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.
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.
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
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.
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.
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.