Divided by 13 10/20 very high gain and lots of HISSSS

[Mars Amp Repair]

Hello all,
More on this Divided by 13 amp. I've got the output xformer replaced and all works now.
Has anyone actually played one of these amps before? This one has super hi gain with both hi & lo inputs to the point that you can barely turn the volume pot up a hair (in the hi channel) and get screaming results. The low channel has similar results but with just a bit less gain but still too high on the pot setting. Perhaps they're trying to emulate the Fenders which have full power at about 3!
Also, the amp in general is verrrrry hissy with volume turned all the way down. V-4 12AX7 is the one I can pull and stop the hiss signal source.
FYI, amp has a pentode 5871 in the V-1 position and a 12AX7 for the rest except for the reverb driver V3 which is a 12AT7. V5 is 12AX7 for PI.
Of course the hiss generator is after V1 & V2 as it is V4 that stops the hiss.
There are no schemos available so I'll just have to ferret it out.
But, has anyone experience using one of this model?
Thanx, glen

[The Dude]

Have you checked bias since the transformer replacement? Maybe the amp is just running so hot that "normal" hiss has turned into an issue.

[Mars Amp Repair]

Thanx, Dude for that possibility.
Idle wattage is set within acceptable range. Glen

[Mars Amp Repair]

Well for anyone who ever works on one of these amps, here's an excerpt from on of the end user forums:
This with regard to how the log volume controls tend to act on the HR Deluxe & Devilles:
I have noticed over the years that many amp builders use volume controls that are nearly unusable. Mainly in non-master volume amps. They go from very little sound to blow the roof off with little in between.
One response:
I have to agree, Fender is one of the worst. Currently I have a Divided by 13 SJT 10/20 that is the same way. I am considering selling it as it is almost not usable at "living room levels".
I'm still searching to see if any end-users note the level of Hissss this amp has. I'm beginning to believe it's a design issue but will continue searhing...g

[Mars Amp Repair]

I found the answer. I say that this is apparently a very 'pretty' boutique amp and the sensitive vol pot could probably be swapped out for a Linear taper to remedy the Fender like operation, HOWEVER even on stage the inherent hiss in the design would still be too objectionable to be acceptable esp if miked. BTW, I verified that the hiss w/vol off is not being created thru the reverb circuit.

Here's the answer from The Gear Page forum:
'With the volume control set low, I also find the hiss level on my SJT 10/20 is higher than expected when compared to other amps. Even with the volume set to zero, the hiss is very noticeable.
I have an ERT33 too. With the 33's reverb channel at noon, it's much quieter than the 10/20. When the 33's click channel is past noon, the hiss is about the same as the 10/20 at low volume. I expect hiss on the higher gain settings.
With the damping switch on up (with the 10/20 amp), the low-volume hiss drops about 8dB SPL which is noticeably quieter and more like my other amps. I measured this with a bargain SPL meter.
I sent the amp back to Fred. He made a minor adjustment, but he said the low-volume setting hiss is normal for the 10/20.
I would be interested in what you find out. Try the damping switch too, and see if it's to your liking'.

I'm always amused when the creator of an amp or any device claims an objectionable issue with it, eg the hiss issue in this case, is NORMAL!! I'll take my $2700 and put it towards an amp that doesn't have objectionable artifacts described by the creator as 'NORMAL'! g

[g1]

Maybe I'll hold off until they release their 'too clever by half' model.

[Tom Phillips]

I was just troubleshooting a very high level hiss problem in a Carr Slant V6. I had it isolated to the reverb return circuit when the owner decided not to spend any further shop time on that issue after I had fixed a couple of other faults. The reverb in the particular Slant V6 had been modified so both channels had reverb so I don't know if the circa 2004 amp always had the problem. Anyway...something failed or someone screwed up. The customer said that he was happy using his reverb pedal and the amp's hiss isn't present with the reverb control full CCW.

Relevant to the Divided by 13 comment that the SJT 10/20 high hiss level is "Normal". Many people are glad that the same person didn't design the high gain phono inputs used in classic tube HiFi equipment.

[Mars Amp Repair]

Maybe I'll hold off until they release their 'too clever by half' model.

Oh man...I must be gettin' old...I'm sure that IS really clever, but I don't get it

[Mars Amp Repair]

I was just troubleshooting a very high level hiss problem in a Carr Slant V6. I had it isolated to the reverb return circuit when the owner decided not to spend any further shop time on that issue after I had fixed a couple of other faults. The reverb in the particular Slant V6 had been modified so both channels had reverb so I don't know if the circa 2004 amp always had the problem. Anyway...something failed or someone screwed up. The customer said that he was happy using his reverb pedal and the amp's hiss isn't present with the reverb control full CCW.

Relevant to the Divided by 13 comment that the SJT 10/20 high hiss level is "Normal". Many people are glad that the same person didn't design the high gain phono inputs used in classic tube HiFi equipment.

I hear ya. I also looked into the reverb being a source for the HISS. Unfortunately not the case here and there is no control you can turn down to eliminate the issue.
I looked up the Carr Slant 6...I'm surprised it doesn't have legs on like the Fender amps do to closer emulate it's namesake

[Tom Phillips]

... I looked up the Carr Slant 6...I'm surprised it doesn't have legs on like the Fender amps do to closer emulate it's namesake...

I think that Mr. Carr is a "Car Guy" and Slant 6 in car guy lingo refers to the block design of a family of 6 cylinder engines. The name doesn't seem to have anything to do with an actual feature of the amp.

[Mars Amp Repair]

I think that Mr. Carr is a "Car Guy" and Slant 6 in car guy lingo refers to the black design of a family of 6 cylinder engines. The name doesn't seem to have anything to do with an actual feature of the amp.

I figured there had to be a number of us old-timers that would understand the Slant 6 reference.
I just know having the distributor on the underside of the slant made it really difficult to replace the points. Dropping the mounting screw was a regular thing.

I just figured if the amp were 'slanted' back...well, you get it.

[g1]

Oh man...I must be gettin' old...I'm sure that IS really clever, but I don't get it

I was just taking a jab at their brand name. And the thing with the 'normal level' of noise, seeming a bit typical of boutique 'form over function' attitudes.