U73b from scratch

[DaveP]

France is far less crowded where I am and housing is very cheap because there are no jobs, which is fine when you are retired!

Contrary to expectations, the English are welcome in France because we buy up their old empty houses and renovate them and pay community tax on them, so win win for us and them.  You must speak French here, which is fair play because its their country after all and any attempt to speak French is appreciated.  On the whole I find that the French have more respect for their country and they look after it better than the English do England.  I think this is due to social cohesion  breaking down in the UK because the rate of immigration has been greater than the rate of assimilation, but like most things in life, the effect is patchy.

The weather here in Central France is completely different from England, which is stuck in a place where the moist air from the tropics makes its way to the cooler North in a condensation cycle, so it has much more wind and rain than continental Europe.  This year in France I have experienced the best summer of my entire life, but you will need a Mac!!

 

[abbey road d enfer]

This year in France I have experienced the best summer of my entire life, but you will need a Mac!!

Please don't start again this Microsoft/Apple war!   ???  :-[  :-X
OK, I'm out...

 

[DaveP]

Finally got around to the frequency response.

The frequency response of the side chain, in a Feed-Forward comp, has to be matched to the main amp very carefully as there is no corrective feedback.

For example, if the bass response of the side-chain is better than the main amp, it will reduce the response too much at the bass end, same thing applies to the top end.

This mismatch  is responsible for the dropping off at both ends in the following charts.  In the original there were circuits to restrict the frequency response to 40-15kHz for FM radio. my version does not have those filter circuits.





It would probably be worthwhile reducing the side-chain output cap from 22uF to 10uF, this would cut the GR a little and flatten the response, there also needs to be a treble cut in the side-chain circuit to boost the top end response as well.  Unfortunately, I don't have time to tweak this any further as I have to make a Harp amp for a friend next.

I will post some final pics when the lettering is done, then it will be shipped to Ruairi  for testing, you never know he may like it as it is. :-\

Best
DaveP

 

[Phrazemaster]

Incredible Dave!

You are definitely one of the venerable fathers of DIY!!

Best,

Mike

 

[DaveP]

Wish I felt like a father instead of a grandfather some mornings Mike :-[

But it's amazing what a good night's sleep will do!

I decided to tweak it after all. 

All it needed was a 200pF cap across the side-chain input pot to roll off the top end to the GR, this lifted the treble on the amp.

Then I changed the side-chain cathode by-pass cap from 100uF to 4.7uF to roll off the bass and so boost the bass in the amp.

The following charts show the before in red and the after in blue.





I finished the lettering today and these are the final pics.





This is the end of my part in the project as it will be shipped to Ruairi tomorrow.

Let's hope he has as much fun with it as I've had.

Best
DaveP

P.S. Sorry about the pics, I put them in a folder afterwards which lost the link :-[

 

[DaveP]

Thanks to everyone who has encouraged me during this project, it makes a big difference.

I will restore all the pictures later, I didn't realise the link info would change when I put them in a folder! Doh!

DaveP

 

[thomasdf]

I am really impressed Dave! I am glad you enjoyed summer in France It was really hot!
How did you achieve the transfer letter in the DIN font? Or where did you find them? I have been looking for something similar for years...!

 

[DaveP]

How did you achieve the transfer letter in the DIN font? Or where did you find them? I have been looking for something similar for years...!

I used Letraset Rubdown Lettering Transfer A5 Sheet including burnisher - Helvetica MC - 10mm  and some smaller fonts as well, if you put that into Amazon it will find it for you
Best
DaveP

 

[DaveP]

Every now and then I wonder which century I'm in.  ???

One simple job to do today.....ship the U73b via FedEx...what could go wrong?

I get online and there is the FedEx lite site which deals with poor lost souls who don't have an account.

I get through all the hoops and provide every insignificant piece of info they could possible want.  Then we come to payment.

Credit card goes through but red box comes up saying they can't get authorisation after my third attempt.  I ring my bank and they say there is no problem but every attempt has been authorised so be careful they might take multiple payments...Great!

I get on to FedEx customer services and they can't help but suggest I try again from a French FedEx site...same thing happens.

I get back to customer services and a nice lady goes through the whole she-bang for me using my card details....same thing happens.

Remembering that its all nicely packed in a FedEx 25kg box I decide not to go with DHL or UPS but to drive 30kms to the nearest FedEx depot, this I do and it is duly booked in, then it comes to payment.  Unfortunately we can't take credit cards, we need a cheque WTF!  As the end is tantalisingly in site, I drive back the 30km to get my cheque book then 30km back to FedEx, then pay and 30kms back home.

