• TalkBass has been independent since 1998. Add your voice.
    Create a free account to reply to discussions, view embedded media, and browse with fewer display ads.
    Join free Log in
    Want zero display ads or expanded classifieds tools? Compare plans.

GGG A/B/Y Amp Switcher Box project (circuit diagrams!)

K

Kooldac

Oct 20, 2008
193
0
Arizona
#1
So, I really wanted a project to let me try circuit board building and I wanted something to utilize a dual amp situation to give me clean and dirty amps. You fine folks linked Invalid Link Removed in a couple threads I've seen. I however have a couple questions related to building this one.

It calls for a TL072 op-amp IC that I've seen discussed before. I am trying to not just dive headlong into this and went researching different parts. Invalid Link Removed discussed this IC and gave sup-par reports for audio fidelity in high-input impedance situations. Looking at GGG's circuit diagram, its impedance would be 1 meg. However, running through their Invalid Link Removed, the audio fidelity is great. Someone want to explain how this works? Or maybe just reassure me i dont need to worry.... lol

Also, where do you guys suggest buying these in small quantities if I cant find them locally? (I haven't checked locally yet, just hypothetical)
 
#2
Bumping this with a slightly different agenda. I wanted to ask DIYstompboxes my answer but their manual account activation is ridiculous - been waiting about 5 days just to post a question.

The build calls for 42TM018 transformers. Reading their tech specs, they give a frequency bottom level of 300 Hz. Seeing as how bass frequencies are mostly underneath that level, that had me very concerned. On the other hand, I've seen fellow TBs post good results about this. I am tempted to just get everything I need and assume I am missing something... but I'd like to understand what I am building.

Any help here?
 
#4
Kooldac said:
So, I really wanted a project to let me try circuit board building and I wanted something to utilize a dual amp situation to give me clean and dirty amps. You fine folks linked Invalid Link Removed in a couple threads I've seen. I however have a couple questions related to building this one.
Click to expand...
I'll see what I can do :)

It calls for a TL072 op-amp IC that I've seen discussed before. I am trying to not just dive headlong into this and went researching different parts. Invalid Link Removed discussed this IC and gave sup-par reports for audio fidelity in high-input impedance situations. Looking at GGG's circuit diagram, its impedance would be 1 meg. However, running through their Invalid Link Removed, the audio fidelity is great. Someone want to explain how this works? Or maybe just reassure me i dont need to worry.... lol
Click to expand...
Hm, I'm going to venture on no need to worry. I use the TL072 with great results.

Some to consider is that the input impedance of any op amp tends to infinity(>1Meg) so the diagram is fine. What I think the website is giving you is the best operating circumstances. Honestly, I don't think you will need to worry about IMHO and IME.

Also, where do you guys suggest buying these in small quantities if I cant find them locally? (I haven't checked locally yet, just hypothetical)
Click to expand...

Small Bear works, but Digikey is really nice to work with and they allow small quantities.

Hope this helps :)
 
#5
Kooldac said:
Also, where do you guys suggest buying these in small quantities if I cant find them locally? (I haven't checked locally yet, just hypothetical)
Click to expand...

Check 'all' of the sites to see who'll get you best deal...Small Bear, All Electronics, Mouser, Effects Connection, Pedal Parts...
W/ most of these, the shipping is $3+, so you have to make it worth your while to order online. Find a couple of other things to order (soldering parts, diodes, etc...).
 
#7
TL072's are fine for most audio purposes. Yes there are "better" by some subjective standards, but a person is in golden-ear territory by that point.

Also you mis-read one of the points made by that page about the TL072- he doesn't say the audio quality is sub-par in hi-z applications, he says that it inherently has a hi z in, and unless that hi z in is particularly important to you, there are better choices for lower THD. In bass instrument applications, especially where a passive bass may be used, you do want a very high z in, and THD is less of a critical factor than in some other audiophile applications.
 
#8
I don't know about those transformers, but if you dig through Mouser/Jameco you may be able to find different xformers with the same specs except a lower frequency range:
Interstage audio transformers
Primary impedance 10k ohms
Secondary impedance 10k ohms
Primary resistance 550 ohms
Secondary resistance 500 ohms
 

Latest posts

Top Bottom
Back