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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

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Old 21st Feb 2024, 1:09 am   #21
DMcMahon
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Default Re: Grundig TK14 - Recording from CD/Record

I think it is unlikely the documention is in error or for another TK but it does look like there are 2 build versions with the different circuitry around the Output DIN pin 3 as referenced above.

Whether it is down to there being a UK and a German version I am very unsure, especially as I have 2 different German TK 14 schematics, one showing pin 3 as an input and the other one showing pin 3 to be an ouput.

I attach one of the UK schematics showing pin 3 to be an output.

I checked my TK 14 and pin 3 is an output as per all the UK documentation I have seen (apart from the OPs User manual which indicates it is an input).

My TK 14 appears to be UK manufactured, although on the base is stamped "Made in W-Germany". Its internal number is 31-5074, somewhere I have the list of all the TKs and their internal numbers which lists the country of manufacture.

More on this later.

David
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Old 21st Feb 2024, 12:10 pm   #22
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Default Re: Grundig TK14 - Recording from CD/Record

If I had to guess how the whole story of the development of the TK14 went, I would put forward the following theory:

1. The TK14 was the low-cost variant of the series.

2. That's why it had fewer connection sockets than its bigger brothers which meant that compromises had to be made in the pinouts.

3. The device was originally developed for the German market. That's why it had the DIN socket standardized in Germany for connection to a radio receiver with a constant current output on pin 1.

4. Originally it was perhaps not intended that someone would want to connect a record player directly to the TK14, but rather it was assumed that record player recordings would take a detour via the radio receiver switched to "Gram", so that the record player signal would appear at its constant current output on pin 1 and be sent to the TK14's Radio input (center socket, pin 1) can be recorded.

5. When someone decided that the device should have a direct connection for a record player, they used pin 3 of the right socket (the one with the two wave symbols), as only this pin was still free. This is how the very unusual hybrid wiring of the socket on the right was created.

6. During the course of production, it was discovered that the current output on pin 1 according to the German standard was not well received abroad but that it was more common there to provide the output signal of a radio or FM tuner as a voltage output (approx. 100 ... 300 mV). Such a signal could only be fed in via pin 3 of the right socket, which would have required very strange adapter cables.

7. That's why Grundig decided to change the radio socket for export so that at pin 1 a constant voltage signal (instead of a constant current signal) could be accepted. This meant that pin 1 could accept both the output of an FM tuner and a record player (but no longer the signal of a German radio receiver).

8. As a result, the turntable input on pin 3 of the socket on the far right was no longer necessary, and pin 3 was connected in parallel to pin 3 of the radio socket, where the high-impedance output signal for the amplifier in the radio was already present. This made the designation of the socket on the right as “output” more plausible again.

9. Such TK14 for export to U.K do not only have a mains voltage of 240 volts (instead of 220 volts in Germany back then) but also a radio input for line level signals. They cannot be connected to a German radio receiver from that era using a standard DIN connection cable; the recording would be far too quiet.

10. By the way, there is an interesting note (page 8) in the English service manual for the TK14 in case someone needs to connect a U.K. TK14 to a radio receiver with a German radio's tape recorder output: When recording from the radio, the connecting cable must be connected to the microphone socket (since the microphone input is suitable for a constant current output). For tape playback via the radio receiver, the cable must be moved from the microphone socket to the radio socket. Which of the users probably understood that?

11. It doesn't surprise me that both TK14 variants are floating around in England. A number of “original German” TK14s were certainly brought to England by troops stationed in Germany.

Nick Salis
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Old 21st Feb 2024, 7:01 pm   #23
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Default Re: Grundig TK14 - Recording from CD/Record

Quote:
Originally Posted by n.salis View Post

10. By the way, there is an interesting note (page 8) in the English service manual for the TK14 in case someone needs to connect a U.K. TK14 to a radio receiver with a German radio's tape recorder output: When recording from the radio, the connecting cable must be connected to the microphone socket (since the microphone input is suitable for a constant current output). For tape playback via the radio receiver, the cable must be moved from the microphone socket to the radio socket. Which of the users probably understood that?
I do not see this note in my UK Grundig TK 14 Instructions for Use manual.

