Pye black box 1004 transistor background noise problem - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

Edward Huggins · 14th Jun 2021, 9:25 am

That high-output Acos cartridge will overload VT1 and will give you a non-linear volume control operation until it distorts at the higher volume settings. You could use one of those cheapo Red Ceramic chinese stereo cartridges often mentioned on here. Bear in mind that your very rare Acos Stereo-Compaible GP91-3SC has a high intrinsic value and will easily sell for £35-00 or more.

Herald1360 · 14th Jun 2021, 12:23 pm

Quote:

Originally Posted by Herald1360

The dual volume pot is a "loudness" control of sorts. The increase in value of R2 as volume is reduced by R11 will give more bass in the cartridge output as the load on it imposed by the relatively low input impedance of the transistor amplifier is reduced by the increasing series resistance of R2.

How effective this is at boosting bass as volume is reduced would be an interesting simulation exercise!

The "ganged pot" loudness control features (in a different implementation) in some other Pye record player amplifier circuits.

The "loudness" effect would seem to be about an 8dB increase in relative bass at low volume from a simple simulation treating the cartridge as a voltage source in series with 800pF capacitor.

Gabe001 · 14th Jun 2021, 3:42 pm

Thank you Graham

Edward, I did see your post in another thread about the cartridge, and for this reason I had purchased a banpa bp2ATC cartidge aka "one of the Chinese red ones". Mounting it will require some thought as it's a clip on, but it can be done, even if I 3d print a mounting clip myself.

The other issue is the output which is around 200-300mv/3cm for the Chinese ceramic ie significantly lower than the ronette the BB was built with which as you know is around 200mv/1cm.

I could replace the Acos with the Chinese ceramic I bought, but I wasn't sure whether I would need to build a small pre amp with a x3 gain to go with it, and a linear power supply from the voltage across the bulb. So when I tried the acos and it sounded good at normal playing volume, and for quite a bit more volume to spare, I thought I'd call it a day. The BB is not going anywhere and I could always revisit this at a later stage.

Gabriel

Edward Huggins · 14th Jun 2021, 8:46 pm

You certainly should not need any kind of pre-amp, nor would I add, or advise, one.

There is sufficient sensitivity and gain through all the AF stages of the Pye's amplifier to allow the average 200/250mV Chinese Ceramic to perform with ease.

14th Jun 2021, 9:25 am	#21
Edward Huggins Dekatron Join Date: Sep 2015 Location: Southwold, Suffolk, UK. Posts: 8,326	Re: Pye black box 1004 transistor background noise problem That high-output Acos cartridge will overload VT1 and will give you a non-linear volume control operation until it distorts at the higher volume settings. You could use one of those cheapo Red Ceramic chinese stereo cartridges often mentioned on here. Bear in mind that your very rare Acos Stereo-Compaible GP91-3SC has a high intrinsic value and will easily sell for £35-00 or more. __________________ Edward.

14th Jun 2021, 3:42 pm	#23
Gabe001 Octode Join Date: Oct 2019 Location: Stockport, Greater Manchester, UK. Posts: 1,639	Re: Pye black box 1004 transistor background noise problem Thank you Graham Edward, I did see your post in another thread about the cartridge, and for this reason I had purchased a banpa bp2ATC cartidge aka "one of the Chinese red ones". Mounting it will require some thought as it's a clip on, but it can be done, even if I 3d print a mounting clip myself. The other issue is the output which is around 200-300mv/3cm for the Chinese ceramic ie significantly lower than the ronette the BB was built with which as you know is around 200mv/1cm. I could replace the Acos with the Chinese ceramic I bought, but I wasn't sure whether I would need to build a small pre amp with a x3 gain to go with it, and a linear power supply from the voltage across the bulb. So when I tried the acos and it sounded good at normal playing volume, and for quite a bit more volume to spare, I thought I'd call it a day. The BB is not going anywhere and I could always revisit this at a later stage. Gabriel

14th Jun 2021, 8:46 pm	#24
Edward Huggins Dekatron Join Date: Sep 2015 Location: Southwold, Suffolk, UK. Posts: 8,326	Re: Pye black box 1004 transistor background noise problem You certainly should not need any kind of pre-amp, nor would I add, or advise, one. There is sufficient sensitivity and gain through all the AF stages of the Pye's amplifier to allow the average 200/250mV Chinese Ceramic to perform with ease. __________________ Edward.