Barley Nectar
152 posts
Oct 30, 2013
6:19 PM
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How do you optimize one of these fine amps for harp? Thanks...BN
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rbeetsme
1409 posts
Oct 30, 2013
6:32 PM
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Send it to Greg Heumann at www.blowsmeawy.com
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JTThirty
228 posts
Oct 30, 2013
7:08 PM
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A stock Kalamazoo is pretty fine as a harp amp. If it hasn't had a recent cap job, then that is certainly a requirement. Boosting the power supply filter caps a bit can provide a little more bottom oomph, but I think Greg would steer you away from doing that just to keep the 'Zoo mojo as is. I've got a C10Q Jensen RI ceramic 10" in place of the original speaker. It compliments the amp really well. Greg installs a line out for some customers to bump up to stage volume through a p.a. or a larger amp.
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Ricky B
http://www.bushdogblues.blogspot.com
RIVER BOTTOM BLUES--crime novel for blues fans available at Amazon/B&N and my blog
THE DEVIL'S BLUES--ditto
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blueswannabe
330 posts
Oct 30, 2013
9:44 PM
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it's already optimized for harp. DOn't mess with it. Only replace parts that are absolutely necessary. For example, I replaced the multicap, the power resistor, a resistor off the 1st jack to the preamp, and put a 3 prong power cord on it. I also had to replace the speaker because ot a broken voice coil. Check out my YouTube video on the changes. I used all stock values.
Last Edited by blueswannabe on Oct 31, 2013 4:03 PM
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SmokeJS
177 posts
Oct 31, 2013
3:46 AM
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My ony experience is with a Heumann optimized Kalamazoo so can't compare to stock. But one thing Greg does is improve its safety with the 3 prong plug and remove/adjust/fix something often called the death cap. My understanding is its a component, presumably a capacitor, which is the only thing standing between you and the equivalent of sticking your tongue in a live electrical socket.
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chromaticblues
1506 posts
Oct 31, 2013
9:40 AM
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There are a lot of things that can be done to upgrade it and IMHO make it a FAR better harp amp.
The problem is if you have to ask then you don't know how to do I would tell you. Knowing how to it is just as important than what to do. It has heater ground issues, The first power resister value is to low, the power caps need to be replaced (and I feel the first phase of the power supply should have a larger cap).
I have 20,20,10 in mine. This tightens the sound and adds bass. The power tube cathode doesn't have a bypass cap (which reduces noise and adds gain at the same time). A 25uf or 47uf at 25 volts will work. I used 25 in mine. Those are faily standard values for amps of that size. Last but not least the preamp cathode resisters are 4.7k. I would replace those with 1.5k, 2.2k or 2.7k. Thats one of those things that you have to hear for yourself. I used 1.5k in mine and it works good, but because of the other things I did before that. If you just put 1.5k cathode resisters in a stock Kaly it will sound like its broke. It will distort and sound muddy!
I also put a larger output transformer.
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blueswannabe
333 posts
Oct 31, 2013
4:02 PM
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@chromatic, do you have a video posting of your zoo?
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Barley Nectar
153 posts
Oct 31, 2013
7:27 PM
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Hmmm, interesting...
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Greg Heumann
2434 posts
Oct 31, 2013
9:07 PM
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@Chromaticblues
We disagree. That's OK, just saying.
As suggested above - I DO recommend keeping it stock. They are simply great harp amps that way. You can try all kinds of things. They will change its tone. "Better"? That's in the ear of the beholder. "Different" is a better word. If you don't know what a good stock one sounds like, why bother changing it before you know?
1) It has heater ground issues? No - a properly operating Zoo is very quiet.
2) The first power resister value is too low (huh?)
3)The 4.7K resistors are fine. The Model 1 comes with 2.2K resistors and it is too gainy for harp. I replace them with 4.7's
4)The stock power filter caps are 20,10,10. Going to 20/20/10 doesn't make a huge difference - personally I LIKE the sound when the power supply can't keep up on note edges. It is part of the Zoo tone.
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***************************************************
/Greg
BlowsMeAway Productions
See my Customer Mics album on Facebook
BlueState - my band
Bluestate on iTunes
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blueswannabe
335 posts
Nov 01, 2013
7:47 AM
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If you leave the zoo stock and you are not satisfied with the sound, e.g. Not bassy enough, use an EQ pedal or lone wolf tone control. That will increase bass. But I followed Greg's advice on this and he is right.
