XFMR drive FX loop?

[rfgordon]

I was perusing a bunch of Fender schematics, and noticed that in the Tone Master there are two transformer-driven FX loops. Link: http://ampwares.com/schematics/tonemaster.pdf

Does anyone have experience with that type of design?

[drz400]

I was perusing a bunch of Fender schematics, and noticed that in the Tone Master there are two transformer-driven FX loops. Link: http://ampwares.com/schematics/tonemaster.pdf

Does anyone have experience with that type of design?

Design by zinkky
Yes I owned one, it was a worthless effects loop, non functional
No return gain at all. I put a good tube loop in and all was fine.

[Aurora]

Lack of gain has nothing to do with the transformer itself.
Using a transformer in an effects loop 'can' be very beneficial in terms of isolating ground loops. The gain of course has to come from the circuits driving/receiving the signal.
Isolating transformers are heavily used in studio settings, and are real problem killers.

[CaseyJones]

Yeah, but...

Why use transformers if you don't have to? They're great if a manufacturer is willing to use premium iron in that application, that's why old Jensens go for the big bucks.

It's like the Tone King is an attempt at an amp that will integrate seamlessly with rack mounted effects. Which 90% of us will never do. How "'80s"!

The whole amp is a clever attempt to re-invent the wheel. That effects loop... a tube buffered effect loop works fine. Like a Dumbleator, maybe?

[Alexo]

If you do use a transformer, bear in mind that it will be just as susceptible to power transformer-induced hum as an output trasformer, and appropriate measures need to be taken to avoid this.

[drz400]

Lack of gain has nothing to do with the transformer itself.
Using a transformer in an effects loop 'can' be very beneficial in terms of isolating ground loops. The gain of course has to come from the circuits driving/receiving the signal.
Isolating transformers are heavily used in studio settings, and are real problem killers.

Yes of course but the loop has no return gain and didnt work with instrument or line level effects. There should have been a cathode follower or plate follower as a drive and make up gain. He tried to do the loop using only transformers (which were expensive) Isolation transformers could have been had for $10 each for that application (not driving into a small load) instead of the $40 transformers used. Another weird oversight was no diodes on any of the relays and they were not on the original schematic either. It popped like mad until I added them.

[jjman]

Interesting that the trannies are in the signal path even when the loop is "bypassed."

[rfgordon]

I can see the cost savings as appealing, perhaps, of using a few small trannies to do the work of more compelx/expensive components. The transformers aren't necessarily bad, I agree, but they do need some help.

I build a one-into-three buffered splitter, based on the AMZ design, that uses small 10k/10k Xicon trannies on all three outputs, with two of them isolated from ground. The unit sounds and works great--but it does have a JFET driving each transformer.

The Tone Master design struck me as odd, so I thought I'd ask y'all for opinions. Not surprised that some thought that amp had issues.

[Ronsonic]

Another weird oversight was no diodes on any of the relays and they were not on the original schematic either. It popped like mad until I added them.

Curious, almost all small signal relays come with those built in nowadays. So much so that getting parts for amps that use relays with the "wrong" polarity can be a problem. I'm thinking Mesa Mk IV here, though there may be others.

Sounds like someone in purchasing wasn't talking to the guys in engineering.

[drz400]

Another weird oversight was no diodes on any of the relays and they were not on the original schematic either. It popped like mad until I added them.

Curious, almost all small signal relays come with those built in nowadays. So much so that getting parts for amps that use relays with the "wrong" polarity can be a problem. I'm thinking Mesa Mk IV here, though there may be others.

Sounds like someone in purchasing wasn't talking to the guys in engineering.

The relays did not have diodes built in. I contacted Fender about it and they said it was an oversight, Diodes should have been there. The designer of the amp missed it basically Also those transformers were not cheap, like $30 each, externally mounted and shielded. A tube would have worked better and saved a bunch of money.