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Bruno Putzeys Balanced Preamp - Group Buy Part 3

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B

burkm

Member
Joined 2010
Thanks for pointing that out.
You are right, but the volume controller I described indicates "129" steps (0-128, see *.TXT file).
This got me confused, thus my erronous statement.
Note: Step "0" and step "1" are identical in attuation (no difference, s. measurements).
 
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A

AndrewT

R.I.P.
Joined 2004
AndrewT said:
Is there any gain? Is the maximum output equal to the input?
Click to expand...

burkm said:
What do you mean by "gain" with respect to that tested passive resistor based ladder attenuator ? Probably a misunderstanding because I haven't been as clear in my description as I wanted to...
Max attenuation available is around 64db (step 1), minimum attenuation (step 128) is 0 db. Some precaution has to be taken into consideration for that "max gain" problem in combination with the BPBP.

I just measured the attenuation of each of the available 128 steps and the maximum plus minimum attenuation achievable to see how it performs in this respect using a 2V signal. And I measured the max / min input resistance for all 128 steps (s. txt file).
That attenuator network is supposed to be inserted in place of the 10 kOhm linear pot of one of my BPBPs in the near future.
Next thing to do: I will have to take a look if any modifications are needed for that replacement. For a complete setup a 2nd 10 kOhm relay board is needed because of that common GND (L/R stereo version) issue, as stated before.
This configuration is available as standard in the balanced version whilst 10 kOhm input resistance is an available option..

The whole set to be fitted into that case mentioned is then:
- BPBP
- 128 steps volume controller incl. IR remote control
- Power supply +/-15 VDC (and may be another +15 VDC ?) depending upon overal power consumption and voltage needs.
- ...some might consider that 4 input relay board additionally which is included with the volume controller already

I ordered the 2nd relay board plus case already after I finished testing the 1st one.
Click to expand...
Ah.
you have not yet assembled the B.Putzeys' balanced vol pot!

Let's see how you attach a standard three lead attenuator to the Balanced vol pot PCB?
 
B

burkm

Member
Joined 2010
Well, I have assembled (and tested) the volume controller already but not installed it yet within the BPBP, because the interconnecting cables (controller => relay board) for the volume controller were missing at first in the delivered package, which have arrived now, and I had to order a 2nd relay board after checking the layout of the 1st because of that common GND "issue". A description of what I got and found out in the meantime is mentioned in those posts above.
One channel of each relay attenuator board - taken as a black box - works like a normal pot and can be connected in an equivalent way. Because of possible noise issues one might opt for short compact shielded cables within that enclosure for hooking up the relay board to the BPBP.

Everything takes its time :)
 
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AndrewT

R.I.P.
Joined 2004
burkm said:
................................
One channel of each relay attenuator board - taken as a black box - works like a normal pot and can be connected in an equivalent way..............
Click to expand...
I don't think so.
I have extra connections in addition to the three leads of a conventional vol pot.
There is a 4 wire connection from the switcher to the PCB and in addition to that there are extra resistors inside the switcher casing and an extra internal connection for that resistor/channel.
These extra resistors and connections were to mimic the way the relay attenuator was implemented.

I think you will find that your standard 3 lead relay controlled switcher will not simply swap in for the 3 lead linear track vol pot.
 
B

burkm

Member
Joined 2010
Mine dosn't.
2 in / 2 out and both share a common GND => makes 3, doesn't it ? For one channel... and "isolated", because that GND is floating. Exactly for that reason I need a 2nd relay board for two channels.
Its a pure resistive network, having a relatively constant input resistance of 10 kOhm. The output resistance varies accordingly depending if you reference it to GND or In.
The "out" is the "wiper" going to the OP amp, the "In" + GND" represents the resistors body. Three contacts.
That the way I measured it.

Am I missing something ?
What additional connections do you have ?
 
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burkm

Member
Joined 2010
If everything else fails I still got the Maya / Hans P. VoICB combination to fall back upon :). Can't test that yet, because one relay doesn't fit / is missing. Didn't check the BOM I got in detail against the PCB layout, thus I didn't realize that this relay has a different footprint as the one provided in the BOM, which I ordered. Realized this when I tried to install it.
Patience is needed... much to do... that's life ;)
 
B

burkm

Member
Joined 2010
Hans Polak said:
A tiny remark: when having 128 steps, max attenuation is not 128*0.5dB but 127*0.5dB.
In your case deviation is 0.23dB at that position

Hans
Click to expand...

I corrected the .TXT file value for theoretical attenuation (127 "real" steps = 63.5 db). Although there are 129 steps available as listed and measured (0-128), step 0 and 1 are identical in attenuation and only count as 1.
 

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  • L168-45 attenuation values.txt
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B

burkm

Member
Joined 2010
burkm said:
No.
I just had a look at the layout of that relay board I got.
The moment of "truth" ;) will certainly come in a short period of time, when I try to integrate it...
Click to expand...

I don't have any schematics for the volume controller and relay board.
Because the PCBs are 2-sided and populated already (soldered it some time ago) it would be quite a hassle to draw a schematic just from the remaining visible part of the layout. I will do some probing around to see whats happening (and what is behind it) when trying to integrate the ladder network into the BPBP.
 
G

GhostMM

Member
Joined 2013
I finish mine some days ago. I use the maya controller with volcb board, i also include two soekris dam1021 in bal configuration.

I am very impressed by the sound, it's truly better than everything i have before. I hear more details than my previous configuration. I use it with a nc400 stereo build and even at full volume you can stick your ear to the speaker it's deadly quiet.
 
T

tfboy

Member
Joined 2006
Guys,
I'm sorry, I should have removed the Excel file on the first post as I wasn't using it.

For those of you who recently added your names to the list and haven't emailed me or heard from me directly, can you please instead email me: hypexpreampgb at xavbroadcast dot co dot uk, filling in the following tempate:

Forum username:
Email address:
Full name (and/or company name):

Number of bare PCBs: 0
Number of SMD-assembled PCBs: 0
Number of pairs of Hypex regs: 0

EU VAT number (if applicable):

Full Invoice address (including postcode, area, country, etc):

Delivery address if different to invoice one
Click to expand...

I will then be able to reply to you individually by email with a quote, etc.

To update the records, I now have left:
8 Bare PCBs
5 Semi-assembled PCBs
5 pairs of Hypex regulators.

I'll update the first post.

Thanks and apologies for the confusion.
 
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