Fidelity record-player IC - UK Vintage Radio Repair and Restoration Discussion Forum

adibrook · 6th Jan 2006, 12:07 am

My friend asked me to fix a record player for them. It's got a blown amp chip (one of those old primitive single chip amps).

It's a typical ''cardboard'' record player that looks like it should have been valve. It has lots of space inside and even cooling vents in the wooden casing. But all that occupies that space is a tiny PCB with a single chip poweramp.

It's made by Fidelity and is red. The chip is pretty old and not made anymore. I remember that it starts off with 6SN7 (yes I DID say chip not valve!)

Why would someone build such a large wooden structure just for a tiny chip amp?

Since the chip is blown and spares are hard to get, i think i'll just replace the whole PCB with a TDA chip. I'll use a 3.5W one i have that needs no external components at all. Then i'll just use the existing volume and tone pots. There are no worries about originality. After all the pcb that was in there is just a dirt cheap poweramp module, so i will replace it with a modern equivelant of a dirt cheap pa module! I think the TDA chip is more efficient and has less distortion too.

The amp is fed from a rectified tap on the gram motor, which is rectified by the looks of it by a single diode and smoothed by one cap! I think a bridge rect and a couple of big modern caps will work well here. The record player had bad hum when the chip worked.

Umm...one question. I think record players need a C and an R in parallel to equalise the sound properly? (i think it's something to do with the recording process on records, certain freqencies are louder?) I've never owned a record player, so i dont know much about that. Can anyone suggest component values?

Thanks.

PS i presume it's a high-output cartridge type since the signal is fed directly into the power amp.

Nickthedentist · 6th Jan 2006, 12:18 am

Hi Adi,

Fidelity made rather old-fashioned players like this well into the 70s, by which time ICs were beginning to find their way into comsumer electronics equipment.

They also made a series of rather cheap and nasty "music centres" (which they called Unit Audio systems) with a BSR turntable + IC amp + radio tuner in a box with a Perspex dustcover, which plugged into a pair of equally awful little speakers. But they were cheap and so sold like hot cakes

. But by the early 80s, they were to be found on skips all round the country

There's a bit about them (including a circuit diagram of a Fidelity using a pair of SN76013N) in Les Lawry-John's book that was published in the 70s, available to download courtesy of Paul: http://www.vintage-radio.info/docs/p...-repair-qa.pdf . See page 75 of the PDF.

Your idea of fitting a new amp module sounds like a great one to me, but beware of overloading the winding on the motor.

You're right about the frequency correction - the bass needs to be boosted (because it's cut before the record is pressed to prevent the grooves from being too "wavy"), and the treble needs to be rolled off (because it's boosted before the recording process so that on playback, the high frequencies can be attenuated, taking any record surface noise with them). But tro start with, I'd just connect the output of the cartridge (which will no doubt be a BSR high output ceramic one, maybe a X5M or something similar) to the input of the amp and see how it sounds.

Good luck,
Nick.

adibrook · 6th Jan 2006, 2:12 am

Thanks Nick.

Well...what can i say. It works. I wish i had a decent record! I asked for a record to test it with, and the bloke gave me IRISH CHRISTIAN HYMNS! UUUUgh it's screwing with my brain...i swear. It's not happy hymns...it's evil mind control music!

The TDA7056 seems to preform pretty well here. The only external components so far are a 5.6K resistor to ground from the tda's input, as suggested by the datasheet (without it it sounds reallllly horrible), a 0.47uf input cap and a 1M pot for volume.

It's hoprribly trebel boosted, as you said, which makes the irish hymns sound even more freaky (i wouldnt want to listen to that on a dark moonless night without an equaliser).

But at least the volume is reasonable. I 1st tested it with a 9V battery, and then the gram motor tap again, rectified with a single diode and smoothed by a 1000uf cap. prototype only...in the finished device i plan to use a bridge and a 4700uf cap or something.

How do i go about making the equaliser for it?

Do you think if i add an equaliser and stuff it will need a preamp?

BTW this is wierd. the original rectifier turns out to be a metal rect!thats strange...why use a silicon chip but a metal rect?

Aub · 6th Jan 2006, 9:23 am

Adi,

Well done on the repair.

