Hypex Ucd180st bypassing opamp and using Tubebuffer

Here in the Netherlands they build a great amplifier module from Hypex (http://www.hypex.nl)the Ucd series. I have the standard serie and i used it for 2 years. The modules sounds perfect, so perfect that with time i got boring. I read a lot of the modifications with were possible but nowhere a read about using a tubebufferstage for the Ucd. Luckely a had experience with the modification of my shanling CD-T100se(http://www.hififever.com/forum/viewtopic.php?t=1738) and so i spend this chrismas holiday by modificate my Ucd amplifier.

Goal:

- Do not use the opamp inputbuffer. Direkt drive the UCD.
- Bypassing the 22uF decoppling capacitor.
- Improve the sound with some more live.

Reminders:

- Input impedance = 10k
- Source must be DC free
- Compensate 4,5 X gain of the opamp

At work:

I removed the decoppling caps of 22uf from the UCD pcb.
They were between the opampinputbuffer and the UCD powerstage. Then i connect the input sym.+ en sym - to the new points on the PCB according the picture below.



Now i only need a max 5 V rmss input signal with i can get from my shanling player by using a higher value of the I/V resistor in my tube output stage.
My shanlingplayer is the first 10 seconds not DC free so i must wait 10 sec before i press play the first time. Other wise the UCD going pumping.

If you have a tubepreamp with has 5 Vrmss output you can use that.

For the people who want to intergrate the tube stage in to the UCD housing i have a nice schematic.



This is the same SRPP circuit i use in my shanling player but with other tubes ( 6N6P ). With enough gain ( 11 X ) and working with a voltage of 40 V and higher so you can use the original UCD power supply. For the heather voltage you can use 12 V by putting two tube heaters in serie.
This SRPP circuit you can build ones a channel for RCA input and twice a channel for symmetrical input.
The sound of this SRPP circuit i perfect, see this link from Polen.

[url]http://www.lampizator.eu/

At how about the sound the UCD are now alive. I like it.

the above schematic i used for the asymmetric input. Below i have the schematic for the symmetric input. i have considerated the difference in impedance between the + ( 10k imp. ) and - ( 1k8 imp. ) input signal.

The 6N6P tubes sounding very good, very powerfull in the low frequenties.

Today i discovered that i used a wrong gain to calculate the output impedance. The gain is 11 times and not 4,5 times. I recalculate the SRPP stages and the impedance correction resistors at the output. I corrected the diagrams above. A mismatch of impedance give with this SRPP stages a higher THD distorsion. If you want calculate the resistors for other applications you like to use this SRPP stages use this worksheet.

www.euronet.nl/~mgw/download/tube_data_publish.xls

This is an interesting setting of your Hi Fi. You got a huge tube amp down there. What brand is it and what tubes it uses?

The transformers look extremely large to me ...

Yes, Alf, the transformers are large. This is a Yaqin MC-100B, see http://www.yaqin.cn/en/products_hf.html.

This an ebay bestseller, you can find him in several stores, f.e. here-with a lot of information: http://cgi.ebay.de/Yaqin-100B-4-x-KT88-Stereo-Tube-Integrated-Amplifier_W0QQitemZ310012275078QQihZ021QQcategoryZ3280QQcmdZViewItem

Kiko

To Koifarm,

how is the Hypex sounding after your mod?

Kiko

Dear KiKo,

How is your holiday? I wish I could afford to have a trip / vacation too.

Oh, that is a Yaqin. From ebay site you showed me, it is pretty expensive ... EUR 400! And not to mention the postage .... wow, I think these toys are just selling at around US$ 350 or so in China.

CAT

Alfcat, yes this is a Yaqin MC100B. I have changed the tubes to EH KT88,EH 6SN7 and EH 5751 goldpin. I also have changed the capacitors in the audio path for Sprague vitamine types.

Kiko, i use the hypex in de asymmetrical setup( one tube a channel ) and i like it very much. Its like a big tube amplifier. The 6N6P tubes i like much better then the JJ ECC99. The hypex has now a fat bass sound and still full in control, the highs a very tube like( silky). The mids are still full of detail. I like it very much and it is a simple mod.

After using the circuit for a month and build several for friends, one thing is very important. If possible let the tubestage warmup for 20 sec and then turn the UCD on. During warmup there is a lot of DC at the output of the tube this can damage the UCD.

If you intergrate the tubestage in to the UCD housing and you use one on/off switch then ad a relais contact shorten the tubestage output to ground. When switch on a timer can drive the relais after 20 sec. to open the relaisontact. The timer can be a simple circuit with NE555 or just RC and fet.

My friends and i like the sound of the 6n6 tube with the UCD.

Hi Alfcat,

I am looking to buy the Yaqin MC100B too.  Do you know where in Shenzhen can I buy it ?  I have found it selling in internet but the www.yaqin.cn official website saying that those selling at internet are fake one.  Thanks.

Yes, I do.

華強北路萬商電器城二樓C115-117 RELYON (x 音坊) 找張國成.

你話四眼仔陳生介紹你來的.