Crowther Audio - Hot Cake Overdrive

Post by **mdd59** » 11 Sep 2008, 20:07

JHS wrote:The newer HCs have a zener diode to decrease the voltage a bit for a softer sound.

There was one odd version for a short time with an additional pnp-trannie and 2/3 diodes (to bias the TL071 opamp into class -A mode). One diode sets the bias-point for the pnp-trannie, the other sets the bias-point for the opamp.
Some of them have a 3rd 1N914 diode between pin 2 and 3 on the 071 (for a bit asym. clip. and a bit more headroom).

Analogguru's schems are correct, same circuit as on my schems from Japan.

The '77 version and RI don't have diodes and a trannie. IC is a uA741C and the circuit is a bit different compared to the newer units with a 071.

BTW: over the years cap values (esp. for the I/O-caps) vary a bit, even on the newer units (IMHO to compensate ICs from different manufactures.

JHS

Mine has what appears to be 914s across pins 2 and 3 and from 3 to ground. I lifted the common ends and put in a internal switch to try both ways. It seems that the clipping with the diodes out of the circuit is less "gatey." Tone and volume wise doesn't appear to change much to me! I would think the diodes are an attempt at some additional, non opamp induced distortion. Very subtle to me.

soulsonic · Post by **soulsonic** » 23 Sep 2008, 11:48

I finally tried this out on the breadboard. It's a cool circuit, but a little too dark for me. I tweaked it just a little bit.
Stay tuned for my layout and pics of the final thing.
I'm using a metal can 741H for maximum mojo!

Greg · Post by **Greg** » 23 Sep 2008, 13:42

soulsonic wrote:I finally tried this out on the breadboard. It's a cool circuit, but a little too dark for me. I tweaked it just a little bit.
Stay tuned for my layout and pics of the final thing.
I'm using a metal can 741H for maximum mojo!

You'll probably find it a bit brighter with a TL072... esp at high Drive settings.
Might be worth a try.

mojah63 · Post by **mojah63** » 23 Sep 2008, 18:30

Mine is a tad dark even with the TL072... It's not annoying enough for me to mess around with though. I used a 50k pot for presence. I want to try a 22k pot equivalent as some models have.
Maybe when I get back from vacation...
P

soulsonic · Post by **soulsonic** » 23 Sep 2008, 23:50

For me, it was the 22nF cap after the 10K resistor that was making it too dark. I changed it to 10nF, and it was much better. I also ended up tweaking the 82n cap to 52n because I didn't have an 82n cap on hand and the 52 sounded good. I'm using a 22K Presence control (a Marshall amp replacement part... available from tubesandmore.com).

mojah63 · Post by **mojah63** » 25 Sep 2008, 10:36

soulsonic wrote:For me, it was the 22nF cap after the 10K resistor that was making it too dark. I changed it to 10nF, and it was much better. I also ended up tweaking the 82n cap to 52n because I didn't have an 82n cap on hand and the 52 sounded good. I'm using a 22K Presence control (a Marshall amp replacement part... available from tubesandmore.com).

Thanks Soulsonic:)
I'll try the suggestions when I get back from vaca...

kurtlives · Post by **kurtlives** » 12 Oct 2008, 01:19

For the Zener diode all I have is an 8.2V and a 9.1V. Should I use one of these or just leave it out?

Also to use the 741 do I need to do any changes? I thought someone said something about changing a 220K resistor.

Cant wait to finish this then analyze it myself and start making changes.

JHS · Post by **JHS** » 13 Oct 2008, 16:37

The uA741 was used in the '77 RI and the early units. The 220k is needed for the uA741, it drops some bass to prevent mud.
For other 741 (LM for ex.) the value must be altered a bit.

The 8,2V Zener is used on later models with 071 IC. W/o this Zener diode the sound is a bit harsh/trebly.

JHS

kurtlives · Post by **kurtlives** » 13 Oct 2008, 18:17

JHS wrote:The uA741 was used in the '77 RI and the early units. The 220k is needed for the uA741, it drops some bass to prevent mud.
For other 741 (LM for ex.) the value must be altered a bit.

The 8,2V Zener is used on later models with 071 IC. W/o this Zener diode the sound is a bit harsh/trebly.

JHS

I thought the Zener was 8V7?

8V2 seems like a better idea to my mind.

kurtlives · Post by **kurtlives** » 18 Oct 2008, 03:17

Ok so in the mail three days ago I received a DIY Hot Cake from a guy selling it over at Aron's.

Tonight I finished my own DIY HC.

All I can say is wow, mine totally killed this other HC. Geez mine is so much more dynamic and lively. I credit this to the use of the silver mica bypass cap and all around good caps and resistors. Wish I could say I used silver solder but I didnt

.

The HC I bought had the two 10mF caps as NP 10mF and a ceramic 100pF bypass cap. It was just muddy and lifeless. It also had the wrong taper for the drive control so it was pretty junky to use.

I should mention both pedals used Torchy's vero layout. Great layout btw man, thanks!

I thought my HC was quite nice though. Really dynamic and responds to your feel/attack. Doesn't have a ton of highs and I find my presence control at about 3'o'clock usually. I was expected way more treble, I thought this was a shimmering Fender dirt tone. I totally agree about the top end of the gain control being useless. I dont push mine past 3 o'clock usually. Anyways I still like it and find it very transparent.

