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Bruno Putzeys Balanced Preamp - Group Buy Part 2

This Group Buy for the assembled PCB is now full.

I am processing a waiting list on a first come / first served basis. If you want to join in, please email me (see below) to register interest in case anyone drops out :) Please note I would like to limit those on the waiting list to one bare PCB, one assembled PCB, one pair of Hypex regulators at most so it's fair for others further down the waiting list.

Update 23rd March: PCBs received :)

This is a follow-on thread from the one Bertel / Robert started for Bruno Putzy's Pre-amp design, here. I (tfboy / Xavier) have taken over the GB duty from Robert and managing this going forward. :)

The pricing below is based on an order of 100 assembled PCBs. We have sufficient numbers from the original shared Excel sheet to go ahead with the group buy :)

Please keep this thread strictly for the GB / ordering process. The discussion of the design can be done in the original thread here

The board comes in two flavours:
  • A bare PCB
  • A semi-assembled PCB with all SMD components and the four high-current Melfs soldered on. All PTH components (Caps, XLR sockets, JST connectors, volume pot, etc) are excluded. You'll have to source these components yourselves and solder them on, but that should be an easy job for the novice.
Independently from the bare PCB or SMD-assembled PCB, you can opt for the Hypex HPR / HNR regulator option. PDF datasheet is here. These are Hypex's own high-precision regulators. You do NOT need to have these: they can be substituted for normal TO220 regulators. Please note, these are supplied in pairs. So when you say a quantity of "1" means you will get one HPR and one HNR. Hypex regs will be supplied unsoldered to the board. This is just an idea to get a group discount (around 30%).

If you don't take the Hypex regulators, youll have to add a pair of regular 12V (L7812+L7912...) regulators to your PTH parts list.

The boards and assembly are being done by Quick Circuits, a local company where I live in the UK. Board spec is 1.6mm FR4 RoHS compliant dual layer board in ENIG finish with green mask and white silkscreen.

Pricing (in GBP):
  • Bare PCB: £3.50+VAT = £4.20
  • SMD-assembled PCB: £27+VAT = £32.40
  • Optional Hypex regulator pair: £16.50+VAT = £19.80 per pair
  • Packaging cost: £2

All assembled boards will be shipped in antistatic bags, wrapped in antistatic bubble wrap, packaged inside a cardboard box :)

Shipping is in addition: I'll be able to give you a cost once I know the shipping address (see below).
Assuming one assembled PCB, approx costs are:
  • UK destination: £4.40 (1st class signed for) / £7.25 (RMSD)
  • EU destination: £10.15 (Royal Mail International Tracked & Signed)
  • USA destination: £12.45 (Royal Mail International Tracked & Signed)
  • Rest of world: £12.45 (Royal Mail International Signed)

For those outside the EU, I'll also print the invoice and affix it to the packaging in one of those transparent "Documents Enclosed" envlopes to reduce any potential issues with Customs.

Tax / VAT explanation

We're dealing with a professional business so they are charging VAT. To try and save money to some of you lucky non-EU people, I'll buy this through my business (Xav Broadcast) which is also VAT registered. What this means is:
  • For those of you living in the UK, you will have to pay the VAT. If you're VAT registered, you can recoup this in your next VAT return (I'll provide a VAT invoice).
  • For those of you living outside the UK but within the EU, you will have to pay the VAT unless you can provide me with your EU Tax code.
  • For those of you living outside the EU, you're lucky, and are exempt from paying VAT. I do not know whether you'll have to pay import duty though, and that's your responsibility. For postal insurance and export purposes, the value has to be declared.


Preferred method: Wire transfer. I would highly recommend Transferwise.com I have used them a lot in the past when sending money abroad in euros or US dollars. They offer a very respectable exchange rate and minimal handling charges. You'll be able to specify the exact amount received in GBP.

Alternatively, you can pay by bank transfer, but this will likely be more expensive than using Transferwise unless you already have an account in GBP.

If you have a UK bank account, a normal transfer is of course the easiest option.

There are a few countried where Transferwise isn't an option at the moment. For those countries, I can arrange a Paypal transfer but would far prefer a bank transfer.

update 6th March 2016:
Over the next few days, I'll start emailing out pro-forma invoices by email. You'll also receive payment details: my UK bank account number and sort code along with IBAN and BIC codes for international transfers.

When you make payment, it is imperative you put your forum username as the reference so I know who has paid.
When using Transferwise, you get the option to provide a reference at step 4:

If you haven't yet used Transferwise, you can use my referral code to get a free transfer: https://transferwise.com/u/909e12

Once I receive your payment, I'll package up your order and deliver it. You'll then receive by email a tracking number and full invoice (which replaces the pro-forma). A copy will be attached to outside packaging for customs for those of you outside the EU.

I would really like to avoid Paypal if at all possible. If you have to use Paypal, please use the Send money to friends and family option and not the Pay for goods or services. Apologies, I had written Paypal Gift in the email sent out; they've changed this to the friends and family title instead:


If you use the one on the left, Paypal take a fee from what you send and I'm left short.

Ordering process

I'll drop using the Excel sheet originally created by Robert: I've set up an email address for the GP. Please send an email to HypexPreampGB -at- xavbroadcast.co.uk (replace the "<space>-at-<space>" with "@") and use the following template:

Forum username:
Full name:

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

EU VAT number (if applicable): xxxx

Invoicing / Delivery address:

John Doe
Abracadabra Inc. (company name if applicable)
123 Sunrise Avenue
Beverly Hills

I've now PMed all those who initially responded to the GB and who read my PM when I took over. I'm aiming to close this GB by Sunday 6th March - I hope to be near the 100 quantities by then. I've decided to do this so that those who've been waiting for some time don't have to wait much longer; it's been going on for some time since Robert started it back in September last year :)

I hope that's all clear. Any questions, just ask :)

A few photos:
Bare board:


Assembled board:
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Thanks to all those who've emailed me. I've replied to them all.

Also, in case you're wondering, I'll send out an invoice by email once I've had a few orders come in. Naturally, I don't want to place the order with QC and only have 10 boards with me stuck with a big bill and lots of very nice unused Preamp modules :)

As soon as we get near the magic numbers, I'll update you all with final costs, etc.

For those ordering from outside the EU, I'll also print and affix the invoice on the outside packaging to mitigate any potential customs issues.

On the plus side, for those ordering bare PCBs, they may well end up being a few pennies cheaper as we'd be getting more than 100 made up :)

I've had confirmation from QC that all assembled boards will be supplied in sealed antistatic bags and wrapped in antistatic bubble wrap. :)

So far, we're up to:
7 Bare PCBs
15 Assembled PCBs
13 pairs of Hypex regs

So off to a good start :D
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The input stage is unity gain buffer.
The differential stage uses equal value resistors so it too is unity gain.

All the gain/attenuation is in the third stage.
The maximum gain is set when the vol pot places near zero ohms to the left of the wiper.
This maximum gain can be reduced by preceding the vol pot with a fixed value resistor. I am hoping to modify the PCB and place an 805 in that input trace to achieve this gain limit.
This modification would turn the system into a low gain version.
Alternatively one never turns the vol pot past 50% rotation. But that is not a nice way to have to operate this pre-amp all the time. It squeezes all the control of attenuation into the first 50% of rotation.
The added resistor gives the option of extending the control to the full 100% of rotation and a maximum gain of +0dB.
Regarding the actual circuit design, I've attached the Gerber files Quick Circuits will use.

I've had a look at them and they seem fine to me - some of the silkscreen positioning could be improved perhaps, but the circuit parts are fine.


  • MicroPreGerbers.zip
    53.9 KB · Views: 125