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HELP, I,m Desperate!!!!!
HELP, I,m Desperate!!!!!
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Old 20th April 2019, 10:24 PM   #1
brucetassin is offline brucetassin  United States
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Location: Loganville, GA
Default HELP, I,m Desperate!!!!!

I,m in need of some serious help.
I built this phono pre from China.

NEW E834 RIAA MM Amplifier Kit Base + Power Supply Kit + Transformer | eBay

I did a lot of research on this design and found at least 10 examples of its implementation. A google search of EAR 834 and several forums. In all the
examples I saw only good/great reviews.

My kit is not boutique quality but the parts are good. I'm using 12AX7LPS tubes.

The amp is not in an enclosure and properly shielded at this time so the "hum" is understandable. I will fix that when I get the amp to work properly.
I posted a request for help in this forum but did not get any workable answers. (wave form).
I noticed some slight changes from one schematic to another and I implemented some in my amp.
The amp seems to overload on higher volume levels.
Any help will be appreciated.
Thanks
Attached Images
File Type: jpg E-834 phono pre.jpg (119.7 KB, 485 views)
File Type: jpg Heater Power Supply.jpg (58.3 KB, 488 views)
File Type: jpg Main Power Supply.jpg (101.9 KB, 473 views)
File Type: jpg REIMA 12AX7.jpg (110.1 KB, 480 views)
File Type: png EAR834thrf.png (205.2 KB, 478 views)
File Type: png German EAR834.png (61.8 KB, 121 views)
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Old 20th April 2019, 10:30 PM   #2
brucetassin is offline brucetassin  United States
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I have a short .WAV file but I cant seen to upload it.
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Old 20th April 2019, 10:57 PM   #3
MAAC0 is offline MAAC0  Portugal
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Quote:
The amp seems to overload on higher volume levels
I'n not a valve guy, but are You using this pre with line level ?
It is intended for record playing. Small signal level.
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Old 21st April 2019, 12:07 AM   #4
rayma is offline rayma  United States
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Quote:
Originally Posted by brucetassin View Post
The amp seems to overload on higher volume levels.
The RIAA network is of the Quad type, where there is no nfb at low frequencies, and the LF gain
is equal to the open loop gain. I would use a different RIAA network that defines the closed loop
gain better, as in the fourth circuit shown. The later EAR circuit uses a jfet cascode input circuit.
What cartridge do you use?

Last edited by rayma; 21st April 2019 at 12:11 AM.
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Old 21st April 2019, 12:30 AM   #5
brucetassin is offline brucetassin  United States
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Thanks Rayma
I have a shure V15 III.
I will change the RIAA network as you suggest.
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Old 21st April 2019, 12:37 AM   #6
rayma is offline rayma  United States
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Quote:
Originally Posted by brucetassin View Post
I have a shure V15 III.
I will change the RIAA network as you suggest.
That should work fine. Use an input loading of 450pF, including the cables.
In the fourth diagram, if you choose NOT to use C3, make sure that the
voltage rating of the RIAA capacitors is 600VDC.
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Old 21st April 2019, 01:22 AM   #7
gigigirl is offline gigigirl
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You may do better posting on Lenco Heaven. There is a huge thread on the EAR clones there, with lots of people building one & also lots of upgrade tips.

Cheers
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Old 27th April 2019, 01:00 AM   #8
brucetassin is offline brucetassin  United States
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Location: Loganville, GA
Hello All,

Thanks to Rayma (a very big thank you) My problem is almost fixed.
I rewired the feed back circuit as shown in schematic #4 (above).
The amp is working much better but the bass is being cut too much.
Now I just need to learn how to calculate the values.
Thanks
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Old 27th April 2019, 01:09 AM   #9
rayma is offline rayma  United States
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Join Date: Apr 2011
Quote:
Originally Posted by brucetassin View Post
Hello All,

Thanks to Rayma (a very big thank you) My problem is almost fixed.
I rewired the feed back circuit as shown in schematic #4 (above).
The amp is working much better but the bass is being cut too much.
Now I just need to learn how to calculate the values.
Thanks
This is a common problem with tube global feedback RIAA circuits.
Theoretical values (that do not take into account the limited open loop gain)
will result in poor bass response. Trimming doesn't work very well because
all the values interact somewhat.
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Old 27th April 2019, 06:50 AM   #10
analog_sa is offline analog_sa  Europe
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Location: Cascais
HELP, I,m Desperate!!!!!
Quote:
Originally Posted by brucetassin View Post
Now I just need to learn how to calculate the values.
Thanks
For this particular circuit you would be better off simulating or measuring. Not sure if precise calculation is easy or straightforward.
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