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Old 16th March 2012, 09:13 PM   #11
fotios is offline fotios  Greece
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Here is the link for volume pot of Audioromy FU-29:
Audioromy FU-29 - regulacja i tuning - Audiostereo.pl
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Old 16th March 2012, 09:48 PM   #12
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Quote:
Originally Posted by fotios View Post
Here is the link for volume pot of Audioromy FU-29:
Audioromy FU-29 - regulacja i tuning - Audiostereo.pl
That thread also contain info on what parts to replace and how to adjust bias and balance etc. But some time is needed to get what they write there(google translate). Far from perfect translation..

Last edited by Join; 16th March 2012 at 09:54 PM.
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Old 16th March 2012, 09:54 PM   #13
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Interesting feedback scheme there. I've always wondered about the push-pull sharing of feedback from one side to the other.
I guess it works well in class A with a sinewave.

In my experience of Chinese amps the first stage upgrade changes are merely to replace capacitors with quality items, makes a huge difference to the sound and is very easy to do.
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Old 16th March 2012, 10:21 PM   #14
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Quote:
Originally Posted by piero7 View Post
I've changed tube with the USSR ones, remake the power supply with a new one, include the filaments power supply to reduce hum
Hum noise is mainly caused from transformers. Here some things that i know about EI type transformers:
1) Core: A good core is made up from "high permeability silicon steel" E and I thin laminates. If laminates are thicker then the core saturation occurs very fast and in sequence will cause increase of magnetizing current. Then the laminates start to crack and this translated in audible "Buzz - Hum" noise.
2) Insulation: Laminates must be completely insulated between them. That is obtained by dipping the transformer in a bath of epoxy varnish. Varnish must be pass completely inside the microscopic gap between laminates, if bubles of air remain after the dipping of core then the core will lose an ammount of its total magnetic permeability. To this, the dipping is executed inside special vessels equiped with air vacuum pump. The transformer is dipped into the varnish, the vessel is closed hermeticaly and then the vacuum pump operated for 5 - 10 mins for a complete removing of air from the vessel and in sequence from the microscopic gap between laminates. Then the laminates are impregnated perfectly with varnish and are completely isolated.
3) Varnish drying: This takes up to 24 hours. But still remains some soft. My practice is, after delivering to leave the transformer on the shelf for 10 days before connect it to power. Then the varnish will be completely hard and the transformer is absolutely noiseless. Under this process, the EI transformer is less noisy from the most toroidals of the market.
4) Power: If the power supply demands e.g. a 800VA transformer, place your order for a 1000VA transformer. This surplus of power will solves lot of problems. And the difference in size and cost is negligible.
5) A copper foil (known as "Belly Band") arround transformer offers a very good isolation of the EMI (Electromagnetic Interference) that can infect the signal.
That is the definition of a good EI type transformer. Is some expensive of course, but is well known that Chinese are generous and not stringies.
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Last edited by fotios; 16th March 2012 at 10:36 PM.
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Old 16th March 2012, 10:30 PM   #15
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Originally Posted by Globulator View Post
In my experience of Chinese amps the first stage upgrade changes are merely to replace capacitors with quality items, makes a huge difference to the sound and is very easy to do.
Thank you. I will have to open up my unit and start taking notes, order new parts and then replace one by one then. Seems like a wise place to start.

What recommended manufacturers are out there or better, what is quality items?

Those caps that I posted a picture of on page#1, do they fit any of the required spec? The schematic is a little hard to read. I got the 4psc. on the picture.

And, what tubes is recommended for the small tubes replacement?

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Old 16th March 2012, 10:37 PM   #16
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Not sure those caps would fit, depends upon the physical size and voltage rating. 0.47 should be fine for the last coupling caps, coupling cap sizes are a funny thing - it's not always bigger is better due to a phenomena known as blocking distortion which can occur in A2 operation (when the grid turns into a diode).
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Old 16th March 2012, 10:46 PM   #17
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About size and performance, I know nothing more than that they did a very noticeable improvement in my MS-12B pre.

From the posted pictures it looks like they will fit. The caps are about 12-14mm dia.(eyeballing..)
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Old 16th March 2012, 10:50 PM   #18
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Default Picture of Audioromy FU-29 PCB

It is borrowed from other member of this forum but is explainfull
Attached Images
File Type: jpg Audioromy FU29.jpg (618.3 KB, 470 views)
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Old 16th March 2012, 10:59 PM   #19
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Default Volume Pot.

If you use your Audioromy directly without preamplifier, it is good to replace this "CRT" volume pot with an ALPS RK27 (2 X 100KA) Blue Velvet. E.g.: ALPS RK27112 Blue Velvet Pots 10K 50K 100K 250K 500K 1M | eBay
The difficulty is that the CRT has knurled shaft, so the same the hole of knob. While the shaft of ALPS is flat. But if you are brave enough, you will find a solution for the knob to fit in ALPS.
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Old 16th March 2012, 11:16 PM   #20
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Default Capacitors

Looking at the pcb, there are just 6 foil capacitors. The red radial at the corners of pcb are probably WIMA MKP. The two axial yellow at the middle are probably "ICEL" MKP made in Italy. IMHO both brands are not so cheap.
For electrolytics, i don't know. Simply that are either Nippon or Panasonic.
People says that NOS are better. I don't know.
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