David
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Old 21st Feb 2024, 7:07 pm   #24
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Default Re: Grundig TK14 - Recording from CD/Record

Quote:
Originally Posted by DMcMahon View Post

Whether it is down to there being a UK and a German version I am very unsure, especially as I have 2 different German TK 14 schematics, one showing pin 3 as an input and the other one showing pin 3 to be an ouput.

David
After rechecking numerous hardcopy and softcopy TK 14 Service Manuals/Schematics I see I made a mistake in saying that 2 different German schematics showed the 2 variants of the pin 3 wiring. In fact both German schematics shows pin 3 wired as an input.

I think both German schematics are identical, they look somewhat different due to the way the Service manuals were scanned resulting in some pages being different orientation and size.

David
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Old 22nd Feb 2024, 12:52 am   #25
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Default Re: Grundig TK14 - Recording from CD/Record

"I do not see this note in my UK Grundig TK 14 Instructions for Use manual."

It's in the Service Manual (attached), not the User Manual.

I have a trilingual (English, German, French) user manual, but this only describes the German TK14 variant. You seem to have another user manual that relates to the U.K. version and of which you have already shown excerpts. I would be interested to receive this manual.

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Old 22nd Feb 2024, 9:31 am   #26
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Default Re: Grundig TK14 - Recording from CD/Record

In post 25 I couldn't upload the service manual. I've uploaded it here:

https://www.mycloud.ch/s/S006276B164...8930E19D8100FB

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Old 22nd Feb 2024, 10:25 am   #27
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Default Re: Grundig TK14 - Recording from CD/Record

Thankyou for the Service manual. I see the Note in question is after the Diode connection modification information. The schematic in this manual shows pin 3 as an input, so the note about connecting to the microphone input to me does not entirely make sense.

In my TK14L Service manual it has the first line after the Diode information i.e. "By using a twin screeneed cable etc" but does not have the second line about connecting to the microphone input.

I do not have a soft copy of the UK User manual but will scan it later.

David

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Old 22nd Feb 2024, 10:35 am   #28
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Default Re: Grundig TK14 - Recording from CD/Record

Largely agree with Post 22, do not disagree with any of it, just a couple of points not very sure about. No knowledge of German radio tape out voltage levels.

The Diode connection information references the radio set delivering approximately 100mV to the diode circuit load and 20mV being fed to the recorder. I do not see how they calculate 20mV, with the 2MOhm to 100kOhm potential divider giving a 1:20 division then why is it not around 5mV ?


David

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Old 22nd Feb 2024, 10:40 am   #29
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Default Re: Grundig TK14 - Recording from CD/Record

Any news/update from the OP (Original Poster) as to his original problem of not being able to record, apart from microphone recording ?

David
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Old 22nd Feb 2024, 10:51 am   #30
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Default Re: Grundig TK14 - Recording from CD/Record

Section of German schematic showing Output DIN pin 3 connected as an input.

David
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Old 22nd Feb 2024, 12:38 pm   #31
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Default Re: Grundig TK14 - Recording from CD/Record

No. It is an input for a device that requires a high-impedance termination, e.g. a record player with a crystal cartridge or a tube FM tuner. The 1M ohm resistor R4 together with the 22k ohm resistor R3 forms a voltage divider so that the several 100 mV of the source is attenuated to approximately microphone level and does not overdrive the input stage.

At this socket (the right one with the wave symbols) only pin 1 is an output (speaker level).

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Old 22nd Feb 2024, 1:19 pm   #32
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Default Re: Grundig TK14 - Recording from CD/Record

Yes totally agree.

At Post 30, where I say Output I was referring to the name of that DIN connector, not that pin 3 was an output.

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Old 22nd Feb 2024, 2:04 pm   #33
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Default Re: Grundig TK14 - Recording from CD/Record

Please excuse me. I misunderstood you.

In the supplement I show a compilation that I made of the sockets of the U.K. variant.

I will write something later on the topic of “constant current tape record output” on German radio receivers.

Nick Salis
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Old 22nd Feb 2024, 3:21 pm   #34
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Default Re: Grundig TK14 - Recording from CD/Record

Yes constant current description will be interesting.

By co-incidence this morning in the post received 2 User manuals for the Grundig TK 7, one English and one German.

