my time with this thing, but I always enjoy make things like this work.
Hey there,
what i noticed, the Little Bear wasn't a preamp for recordplayer. It has no riaa-Network.
It works between CD-Player and power amp/output stage, that's his Job :^)
Sincerely
Andreas
what i noticed, the Little Bear wasn't a preamp for recordplayer. It has no riaa-Network.
It works between CD-Player and power amp/output stage, that's his Job :^)
Sincerely
Andreas
I replaced all the caps with nichicon higher voltage ones (50v) and the buzz was still there, but the gain seemed to increase. I ordered and attempted to replace the potentiometer with another chinese 50k sealed unit, but it was not the right one. It has 8 pins, but does not fit in the board. Of course, I ruined the original one trying to get it out of the board. The original has no markings. How the hell do I get a replacement?