I don't think you need an equalisation on a ceramic cartridge and I'm pretty sure that's what will be fitted to this budget player, or it may even have a crystal cartridge. RIAA equalisation is only usually used with magnetic or moving iron cartridges, which also have a very small output of a few mV (for magenitic) or a few hundred micro volts (for moving iron) compared with the ceramic cartrige's 100-200mV and 0.5 to 1V for crystal.

You could certainly use a cheap magnetic cartridge, with an equaliser, to get a better sound, but it probably wouldnt be worth it in this case.

There should be some simple equalisation circuits about somewhere, probably based on an op amp.

regards

Aub

peter_sol · 6th Jan 2006, 9:24 am

Hi
Normally with these IC amps the input impedance is too low for a crystal pickup, causing lack of bass .
As the pickup requires around a 1 megohm load the simplest solution is to fit a 1 meg resistor from the wiper of the v/c to the amp input (after breaking the circuit there first)
this may decrease the gain but you will have bags to play with anyway.
Cheers
Peter.

Aub · 6th Jan 2006, 9:26 am

Forgot to say, make sure the cermic or crystal cartridge is seeing a nice high impedance ( about 1Mohm ), or this will reduce bass response if too low.

Aub

AndiiT · 6th Jan 2006, 10:34 am

Hi
I am probably trying to "shut the stable door after the horse has bolted" here but here goes....

The Record player that you describe is almost certainly a Fidelity HF43 which was the "upgrade" for the earlier HF35 valve model.
The HF43 uses an SN76013ND (or similar) Audio chip; which wern't the most reliable of chips, that said it has been claimed that in Fidelity equipment that use these chips their unreliability could be contributed to the fact that a 24 Volt supply was used which (I am led to believe) was close to the upper operating voltage limit of the device.

Re equalisation for the cartridge; this will almost certainly be a BSR X5M Crystal/Ceramic type which has a high output and due to its design, and the fact that it can be fed into a high impedance load (1 to 2 Megohms), has the equalisation "built in" as it were, so a linear amplifier design can be used if you are going to (already have?) replace the amplifier as a complete unit.

Regards
Andrew

Sideband · 6th Jan 2006, 1:27 pm

Adi.

As you have plenty of gain to play with, once you have sorted out the power supply refinements you could try a 1 meg resistor in series with the input from the cartridge as already suggested to improve the bass and then parallel that with a capacitor somewhere between 47 and 100pF. You can play around with the value to give best treble response. I used to do this with ceramic and crystal cartridges and it gave good results.

Rich.

adibrook · 6th Jan 2006, 2:16 pm

Ok. So far i'v got the highest gain by connecting a 1M resistor from the cartridge to ground (therefore giving it a 1M load?) and then connecting it via a capacitor to the chips input, which has 5K resistor on it as the datasheet suggested to ground.

It's very loud then but trebely. Maybe a 1M resistor with a series 100pf cap.That sounds allright.

How loud were these things supposed to be originally? The speaker in there is prety poor, and with the TDA7056 going foll blast and getting rather hot the unit is quiet loud. But then again i doubt it would have been that loud in normal use, so may as well make it quieter but more bassy?

Aub · 6th Jan 2006, 2:33 pm

Adi,
I would do as Richard suggested, then play about with the value of the resister which is currently 5K. I would guess you'd need to inrease it's value to avoid too much of a voltage drop. It all depends on how much gain you have.

Aub

Sideband · 6th Jan 2006, 2:35 pm

Quote:

Originally Posted by adibrook

. Maybe a 1M resistor with a series 100pf cap.That sounds allright.

No. Put the 1 meg in series with the cartridge with the small value capacitor across it. At this stage I wouldn't put a capacitor in series with the cartridge at all.

Rich.

adibrook · 6th Jan 2006, 3:05 pm

Ok. thanks for all the advice.

I was thinking. I played about with different values of caps and resistors and 100pf with 1m or 470K sounds good. the 1M setting is alot more bassy, but the 470K is louder. I was thinking...why not replace tha resistor witht he tone control pot? Then the owner can change from anythign to very high trebel to bass? i could stick in a series resistor of 100K or so just so that you cant turn the trebel up tooo much.