Correction; I followed Greg's advise on this and, in my opinion, I would agree with him. There is no right or wrong on this. It's all subjective. I wanted to keep the character of the zoo as it was stock.
@Chromatic, I don't think Greg is dissing you in any way.
Last Edited by blueswannabe on Nov 01, 2013 8:11 AM
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chromaticblues
1507 posts
Nov 01, 2013
7:48 AM
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@ Greg I'm wasn't trying to say you were not correct.
My post had nothing to do with what you do.
But I will have a civil discussion about it.
I believe the very first thing anyone should do is get to work right in it's stock form and see if that is the sound you had in your head.
If not your options are get rid of it and keep buying amps or figure out how to make one work for you and be done with it!
1) The Zoo transformer 6.3 volt secondary winding doesn't have a center tap! EVERY cheap amp that was built this way has heater hum!
2) Measure the voltage at the plate and the grid of the power tube. The voltage at the grid is higher.
If the first power resister is replaced with a 4.7k resister the are about the same.
I thought the original model 1 had a 1k first power resister and they "fixed" the problem by raising the value to 3.3k.
The point of that part is something between 4.7k and 10k is better than the way it was stock.
Again just pointing out improvements (design flaws)!
3) Your right 20-20-10 isn't much as a difference, but the poster was asking for improvements and this does add a liitle tighter bass and helps with noise reduction.
As far as 4.7k preamp resister go, if you think they are fine that's fine. That's one of those things that could change day to day. I'll bet if you had a model one with 2.2k or 2.7k resister that they would be days that you say hmm that does sound cool! Different, but cool!
I tried lowering the value in one years ago and I hated it. I really didn't know much about it back then and there probably has to be other mods made before this becomes a good idea?
When you lower the preamp resister value it draws more current so it does get the same Zoo tone with a little more fatness once you get into the sweet spot of the volume. It does changs the sound a little, but I like it.
You failed to mention the lack of power tube bypass cap? Why would a company do that? Why would a company build amps without a center tapped 6.3 volt winding?
Electrically speaking how would these things affect an amp?
I know those aren't the only amps that were made that way, but I also know there weren't high quality amps ever made that way!
Yes it looks like we do disagree.
Don't get me wrong I love my little Zoo and I think they are cool little amps.
I was just sharing some of the stuff I spent hours on!
IT HAD NOTHING TO DO WITH WHAT YOU DO!
The nice thing about these old amps is; it's easy to solder something in and try to see if you like it or not.
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Barley Nectar
154 posts
Nov 01, 2013
8:47 AM
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There seems to be an issue with the face plate flexing thus causing stress to the components. Is there a simple fix for this? Thanks for the help...BN
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Greg Heumann
2435 posts
Nov 01, 2013
8:54 AM
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@Chromatic - no worries. You clearly have the knowledge and skills to make up your own mind and do the work safely! Now - why they didn't use a center tapped transformer design? Maybe the part wasn't available off the shelf. But surely the factory wanted to save $$. This was sold an entry level amp - it was pretty cheap - even then. But the hum level is so low on a rebuilt amp that has never been an issue for my hundreds of customers and that includes in the recording studio.
@Barley - - yes, the front panel (except on brown face models) can flex, and the resistors leading from the input jacks to the preamp tube socket will repeatedly stress the tube socket lugs until one breaks. I drill a hole in the chassis and use a screw to anchor it to the front cabinet rail. Problem solved. That is part of the standard rebuild I do on every amp.
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***************************************************
/Greg
BlowsMeAway Productions
See my Customer Mics album on Facebook
BlueState - my band
Bluestate on iTunes
Last Edited by Greg Heumann on Nov 01, 2013 8:57 AM
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Barley Nectar
155 posts
Nov 01, 2013
9:06 AM
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OK, now I see. Drill thru the cab side rails and into the face plate up high. One screw on each side. Yep, that will stiffen it up. I was hopeing for something more discreet. Greg, I am missing one rear cover panel. Do you have a spare that you would be willing to sell? Mine is the black Model 2. My email Gerstka@verizon.net. Many thanks guys...BN
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blueswannabe
336 posts
Nov 01, 2013
11:45 AM
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Anchoring the front panel to the front panel side rail is a mod that I will be doing soon. When I bought the amp (retrived out of the garbage and ariving in pieces) the resistor from the jack to the pre-amp was broken. I lucked out it could have been the tube socket tab that broke off.
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