AKAI 1722W/L R2R Play/ Rec Level Calibration

[hsbhachu3d]

If you're here to answer me, you probably know what I'm going to ask.

There are no Level calibration pots inside the deck at all. Or did I miss them?

I am trying to adjust the record level because the left channel is lower than the right even at 0VU, down by about half. Got the service manual from hifiengine and no luck. Even the manual has nothing written about Amplifier Adjustment. It only tells you how to verify the correct functionality, like where to put your multimeter probes to check that the bias is right Lol.

There are no pots like I said inside the deck or maybe I missed them. Any advice?

[saxmaniac]

I don't think there's any adjustment for this but you could trace the signal to the meter and see if there's any faulty component or whether the meter itself is faulty. I assume you only have problem with the meter and the signal itself is ok?

[hsbhachu3d]

Nope. The meter is good. Levels are both equal during playback. Even a -3db 250hz tape playing shows -3 with the volume pots at the same position. The record inputs are also equal with both the volume the pots at the same position. Just the recording is dipped on the left channel. I am poor at looking through circuits as this was something I was well at say 3-5 years ago. I can link a schematic if that helps

[Grubhead]

It will have an automatic level control. Possible faults could originate with the record switch, bad contacts, and the electronics for the record amp. Check the voltages around the transistors shown on the diagram with the parts connected to record.

[radiotechnician]

On a machine of that age, I would replace C1, 2, 5, 7 and 8 ,
and measure each to see see if it had dried out.

New capacitors are low in price.

If you owned an oscillator and a wide range AC voltmeter,
you could measure the preamp gain.

A modern DVM wont do, unless it has frequency response
flat from 20 Hz to over 20 kHz.

[TIMTAPE]

Originally Posted by hsbhachu3d

Nope. The meter is good. Levels are both equal during playback. Even a -3db 250hz tape playing shows -3 with the volume pots at the same position. The record inputs are also equal with both the volume the pots at the same position. Just the recording is dipped on the left channel.

First you must confirm PLAYBACK response is accurate. It may be true for 250Hz but could fall away sharply above that frequency. Check the tape head and the tape's contact with it, as per the manual.

[hsbhachu3d]

Timtape,

Backtension - checked
tape to head contact - checked
Azimuth - Checked
Degauss - Checked
250hz - 1000hz - checked - equal on both channels as per VU

Radiotechnician -

Capacitors you mentioned - only those in the left channel that's low - replaced
The pair of transistors in left preamp replaced



So far - minor but noticeable difference. Record level on left is still significantly low.

[mitajohn]

Have you checked the bias for both channels?

[radiotechnician]

Take a peek at the two hum buckers L1 and L2. Are the 20 turn coils
damaged, or shorted ?

If the assumption is made that something is amiss with the head itself,
it can be confirmed by swapping the head connection leads, at the head.
Then see if the problem moves to the other channel.

Do not change the bias for this test.

That said, very careful soldering must be done.

As an Akai tech, when those machines were current, if we suspected this,
we would just try a new head, since spares were at hand.

(Philips (El 3434A) were a bit different. Signals to the head were picked off
at a current sensing resistor (100 ohms )which was part of the machine design. This permitted more precise calibration.)

[hsbhachu3d]

Gotcha. flipped the head wires and same thing. the left of the head was connected to the right and the right to the left. This time the recording on the right had dipped. The head is the culprit. Its a model P4-150 . Hit a dead end. No idea where to get a replacement. OR. I could just find the resistor that feeds into the record for the left channel and reduce it's value to just record at a higher level, but, from the schematic, it looks like the amp is being used as the record circuit.

[radiotechnician]

We had a supplier of generic heads, and adapter kits. The company was called
Nortronics. They might be still out there in some form.

http://lcweb2.loc.gov/master/mbrs/re...ifications.pdf

[TIMTAPE]

The only reason a tape head normally loses its highs on playback is:

1. poor tape to head contact ( more correctly tape to head gap contact)

2. the gap has opened out (short black vertical line) and the head must be replaced.

Usually the gap hasnt opened out and it's poor contact (1)

Again are you sure the left track pole piece is clean as a whistle and the tape is sitting intimately on the left (upper) gap without obstruction? Usually we can only check these things in a strong light and with the aid of magnification. The machines needs to be laid on its back of course.

[hsbhachu3d]

Timtape, you missed the point boss,

It hasnt lost highs. It is a low record level on the left may I reiterate. The audio Eq is perfect both low to high. The playback level is normal on both channels . just a low record lavel on the left. Please go through the posts over again.

[TIMTAPE]

My mistake, apologies. Hope you find the cause of the level discrepancy.