Also maybe fit a fixed 12V voltage reg to helop smoothe ripple and control voltage to maximum 12V. It shouldnt get too hot since it's only a little amp...and thers plenty of room inside for a heatsink.

Appart from that it's goign really well.

AndiiT · 6th Jan 2006, 7:09 pm

Quote:

Originally Posted by adibrook

How loud were these things supposed to be originally? The speaker in there is prety poor, and with the TDA7056 going foll blast and getting rather hot the unit is quiet loud. But then again i doubt it would have been that loud in normal use, so may as well make it quieter but more bassy?

Hi Again,
I have just done a search on Google for a Data sheet for the Sn76013ND but could only come up with a similar IC which boasts a 2.5 Watt output; I am guessing that the record player would not be increadibly loud with the original amplifier fitted, and also suspect that one of the reasons that Fidelity used a 24 Volt supply, may have been an attempt to "force" increased volume (distortion?

) out of the unit.

I personally think that a 12 Volt regulator, as mentioned elsewhere, would be a good idea in this case
I have also tried to enclose a picture to confirm that this is indeed the model we are talking about

Andrew

g1wosjohn · 6th Jan 2006, 7:26 pm

Hi.Seem to recall the 24vlt tap on the motor was for the heater of the SINGLE output VALVE they used,cost effective to use the same 24vlts for the Solid state Version ??.They also used a Red? high output xtal cartridge on the Valve version.John G1WOS.

AndiiT · 6th Jan 2006, 7:44 pm

Quote:

Originally Posted by g1wosjohn

Hi.Seem to recall the 24vlt tap on the motor was for the heater of the SINGLE output VALVE they used,cost effective to use the same 24vlts for the Solid state Version ??.They also used a Red? high output xtal cartridge on the Valve version.John G1WOS.

Hi
The valve version used a 90 volt tap on the motor transformer to power the series fed heaters of a UY85 and UL84. (there may have been a single valve version but I can only recall the dual valve model)
The IC version utilses a slightly different motor arrangement with an overwind on the motor transformer (as opposed to the autotransformer arrangement with the valve model) providing around 24 Volts AC

Physically the motors have identical castings and mountings, the only difference being that the motor with the 90 volt tap had only three leads (black, white and brown I think) as opposed to the four leads (Blue, Brown and two white?) on the lower voltage one

I believe that the earlier valve models would have the red BSR cartridge (X3H?) whilst later models (such as the HF35 I owned - still a valve model) had a BSR X5H "stereo compatible" cartridge coloured black

6th Jan 2006, 12:07 am	#1
adibrook Retired Dormant Member Join Date: Dec 2004 Location: Weymouth, Dorset, UK. Posts: 377	Fidelity record-player IC My friend asked me to fix a record player for them. It's got a blown amp chip (one of those old primitive single chip amps). It's a typical ''cardboard'' record player that looks like it should have been valve. It has lots of space inside and even cooling vents in the wooden casing. But all that occupies that space is a tiny PCB with a single chip poweramp. It's made by Fidelity and is red. The chip is pretty old and not made anymore. I remember that it starts off with 6SN7 (yes I DID say chip not valve!) Why would someone build such a large wooden structure just for a tiny chip amp? Since the chip is blown and spares are hard to get, i think i'll just replace the whole PCB with a TDA chip. I'll use a 3.5W one i have that needs no external components at all. Then i'll just use the existing volume and tone pots. There are no worries about originality. After all the pcb that was in there is just a dirt cheap poweramp module, so i will replace it with a modern equivelant of a dirt cheap pa module! I think the TDA chip is more efficient and has less distortion too. The amp is fed from a rectified tap on the gram motor, which is rectified by the looks of it by a single diode and smoothed by one cap! I think a bridge rect and a couple of big modern caps will work well here. The record player had bad hum when the chip worked. Umm...one question. I think record players need a C and an R in parallel to equalise the sound properly? (i think it's something to do with the recording process on records, certain freqencies are louder?) I've never owned a record player, so i dont know much about that. Can anyone suggest component values? Thanks. PS i presume it's a high-output cartridge type since the signal is fed directly into the power amp. Last edited by Darren-UK; 14th Jun 2007 at 2:19 pm. Reason: General tidying.

