Single ended ODS

[maxfac]

Hi all, great forum, I've been around awhile but not posted much as yet.
I mainly play at home and smaller jams so I'm interested in getting some D style tones at low volumes. To this end I have built a D-lite style pre with a VVR equipped SE EL84 power amp on a old Blackheart BH5 chassis, borrowing heavily from Mats SE HRM andthe Violeta amp. The cleans sound pretty good but the OD is not as smooth as I would like,maybe I'm expecting too much from a SE amp ? I've attached a sch. file and pics and would welcome any comments or suggestions. If the input and the coupling after the tonestack look odd the extra components are there to stop DC getting on to the volume pots causing crackling.

Cheers Andy

[alvarezh]

Nice Andy, thanks for sharing.

I have a BH5 which I have been trying for some time to do something useful with, in that context, a have a couple of questions for you:

1) Did you replaced the P.T. with one with more capacity for the extra tube, or were you able to find out the specs of the installed one and know for a fact it can take the extra load.

2) I use a Mac, your Eagle schematic file gives an error upon loading and will not open the file. BTW, I have the latest version. Perhaps you could upload a pdf, gif, or jpg file?

Thank you in advance and congrats on your build.

Enjoy!

[hywelg]

Hi Andy. I've been loitering here for quite a while and have been especially interested in all discussions about low power D style amps. I was waiting on Barry at ampmaker doing some clips of his Double Six as I thought that would be a good place to start grafting a Dumble pre onto a clean SE poweramp. He's stopped taking orders for the time being whilst relocating so thats on hold for the moment.

Where about in Notts are you? I'm in West Bridgford.

[10thTx]

With the experiments I've done with SE and low watt D-inspired amps, I'd be tempted to try this to get a smoother OD tone.

BTW, nice having a SCH file to use! Thanks.

With respect, 10thtx

[hywelg]

Having trouble replying to your PM Andy. php server error

my email is hywel dot harris at googlemail dot com

Cheers

[maxfac]

Hi Horacio
Sorry you couldn't open the file I've attached a GIF hope this is ok. I used both the PT and OT from the BH5, I found the PT specs on the net (can't remember where) and satisfied myself that it would be ok,experience seems to bear this out, no overheating or bangs or flashes even after an hour or two of use.
Hope this helps.

Cheers Andy

[maxfac]

With the experiments I've done with SE and low watt D-inspired amps, I'd be tempted to try this to get a smoother OD tone.

BTW, nice having a SCH file to use! Thanks.

With respect, 10thtx

Thanks for all your suggestions. I wonder if you could explain some of your ideas before I work my way through them. Have I got this right? The plate bypass caps shave off the top end and the lower caps on OD2 and EL84 reduce bass, but can you explain the circuit around the OD master ? What effect on the EL84 grid reference will putting the ratio trimmer after the master.

Regards Andy(Maxfac)

[10thTx]

The plate bypass caps shave off the top end and the lower caps on OD2 and EL84 reduce bass,

correct

the circuit around the OD is a psuedo-sorta-kinda 5E3 tone stack & I have found it useful in my D inspired builds such as the Tweed Overdrive Special and Tweed BluezMeister.

What effect on the EL84 grid reference will putting the ratio trimmer after the master.

I apologize, but I don't understand the question?


With respect, 10thtx

[alvarezh]

Thank you kindly Andy for the information, much appreciated.

Cheers!

[maxfac]

What effect on the EL84 grid reference will putting the ratio trimmer after the master.

I apologize, but I don't understand the question?


With respect, 10thtx[/quote]

Hi, I'm not sure I do either, but here goes. Because I've got separate master vols for each channel (I did this to balance the clean/od outputs) the grid of the EL84 on either channel sees the respective master vol at 1M at the moment. I just wondered what difference altering the od master set-up would have on this resistance ? Does it matter at all ? I'm not too hot on the theory side of things but I'm eager to learn.

Regards Andy

[maxfac]

Hi
I thought I would post an update on smoothing out the od on my SE ODS. First off I discovered a dodgy bass pot and when changing it realised I had changed the mid pot to a 250k from a 100k, however I hadn't changed the 0.047 to a 0.01 cap. The tonestack now worked better, much more bass and more balanced generally but the od still wasn't as smooth as I wanted. I decided to look at cutting the top end after OD2 as suggested by 10thTx, but opted for the treble bleed mod (a 1000pF cap + 150k resistor to ground before OD level trimmer) instead as I wanted to keep a separate OD Master Vol. This improved things greatly but it now seemed dull and also fuzzy on the bass end. Again following 10thTx's suggestion I lowered the cathode bypass cap on OD2 to a 1uF. The OD now sounds great and balnces really well with the clean channel. I've attached updated sch. and gif. files. BTW I've also changed the caps on the 3 way bright switch as the 250pF was pretty much unusable anyway.
Credit to 10thTx for nudging me in the right direction.

Cheers Andy

[10thTx]

Thanks for sharing your results! That's great. Glad it worked out for you.

with respect, 10thtx

[stiltamp]

Thanks to all for sharing and working out too.

With respect, Manfred

[Colossal]

Maxfac,

Do you find that 1MA is a good fit for both Clean and OD Master Volumes? Are getting a good balance between Clean and OD levels?

Thanks.

[maxfac]

Hi Colossal
The separate 1MA Masters seem to give a good balance between the channels, the OD side is still louder of course but OD gain on 5 and OD Master on 5 gives a slight boost compared to the clean gain on 5 and Clean Master on 7.One thing I have noticed is that the EL84 seems to be slammed too hard with the Masters on full giving a harsh edge to the distortion. I've tried a 220k resisitor to ground before the grid stopper on the EL84 but to no effect. Any suggestions?

Cheers Andy