Roland Space Echo BA662 voltages

[Bernardduur]

Hey all!

My Roland Space Echo is going better and better....... one thing I notice is that it sound different when the speed is slowed down compared to other space echoes....... with the speed slowed down it gets muddy and bassy

I know this is a normal function of a band echo BUT the Space Echo has an EQ to take care of this........ when the motor is slowed down an EQ section takes care of more highs to compensate for this..... (This EQ is made with the legendary BA662 IC, now really hard to find.....)

Normally

As in my unit this does not happen. I checked the connections and all voltages change right when I turn up and down the speed knob. Except when I measure the voltage at the gate pin of the BA662; on the cable and connections I measure a voltage between -5 and -12V but when I measure at the IC I get continous a voltage of -14V that changes very little.
The only things between the supply voltage and the IC are a resistor (10k) and a trimpot (20k) but those check out just fine.... (replaced em).

Can someone with a Space Echo measure the gate voltage at the IC (pin1); should it be -14V or is the IC busted???

[soundguruman]

Voltage controlled amplifier BA662
Found on another forum, might be interesting: word on the street has always been that the A's are hand selected for their lower dc offset - and the B's make up the rest of the lot. With that in mind you should be careful using the BA662B as the potentially worse DC offset will most likely be heard as a click at the start of notes. You're probably better off with a good BA6110. The BA662 datasheet is still around so you may want to take a peak at it to confirm.
BA662 search, BA662 datasheet, BA662 buy, BA662 sell - IC2IC.COM : marketplace for brokers and distributors of electronic components

[Jazz P Bass]

Which model number are we talking about?
Can you post the relevant circuit?

[Bernardduur]

Roland Space Echo RE-501

Rec EQ

roland_service_manual_re501_sre555.pdf

[Jazz P Bass]

I cannot find a datasheet for the BA662.
What little I did come across indicates Pin #1 is a currnt input.
So it may not be possible to "see" any change.
Do you test a voltage change at the 22K pot end of the 10K resistor?
Schematic indicates -5.5Vdc /Slow & -13.5Vdc Fast.
If the other end of the 10K resistor proves out (continuity) that it does indeed go to pin #1, then the input is getting the info.
What I would be looking at is the output pin #6.
Is there a frequency change there?
The feedback loop is where the treble change will take place.
Those parts will have to be verified as good.

[Bernardduur]

I tested the voltage at the cable (wire comeing from the PSU board) and at the 22k potmeter; there the voltage was between -5 and -12 (approx; by turning the speed potmeter). If I try to measure the voltage at pin 1 (or the end of the 10k resistor) I measure -14V cont with a very little change by turning the potmeter...........

I will check the freq. change........ don't have the equip now to measure it but I can make some way to do that

[Bernardduur]

I cannot find a datasheet for the BA662.
What little I did come across indicates Pin #1 is a currnt input.
So it may not be possible to "see" any change.
Do you test a voltage change at the 22K pot end of the 10K resistor?
Schematic indicates -5.5Vdc /Slow & -13.5Vdc Fast.
If the other end of the 10K resistor proves out (continuity) that it does indeed go to pin #1, then the input is getting the info.
What I would be looking at is the output pin #6.
Is there a frequency change there?
The feedback loop is where the treble change will take place.
Those parts will have to be verified as good.

I tested it both with scope as with my ears (just audio probing) and I hear NO difference in EQ / tone...... just the same. Guess the IC is broken!

[Jazz P Bass]

Before you abandon the ic:
Did you verify continuity from the 10K resistor to pin #1 of the IC?
Did you verify (replace) the components in the feedback path of the IC?
(this is where you will get the treble boost)

[Bernardduur]

Good call!

I have checked the cont. of the 10k to pin 1 but I have not replaced the feedback path...... I'll do that!

[Jazz P Bass]

The 220K pot, what was the old one set at?
Where is the new one set at?
This pot is the current adjustment for the IC, pin #1.
I guess I would start with it in the middle of it's sweep.

[Bernardduur]

I've checked the feedback path and that one is OK! All values match and replacement of the cap has no avail!

The pot was set to it's middle and I've tried other settings too...... no luck!