14-Pin Op-Amps in an OD-1 Clone

[SteveG]

Hi,

I've just built an OD-1 clone ('B' version), and had an interesting experience with op-amps.

Here are the results of trying four NEC C4741C and two LM324N chips:

1st 4741 - No sound in 'Bypass' or 'On' Chip pulling a ton of current - obviously a dud.
2nd 4741 - Normal sound in 'Bypass' mode, no sound when 'On'.
1st LM324 - Normal operation in both modes. Good sound.
3rd 4741 - Normal sound in bypass mode, good sound but very quiet when 'On'.
4th 4741 - Normal sound in Bypass mode, really bad sounding distortion when 'On'.
2nd LM324 - Normal operation in both modes. Good sound.

Now, I haven't had a chance to look into it any further at this point, but I'm wondering if I've inadvertently run into the reason Roland/Boss stopped using quad op-amps in this circuit back in the late seventies. Ignoring the first sample, which was obviously faulty, I'm guessing that the other 4741's will test OK. It seems too much of a co-incidence that the op-amp sections involved in the bypass mode in three different 4741's all work fine. Maybe this chip is inherently unsuitable for this circuit for some reason? Of course, I could just have a bad batch, but the supplier has stated that they originate from a legitimate supplier, and has had no other complaints.

The other thought to come from this is that possibly something like this is the genesis of the myth (IMHO) that the particular chip used in a TS/OD-1 is always a critical factor to 'good tone'?

Anyone have a similar experience or thoughts on the subject?

-Steve

[Mark Hammer]

It was my understanding they used the RC3403, which is also a quad op-amp, employing the same pinout as the LM324, TL074, and C4741C.

At the same time, the other version of the OD-1 just uses a JRC4558, substituting the more commonly encountered bipolar transistor input and output buffers (the RC3403-based version, as shown, uses two op-amp stages for those same input/output buffer stages.)

[SteveG]

Hi Mark,

Thanks for the reply.

According to the BossArea website the 4741 op-amp was also used for a short time. The 3403 seems to be rather difficult to get hold of.

I'd take some convincing that choice of (correctly functioning) op-amp makes much difference in this circuit, but I was looking forward to proving this to myself.

BTW, comparing the 'quad' version of the OD-1 to the 'buffered dual' version is interesting, in that they sound remarkably similar. This is what I expected, but goes against popular internet wisdom. What small difference there is probably stems from the dual version having a much higher input impedance, IMO.

Steve