Nagra DH schematic please - UK Vintage Radio Repair and Restoration Discussion Forum

jascha · 9th May 2018, 8:55 am

Hi everyone,

I obtained a Nagra DH loudspeaker unit that I wish to restore, such as recapping it and checking other components but am struggling trying to find a schematic for it. Any chance somebody might have a pdf please to share?
I also wish to be able to use the unit with an external power supply however my unit hasn’t got a power supply socket as it’s an early model. I read somewhere that the batter suoooy is floating and therefore it shouldn’t be used with an external supply. Later models however were adapted so they can be used with power supplies. Any assistance would be much appreciated.

Thanks

Argus25 · 9th May 2018, 1:23 pm

HI,

I have one of these speakers too, but I have never found the manual for it. I had a quick search on Google images and the one attached shows up, which has very poor resolution sadly.

In any case, despite that poor resolution, it is easy to see the circuit architecture, with and NPN/PNP pair then another pair and then another PNP pair.

So if you cannot get the schematic from someone with a manual prepared to scan it for you, no matter, you could always trace it out from the actual speaker,noting the transistor types there, as it is a very simple circuit and easy to see what is going on.

I also have a Nagra 4.2 recorder. I have always admired the Kudelski engineering quality. In fact this recorder has in it a capston servo control system, to crytsal lock its speed, which uses the same transistor array (4 quadrant multiplier) used as a phase detector, that was patented by Gilbert as a "Gilbert Cell" a couple of years after Nagra were using it. Nagra were well ahead of the curve.

jascha · 9th May 2018, 2:01 pm

Hi, many thanks for your help. I did see the same schematic on the radio museum website but didn’t yet figure out how to download it from them. I am hoping to get the circuit board out of the cabinet but am having trouble unfastening one of the 4 nuts which happens to hold the metal bracket to the chassis. It’s almost impossible to get any tool that would work so probably I have to invent something which would give me access to the bottom but and undo it.

Herald1360 · 10th May 2018, 10:22 am

As an RM member, I can state that the circuit scan there when downloaded is perfectly clear and readable.

I believe that as a non member, you can obtain free downloads but the process is deliberately slow to frustrate wholesale information grabbing.

I suspect the image Argus25 found is just a blown up version of the thumbnail on the RM page.

If it helps, the transistors are (laid out as in circuit):

ASY29 ASY27 OC22
ASY27 ASY29 OC22

The "drivers" are selected for beta>50 and the outputs for beta>45.

The bias chain resistors on the first stage are also "select on test" values.

9th May 2018, 8:55 am	#1
jascha Hexode Join Date: Nov 2005 Location: Kent, UK. Posts: 332	Nagra DH schematic please Hi everyone, I obtained a Nagra DH loudspeaker unit that I wish to restore, such as recapping it and checking other components but am struggling trying to find a schematic for it. Any chance somebody might have a pdf please to share? I also wish to be able to use the unit with an external power supply however my unit hasn’t got a power supply socket as it’s an early model. I read somewhere that the batter suoooy is floating and therefore it shouldn’t be used with an external supply. Later models however were adapted so they can be used with power supplies. Any assistance would be much appreciated. Thanks

9th May 2018, 1:23 pm	#2
Argus25 No Longer a Member Join Date: Oct 2016 Location: Maroochydore, Queensland, Australia. Posts: 2,679	Re: Nagra DH schematic please HI, I have one of these speakers too, but I have never found the manual for it. I had a quick search on Google images and the one attached shows up, which has very poor resolution sadly. In any case, despite that poor resolution, it is easy to see the circuit architecture, with and NPN/PNP pair then another pair and then another PNP pair. So if you cannot get the schematic from someone with a manual prepared to scan it for you, no matter, you could always trace it out from the actual speaker,noting the transistor types there, as it is a very simple circuit and easy to see what is going on. I also have a Nagra 4.2 recorder. I have always admired the Kudelski engineering quality. In fact this recorder has in it a capston servo control system, to crytsal lock its speed, which uses the same transistor array (4 quadrant multiplier) used as a phase detector, that was patented by Gilbert as a "Gilbert Cell" a couple of years after Nagra were using it. Nagra were well ahead of the curve. Attached Thumbnails Last edited by Argus25; 9th May 2018 at 1:36 pm.

9th May 2018, 2:01 pm	#3
jascha Hexode Join Date: Nov 2005 Location: Kent, UK. Posts: 332	Re: Nagra DH schematic please Hi, many thanks for your help. I did see the same schematic on the radio museum website but didn’t yet figure out how to download it from them. I am hoping to get the circuit board out of the cabinet but am having trouble unfastening one of the 4 nuts which happens to hold the metal bracket to the chassis. It’s almost impossible to get any tool that would work so probably I have to invent something which would give me access to the bottom but and undo it.

10th May 2018, 10:22 am	#4
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,536	Re: Nagra DH schematic please As an RM member, I can state that the circuit scan there when downloaded is perfectly clear and readable. I believe that as a non member, you can obtain free downloads but the process is deliberately slow to frustrate wholesale information grabbing. I suspect the image Argus25 found is just a blown up version of the thumbnail on the RM page. If it helps, the transistors are (laid out as in circuit): ASY29 ASY27 OC22 ASY27 ASY29 OC22 The "drivers" are selected for beta>50 and the outputs for beta>45. The bias chain resistors on the first stage are also "select on test" values. __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O