6th Jan 2006, 12:18 am	#2
Nickthedentist Dekatron Join Date: Jan 2005 Location: Oxford, UK. Posts: 17,861	Re: strange record player! Hi Adi, Fidelity made rather old-fashioned players like this well into the 70s, by which time ICs were beginning to find their way into comsumer electronics equipment. They also made a series of rather cheap and nasty "music centres" (which they called Unit Audio systems) with a BSR turntable + IC amp + radio tuner in a box with a Perspex dustcover, which plugged into a pair of equally awful little speakers. But they were cheap and so sold like hot cakes. But by the early 80s, they were to be found on skips all round the country There's a bit about them (including a circuit diagram of a Fidelity using a pair of SN76013N) in Les Lawry-John's book that was published in the 70s, available to download courtesy of Paul: http://www.vintage-radio.info/docs/p...-repair-qa.pdf . See page 75 of the PDF. Your idea of fitting a new amp module sounds like a great one to me, but beware of overloading the winding on the motor. You're right about the frequency correction - the bass needs to be boosted (because it's cut before the record is pressed to prevent the grooves from being too "wavy"), and the treble needs to be rolled off (because it's boosted before the recording process so that on playback, the high frequencies can be attenuated, taking any record surface noise with them). But tro start with, I'd just connect the output of the cartridge (which will no doubt be a BSR high output ceramic one, maybe a X5M or something similar) to the input of the amp and see how it sounds. Good luck, Nick. Last edited by Nickthedentist; 6th Jan 2006 at 12:34 am.

6th Jan 2006, 2:12 am	#3
adibrook Retired Dormant Member Join Date: Dec 2004 Location: Weymouth, Dorset, UK. Posts: 377	Re: strange record player! Thanks Nick. Well...what can i say. It works. I wish i had a decent record! I asked for a record to test it with, and the bloke gave me IRISH CHRISTIAN HYMNS! UUUUgh it's screwing with my brain...i swear. It's not happy hymns...it's evil mind control music! The TDA7056 seems to preform pretty well here. The only external components so far are a 5.6K resistor to ground from the tda's input, as suggested by the datasheet (without it it sounds reallllly horrible), a 0.47uf input cap and a 1M pot for volume. It's hoprribly trebel boosted, as you said, which makes the irish hymns sound even more freaky (i wouldnt want to listen to that on a dark moonless night without an equaliser). But at least the volume is reasonable. I 1st tested it with a 9V battery, and then the gram motor tap again, rectified with a single diode and smoothed by a 1000uf cap. prototype only...in the finished device i plan to use a bridge and a 4700uf cap or something. How do i go about making the equaliser for it? Do you think if i add an equaliser and stuff it will need a preamp? BTW this is wierd. the original rectifier turns out to be a metal rect!thats strange...why use a silicon chip but a metal rect?

6th Jan 2006, 9:23 am	#4
Aub Nonode Join Date: Mar 2005 Location: Nuneaton, Warwickshire, UK. Posts: 2,039	Re: strange record player! Adi, Well done on the repair. I don't think you need an equalisation on a ceramic cartridge and I'm pretty sure that's what will be fitted to this budget player, or it may even have a crystal cartridge. RIAA equalisation is only usually used with magnetic or moving iron cartridges, which also have a very small output of a few mV (for magenitic) or a few hundred micro volts (for moving iron) compared with the ceramic cartrige's 100-200mV and 0.5 to 1V for crystal. You could certainly use a cheap magnetic cartridge, with an equaliser, to get a better sound, but it probably wouldnt be worth it in this case. There should be some simple equalisation circuits about somewhere, probably based on an op amp. regards Aub

6th Jan 2006, 9:24 am	#5
peter_sol Octode Join Date: Aug 2003 Location: Welwyn Garden City, Herts. UK. Posts: 1,906	Re: strange record player! Hi Normally with these IC amps the input impedance is too low for a crystal pickup, causing lack of bass . As the pickup requires around a 1 megohm load the simplest solution is to fit a 1 meg resistor from the wiper of the v/c to the amp input (after breaking the circuit there first) this may decrease the gain but you will have bags to play with anyway. Cheers Peter.