The German manual details the Diode connection, so does the English manual but with the briefest of description details, it does not even show/list the DIN pin numbers.

David
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Old 22nd Feb 2024, 5:36 pm   #35
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Default Re: Grundig TK14 - Recording from CD/Record

TK 14 UK Instructions Manual attached here.

David
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Old 22nd Feb 2024, 9:32 pm   #36
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Default Re: Grundig TK14 - Recording from CD/Record

Quote:
Originally Posted by deadwax View Post
Quote:
Originally Posted by ben View Post
There must be a fault in the Grundig. Does the recording level react?
No recording level reaction at-all although I have recorded with a microphone successfully in the adjacent DIN socket.
Does the Magic Eye recording level work when you do sucessful microphone recordings ?

David
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Old 23rd Feb 2024, 6:38 pm   #37
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Default Re: Grundig TK14 - Recording from CD/Record

Quote:
Originally Posted by n.salis View Post

At the moment we don't know which variant of the TK14 the requester in post #1 has. If he has a "UK" version, he would not be able to feed an external signal, such as from a record player or CD player, into pin 3 of the socket on the right. In the enclosure I have therefore drawn a cable that he can connect to the microphone input and can then record the signal from his the CD player. This version of the cable from the CD player to the TK14 works with all TK14 variants.

The TK14 would have to be switched to microphone during recording.

Nick Salis
Is there an advantage of doing it this way, compared to doing it as I would do it by connecting the CD input into pin 1 of the middle Radio/Gram/Diode DIN ?

It is not clear if the OP has tried this pin 1 during his unsucessful recording attempts.

David
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Old 23rd Feb 2024, 8:22 pm   #38
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Default Re: Grundig TK14 - Recording from CD/Record

If the OP has the U.K. version of the TK14, he can put the CD signal on pin 1 of the middle socket. However, he has to connect the CD player's two stereo channels together using 10k ohm resistors so that he gets the mono signal he needs. (However, if the OP has the German version of the TK14, then feeding the CD signal to pin 1 of the middle socket would massively overdrive the device's input amplifier; a completely distorted recording would result).

In terms of quality, the recording is just as good as if he used the cable according to post #20 and fed it in via the microphone input (left socket). In both cases, the high-level CD signal is attenuated to microphone level, in the first case via resistor R4 (1M ohm) built into the TK14, in the second case via the 2M ohm resistors (1M would also do) built into the adapter cable.

I drew the adapter cable according to post #20 so that it works with all TK14 versions (be they German or U.K.). Maybe the OP doesn't even know which variant of TK14 he has.

P.S. The two output channels of the CD player should not simply be connected in parallel to get a mono signal. Its outputs are intended to see an input impedance of at least 10k ohms. The output impedance of a CD player is about 1k Ohm. If both channels of the CD player were connected together, each output would see the other channel's 1k ohm output impedance as a load. This can cause distortion or even overheating of the CD player's output stage.

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Old 24th Feb 2024, 11:45 am   #39
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Default Re: Grundig TK14 - Recording from CD/Record

Ah yes can now see the change to the input resistor on pin 1 of the middle (Radio/Gram/Diode) DIN when comparing the German and UK schematics. So it was changed from 22k (R2) to 1M (R4).

The stated input sensitivity being 80mV for the UK version, cannot find the sensitivity value for the German version. On the TK 23 its Diode input with 22k (R1) is stated as 11.5mV in one manual and as 2mV in another manual.

Pretty sure on my previous TK 14 (now sold) that could record line input into pin 1 without adding a series dropper resistor. But on some other similar TKs sometimes had to add a dropper resistor typically around 470k in the cable. It depended upon the level of the line signal which can vary quite a lot from different amps etc.

Cannot do any operation recording checks on my current TK 14 because the top mechanics were badly seized up, so stripped out virtually everything on top for cleaning and relubrcating. No idea at the moment where all the parts are.

Yes know about adding resistors to combine stereo output into a mono signal. I find depending upon what amp/deck/tuner etc is used, sometimes one does not need to join the 2 stereo channels together via resistors and other times it is necessary when the sound is obviously distorted.

