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Denon DRM-540 Cassette Deck Measurements

MRC01

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Seeing @amirm 's review of the Otari reel to reel tape deck motivated me to do some calibration and measurements of a Denon DRM-540 that I bought on eBay for about $50. I don't have a scope or fancy testing gear, so I used my ESI Juli@ sound card. That should be more than sufficient for an old tape deck.

First I cleaned and demagnetized the heads. Boy did that bring back some nostalgia! Next I used calibration tape having 3 kHz and 8 kHz tones. I used the 3 kHz tone to adjust the speed and playback gain / channel balance, and the 8 kHz tone to adjust the head azimuth / alignment. Channel balance wasn't quite the same for these 2 tones so I spent some time going back & forth with alignment and gain pots to minimize and balance the difference. I don't have a scope, so I adjusted azimuth by tweaking the head alignment screw while playing the 8 kHz tone, to find the position that maximizes the output level.

I twirled the adjusting pot through its full range a few times to clean it, then set it as close as I could. The closest I could get it was within about 0.3 % to correct speed, and my calibration tape probably ain't perfect so that's about as good as it gets.

cal-spectrum-3k.png

cal-spectrum-8k.png

The spikes are thinner than the measurements I took on the old walkman that I restored, suggesting this deck has more stable speed / lower jitter.

I tested frequency response by playing REW sweeps and recording them on old BASF Reference Master II tapes. Back in the day, these were some of the best cassette tapes available. I measured it without Dolby, with Dolby B, and with Dolby C. The flattest response was with Dolby B, so that's what I show below.

Here's frequency response at different recording levels: -20, -10, -3 and +3 dB:
fr-levels-dolbyB.png

It's got a wonky dip at 56 Hz, which surprised me. But, this tired old deck still has decently flat response, decent channel balance throughout the spectrum, and meets its specifications.

Here's what distortion looks like at different recording levels:
-20 dB:
dis-m20-dolbyB.png


-10 dB:
dis-m10-dolbyB.png


-3 dB:
dis-m3-dolbyB.png


+3 dB:
dis-p3-dolbyB.png

Above we can see that at +3 dB the tape is approaching saturation, with distortion around -30 dB or 3%. The range from -10 dB to -3 dB looks like the sweet spot, good tradeoff between frequency response and noise/distortion.

Overall, the deck seems to be restored and working well enough, producing classic 1980s sound quality. We are so spoiled today! Most phones and dongles outperform this tape deck. But it was fun to calibrate and feels good to rescue a piece of equipment from going to the dump.
 
OP
MRC01

MRC01

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Here's an example of what it sounds like.
clip-original
clip-recording
The original is the 96-24 master downsampled to 44-16 in Audacity. The recording is recorded on the deck from the 96-24 master played from my sound card (ESI Juli@), then played back on the deck, captured in 44-16 on my sound card.
 

abdo123

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Why don't you use the RTA window setting in REW so you can get results similar to Amir?

it's not really Apples to Apples right now.
 
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MRC01

MRC01

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This is not a 3-head deck, so I can't play back the recording while making it, which RTA seems to require. But I did a related test: recorded a 1 kHz tone from REW, then played it back and looked at the spectrum.

First, a close-up to see its speed stability or jitter. The speed adjustment is spot-on, but we see some obvious side bands.
jit-1khz.png


Next, zoom out to see the distortion products.
jit-1khz-far.png

I scaled the fundamental to exactly 80 dB, so the 2nd & 3rd harmonics are just a smidge below -60 dB. Interestingly, the power supply harmonics are louder than this distortion.

This deck has a fine bias control on the front panel. I tested that effect, results here:
fr-bias-dolbyB.png

The middle (blue) is knob centered. Top (fuschia) is bias -5 (knob all the way CCW). Bottom (green) is bias +5 (knob all the way CW). Looks like I should tweak the internal bias pot up just a smidge to flatten the slight rise in FR for this particular tape (BASF Reference II Master).
PS: observe that the fine bias has the biggest impact on high frequencies, but it also has a smaller opposite impact on lows. It tilts the entire spectrum like a see-saw around a "pivot point" of 1 kHz.
 
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DanTheMan

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I used to own this deck, but it stopped working several years ago and I couldn’t find anyone to repair it. Loved it for many, many years. Always enjoyed calibrating it. Shame it died. My last remaining deck is a Nakamichi BX 1. To be honest, I don’t think it sounds as good as the one you have.
 
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