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Audioromy FU29 improvement and upgrades?

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Hi!

I got my Audioromy FU29 from a friend for about $250. It have ran 6-700hours now and it got the original china tubes installed.

The sound is nice and "full", decent dynamics but far from SE-performance. It's now running a pair of Tannoy 607 markII series(from '92-'94-ish) with a decent result. A little "boxy" bass if you play music with powerful bass like hip-hop and such(not so often that happens anymore..), but overall the soundstage in my impression is pleasant to my ears.

Sound is pretty good, but far from perfect. So, in the true diyaudio-spirit:

How to make the Audioromy FU29 improve performance and sound quality?
*It is unmodified in it's current state.

*While waiting for the FU29 I ordered a pair of GU-29 tubes from Russia, highest military grade, came from the same box, same manifacturing date etc. Price ended up at $13,10 including shipping for the pair.

*Issues with my level pot(gain level) so that I cannot use more than 6-7steps on the pot to play music and a max of about 11'o clock on the pot for max levels due to distortion etc.
Discussing this issue with fotios led to the idea to just de-solder the pot and bypass it completely with wires= I get a power-amp that need a pre-amp on every input?. For me that is no problem. I got a modified Yaquin MS-12B pre-amp for the task.

GU29 russian tubes:
20120316_115856.jpg
and the box:
20120316_115936.jpg


Can the "paper-in-oil" russian caps be used for something? Leftovers after preamp mods.

P1010075.jpg


They replaced these in preamp:


P1010079.jpg



I will try to get the schematic for the Audioromy and post it. My idea with this thread is to share, learn and quality-control of modifications.

As things progress I will start on the project and take a lot of pictures, before and after.


Have a nice day.. :)

-join-
 
Measured input resistance acc. to this diagram fotis provided(thanks!)

Measuring results:

Unplugged signal cable, unplugged main power direct measure from rca contact. Did NOT unplug speakers.

Ohm-setting: 200k

steps from left:
1-12= 92,2kohm
13-15= 92,1
16=92,0
17=91,9
18=91,8
19=91,6
20=91,5
21=91,3
22=91,1
23=90,9
24=90,4
25=89,7
26=89,0
27=88,1
28=87,1
29=86,1
30=85,2
31=84,0
32=82,9
33=81,6
34=80,2
35=79,5
36-38=79,2
Stop

How accurate my results are is unknown, it is a cheap type digital multimeter.

I will have to learn about calculating gain structure.. :)

-join-
 

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  • audioromy fu-29 pot Z.jpg
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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.
 
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. :D
 
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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?

-join-
 
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.
 
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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