David
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Old 24th Feb 2024, 7:41 pm   #40
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Default Re: Grundig TK14 - Recording from CD/Record

A short explanation of how the constant current output on the tape jack of German radios came about.

Immediately after the war, Germany was the first supplier of tape recorders for home use.

The question arose as to how to record radio broadcasts onto tape. The only sound output that could be tapped on radios was the socket for connecting an external speaker. If the radio was set to average volume, a voltage of a few hundred millivolts was created at the socket. This voltage was high enough for the tape recorder's input amplifier.

Connecting the tape recorder to the speaker output of the radio had the following disadvantages:

1. Dependence on the speaker volume on the radio: The volume control of the radio was not allowed to be adjusted during recording, as it also had an influence on the tape recording. The volume had to remain at a certain level so that the recording did not become noisy and humming.

2. The speaker output of a period tube radio has an amplitude response that is anything but linear. In order to compensate for the weaknesses of the loudspeaker in the housing, the frequency response was pre-equalized so that the listener had an acceptable sound quality.

3. When the pre-equalized recording was played back through the radio's amplifier and speakers, the signal went through the pre-equalizing again, and the result was completely exaggerated bass and treble (and hiss) reproduction.

4. To minimize the problem, the operating instructions for the tape recorder stated that you should turn the bass adjuster to minimum and the treble adjuster to maximum when recording on the radio. This resulted in a tape recording that was not noticeable due to either exaggerated bass or dull treble reproduction. But the frequency response of the recording was still far from linear and listening at the same time was no joy because of the lack of bass.

5. The connected tape recorder could have a negative influence on the playback of the radio broadcast via the radio loudspeaker. In the extreme case of a short circuit in the cable from the loudspeaker output of the radio to the sound input of the tape recorder, the volume of the radio became lower or inaudible.

The aim was now to find where there was an audio signal in the radio that was independent of the volume and tone controls, so that the tape recorder could make a recording that also worked with the radio on silent and that was independent of the setting of the radio's tone controls . The point where such a signal can be tapped is the input of the volume potentiometer. Using the example of the Quad 22 preamplifier one can see such a solution, where the RCA socket T.O. (Tape Output) is connected directly to the input of the volume control potentiometer. If a tape recorder with too low an impedance is connected to a socket wired in this way, the volume of the radio will be too quiet and/or the bass will be missing. This phenomenon is known to all owners of Quad 22 preamplifiers and Revox A77 (or other transistorized) tape recorders with lower than approx. 100k Ohm input impedance.

Most home tape recorders had an additional microphone input that could deliver a sufficiently strong signal for the tape recorder's recording head with an input voltage of just a few millivolts.

This is how the idea arose to continue to pick up the audio signal at the radio's input of the volume potentiometer, but to decouple it using a high-resistance series resistor.

Inserting the resistor resulted in the output impedance of the circuit being
high and becoming a constant current output, the output voltage of which is low and varies depending on the input impedance of the connected tape recorder.

The input impedance of the tape recorder was dimensioned so that the resulting voltage approximately corresponds to that of a microphone and can therefore be fed to the same input stage of the tape recorder that is also used for the microphone.

The concept was laid down in the DIN 45310 standard. Unfortunately, I don't have the first version of the standard from October 1958 and the second version from January 1964, but the successor from August 1974 says:

Tape connection socket on radios (DIN 3 pin female for mono radios, DIN 5 pin female for stereo radios):

1. Load resistance(s) on contact 1 (mono radios) or on contacts 1 and 4 (stereo radios) can be up to 47k ohms (In my experience, there are a number of tape recorders that had a higher or even lower input resistance.)

2. The output voltage should be tapped in the radio receiver in such a way that it is not influenced by the volume setting or the timbre setting (in my experience, the latter was sometimes not adhered to).

3. The output resistance should be large compared to the input resistance of 47k ohms of the tape recorder.

4. A voltage of at least 0.1 mV per kOhm load resistance must be achieved. (This is THE KEY to understanding the DIN connector tape output of a German radio.)

5. For example, if a typical tape recorder with a DIN socket (Grundig TK14 in the original German version) is used to connect to a radio, it has an input impedance of approx. 50 kOhm. A radio according to the standard has an output voltage of at least 0.1 mV per kOhm load resistance, so 50 mV is created at the input of the tape recorder (0.1 mV x 50 =) 5 mV.