6th Jan 2006, 9:26 am	#6
Aub Nonode Join Date: Mar 2005 Location: Nuneaton, Warwickshire, UK. Posts: 2,039	Re: strange record player! Forgot to say, make sure the cermic or crystal cartridge is seeing a nice high impedance ( about 1Mohm ), or this will reduce bass response if too low. Aub

6th Jan 2006, 10:34 am	#7
AndiiT Octode Join Date: Aug 2005 Location: Saltburn-East, Cleveland, UK. Posts: 1,786	Re: strange record player! Hi I am probably trying to "shut the stable door after the horse has bolted" here but here goes.... The Record player that you describe is almost certainly a Fidelity HF43 which was the "upgrade" for the earlier HF35 valve model. The HF43 uses an SN76013ND (or similar) Audio chip; which wern't the most reliable of chips, that said it has been claimed that in Fidelity equipment that use these chips their unreliability could be contributed to the fact that a 24 Volt supply was used which (I am led to believe) was close to the upper operating voltage limit of the device. Re equalisation for the cartridge; this will almost certainly be a BSR X5M Crystal/Ceramic type which has a high output and due to its design, and the fact that it can be fed into a high impedance load (1 to 2 Megohms), has the equalisation "built in" as it were, so a linear amplifier design can be used if you are going to (already have?) replace the amplifier as a complete unit. Regards Andrew

6th Jan 2006, 1:27 pm	#8
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,577	Re: strange record player! Adi. As you have plenty of gain to play with, once you have sorted out the power supply refinements you could try a 1 meg resistor in series with the input from the cartridge as already suggested to improve the bass and then parallel that with a capacitor somewhere between 47 and 100pF. You can play around with the value to give best treble response. I used to do this with ceramic and crystal cartridges and it gave good results. Rich. __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman.....

6th Jan 2006, 2:16 pm	#9
adibrook Retired Dormant Member Join Date: Dec 2004 Location: Weymouth, Dorset, UK. Posts: 377	Re: strange record player! Ok. So far i'v got the highest gain by connecting a 1M resistor from the cartridge to ground (therefore giving it a 1M load?) and then connecting it via a capacitor to the chips input, which has 5K resistor on it as the datasheet suggested to ground. It's very loud then but trebely. Maybe a 1M resistor with a series 100pf cap.That sounds allright. How loud were these things supposed to be originally? The speaker in there is prety poor, and with the TDA7056 going foll blast and getting rather hot the unit is quiet loud. But then again i doubt it would have been that loud in normal use, so may as well make it quieter but more bassy?

6th Jan 2006, 2:33 pm	#10
Aub Nonode Join Date: Mar 2005 Location: Nuneaton, Warwickshire, UK. Posts: 2,039	Re: strange record player! Adi, I would do as Richard suggested, then play about with the value of the resister which is currently 5K. I would guess you'd need to inrease it's value to avoid too much of a voltage drop. It all depends on how much gain you have. Aub

6th Jan 2006, 3:05 pm	#12
adibrook Retired Dormant Member Join Date: Dec 2004 Location: Weymouth, Dorset, UK. Posts: 377	Re: strange record player! Ok. thanks for all the advice. I was thinking. I played about with different values of caps and resistors and 100pf with 1m or 470K sounds good. the 1M setting is alot more bassy, but the 470K is louder. I was thinking...why not replace tha resistor witht he tone control pot? Then the owner can change from anythign to very high trebel to bass? i could stick in a series resistor of 100K or so just so that you cant turn the trebel up tooo much. Also maybe fit a fixed 12V voltage reg to helop smoothe ripple and control voltage to maximum 12V. It shouldnt get too hot since it's only a little amp...and thers plenty of room inside for a heatsink. Appart from that it's goign really well.

6th Jan 2006, 7:26 pm	#14
g1wosjohn Retired Dormant Member Join Date: Jan 2006 Location: Bristol, UK. Posts: 13	Re: strange record player! Hi.Seem to recall the 24vlt tap on the motor was for the heater of the SINGLE output VALVE they used,cost effective to use the same 24vlts for the Solid state Version ??.They also used a Red? high output xtal cartridge on the Valve version.John G1WOS.