SOS... problems with Lehmann BCL ("Lovely Cube")... - diyAudio
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Old 31st October 2011, 05:44 PM   #1
diyAudio Member
Join Date: Oct 2011
Default SOS... problems with Lehmann BCL ("Lovely Cube")...

Hi to everyone. Is my first post.

I have the next problem with the Lehmann BLC ("Lovely Cube")

With the gain at 0db. I have not amplification. I have to put the volume to maximum to hear the same volume as I listen to my Sansa Clip + directly without amplificator. Even a little less with "lovely".

With the gain to 10, 18 and 20dB I have changes in the output sound. I have SOME LITTLE amplification but I have yet to set the volume to maximum to have enough volume to hear worthily.

I have to say that I don't have hearing problems. My Lovely does not amplify the input signal !!!

Attached photos of my PCB front and bottom.

* Will note that I've made ​changes of components for originals equivalents. All changes with same capacity in the case of capacitors and the same resistance in the case of resistors ( I've only changed the value of the four 1K2 resistances by 1K5).

* I changed the LM317 and LM337 by originals 337T and 317T with bigger heatsinks.
* I changed BD139 and BD140 by BD139-16S and BD140-16S.
* I changed BC550 and BC560 by BC550CG and BC560CG.
* Input bigger capacitors have different format but are same capacity and voltage that stock lovely clone. Smaller input capacitors are MKP 22nF/1000V. (i had tested with originals and i had the same problem).
* 22nF opamp capacitors are KP1837.
* 100pF opamp capacitors are LCR FSC (100pF/160V./2,5%)
* Opamp is original 2134 . With 2134 and 2111AM lovely stock i have the same problem.

I have reviewed all solders. I have tested dip switches for gain function properly off and on.
All components are in place. I have measured voltages with digital multimeter:

- BD140 BD139: collector-base .- 14v.
collector-emitter .- 14v.
base-emitter .- 0.6v.

- BC550C BC560C: collector-base .- 15v.
base-emitter .- 0.6v.

- LM317T LM337T : Adj .- 13.8 v.
Input .- 21.6 v.
Output .- 15.0 v. (-15.0 for LM337T)

- OPAMP 2134 is receiving 14.7 v.

I have replaced the opamp with the stock. I have changed the sound source by putting my phone with the maximum volume.
Despite all this I still have to put the volume to maximum to hear the music. Even on 20db. gain !!.
With 0dB. even I noticed that the sound is attenuated.

HELP !! I'm pretty worried. I do not understand what is happening. Any suggestions.???
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Old 31st October 2011, 08:15 PM   #2
diyAudio Member
Join Date: Feb 2005
Location: Watertown, NY
Check your R15/16, R17/18 and R21/22 (L/R channels) for the correct values. These resistors set the gain of the op amps.
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Old 31st October 2011, 10:53 PM   #3
diyAudio Member
Join Date: Oct 2011
Thanks Odysseybmx414, all this resistors are OK. (4,7K).

I have checked all resistors in its places and values.

Last edited by Miky2011; 31st October 2011 at 11:11 PM.
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