6. Another example from that time: The well-known Philips RK14 (EL3541) had an input impedance of 100k ohms. The output voltage of the radio becomes (0.1 mV x 100 =) 10 mV.

7. The Revox A77 has an input impedance of 33k ohms at the radio input. The output voltage of the radio becomes (0.1mV x 33 =) 3.3 mV.

8. The DIN 45310 version from December 1985 not only specifies the minimum voltage per kOhm of load resistance (still 0.1 mV) but also the maximum value (2 mV).

9. For a radio that outputs the maximum voltage, the voltage at the input of the tape recorder would be (2 mV x 50 =) 100 mV for the TK14, (2 mV x 100 =) 200 mV for the RK14 and (2 mV x 33 =) 66 mV for the A77.

Of course, the above voltages also depend on how loud the radio station is modulated. For FM reception, the standard assumes that the transmitter has a frequency deviation of 22.5 kHz (mono) or 20 kHz (stereo). These assumptions come from times when the technicians in the radio stations were graduated engineers and there was no competition as to which station broadcast the loudest. Today's roaring transmitters have significantly higher frequency deviation, so that the output voltages at the radio's tape output are generally higher than they were back then.

From the numbers above one can see that the impedance and voltage ratios do not slavishly follow the norm, but in general one can say that there is between around 10 mV and 100 mV at the radio input of the tape recorder, which must be processed by the input amplifier without distortion and noise.

Advantage of the DIN socket according to DIN 45310 on the radio:

1. The connection from the radio to the tape recorder and back can be done using just one cable with 3 or 5-pin plugs.

2. The radio's ratio detector is not loaded by the tape connection. In extreme cases, a serious short circuit can occur on the tape output socket without the radio listener noticing anything.


Disadvantage of the DIN socket according to DIN 45310 on the radio:

1. The fact that the wires from the radio to the tape recorder is in the same cable jacket as the wires from the tape recorder to the radio has the disadvantage that a certain amount of crosstalk occurs. This is not so much of a problem with simple tape recorders. With better machines, such as the Revox A77, it has the disadvantage that an echo occurs during recording if the Revox is switched to after tape monitoring. This will ruin the recording.

2. The tape socket output impedance is relatively high. In order to avoid high frequency loss, the cable should not be longer than approx. 2m (it also depends on the quality of the cable, high capacity cables are a disadvantage).

3. The fact that the output voltage at the radio's tape jack is low requires a preamplifier stage in the tape recorder (the same as that required for microphone recording). This amplifier stage adds noise. That's a shame, because there is such high audio voltages in the radio itself (at the ratio detector), which would allow it to be fed into the tape recorder after the preamplifier stage, so that a bit of noise could be saved. Since the tape recorders and tapes of the time were already noisy, this argument was probably not of great importance.

4. The idea of implementing tape connections according to the DIN 45310 standard worked in Western Europe. But when more and more foreign, transistorized tape recorders appeared, especially those from Japan with RCA sockets, great chaos began. There were masses of adapter cables manufactured, sold and used that had a DIN cable connector on one side and two (mono) or four (stereo) RCA cable connectors on the other side. While playback from the tape via the radio amplifier worked, the tape recording often didn't work correctly: the recordings were too quiet and noisy. There were only a few specialist dealers who realized that the DIN tape output of the radio did not have to be routed to the so-called line input of the tape recorder but to the microphone input. The latter had approximately the same parameters as a radio input on a tape recorder according to DIN 45310. There were also specialist dealers who bridged the series resistance of approx. 1M ohm to 2.2M ohm between the ratio detector and the tape output socket, which resulted in the ratio detector being subjected to too low an impedance load and reception being impaired. This is especially true when the line input of the connected tape recorder becomes significantly lower impedance when the device is switched off.

5. As we noted earlier in this thread, Grundig delivered at least a version of the TK14 model abroad in which the DIN round socket for the radio connection remained in place, but pin 1 was not wired according to DIN 45310 but as a line level input. In my opinion, it would have been better if devices that were delivered abroad had been equipped with RCA sockets, where wiring, levels and impedances would be clear to more than just those in the know.

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