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Bruno Putzeys Balanced Preamp - Group Buy Part 3

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This GB is now CLOSED and I do not have any components left. Thank you all for your interest - I might do another one soon, time permitting! :)

Previous thread here.

Background / original technical discussion thread HERE. A lengthy but very worthwhile read. Most technical questions will be covered in that thread.

This GB will be similar to beforehand with three options:

1. Bare PCB.
2. Assembled PCB with only the SMDs assembled. You'll still have to source all through-hole components and solder yourself.
3. Hypex regulator upgrade option. As last time, these will be supplied in pairs, so a quantity of 1 means one pair of regs. Shipped loose in the package, you'll have to solder to board - this is also a chance to get some at a reduced rate for other projects you might have on the go too :)

The BoM is here, in Excel format and in PDF format

Edit: spreadsheet should no longer be used as the GB is now finished.
Spreadsheet: >> THIS SHARED DOC <<.

All prices are in British pounds (GBP).

Final price per bare PCB (batch of 20): £6.00 + VAT = £7.20
Qty 20: £12 + VAT = £14.40
Qty 50: £6 + VAT = £7.20
Qty 100: £4 + VAT = £4.80


Final price per assembled PCB (batch of 70): £31.00 + VAT = £37.20
Qty 20: £40 + VAT = £48.00
Qty 50: £33 + VAT = £39.60
Qty 100: £27 + VAT = £32.40


Based on a quantity of 50 - 100 pairs of HPR/HNR Hypex regulators, one pair would cost around GBP 20 + VAT = £24.00

VAT will be applicable to EU people (unless purchasing through a VAT-registered business). Non-EU people will not have the VAT added (but you may have import duties outside of my control). Shipping to non-EU people will have a customs declaration form attached to the package :)

I appreciate there is / was a lot of interest for this first time round, and I have received quite a few PMs from people who unfortunately missed out, so if we can get enough people on board, it will be worthwhile doing it again.

Packaging and shipping
Packaging is a flat £2.00 + VAT to cover for boxes, anti-static bubble wrap, anti-static bags, etc.
Postage is at cost to me to send Royal Mail (International) Signed For or possibly courier depending on cost. Non-EU parcels will also have CN22 Customs Declaration form filled in.

Please email me "HypexPreAmpGB @ xavbroadcast dot co dot uk" with the following details:
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

Any questions, just ask :)
 
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I have one question:

If I'm not wrong the power supply should be +12/-12 V.

Instead of any transformer, I'm planning to use the auxiliary +24/-24 (500mA) power supply from my SMPS1200/400 PS to feed just before the 1000uf caps. I would install LM7815 and LM7915 regulators at the +24/-24 output and then connect to the 1000uf/35V caps.

Will it work?
 
1 board.
Each board is stereo. And you have two pairs of switchable inputs. All are Neutrik balanced XLR sockets.
Each board can take one set / pair of regulators. You don't need the Hypex ones, you can use regular regs if you want.

Thanks. I am trying to skim the articles and prior threads to find out how much gain does it have, if any?
 
It's not unity gain.

The gain is set by the vol pot.
The residual resistances at the vol pot extremes effectively sets the limits of the attenuation and gain.
Typically expect >>+40dB of gain at the top end and <-50dB of attenuation at the bottom end.
But the steepness of the rate of change towards the ends of the vol pot track make the last ten to twenty degrees of rotation nearly useless. Expect only the middle 200degrees of rotation be be an effective control and half of that will be gain (i.e. >+0dB)
I found all my range of volume adjustment was squeezed into less than 90 degrees of rotation. I changed to a stepped vol pot, to set the attenuations of the inverting opamp stage. Much better.
 
It's not unity gain.
I changed to a stepped vol pot, to set the attenuations of the inverting opamp stage. Much better.

Hi Andrew T,

Can you explain your solution? I have concerns about the consquences if the wiper of the pot fails. The maya solution is really neat but is overkill for what I'm looking for: just a replacement for the pot

I dont get the stepped volume pot. From other threads i read the suggestion for a 5Kpot +5K resistor, is this the change? Or did you use a stepped ladder switch and if so do you have suggestions for values using a 23 step switch like eg. this:
http://www.analogmetric.com/goods.php?id=1000

Thanks!

Gerben
 
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