Salas hotrodded blue DCB1 build

Jump to Latest
L

lugili

Member
Joined 2014
Attenuator/pot for balanced setup

Hi all,

my first post here and thanks for all the insights I was already able to gather on this thread. Quite amazing, really.

Just ordered two pcbs from Tea-Bag to build a balanced device.

What stepped attenuator/pot do people use or recommend for a balanced setup? I understand it should be 20kOhm.

I assume price is also a factor here ... so, also thoughts on price/performance welcome.

Did someone make comparisons?

Thanks,
lugili
 
B

bambadoo

Member
Joined 2003
Salas said:
DC couple the scope input for under 200ΗΖ squarewaves. They got a small value capacitor normally on AC input position.

The long run DCB1 subjective feedback merits the bass area so a feeling of lightness there its possibly due to a peripheral circuit or 600 Ohm input amplifier? On anything > 5kOhm it should do well.
Make sure that the input impedance of the LDR is easy on the source equipment used.
Also high hot-rod enhances the feeling of tonal completeness. Let it run in its electrolytics first before any further mod planning in any case.
Click to expand...

Thanks alot. Got rid of the LDR volume control and just use a TDK cp2511 pot right now. No lightness in the bass. That is for sure :)

Have ordered a 25k log stepped attenuator to test.

Will take the ldrs to the bench and do some measurements and work on it before trying again.
 
S

stajo

Member
Joined 2011
LDR will be hard to use balanced since the Silonex NSL-32SR2 are biatches of being unlinear to match over full spectrum. Single ended they sing very nice tho, and can be confed very low, to the kilo if needed.

Salas I havent forgot you, I have a guest and match on when I have the time. Im up to some 25ish different pairs now, closely matched at different voltages and biased. The hard ones in both pentode and triode mode. Some 10-15 to go before I ship. Have put some D3As, C3Gs along with other triodes, tetrodes and pentodes to try out.
 
Salas

Salas

diyAudio Chief Moderator
Joined 2002
Paid Member
stajo said:
Salas I havent forgot you, I have a guest and match on when I have the time. Im up to some 25ish different pairs now, closely matched at different voltages and biased. The hard ones in both pentode and triode mode. Some 10-15 to go before I ship. Have put some D3As, C3Gs along with other triodes, tetrodes and pentodes to try out.
Click to expand...

No worries, since no imminent plans. Just stashing some good samples to be handy for possible ideas.
 
J

jslot

Member
Joined 2011
jslot said:
Salas and AndrewT, thank you both for the insight.

I measured the output of the Squeezebox, it is about 8,5 Ohm ( yes, that low )

Checking a couple of service manuals that I saved gives the following:

Philips: range from 120Ohm to 1K
Pioneer does not specify anything
Technics SL-PG490 says 1K, load impedance greater than 10K ( here's 1:10 )
Sony only specifies output voltage at 50K, and says load impedance greater than 10K.

When I demo the repaired players they can be connected with a 50 cm interlink of standard plus quality ( simple interlink but not the very cheapest type that fall apart by looking at them ). I cannot demo with expensive interlinks because they grab the connector with too much power to easily put them on and off the gear to be demonstrated.

Will 10K be fine ( enough for demo purpose? )
For personal use it is only the squeezebox, and that will be 1:100 so more then fine
Click to expand...
Never got an answer to the questions above, so ordered a 10K pot from tocos. Got it today, and could not believe my meter when discovering a difference between the two resistance tracks of 600Ohms. Corrected this by soldering 600Ohms resistor between the signal in, and the pot on one side. Tracking is really good now.

Time to listen, and I am torn by the result. Mids and highs have opened up very nicely, like that. But it has cost me the nice energetic bass the system had when the 50K Alps Blue was in there.
Adding a 10K resistor in series did not alter the sound so much I could hear it, so tomorrow will add another 10K to see if enlarging the resistance brings back the bass drive.
 
J

jslot

Member
Joined 2011
Thanks for your reply Davym!

During my lunch break I added an extra 10K, and that brought more energy back into the bass, although I really start to notice that I need to turn the volume up further to get the same sound level.

Perhaps it will be better to buy the 50K Tocos, hoping that the mids and highs will stay at the same level. Another idea would be to feed the signal straight into a DCB1 to buffer it, then to the 10K potentiometer, and finally to a second DCB1 to lower the output impedance.

Any ideas about what is the best solution?
 
D

davym

Member
Joined 2013
Strangely enough a 50K Tocos pot arrived here two days ago from an ebay seller in Taiwan called wonderco-buy, I have not had the time to try it yet but it was not expensive and only took about a week to get here which was surprising. I was using miniature DACT stepped attenuators in my projects but I much prefer the sound and fine adjustment from the Tocos, providing the channels are not too mismatched, it's a far better pot. I have only tried the pot's on the input of the DCB1 so far, not sure about connecting one to the output but I might try that at some point. Maybe Salas can advise about that, I am under the impression that it's best to keep the current across the carbon track as low as possible.
 
J

jslot

Member
Joined 2011
Thanks Salas!

Davym, I am very curious how the 50K Tocos will do in your system! I bought the 10K from the same seller, and he is very fast indeed!
The low price might have something to do with the quality, the taper closest to the shaft measures 600Ohm higher than the back one. Tracking is ok after soldering a 600R resistor in series with the back taper. Could you measure your 50K pot before mounting it?
 
D

davym

Member
Joined 2013
Salas - cheers mate that confirms what I thought.

jslot - I noticed the same tracking problem with the original 20K Tocos pot I got from hifi collective last year. I complained and got a full refund and an apology. I got another 20K Tocos from ebay (cant remember the sellers name) and it was the same. I found it a problem at very low volume, one channel would cut out completely before the other. I started using the miniature DACT pots but as usual fine adjustment was an issue and they sound quite harsh in comparison with less bass clout.

Pre loading the 20K Tocos pot with the paralleled 47K resistors made it very useable range wise and solved the noticeable imbalance at very low volume but I still ordered a 50K to try. I'll measure the 50K one later (if I get time) and get back to you.
 
You must log in or register to reply here.
Top Bottom