IBart

Re: OP-6 from scratch
« Reply #40 on: October 22, 2019, 12:20:18 PM »
Similarly to you Dave......
My dad said to me, what his father he told me had said to him , which is '' work hard and play hard ''.... and its still my moto to this day  :)


DaveP

Re: OP-6 from scratch
« Reply #41 on: November 09, 2019, 06:42:13 AM »
The two parts are now finalised, that's the pre-amp and the remote power supply.

These are the final schematics:-



C13 was chosen to maximise the low end which is now flat down to 15Hz.

C19 rolls off the response over 35kHz as there are a lot resonances around 75kHz otherwise.

C4/R6 make the response flat to 20kHz, after which it declines .



R16 is there to bleed off the voltage after switch-off.

C16 is to remove any HF hash that escapes the smoothing caps.

I'll post some pics later on today along with some more input/output data.

Ian Barter has kindly bought the amp and he will no doubt give his impressions further down the line after I ship it to him, next week.

Best
DaveP
Soundcloud: Delayed Action.

DaveP

Re: OP-6 from scratch
« Reply #42 on: November 09, 2019, 11:34:41 AM »
Three pics of the remote power supply.







Here's the finished OP-6 interior,  the choke has a mumetal foil screen held in place with copper foil.
The small 12,000 hour 180uF 420V caps have transformed the power supplies I make since I started 13 years ago.



The audio path is all polypropylene.  Heaters are all DC.



Before I started this project, I decided that I would only do it if I could get a genuine Weston meter and RCA Daven knob, they were on Ebay within a week of each other, those two alone were over $260, so a big investment in pure cosmetics!

DaveP


Soundcloud: Delayed Action.

Fuzz Face

Re: OP-6 from scratch
« Reply #43 on: November 09, 2019, 01:48:26 PM »
Wow great build. The power supply looks impeccable, the meter and knob are very cool, and I love the way you did your grounding.

Thanks for sharing all these beautiful pics and schematics.

Re: OP-6 from scratch
« Reply #44 on: November 10, 2019, 09:34:06 PM »
Wow great build....
Thanks for sharing all these beautiful pics and schematics.

+10.   Thanks Dave 😊 
I vicariously get to enjoy the building of DIY valve amps thanks to threads like these.  Your "start to finish" threads are top notch.

Do you have any thoughts or opinions on how it performed and sounded in situ yourself?   


DaveP

Re: OP-6 from scratch
« Reply #45 on: November 11, 2019, 04:23:52 AM »
Thanks for your support.

I turned 70 in October and I'm obliged to understand I'm in the last chapter, so I guess there is inevitably a legacy element about these projects.

My generation grew up with DIY so that has been theme of my projects, to show what is possible with consistent effort.

I hope that it inspires later generations to continue to work with tubes and components and get their hands dirty!

Best
DaveP

Soundcloud: Delayed Action.

Re: OP-6 from scratch
« Reply #46 on: November 11, 2019, 08:18:20 AM »
Three pics of the remote power supply.

Before I started this project, I decided that I would only do it if I could get a genuine Weston meter and RCA Daven knob, they were on Ebay within a week of each other, those two alone were over $260, so a big investment in pure cosmetics!

DaveP

Very nice build.  I am very familiar with the OP6.  (have one, missing p/s!)  Is the 2 amp fuse a little too much, with 230 v primary?  One would think that 1/2 A or 1 A would be sufficient...we don't like seeing power transformer burnouts in the event the diodes short, etc.  I recall the original power supplies for the Western Electric, Raytheon, and similar remote amps had a simple 5Y3 type rectifier for HT and simply ran AC for heater power...

DaveP

Re: OP-6 from scratch
« Reply #47 on: November 11, 2019, 08:27:18 AM »
You are probably right, 2A is excessive, but because I now use such big smoothing caps, I was concerned about the initial current inrush.

DaveP
Soundcloud: Delayed Action.

ruffrecords

Re: OP-6 from scratch
« Reply #48 on: November 11, 2019, 11:51:44 AM »
You are probably right, 2A is excessive, but because I now use such big smoothing caps, I was concerned about the initial current inrush.

DaveP

Which is why it is always a good idea to specify slo blo fuses with tube gear.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

L´Andratté

Re: OP-6 from scratch
« Reply #49 on: November 11, 2019, 03:41:07 PM »
I turned 70 in October

My very best wishes to you and yours! :D
"Why not get an assistant to work the faders? Real vintage! And maybe cheaper... ;)"


Re: OP-6 from scratch
« Reply #50 on: November 11, 2019, 04:30:12 PM »
I turned 70 in October...

Best wishes Dave.


DaveP

Re: OP-6 from scratch
« Reply #51 on: November 11, 2019, 04:30:46 PM »
The project is now finished, the meter went in today.

I forgot to put it on the schematic, but it's just fed from the output via a 3.6k resistor like normal.



Also the two series LEDs are fed from the heater supply through a 560 ohm resistor which gives around 10mA and a nice light as you can see:-



Finally the back goes on and its serial number..............Done

.

I will post some results of my level & noise tests in another post.

Best
DaveP

Soundcloud: Delayed Action.

Re: OP-6 from scratch
« Reply #52 on: November 11, 2019, 06:06:44 PM »
Hey Dave

Very nice as usual !

Bravo  ;)

Cheers
Zam

DaveP

Re: OP-6 from scratch
« Reply #53 on: November 11, 2019, 06:28:25 PM »
Before I fitted the VU meter I ran it up to max output, it actually produced a clean 60Vp-p on the 'scope into a 10k load, this is 21.2Vrms or +28.6dB at 1kHz.  However, it cannot reproduce a clean 10kHz at that level.  It's worth noting that 60Vp-p at the secondary is 300Vp-p at the primary which is down to the amazing choke loading.

With the VU meter fitted we are limited to 1 or 2V output unless we want to bend the pointer or burn out the diodes!  At this modest level the full undistorted frequency response  is available.

I will attempt to test the S/N ratio as soon as I have time, I suspect it may well be better at the lowest gain (most NFB).  I don't have the facilities (or ears!) to test the sound quality, but I expect Ian Barter will report on that for me.

Best
DaveP
Soundcloud: Delayed Action.

DaveP

Re: OP-6 from scratch
« Reply #54 on: Today at 06:31:58 PM »
OK, I tested the OP-6 for noise at three different gain settings, the lowest 37dB, 55dB and the highest 70dB.

What soon became obvious was that the maximum output of the VU meter limited the S:N ratio because it topped out at around 5Vrms.  So as the EIN was around 3uV in all cases, the lowest gain gave the lowest noise at the output as this table shows:-

Gain     Gain factor   Noise     Output noise   Output   S:N Ratio     dB
37dB             70.8           3uV             212uV               5V            23584      87.4

55dB            563             3uV            1.689mV           5V             2960        69.4

70dB          3126            3uV            9.378mV           5V              533          54.5

It would be possible to disconnect the VU meter and run the output right up to 50V and then pad it down again to improve on that 70dB figure which would then add 20dB to the S:N ratio.

But to be honest I doubt it would ever need to be run at much more than 55dB in practice.

Hope you all enjoyed the project and thanks for the support

Best
DaveP
Soundcloud: Delayed Action.


 

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