If I switched the TL071 to a LM741 would I be just loosing highs and all around cut through/clearness? Any suggested mods that some of you like to do right away?

soulsonic · Post by **soulsonic** » 18 Oct 2008, 20:27

I think the 741 has a really great sustaining distortion when the gain is maxed.
I've only ever used a 741 in mine so I can't compare it directly to the TL071... and I can't try swapping it because the board is made for the TO-18 metal can package 741.

ryanuk · Post by **ryanuk** » 07 Nov 2008, 10:00

I've built a few little stompboxes and am thinking of building a Hotcake clone for a guitarist pal.

I'm consdering using the `77 design for simplicity. The 2003 seems a little more complicated due to the relay switching and is missing values for the transistor and couple of resistors

There is a lot of info on the hotcoke in this forum but its not clear whether anyone has had success building a clone from the `77 schematic??

I'd like to hear from anyone who has built the '77. Did you switch it using the simple spst switching in the schematic, or did you use true bypass and switch the entire ciruit in/out of the single path??

Have I made the right decision of using the `77 design?? Does the 2003 sound better?? If so, can I incorporate any of the 2003 features into the `77 design??

Bajaman, Analogguru - you appear to be the experts on this. Help me out.

RyUK

MoreCowbell · Post by **MoreCowbell** » 07 Nov 2008, 10:14

Hi....here's a 9 page thread on the Hotcake....didn't know if you saw this or not.

https://www.freestompboxes.org/viewtopic ... it=hotcake

JHS · Post by **JHS** » 07 Nov 2008, 10:24

I built both with true bypass and prefer the sound of the '77 HC over the new HC. Due to the uA741C a bit warmer and more natural sounding. IMHO building a hybrid ('77 front with a 2003 tone control) would be a good idea.

JHS

ryanuk · Post by **ryanuk** » 07 Nov 2008, 10:59

MoreCowbell - yeah I read through the 9 page discussion but it seemed to focus on the 2003 design. I wanted to speak to someone who had actually built a 77 to get some pointers.

JHS - thanks for your reply!!
You did use the analogguru 77 schem??
Did you design your own layout or use one from the net??
Any substutions??

I think I will take you advice and will try building the 77 with a pot instead of the prescence switch.

Only issue is that I having some issues locating some cap values in the UK - specifically the 82n and 12n. Could I substitute with 10n and 68n??

Post by **modman** » 07 Nov 2008, 14:17

ryanuk wrote: I think I will take you advice and will try building the 77 with a pot instead of the prescence switch.

Better to tackle the 2007 version and sub the IC and add the 220k resistor.

ryanuk wrote: Only issue is that I having some issues locating some cap values in the UK - specifically the 82n and 12n. Could I substitute with 10n and 68n??

This has an influence on the feedback filter, do have a look at Bajaman's suggestions here, because the resistor should be adapted too.

I have the impression that because this circuit is all about subtle distortion (vs. supergain) it's very sensitive to the amp and types of pickups used.

I know this has now turned into a 10 page thread and that seems very heavy. Still, there is hardly any bullshit and every aspect of the circuit in properly analyzed and documented. If you have questions, they'll be very welcome but remember that the forum server sends off notifications messges to a great deal of people who have posted in this thread , so you'll be more likely to get answers here.

soulsonic · Post by **soulsonic** » 09 Nov 2008, 23:58

Here are the pics of mine!

Here's the board before I had to chop it up to fit in the box with the battery.

You can see why I called it the "Mojo Cake"!

I used vintage resistors and caps and even vintage circuit board material! Despite all the noisy mojo parts, the circuit really isn't very noisy at all. Of course, I didn't only use carbon comps, I used a few high-end metal films here and there. I just used whatever felt right and it turned out very nice.
The metal can 741 sounds really awesome, by the way... This thing gets total Santana tone. Ha!

If anyone wants a copy of this layout, let me know, and I'll post it up here. Good luck finding a metal can 741 for less than $10.

analogguru · Post by **analogguru** » 10 Nov 2008, 00:35

If anyone wants a copy of this layout, let me know, and I'll post it up here. Good luck finding a metal can 741 for less than $10.

Really ? Hey, I am gonna getting rich with my junk-box.

There is not a difference between plastic-dip and Metal-can 741´s. But there can be a big difference between manufacturers - compare old datasheets.

Who is the manufacturer of your metal-canned 741´s ? Fairchild ?

analogguru

soulsonic · Post by **soulsonic** » 10 Nov 2008, 00:50

analogguru wrote: Hey, I am gonna getting rich with my junk-box.

Yes. Me, too.

Who is the manufacturer of your metal-canned 741´s ? Fairchild ?

I do not know; there are no obvious markings other than "741" stamped on the top. I have one more; I can take some detailed photos of it and maybe you can tell me?

I also have an entire bag of non-labeled metal can ICs. I thought they were 741s or something similar, but they don't function in circuits with the usual single amp pinout, so they must be something else... I should put up some pics of those too because I'd really like to find out what they are.

ryanuk · Post by **ryanuk** » 19 Nov 2008, 15:46

soulsonic wrote:anyone wants a copy of this layout, let me know, and I'll post it up here. Good luck finding a metal can 741 for less than $10.

soulsonic - your hotcake build looks fantastic !!!!!

could you post your layout ?? did you sub any components??

RyUK

Crowther Audio - Hot Cake Overdrive [traced]