The FedEx website should have supplied a reference number or error number so that it would have been clear to their customer service people what had happened, I can't believe this problem was unique to me.  I guess Amazon has spoilt it for me, they are so slick, FedEx look sick by comparison.

As for cheques, half the people in France are still using them, even for petrol and the super market, imagine the queues!  Strange thing is, they invented the chip and pin system used everywhere else!!

Anyway rant over, Shipment is on its way to Ruairi.

Best
DaveP

 

[abbey road d enfer]

Every now and then I wonder which century I'm in.  ???

One simple job to do today.....ship the U73b via FedEx...what could go wrong?

I get online and there is the FedEx lite site which deals with poor lost souls who don't have an account.

I get through all the hoops and provide every insignificant piece of info they could possible want.  Then we come to payment.

Credit card goes through but red box comes up saying they can't get authorisation after my third attempt.  I ring my bank and they say there is no problem but every attempt has been authorised so be careful they might take multiple payments...Great!

I get on to FedEx customer services and they can't help but suggest I try again from a French FedEx site...same thing happens.

I get back to customer services and a nice lady goes through the whole she-bang for me using my card details....same thing happens.

Remembering that its all nicely packed in a FedEx 25kg box I decide not to go with DHL or UPS but to drive 30kms to the nearest FedEx depot, this I do and it is duly booked in, then it comes to payment.  Unfortunately we can't take credit cards, we need a cheque WTF!  As the end is tantalisingly in site, I drive back the 30km to get my cheque book then 30km back to FedEx, then pay and 30kms back home.

The FedEx website should have supplied a reference number or error number so that it would have been clear to their customer service people what had happened, I can't believe this problem was unique to me.  I guess Amazon has spoilt it for me, they are so slick, FedEx look sick by comparison.

I had a similar problem with JCWhitney Auto Parts. Couldn't pay online, phoned them, place a telephone order,  didn't work, called my bank; they said the vendor's system was corrupting the authorization numbers. At least, they didn't ask me for a cheque  :
Ended up cancelling my order and ordering from AutohausAZ; took only a few minutes.

As for cheques, half the people in France are still using them, even for petrol and the super market, imagine the queues! 

That is very true in the provinces, populated with old geezers  .

Strange thing is, they invented the chip and pin system used everywhere else!!

Still, for many people, there is nothing like the Compte Cheque Postal; I hate it when I go to pick the registered mail and I have to wait for the people cashing money.
Roland Moreno just happened to be born French, it does not make the entire population technology-savvy  .
At the toll on the motorway, there are people paying with cheques; at the same time I go through the telepayment gate at 20 mph; that's diversity  ;D

 

[ruairioflaherty]

The compressor arrived in L.A. today.

Let the listening and measuring begin!

 

[DaveP]

This is the final schematic that Ruairi will be testing.



All the modifications were due to the original transformers being no longer available, but it is possible to use all Edcor transformers with these mods.  For example: R40 has been changed from 10K to 4.7k so that the lack of performance of the Edcor TX, in this application, can be used.  The increased feedback flattens the frequency response, the subsequent loss of gain is made up by the OPT having a lower ratio with  a 600 ohm output.  This changes the output resistance from 40 ohms in the original to 80 ohms in the final version, which makes very little difference.

I have used the original component numbers wherever possible.

Best
DaveP

 

[thomasdf]

Can't wait to hear how it sounds Impressive work Dave, I still can't believe it!

 

[tubegeek]

I'm so late to this party, but WHAT A PARTY!

 

[DaveP]

We do our best. ;D

Ruairi has tested it as is, but he wanted to change the attack and release  to something more modern before giving his report.

He is a busy man with a family so he has to fit it in when he can.

Best
DaveP

 

[gato]

Looking forward to hearing more about it!

 

[etheory]

Did anything happen with this? It was a pretty cool project. I hope you ended up finishing it.

 

[DaveP]

Yes it was finished and it went to Ruairi O Flaherty in august of last year.

He did some initial testing but wanted to mod the original timings, I think this is where it's stuck at the moment.

He is a busy family man who has to earn his living, so I don't pester him.

My "from scratch" compressors and pre-amps are for sale with EMMR or in this case Ruairi as it was a mastering comp, if anyone is interested make them an offer.  I am retired and do this as my hobby, I get my fun from  the challenge of making them, I don't care too much about the money as long as someone isn't taking the the piss!

Best
DaveP

P.S.
Just realized you are the same guy I'm following on soundcloud 8)

 

[etheory]

Congrats on finishing it, it was an awesome build to follow the thread for!

P.S.
Just realized you are the same guy I'm following on soundcloud 8)

Oh awesome! What's your soundcloud name I'll follow you back? Thanks for the follow!

 

[DaveP]

It's the footer on my posts

Thanks
DaveP