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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 15th May 2020, 2:48 pm   #1
spline_labs
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Default Philips EL-3534 as a Recording Preamp for Guitar

I was given a Philips EL-3534 in fairly rough condition yesterday, when I plugged it in and turned it on, the mechanical parts all seemed to be working.

After looking up the schematics, I realized the circuitry used a lot of germanium transistors that are sought after in vintage guitar pedals. Of course, I had to plug my guitar directly into the microphone input and mess with the volume controls and balance... I got an excellent sound coming out of my guitar speaker cabinet! I was going direct from Right Speaker Out to the cab speaker. Left speaker out seemed to be much louder than the right.

I tested the voltage and current coming from the headphone output, and realized that it would be safe to use this output into the input of a guitar amp. I put this into my Princeton and it sounded awesome but was very loud!

I realized that I could only get the audio from the microphone input to play through the headphone output by having the spindles turning and I would rather use it in one of the "off" positions. Not too sure how I will go about modifying the preamp + output circuit to work when an "off" position is selected... any suggestions on how I could do this?

Also, I need the playback mode to be set to "P-A" in order to get the headphone out to work. However, this also makes the built-in speaker play the audio from the mic input. This seems to be an easier fix, since I could use a 5W dummy resistor in its place. Does anyone know the speaker impedance that I am looking to match with my dummy load?

Cheers,
Joe
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Old 17th May 2020, 5:40 am   #2
ricard
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Default Re: Philips EL-3534 as a Recording Preamp for Guitar

For some reason, the headphone output on Philips machines of that vintage is intended solely for record monitoring and outputs no signal on playback. Interesting that it also outputs a signal in PA mode - I don't think I've ever tried that.

The switching on these machines is rather intricate so I'd probably try to get it to do what I wanted without resorting to rewiring the electronics.

I believe these machines were intended to use 5.6 ohm speakers.
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Old 17th May 2020, 9:54 am   #3
TIMTAPE
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Default Re: Philips EL-3534 as a Recording Preamp for Guitar

I remember reading how long ago the great Chet Atkins got a technician he knew to make up such a distortion box for his electric guitar but I confess to being a little sceptical about the modern claim that Germanium transistors produce something special in fuzz tone.

https://www.proaudioland.com/news/ge...edals-popular/

This article speaks of vintage guitar pedals using them. What it doesnt say is that in those days Gernamium transistors were all there were. Silicon trannies only became widely used in the mid to late 1960's. So those early people like Chet werent trying to create a "vintage" tone but a fuzz tone. We tend to see these devices as having something special because they're old.

Fuzz tone is achieved by deliberately clipping the waveform and then rolling off the highs. It's so distorted that the transistor's characteristics become almost irrelevent. I suspect it would be the same if we used a silicon transistor.

The distorted sound most electric guitarists have sought is the smoother harmonic distortion of an overdriven output stage, usually in a valve amp. Apparently it's not so much the valves as the output transformer when it goes into saturation. Analog magnetic tape can achieve a similar effect in the right conditions.

Coincidentally I just serviced the mono version of that Philips machine. The playback preamp was incredibly crackly which is common with old Germanium transistors. I just replaced the first stage PNP Germanium with a PNP Silicon. The crackling went away.
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